Cysts and Cystlike Lesions of the JawsA cyst is a pathologic cavity fi lled with fl uid, lined by epithelium,and surrounded by a defi nite connective tissue wall. The cysticfl uid either is secreted by the cells lining the cavity or derivesfrom the surrounding tissue fl uid.Clinical FeaturesCysts occur more often in the jaws than in any other bone becausemost cysts originate from the numerous rests of odontogenic epitheliumthat remain after tooth formation. Cysts are radiolucent lesions,and the prevalent clinical features are swelling, lack of pain (unlessthe cyst becomes secondarily infected or is related to a nonvital tooth),and association with unerupted teeth, especially third molars.Radiographic FeaturesLOCATIONCysts may occur centrally (within bone) in any location in the maxillaor mandible but are rare in the condyle and coronoid process. Odontogeniccysts are found most often in the tooth-bearing region. Inthe mandible, they originate above the inferior alveolar nerve canal.Odontogenic cysts may grow into the maxillary antrum. Some nonodontogeniccysts also originate within the antrum (see Chapter 27 ).A few cysts arise in the soft tissues of the orofacial region.PERIPHERYCysts that originate in bone usually have a periphery that is welldefi ned and corticated (characterized by a fairly uniform, thin, radiopaqueline). However, a secondary infection or a chronic state canchange this appearance into a thicker, more sclerotic boundary ormake the cortex less apparent.SHAPECysts usually are round or oval, resembling a fl uid-fi lled balloon.Some cysts may have a scalloped boundary.INTERNAL STRUCTURECysts often are totally radiolucent. However, long-standing cysts mayhave dystrophic calcifi cation, which can give the internal aspect asparse, particulate appearance. Some cysts have septa, which producemultiple loculations separated by these bony walls or septa. Cysts thathave a scalloped periphery may appear to have internal septa. Occasionallythe image of bony ridges produced by the peripheral scallopingare positioned so that their image overlaps the internal aspect ofthe cyst, giving the false impression of internal septa.EFFECTS ON SURROUNDING STRUCTURECysts grow slowly, sometimes causing displacement and resorption ofteeth. The tooth resorption often has a sharp, curved shape. Cysts canexpand the mandible, usually in a smooth, curved manner, and changethe buccal or lingual cortical plate into a thin cortical boundary.Cysts may displace the inferior alveolar nerve canal in an inferiordirection or invaginate into the maxillary antrum, maintaining a thinlayer of bone that separates the internal aspect of the cyst from theantrum.Odontogenic CystsRadicular CystSynonymsPeriapical cyst, apical periodontal cyst, and dental cystDefi nitionA radicular cyst is a cyst that most likely results when rests of epithelialcells (Malassez) in the periodontal ligament are stimulated to proliferateand undergo cystic degeneration by infl ammatory products froma nonvital tooth.Clinical FeaturesRadicular cysts are the most common type of cyst in the jaws. Theyarise from nonvital teeth (i.e., teeth that have lost vitality because ofextensive caries, large restorations, or previous trauma). Often radicularcysts produce no symptoms unless secondary infection occurs. Acyst that becomes large may cause swelling. On palpation the swellingmay feel bony and hard if the cortex is intact, crepitant as the bonethins, and rubbery and fl uctuant if the outer cortex is lost. The incidenceof radicular cysts is greater in the third to sixth decades andshows a slight male predominance.Radiographic FeaturesLocation. In most cases the epicenter of a radicular cyst is locatedapproximately at the apex of a nonvital tooth ( Fig. 21-1 ). Occasionallyit appears on the mesial or distal surface of a tooth root, at the openingof an accessory canal, or infrequently in a deep periodontal pocket.Most radicular cysts (60%) are found in the maxilla, especially aroundincisors and canines. Because of the distal inclination of the root, cysts343344 PART V RADIOGRAPHIC INTERPRETATIONFIG. 21-1 Radicular Cysts. In A note that the epicenteris apical to the lateral incisor and the presence of aperipheral cortex (arrows). In B note the lack of a welldefined peripheral cortex because this cyst was secondarilyinfected and that the root canal of the lateral incisoris abnormally wide and it is visible at the root apex.A BFIG. 21-2 A, A periapical fi lm of a radicular cyst reveals a lesion with a well-defi ned cortical boundary(arrows). Note that the presence of the inferior cortex of the mandible has infl uenced the circularshape of the cyst. B, A coronal cone beam CT image of a radicular cyst related to the buccal root ofa maxillary molar. Note the circular shape of the cyst as it invaginates the maxillary sinus. (CourtesyDr. Bernard Friedland, Harvard University.)A Bthat arise from the maxillary lateral incisor may invaginate the antrum.Radicular cysts may also form in relation to a nonvital deciduousmolar and be positioned buccal to the developing bicuspid.Periphery and Shape. The periphery usually has a well-defi nedcortical border ( Fig. 21-2 ). If the cyst becomes secondarily infected,the infl ammatory reaction of the surrounding bone may result in lossof this cortex (see Fig. 21-1, B ) or alteration of the cortex into a moresclerotic border. The outline of a radicular cyst usually is curved orcircular unless it is infl uenced by surrounding structures such as corticalboundaries.Internal Structure. In most cases the internal structure of radicularcysts is radiolucent. Occasionally, dystrophic calcifi cation maydevelop in long-standing cysts, appearing as sparsely distributed,small particulate radiopacities.Effects on Surrounding Structures. If a radicular cyst is large,displacement and resorption of the roots of adjacent teeth may occur.The resorption pattern may have a curved outline. In rare cases thecyst may resorb the roots of the related nonvital tooth. The cyst mayinvaginate the antrum, but there should be evidence of a corticalboundary between the contents of the cyst and the internal structureof the antrum ( Fig. 21-2, B ). The outer cortical plates of the maxillaor mandible may expand in a curved or circular shape ( Fig. 21-3 ).Cysts may displace the mandibular alveolar nerve canal in an inferiordirection.Differential DiagnosisDifferentiation of a small radicular cyst from an apical granulomamay be diffi cult and in some cases impossible. A round shape, a wellCHAPTER21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 345defi ned cortical border, and a size greater than 2 cm in diameter aremore characteristic of a cyst. Other periapical radiolucencies to considerare an early stage of periapical cemental dysplasia and an apicalscar or a surgical defect because in such cases, normal bone may neverfi ll in the defect completely. The patient s history helps with the differentiation.Radicular cysts that originate from the maxillary lateralincisor and are positioned between the roots of the lateral incisor andthe cuspid may be diffi cult to differentiate from an odontogenic keratocystor a lateral periodontal cyst. The vitality of the involved toothshould be tested. A nonvital tooth may have a larger pulp chamberthan neighboring teeth because of the lack of secondary dentin, whichnormally forms with time in the pulp chamber and canal of a vitaltooth (see Fig. 21-1 ).A large radicular cyst that has invaginated the maxillary antrummay collapse and start fi lling in with new bone ( Fig. 21-4 ). Withbiopsy, the histologic analysis may result in an erroneous diagnosis ofossifying fi broma or a benign fi bro-osseous lesion. Radiographically,the important feature is that the new bone always forms fi rst at theperiphery of the cyst wall as the cyst shrinks and not in the center ofthe cyst; this is a different pattern of bone formation than is seen withbenign fi bro-osseous lesions.ManagementTreatment of a tooth with a radicular cyst may include extraction,endodontic therapy, and apical surgery. Treatment of a large radicularcyst usually involves surgical removal or marsupialization. TheFIG. 21-3 A and B, Two images of a radicular cyst originating from a nonvital deciduous secondmolar show expansion of the buccal cortical plate to a circular or hydraulic shape (arrows) and displacementof the adjacent permanent teeth.A BFIG. 21-4 Axial (A) and coronal (B) CT images with use of a bone algorithm of a collapsing radicularcyst within the sinus. Note the unusual shape and the fact that new bone is being formed from theperiphery (arrows) toward the center. (Courtesy Drs. S. Ahing and T. Blight, University of Manitoba.)A B346 PART V RADIOGRAPHIC INTERPRETATIONradiographic appearance of the periapical area of an endodonticallytreated tooth should be checked periodically to make sure that normalhealing is occurring ( Fig. 21-5 ). Characteristically, new bone growsinto the defect from the periphery, sometimes resulting in a radiatingpattern resembling the spokes of a wheel. However, in a few casesnormal bone may not completely fi ll the defect, especially if a secondaryinfection or a considerable amount of bone destruction, includingthe buccal and lingual cortical plates, has occurred. Recurrence of aradicular cyst is unlikely if it has been removed completely.Residual CystDefi nitionA residual cyst is a cyst that remains after incomplete removal of theoriginal cyst. The term residual is used most often for a radicular cystthat may be left behind, most commonly after extraction of a tooth.Clinical FeaturesA residual cyst usually is asymptomatic and often is discovered onradiographic examination of an edentulous area. However, theremay be some expansion of the jaw or pain in the case of secondaryinfection.Radiographic FeaturesLocation. Residual cysts occur in both jaws, although they arefound slightly more often in the mandible. The epicenter is positionedin the former periapical region of the involved and missing tooth. Inthe mandible the epicenter is always above the inferior alveolar nervecanal ( Fig. 21-6 ).Periphery and Shape. A residual cyst has a cortical marginunless it becomes secondarily infected. Its shape is oval or circular.Internal Structure. The internal aspect of a residual cyst typicallyis radiolucent. Dystrophic calcifi cations may be present in longstandingcysts.Effects on Surrounding Structures. Residual cysts can causetooth displacement or resorption. The outer cortical plates of the jawsmay expand. The cyst may invaginate into the maxillary antrum ordepress the inferior alveolar nerve canal.Differential DiagnosisWithout the patient s history and previous radiographs, the clinicianmay have diffi culty determining whether a solitary cyst in the jaws isa residual cyst. Other examples of common solitary cysts includeodontogenic keratocysts. A residual cyst has greater potential forexpansion compared with an odontogenic keratocyst. The epicenterof a Stafne developmental salivary gland defect is located below themandibular canal (and thus is unlikely to be odontogenic innature).ManagementThe treatment for residual cysts is surgical removal or marsupialization,or both, if the cyst is large.Dentigerous CystSynonymFollicular cystDefi nitionA dentigerous cyst is a cyst that forms around the crown of anunerupted tooth. It begins when fl uid accumulates in the layers ofreduced enamel epithelium or between the epithelium and the crownof the unerupted tooth. An eruption cyst is the soft tissue counterpartof a dentigerous cyst.Clinical FeaturesDentigerous cysts are the second most common type of cyst in thejaws. They develop around the crown of an unerupted or supernumerarytooth. The clinical examination reveals a missing tooth orteeth and possibly a hard swelling, occasionally resulting in facialasymmetry. The patient typically has no pain or discomfort. Dentigerouscysts around supernumerary teeth account for about 5% of alldentigerous cysts, most developing around a mesiodens in the anteriormaxilla.FIG. 21-5 A Radicular Cyst That Is Healing After EndodonticTreatment. Arrows show the original outline of the cyst; note that thenew bone grows toward the center from the periphery.FIG. 21-6 The epicenter of this infected residual cyst is above theinferior alveolar nerve canal and has displaced the canal in an inferiordirection (arrows). Note that the cortical boundary is not continuousaround the whole cyst.CHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 347Radiographic FeaturesLocation. The epicenter of a dentigerous cyst is found just abovethe crown of the involved tooth, most commonly the mandibular ormaxillary third molar or the maxillary canine ( Fig. 21-7 ). An importantdiagnostic point is that this cyst attaches at the cementoenameljunction. Some dentigerous cysts are eccentric, developing from thelateral aspect of the follicle so that they occupy an area beside thecrown instead of above the crown (see Fig. 21-7, D ). Cysts related tomaxillary third molars often grow into the maxillary antrum and maybecome quite large before they are discovered. Cysts attached to thecrown of mandibular molars may extend a considerable distance intothe ramus.FIG. 21-7 Dentigerous Cysts. A, A cyst surrounds the crown of a third molar (arrows). B, The cysthas caused resorption of the distal root of the second molar (arrow). C, A cyst that involves the ramusof the mandible. D , A dentigerous cyst that is expanding distally from the involved third molar.ACDB348 PART V RADIOGRAPHIC INTERPRETATIONPeriphery and Shape. Dentigerous cysts typically have a welldefined cortex with a curved or circular outline. If infection is present,the cortex may be missing.Internal Structure. The internal aspect is completely radiolucentexcept for the crown of the involved tooth.Effects on Surrounding Structures. A dentigerous cyst has apropensity to displace and resorb adjacent teeth ( Figs. 21-7 and 21-8 ).It commonly displaces the associated tooth in an apical direction ( Fig.21-9 ). The degree of displacement may be considerable. For instance,maxillary third molars or cuspids may be pushed to the fl oor of theorbit (see Fig. 21-8 ), and mandibular third molars may be movedto the condylar or coronoid regions or to the inferior cortex of themandible. The fl oor of the maxillary antrum may be displaced as thecyst invaginates the antrum ( Fig. 21-10 ), and the cyst may displacethe inferior alveolar nerve canal in an inferior direction. Thisslow-growing cyst often expands the outer cortical boundary of theinvolved jaw.Differential DiagnosisBecause the histopathologic appearance of the lining epithelium is notspecifi c, the diagnosis relies on the radiographic and surgical observationof the attachment of the cyst to the cementoenamel junction.However, histopathologic examination must always be done to eliminateother possible lesions in this location.One of the most diffi cult differential diagnoses to make is betweena small dentigerous cyst and a hyperplastic follicle. A cyst should beconsidered with any evidence of tooth displacement or considerableexpansion of the involved bone. The size of the normal follicular spaceis 2 to 3 mm. If the follicular space exceeds 5 mm, a dentigerous cystis more likely. If uncertainty remains, the region should be reexaminedin 4 to 6 months to detect any increase in size or any infl uenceon surrounding structures characteristic of cysts.The differential diagnosis also may include an odontogenic keratocyst,an ameloblastic fi broma, and a cystic ameloblastoma. An odontogenickeratocyst does not expand the bone to the same degree as adentigerous cyst, is less likely to resorb teeth, and may attach furtherapically on the root instead of at the cementoenamel junction. It maynot be possible to differentiate a small ameloblastic fi broma or cysticameloblastoma from a dentigerous cyst if there is no internal structure.Other rare lesions that may have a similar pericoronal appearanceare adenomatoid odontogenic tumors and calcifi ed odontogeniccysts, both of which can surround the crown and root of the involvedtooth. Evidence of a radiopaque internal structure should be soughtin these two lesions. Occasionally a radicular cyst at the apex of aFIG. 21-8 A, This panoramic image reveals the presence of a large dentigerous cyst associated withthe left maxillary cuspid (arrow), which has been displaced. Notice the displacement and resorptionof other teeth in the left maxilla. B and C, Coronal and axial CT images of the same case showingsuperior-lateral displacement of the cuspid, expansion of the anterior wall of the maxilla, and expansionof the cyst into the nasal fossa.AB CCHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 349FIG. 21-9 A and B, These panoramic fi lms of the same case taken several years apart demonstratesuperior-posterior displacement of a maxillary third molar by a dentigerous cyst.A BFIG. 21-10 Dentigerous cysts displacing teeth. A, The third molar has been displaced to the inferiorcortex. B, The developing second molar has been displaced into the ramus by a cyst associated withthe fi rst molar. Axial (C) and coronal (D) CT images with bone algorithm reveal a maxillary thirdmolar displaced into the space occupied by the maxillary antrum; note the presence of a cortexbetween the cyst and the antrum.A BC D350 PART V RADIOGRAPHIC INTERPRETATIONprimary tooth surrounds the crown of the developing permanenttooth positioned apical to it, giving the false impression of a dentigerouscyst associated with the permanent tooth. This occurs most oftenwith the mandibular deciduous molars and the developing bicuspids.In these cases the clinician should look for extensive caries or largerestorations in a primary tooth that would indicate a radicular cyst.ManagementDentigerous cysts are treated by surgical removal, which may includethe tooth as well. Large cysts may be treated by marsupializationbefore removal. The cyst lining should be submitted for histologicexamination because ameloblastomas have been reported to occur inthe cyst lining. In addition, squamous cell carcinoma has been reportedto arise from the cyst lining of chronically infected cysts. Mucoepidermoidcarcinoma also has been reported.Buccal Bifurcation CystSynonymsMandibular infected buccal cyst, paradental cyst, and infl ammatoryparadental cystDefi nitionThe source of epithelium probably is the epithelial cell rests in theperiodontal membrane of the buccal bifurcation of mandibularmolars. The histopathologic characteristics of the lining are not distinctive.The etiology of proliferation is unknown; one theory holdsthat infl ammation is the stimulus, but infl ammation is not alwayspresent. The World Health Organization includes these cysts underinfl ammatory cysts.It is possible that the paradental cyst of the third molar and thebuccal bifurcation cyst (BBC) (associated with fi rst and secondmolars) are the same entity. The BBC is certainly a distinct clinicalentity. An associated enamel extension into the furcation region ofthird molars with paradental cysts has not been documented withmolars involved in a BBC. Also, the infl ammatory component associatedwith paradental cysts is not always present with BBCs.Clinical FeaturesA common sign is the lack of or a delay in eruption of a mandibularfi rst or second molar. On clinical examination the molar may bemissing or the lingual cusp tips may be abnormally protrudingthrough the mucosa, higher than the position of the buccal cusps.The fi rst molar is involved more frequently than is the second molar.The teeth are always vital. A hard swelling may occur buccal to theinvolved molar, and if it is secondarily infected, the patient has pain.The age of detection is younger, within the fi rst two decades for a BBCrather than the third decade with a paradental cyst of the thirdmolar.Radiographic FeaturesLocation. The mandibular fi rst molar is the most common locationof a BBC, followed by the second molar. The cyst occasionally isbilateral. It is always located in the buccal furcation of the affectedmolar ( Fig. 21-11 ). On periapical and panoramic fi lms the lesion mayFIG. 21-11 Bilateral Buccal BifurcationCysts. A, A panoramic imageshowing cysts related to the mandibularfi rst molars. The occlusal surface of eachtooth has been tipped in relation to theother teeth and adjacent teeth havebeen displaced. B and C, Occlusal fi lmsof the same case. Note the smoothcurved expansion of the buccal cortexand the displacement of the roots of thefi rst molars into the lingual cortical plate(arrows).AB CCHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 351appear to be centered a little distal to the furcation of the involvedtooth.Periphery and Shape. In some cases the periphery is not readilyapparent, and the lesion may be a very subtle radiolucent regionsuperimposed over the image of the roots of the molar. In other casesthe lesion has a circular shape with a well-defi ned cortical border.Some cysts can become quite large before they are detected.Internal Structure. The internal structure is radiolucent.Effects on Surrounding Structures. The most striking diagnosticcharacteristic of a BBC is the tipping of the involved molar sothat the root tips are pushed into the lingual cortical plate of themandible (see Fig. 21-11, B and C ) and the occlusal surface is tippedtoward the buccal aspect of the mandible (see Fig. 21-11, A ). Thisaccounts for the lingual cusp tips being positioned higher than thebuccal tips. This tipping may be detected in a panoramic or periapicalfi lm if the image of the occlusal surface of the affected tooth is apparentwhereas the unaffected teeth are not. The best diagnostic fi lm isthe cross-sectional (standard) mandibular occlusal projection, whichdemonstrates the abnormal position of the tooth roots. If the cystis large enough, it may displace and resorb the adjacent teeth andcause a considerable amount of smooth expansion of the buccalcortical plate. If the cyst is secondarily infected, periosteal new boneformation is seen on the buccal cortex adjacent to the involved tooth( Fig. 21-12 ).Differential DiagnosisDiagnosis of a BBC relies entirely on clinical and radiographic information.The major differential diagnosis includes lesions that couldelicit an infl ammatory periosteal response on the buccal aspect ofmandibular molars, such as a periodontal abscess or Langerhans cellhistiocytosis (see Fig. 21-12 ). The fact that only a BBC tilts the molaras described helps to differentiate it from other lesions. Also in thedifferential diagnosis is the dentigerous cyst. However, the epicenterof a dentigerous cyst is different because a BBC starts near the bifurcationregion of the tooth and does not surround the crown, as does adentigerous cyst.ManagementA BBC usually is removed by conservative curettage, although somecases have resolved without intervention. The involved molar shouldnot be removed. BBCs do not recur.Keratocystic Odontogenic TumorSynonymsOdontogenic keratocyst and primordial cystDefi nitionThe World Health Organization has reclassifi ed this cystic lesion intoa unicystic or multicystic odontogenic tumor on the basis of thetumorlike characteristics of the lining epithelium. Because the grossand radiographic appearance of keratocystic odontogenic tumor(KOT) is cystic in nature, this neoplasm is presented in this chapter.Unlike most cysts, which are thought to grow solely by osmotic pressure,the epithelium in the KOT appears to have innate growth potential,consistent with a benign tumor. This difference in the mechanismof growth gives KOT a different radiographic appearance from cysts.The epithelial lining is distinctive also because it is keratinized (hencethe name) and thin (four to eight cells thick). Occasionally budlikeproliferations of epithelium grow from the basal layer into the adjacentconnective tissue wall. Also, islands of epithelium in the wall maygive rise to satellite microcysts. The inside of the cyst often containsa viscous or cheesy material derived from the epithelial lining.Clinical FeaturesKOTs account for about one tenth of all cystic lesions in the jaws. Theyoccur in a wide age range, but most develop during the second andthird decades, with a slight male predominance. The cysts sometimesform around an unerupted tooth. KOTs usually have no symptoms,although mild swelling may occur. Pain may occur with secondaryinfection. Aspiration may reveal a thick, yellow, cheesy material(keratin). It is important to note that, unlike cysts, KOTs have a highpropensity for recurrence, possibly because of small satellite cysts orfragments of epithelium left behind after surgical removal of thecyst.Radiographic FeaturesLocation. The most common location of KOT is the posteriorbody of the mandible (90% occur posterior to the canines) and ramus(more than 50%) ( Fig. 21-13 ). The epicenter is located superior to theinferior alveolar nerve canal. This type of cyst occasionally has thesame pericoronal position as, and is indistinguishable from, a dentigerouscyst ( Fig. 21-13, B ).Periphery and Shape. As with cysts, KOTs usually show evidenceof a cortical border unless they have become secondarily infected. Thecyst may have a smooth round or oval shape identical to that of othercysts, or it may have a scalloped outline (a series of contiguous arcs)(see Figs. 21-13 and 21-15, C ).Internal Structure. The internal structure is most commonlyradiolucent. The presence of internal keratin does not increase theradiopacity. In some cases curved internal septa may be present, givingthe lesion a multilocular appearance (see Figs. 21-13 and 21-14, A ).Effects on Surrounding Structures. An important characteristicof the KOT is its propensity to grow along the internal aspect of thejaws, causing minimal expansion ( Fig. 21-15 ). This occurs throughoutthe mandible except for the upper ramus and coronoid process, whereconsiderable expansion may occur ( Fig. 21-14, C ). Occasionally theFIG. 21-12 Occlusal views of two examples of buccal bifurcationcysts that have been secondarily infected; note the laminated periostealnew bone formation on the buccal aspect of the fi rst molars and alsothe abnormal position of the roots of the fi rst molar in B. (CourtesyDr. Doug Stoneman, University of Toronto.)A B352 PART V RADIOGRAPHIC INTERPRETATIONFIG. 21-13 In panoramic image A a large keratocystic odontogenic tumor occupies the ramus andbody of the mandible; note the septa (black arrow), inferiorly displaced mandibular canal (white arrow),and the root resorption. The keratocyst in B has a pericoronal position relative to the impacted thirdmolar and the distal margin has a scalloped shape.A BFIG. 21-14 A, Cropped panoramic image of a keratocystic odontogenic tumor occupying the mandibularramus; note the septa (arrow). B and C, Two axial CT images with bone algorithm of the samecase demonstrating very little expansion in the body (B) but signifi cant expansion in the upper ramusin C (arrows).AB CCHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 353expansion of large lesions may exceed the ability of the periosteum toform new bone, thus allowing the cystic wall to contact soft tissueperipheral to the outer cortex of the mandible ( Fig. 21-16 ). The relativelyslight expansion common with these lesions probably contributesto their late detection, which occasionally allows them to reach alarge size. KOTs can displace and resorb teeth but to a slightly lesserdegree than dentigerous cysts. The inferior alveolar nerve canal maybe displaced inferiorly. In the maxilla this cyst can invaginate andoccupy the entire maxillary antrum.Differential DiagnosisWhen in a pericoronal position, a KOT may be indistinguishable froma dentigerous cyst. The lesion is likely to be a KOT if the cystic outlineis connected to the tooth at a point apical to the cementoenamel junctionor if no expansion of the cortical plates has occurred. Also,although KOTs can develop occlusal to developing teeth, often thefollicle of the involved tooth is not enlarged as in dentigerous cysts.The typical scalloped margin and multilocular appearance of the KOTmay resemble an ameloblastoma, but the latter has a greater propensityto expand. A KOT may show some similarity to an odontogenicmyxoma, especially in the characteristics of mild expansion andmultilocular appearance. A simple bone cyst often has a scallopedmargin and minimal bone expansion, as with the KOT; however, themargins of a simple bone cyst usually are more delicate and oftendiffi cult to detect. If several KOTs are found (which occurs in 4% to5% of cases), these tumors may constitute part of a basal cell nevussyndrome.ManagementIf a KOT is suspected, referral to a radiologist for a complete radiologicexamination is advisable. Because this tumor has a propensityto recur, an accurate determination of the extent and location of anycortical perforations with soft tissue extension is best achieved withcomputed tomography (CT). In the case of multiple cysts and thepossibility of basal cell nevus syndrome, a thorough radiologic examinationthat includes CT is required. This allows accurate determinationof the number of cysts and other osseous characteristics thatconfi rm the diagnosis.Surgical treatment may vary and can include resection, curettage,or marsupialization to reduce the size of large lesions before surgicalexcision. More attention usually is devoted to complete removal of thecystic walls to reduce the chance of recurrence. After surgical treatment,it is important to make periodic posttreatment clinical andradiographic examinations to detect any recurrence. Recurrent lesionsusually develop within the fi rst 5 years but may be delayed as long as10 years.FIG. 21-15 A large keratocysticodontogenic tumor (KOT) occupyingmost of the right body and ramus ofthe mandible. A, Despite the largesize, the buccal and lingual corticalplates of the mandible have beenexpanded only slightly, as can be seenin the occlusal fi lm (B). C, A KOTwithin the body of the mandible;note the lack of expansion and thecyst scalloping between the roots ofthe teeth.ACB354 PART V RADIOGRAPHIC INTERPRETATIONtelorism, and mild prognathism. Calcifi cation of the falx cerebri andother parts of the dura occur early in life.Radiographic FeaturesLocation. The location is the same as that of solitary KOTs,as described previously. The multiple KOTs may develop bilaterallyand can vary in size from 1 mm to several centimeters in diameter( Fig. 21-17 ).Other Radiographic Features. The reader should refer to thepreceding radiographic description of KOTs. In addition, a radiopaqueline of the calcifi ed falx cerebri may be prominent on the posteroanteriorskull projection. Occasionally this calcifi cation may appearlaminated.Differential DiagnosisThe presence of a cortical boundary and other cystic characteristicsdifferentiate basal cell nevus syndrome from other abnormalitiescharacterized by multiple radiolucencies (e.g., multiple myeloma).Cherubism appears as bilateral multilocular lesions but usually hassignifi cant jaw expansion, which is not characteristic of basal cellnevus syndrome. Also, cherubism pushes posterior teeth in an anteriordirection, a distinctive characteristic. Occasionally patients withmultiple dentigerous cysts may show some similarities, but dentigerouscysts are more expansile.ManagementThe KOTs are treated more aggressively than other solitary KOTsbecause there appears to be an even greater propensity for recurrence.FIG. 21-16 A, This cropped panoramic image reveals a large keratocystic odontogenic tumor occupyingmost of the ramus; note the scalloping margin (arrows). B, This axial CT with soft tissue windowof the same case showing perforation of the medial cortex and contacting the medial pterygoid muscle(arrow).A BBasal Cell Nevus SyndromeSynonymsNevoid basal cell carcinoma syndrome or Gorlin-Goltz syndromeDefi nitionThe term basal cell nevus syndrome comprises a number of abnormalitiessuch as multiple nevoid basal cell carcinomas of the skin,skeletal abnormalities, central nervous system abnormalities, eyeabnormalities, and multiple KOTs. It is inherited as an autosomaldominant trait with variable expressivity.Clinical FeaturesBasal cell nevus syndrome starts to appear early in life, usually after5 years of age and before 30 years of age, with the development ofKOTs within the jaws and skin basal cell carcinomas. Typically thereare multiple KOTs, usually appearing in multiple quadrants andearlier in life than solitary KOTs do. The recurrence rate of KOTs inthis syndrome appears to be higher than with the solitary variety. Athorough radiologic examination including CT imaging is requiredto detect all the jaw lesions. The skin lesions are small, fl attened, fl eshcoloredor brown papules that can occur anywhere on the body butare especially prominent on the face, neck, and trunk. Occasionallythe basal cell carcinomas will form later in life than the jaw lesions ornot at all. Skeletal anomalies include bifi d rib (most common) andother costal abnormalities such as agenesis, deformity, and synostosisof the ribs, kyphoscoliosis, vertebral fusion, polydactyly, shortening ofthe metacarpals, temporal and temporoparietal bossing, minor hyperCHAPTER21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 355Radiographic FeaturesLocation. A total of 50% to 75% of lateral periodontal cystsdevelop in the mandible, mostly in a region extending from the lateralincisor to the second premolar ( Fig. 21-18 ). Occasionally these cystsappear in the maxilla, especially between the lateral incisor and thecuspid.Periphery and Shape. A lateral periodontal cyst appears as awell-defi ned radiolucency with a prominent cortical boundary and around or oval shape. Rare large cysts have a more irregular shape.Internal Structure. The internal aspect usually is radiolucent.The botryoid variety may have a multilocular appearance, althoughthis aspect is related more to the histologic appearance.Effects on Surrounding Structures. Small cysts may efface thelamina dura of the adjacent root. Large cysts can displace adjacentteeth and cause expansion.Differential DiagnosisBecause the location and radiographic appearance of a lateral periodontalcyst are similar in other conditions, the following lesionsshould be included in the differential diagnosis: a small KOT, mentalFIG. 21-17 A, Panoramic image of a case of basal cell nevus syndrome; note the small Keratocysticodontogenic tumor (KOT) related to the unerupted left mandibular third molar and a large KOT withinthe left maxilla that has displaced the left maxillary third molar (arrow). B, Axial CT of the same case;note the small mandibular KOT (long arrow) seen in the panoramic image and another small KOT(short arrow) in the right mandible not seen in the panoramic fi lm. C, Another axial CT from the samecase revealing the large KOT in the left maxilla and two other KOTs not readily apparent in the panoramicimage.AB CIt is reasonable to examine the patient yearly for new and recurrentcysts. A panoramic fi lm may not be an adequate screening fi lm (seeFig. 21-17 ) and therefore CT is the modality of preference. Referralfor genetic counseling may be appropriate.Lateral Periodontal CystDefi nitionLateral periodontal cysts are thought to arise from epithelial rests inperiodontium lateral to the tooth root. This condition usually is unicystic,but it may appear as a cluster of small cysts, a condition referredto as botryoid odontogenic cysts. It has been postulated that the lateralperiodontal cyst is the intrabony counterpart of the gingival cyst inthe adult.Clinical FeaturesThe lesions usually are asymptomatic and less than 1 cm in diameter.The disorder has no apparent sexual predilection, and the age distributionextends from the second to the ninth decades (the mean ageis about 50 years). If these cysts become secondarily infected, they willmimic a lateral periodontal abscess.356 PART V RADIOGRAPHIC INTERPRETATIONforamen, small neurofi broma, or a radicular cyst at the foramen of alateral (accessory) pulp canal. The multiple (botryoid) cysts with amultilocular appearance may resemble a small ameloblastoma.ManagementLateral periodontal cysts usually do not require sophisticated imagingbecause of their small size. Excisional biopsy or simple enucleation isthe treatment of choice because these cysts do not tend to recur.Glandular Odontogenic CystSynonymSialo-odontogenic cystDefi nitionThe glandular odontogenic cyst is a rare cyst derived from odontogenicepithelium with a spectrum of characteristics including salivarygland features such as mucus-producing cells. Some authors hypothesizea relationship to a central mucoepidermoid carcinoma.Clinical FeaturesThere is a slight female predominance with a mean age ranging from46 to 50 years. This cyst has an aggressive behavior and a tendency torecur after surgery.Radiographic FeaturesLocation. This cyst occurs more commonly in the mandible andmost often in the anterior mandible and in the maxilla, commonlythe globulomaxillary region.Periphery and Shape. There is usually a cortical boundary thatmay be smooth or scalloped.Internal Structure. This cyst has been reported in both unilocularand multilocular appearances ( Fig. 21-19 ).Effects on Surrounding Structures. Expansion of the outer corticalplates of the jaws with regions of perforation through the cortexhas been reported. Displacement of teeth is a common feature.Differential DiagnosisThis cyst can appear identical to an ameloblastoma and in some casesmay be similar to a KOT. It is interesting to note that similar multilocularappearances have been associated with central mucoepidermoidcarcinomas.TreatmentBecause of the high rate of recurrence with conservative treatmentssuch as enucleation, more aggressive treatment including resectionmay be considered. Treated cases should be followed with periodicradiographic examinations to assess for recurrence.Calcifying Cystic Odontogenic TumorSynonymsCalcifying odontogenic cyst, calcifying epithelial odontogenic cyst,or Gorlin cystDefi nitionThe World Health Organization now categorizes this entity as a tumor.Calcifying cystic odontogenic tumors (CCOTs) are uncommon, slowgrowing,benign lesions. They occupy a spectrum ranging from a cystto an odontogenic tumor, with characteristics of a cyst alone or sometimesthose of a solid neoplasm (epithelial proliferation and a tendencyto continue growing). This lesion may manufacture calcifi edtissue identifi ed as dysplastic dentin, and in some instances the lesionis associated with an odontoma. This lesion also sometimes containsa more solid component that gives it an appearance resembling anameloblastoma, although it does not behave like one.FIG. 21-18 A lateral periodontal cyst in the mandibular premolarregion; note the classic well defi ned cortical border.FIG. 21-19 A, Cropped panoramic image of a glandular odontogeniccyst with a multilocular appearance very similar to an ameloblastoma.B, Axial CT image detailing the multilocular internal cystic structure.ABCHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 357Clinical FeaturesCCOTs have a wide age distribution that peaks at 10 to 19 years ofage, with a mean age of 36 years. A second incidence peak occursduring the seventh decade. Clinically, the lesion usually appears as aslow-growing, painless swelling of the jaw. Occasionally the patientcomplains of pain. In some cases the expanding lesion may destroythe cortical plate, and the cystic mass may become palpable as itextends into the soft tissue. The patient may report a discharge fromsuch advanced lesions. Aspiration often yields a viscous, granular,yellow fl uid.Radiographic FeaturesLocation. At least 75% of CCOTs occur in bone, with a nearlyequal distribution between the jaws. Most (75%) occur anterior to thefi rst molar, especially associated with cuspids and incisors, where thecyst sometimes manifests as a pericoronal radiolucency.Periphery and Shape. The periphery can vary from well defi nedand corticated with a curved, cystlike shape to ill defi ned andirregular.Internal Structure. The internal aspect can vary in appearance.It may be completely radiolucent; it may show evidence of small fociof calcifi ed material that appear as white fl ecks or small smoothpebbles; or it may show even larger, solid, amorphous masses ( Fig.21-20 ). In rare cases the lesion may appear multilocular.Effects on Surrounding Structures. Occasionally (20% to 50%of cases) this tumor is associated with a tooth (most commonly acuspid) and impedes its eruption. Displacement of teeth and resorptionof roots may occur. Perforation of the cortical plate may be seenradiographically with enlarging lesions.Differential DiagnosisWhen no internal calcifi cations are evident and this lesion has a pericoronalposition, it may be indistinguishable from a dentigerous cyst.Other lesions that have internal calcifi cations to be considered includean adenomatoid odontogenic tumor, ameloblastic fi bro-odontoma,and calcifying epithelial odontogenic tumor. The common locationfor the CCOT is not common for either the fi bro-odontoma or thecalcifying epithelial odontogenic tumor. Finally, long-standing cystsmay have dystrophic calcifi cation, giving a similar appearance.ManagementThis tumor can be treated with enucleation and curettage. Becauseclinicians generally have little experience with the more solid neoplasticvariants, it is wise to follow treatment with periodic radiographicevaluations for recurrence.FIG. 21-20 A and B, Calcifying cystic odontogenictumor (CCOT) related to the lateral incisor.Note the well-defi ned corticated border, internalcalcifi cations, and resorption of part of the root ofthe central incisor. C, Axial CT image of a largeCCOT invaginating into the maxillary sinus; notethe small calcifi cations along the posterior border(arrow).ACB358 PART V RADIOGRAPHIC INTERPRETATIONNonodontogenic CystsNasopalatine Duct CystSynonymsNasopalatine canal cyst, incisive canal cyst, nasopalatine cyst, medianpalatine cyst, and median anterior maxillary cystDefi nitionThe nasopalatine canal usually contains remnants of the nasopalatineduct, a primitive organ of smell, and the nasopalatine vessels andnerves. Occasionally a cyst forms in the nasopalatine canal when theseembryonic epithelial remnants of the nasopalatine duct undergo proliferationand cystic degeneration.Clinical FeaturesNasopalatine duct cysts account for about 10% of jaw cysts. The agedistribution is broad, with most cases being discovered in the fourththrough sixth decades. The incidence is three times higher in males.Most of these cysts are asymptomatic or cause such minor symptomsthat they are tolerated for long periods. The most frequent complaintis a small, well-defi ned swelling just posterior to the palatine papilla.This swelling usually is fl uctuant and blue if the cyst is near thesurface. The deeper nasopalatine duct cyst is covered by normalappearingmucosa unless it is ulcerated from masticatory trauma. Ifthe cyst expands, it may penetrate the labial plate and produce a swellingbelow the maxillary labial frenum or to one side. The lesion alsomay bulge into the nasal cavity and distort the nasal septum. Pressurefrom the cyst on the adjacent nasopalatine nerves that occupy thesame canal may cause a burning sensation or numbness over thepalatal mucosa. In some cases cystic fl uid may drain into the oralcavity through a sinus tract or a remnant of the nasopalatine duct.The patient usually detects the fl uid and reports a salty taste.Radiographic FeaturesLocation. Most nasopalatine duct cysts are found in the nasopalatineforamen or canal. However, if this cyst extends posteriorlyto involve the hard palate ( Fig. 21-21 ), it often is referred to as amedian palatal cyst ( Fig. 21-22 ). If it expands anteriorly between thecentral incisors, destroying or expanding the labial plate of bone andcausing the teeth to diverge, it sometimes is referred to as a mediananterior maxillary cyst. This cyst may not always be positionedsymmetrically.Periphery and Shape. The periphery usually is well defi ned andcorticated and is circular or oval in shape. The shadow of the nasalspine sometimes is superimposed on the cyst, giving it a heartshape.FIG. 21-21 Two examples of nasopalatineduct cysts. Note the uniform periodontalmembrane space around all the apices.ABCHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 359Internal Structure. Most nasopalatine duct cysts are totally radiolucent.Some rare cysts may have internal dystrophic calcifi cations,which may appear as ill-defi ned, amorphous, scattered radiopacities.Effects on Surrounding Structures. Most commonly this cystcauses the roots of the central incisors to diverge, and occasionallyroot resorption occurs. Seen from a lateral perspective, the cyst mayexpand the labial cortex and the palatal cortex ( Fig. 21-23 ). The fl oorof the nasal fossa may be displaced in a superior direction.Differential DiagnosisThe most common differential diagnosis is a large incisive foramen.A foramen larger than 6 mm may simulate the appearance of a cyst.However, a clinical examination should reveal the expansion characteristicof a cyst and other changes that occur with a space-occupyinglesion, such as displacement of teeth. A lateral view of the anteriormaxilla, with an occlusal fi lm held outside the mouth and against thecheek, also can help in making the differential diagnosis, as can across-sectional (standard) occlusal view. If doubt still exists, comparisonwith previous images may be useful, or aspiration may beattempted, or another image may be made in 6 months to 1 year toassess any change in size. A radicular cyst or granuloma associatedwith a central incisor is similar in appearance to an asymmetric nasopalatinecyst. The presence or absence of the lamina dura and enlargementof the periodontal ligament space around the apex of the centralincisor indicate an infl ammatory lesion. A vitality test of the centralincisor may be useful. A second periapical view taken at a differenthorizontal angulation should show an altered position of the imageof a nasopalatine duct cyst, whereas a radicular cyst should remaincentered about the apex of the central incisor.FIG. 21-22 A, Axial CT image of a nasopalatine duct cyst positioned palatal to both maxillary centralincisors (arrows). B, Coronal CT image of the same case.A BFIG. 21-23 A nasopalatine canal cyst viewed from two perspectives: (A) a standard occlusal viewand (B) from the lateral aspect, which is created by placing the fi lm outside the mouth against thecheek and directing the x-ray beam at a tangent to the labial surface of the central incisors.A B360 PART V RADIOGRAPHIC INTERPRETATIONManagementThe appropriate treatment for a nasopalatine cyst is enucleation, preferablyfrom the palate to avoid the nasopalatine nerve. If the cyst islarge and the danger exists of devitalizing the tooth or creating a nasooralor antro-oral fi stula, the surgeon may elect to marsupialize thecyst.Nasolabial CystSynonymNasoalveolar cystDefi nitionThe exact origin of nasolabial cysts is unknown. They may be fi ssuralcysts arising from the epithelial rests in fusion lines of the globular,lateral nasal, and maxillary processes. Alternatively, the source of theepithelium may be from the embryonic nasolacrimal duct, whichinitially lies on the bone surface.Clinical FeaturesWhen this rare lesion is small, it may produce a very subtle, unilateralswelling of the nasolabial fold and may elicit pain or discomfort.When large, it may bulge into the fl oor of the nasal cavity, causingsome obstruction, fl aring of the alae, distortion of the nostrils, andfullness of the upper lip. If infected, it may drain into the nasal cavity.It usually is unilateral, but bilateral lesions have occurred. The age ofdetection ranges from 12 to 75 years, with a mean age of 44 years.About 75% of these lesions occur in females.Radiographic FeaturesLocation. Nasolabial cysts are primarily soft tissue lesions locatedadjacent to the alveolar process above the apices of the incisors.Because this is a soft tissue lesion, plain radiographs may not showany detectable changes. The investigation could include either CT ormagnetic resonance imaging (MRI), both of which can provide animage of soft tissues ( Fig. 21-24 ).Periphery and Shape. Thin axial CT images with use of the softtissue algorithm with contrast reveal a circular or oval lesion withslight soft tissue enhancement of the periphery.Internal Structure. In CT images with the soft tissue algorithmthe internal aspect appears homogeneous and relatively radiolucentcompared with the surrounding soft tissues.Effects on Surrounding Structures. Occasionally a cyst causeserosion of the underlying bone ( Fig. 21-25 ), producing an increasedradiolucency of the alveolar process beneath the cyst and apical tothe incisors. Also, the usual outline of the inferior border of the nasalfossa may become distorted, resulting in a posterior bowing of thismargin.Differential DiagnosisThe swelling caused by an infected nasolabial cyst may simulate anacute dentoalveolar abscess. It is important to establish the vitality ofthe adjacent teeth. This cyst may also resemble a nasal furuncle if itpushes upward into the fl oor of the nasal cavity. A large mucousextravasation cyst or a cystic salivary adenoma should also be consideredin the differential diagnosis of an uninfected nasolabial cyst.ManagementThe nasolabial cyst should be excised through an intraoral approach.These cysts do not tend to recur.Dermoid CystDefi nitionDermoid cysts are a cystic form of a teratoma thought to be derivedfrom trapped embryonic cells that are totipotential. The resultingcysts are lined with epidermis and cutaneous appendages and fi lledwith keratin or sebaceous material (and in rare cases with bone, teeth,muscle, or hair, in which case they are properly called teratomas).Clinical FeaturesDermoid cysts may develop in the soft tissues at any time from birth,but they usually become clinically apparent between 12 and 25 yearsof age, about equally distributed between the sexes. The swelling,which is slow and painless, can grow to several centimeters in diameter,and when located in the neck or tongue, it may interfere with breathing,speaking, and eating. Depending on how deep the cyst is positionedin the neck, it can deform the submental area. On palpationFIG. 21-24 A nasolabial cyst shown in an axial CT image with a softtissue algorithm. Note the well-defi ned periphery and the erosion ofthe labial aspect of the alveolar process (arrow).FIG. 21-25 An occlusal view of a nasolabial cyst. The radiographshows erosion of the alveolar bone (o) and elevation of the fl oor of thenasal fossa (arrows). (From Chinellato LE, Damante JH: Oral Surg OralMed Oral Pathol 58:729-735, 1984.)CHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 361these cysts may be fl uctuant or doughy, according to their contents.Because they usually are in the midline, they do not affect the teeth.Radiographic FeaturesBecause dermoid cysts are soft tissue cysts, diagnostic imaging is bestaccomplished by CT or MRI.Location. A dermoid cyst is a rare developmental anomaly thatmay occur anywhere in the body. About 10% or fewer arise in the headand neck, and only 1% to 2% develop in the oral cavity. Of these,about 25% occur in the fl oor of the mouth and on the tongue. Theymay be midline or lateral in location.Periphery and Shape. The periphery of the lesion usually is welldefi ned by more radiopaque soft tissue of this cyst compared withsurrounding soft tissue, as seen in CT scans.Internal Structure. Dermoid cysts seldom have any internal mineralizedstructures when they occur in the oral cavity; therefore theyare radiolucent on conventional radiographs. However, a CT scan ofthe area may reveal a soft tissue multilocular appearance ( Fig. 21-26 ).If teeth or bone form in the cyst, their radiopaque images, with characteristicshapes and densities, are apparent on the radiograph.Differential DiagnosisLesions that are clinically similar to dermoid cysts are ranula (unilateralor bilateral blockage of Wharton s ducts), thyroglossal duct cysts,cystic hygromas, branchial cleft cysts, cellulitis, tumors (lipoma andliposarcoma), and normal fat masses in the submental area.ManagementDermoid cysts do not recur after surgical removal.Former CystsWith time it has become clear that some names used to describedistinct entities are no longer valid. These names include primordialcysts (now recognized largely to be KOTs), median palatal cysts(now recognized as a variant of the nasopalatine duct cyst), andmedian mandibular and globulomaxillary cysts (because the entrapmentof epithelium theory is no longer accepted). Globulomaxillarycysts are now recognized to be radicular or lateral periodontal cystsor KOTs.Cystlike LesionsSimple bone cysts (SBCs) are included in this chapter because of theirhistoric classifi cation and because the characteristics and behaviorseen in diagnostic imaging are cystic in nature. However, it is importantto remember that these lesions are not true cysts.Simple Bone CystSynonymsTraumatic bone cyst, hemorrhagic bone cyst, extravasation cyst, progressivebone cavity, solitary bone cyst, and unicameral bone cystDefi nitionAn SBC is a cavity within bone that is lined with connective tissue. Itmay be empty, or it may contain fl uid. However, because it has noepithelial lining, it is not a true cyst. The etiology of SBCs is unknown,although they may be a localized aberration in normal bone remodelingor metabolism. This theory is supported indirectly by the fact thatthese bony cavities often occur inside lesions of cemento-osseousdysplasia and fi brous dysplasia. No evidence exists to support a traumaticcause.Clinical FeaturesSBCs are very common lesions. Most occur in the fi rst two decades oflife, with a mean age of 17 years. The lesion shows a male predominanceof approximately 2 : 1. Multiple SBCs can develop, especiallywhen the disorder occurs with cemento-osseous dysplasia. The occurrenceof SBCs in cemento-osseous dysplasia is seen in an older population,with a mean age of 42 years, and with a female predominance of4 : 1. SBCs are asymptomatic in most cases, but occasionally pain ortenderness may be present, especially if the cyst has become secondarilyinfected. Expansion of the mandible or tooth movement is possiblebut unusual. The teeth in the affected region usually are vital. MostSBCs are discovered only by chance, during radiographic examinations,and for this reason they can become quite large. There is no significant incidence of pathologic fractures. Aspiration usually producesonly a few milliliters of straw-colored or serosanguineous fl uid.Radiographic FeaturesLocation. Almost all SBCs are found in the mandible ( Fig.21-27 ); in rare cases they develop in the maxilla. The lesion can occuranywhere in the mandible but is seen most often in the ramus andposterior mandible in older patients. SBCs also frequently occur withcemento-osseous and fi brous dysplasia.Periphery and Shape. The margin may vary from a well-defi ned,delicate cortex to an ill-defi ned border that blends into the surroundingbone. The boundary usually is better defi ned in the alveolarprocess around the teeth than in the inferior aspect of the body of themandible. The shape most often is smooth and curved, like a cyst,with an oval or scalloped border. The lesion often scallops betweenthe roots of the teeth (see Fig. 21-27 ).FIG. 21-26 A CT scan of a dermoid cyst showing an encapsulatedmass on the left and several soft tissue loculations. (From Hunter TB,Paplanus HS, Chemin MM et al: AJR Am J Roentgenol 141:1239-1240,1983.)362 PART V RADIOGRAPHIC INTERPRETATIONInternal Structure. The internal structure is totally radiolucent,but occasionally it may appear multilocular, although the lesion doesnot contain true septa. This appearance is the result of pronouncedscalloping of the endosteal surface of either the buccal or lingual plates( Fig. 21-28 ). The ridges of bone produced by the scalloping give theappearance of septa on a lateral view of the mandible.Effects on Surrounding Structures. In most cases these lesionshave no effect on the surrounding teeth, although rare cases of toothdisplacement and resorption have been documented. Often the lesioninvolves all the bone around the roots of the teeth but leaves thelamina dura intact or only partly disrupted ( Fig. 21-29 ). Similarly, thesparing of the cortical boundary of the crypt around a developingtooth is characteristic. As previously mentioned, these lesions have apropensity to scallop the endosteal surface of the outer cortex of themandible. SBCs also have a tendency to grow along the long axis ofthe bone, causing minimal expansion ( Fig. 21-30 ). However, expansionof the involved bone can occur and is more common with largerlesions ( Fig. 21-31 ).Differential DiagnosisAn SBC may have an appearance similar to that of a true cyst, especiallya KOT. This is because KOTs tend to grow along bone with veryFIG. 21-27 A panoramic fi lm demonstrating an SBC (A), an occlusal fi lm (B), and a periapical fi lm(C). The occlusal fi lm shows that no expansion has occurred in the buccal or lingual cortical plates.Except for the superior border, the borders are ill defi ned and the lesion has scalloped around theteeth and thinned the inferior border of the mandible, but the lamina dura is still present.A B CFIG. 21-28 A, A simple bone cyst has a multilocular appearance in this lateral oblique view of themandible. B, The periapical view appears to show internal septa (arrows) because of the scalloping ofthe endosteal surface of the cortical plates, as seen in the inferior cortex (arrows) in A and of theendosteal surface of the buccal cortex in the occlusal view (C).A B CFIG. 21-29 A simple bone cyst in which the lamina dura is maintainedon most root surfaces involved with the lesion except for themesial surface of the distal root tip of the fi rst molar.CHAPTER 21 CYSTS AND CYSTLIKE LESIONS OF THE JAWS 363FIG. 21-30 A and B, A simple bone cyst extending from the fi rstbicuspid posteriorly to the base of the ramus and occupying most ofthe mandible. Considering the extent of the lesion, very little expansionof the buccal or lingual cortical plates has occurred, as can beseen in the axial CT image (B) with bone algorithm.AB FIG. 21-31 A simple bone cyst (arrow) positioned in the anterior ofthe mandible. Note that the superior aspect of the peripheral cortexis better defi ned than the inferior border and that evidence exists ofsome expansion of the mandible s lingual cortex, which in part maydue to muscle attachment at the genial tubercles.FIG. 21-32 An axial CT image with a bone algorithm displaying asmall simple bone cyst in the process of healing (arrow). Note the fi neinternal granular bone and very slight expansion of the ramus.little expansion and often have scalloped borders similar to those ofan SBC. However, KOTs usually have a more defi nite cortical boundary,resorb and displace teeth, and occur in an older age group. Becausethe SBC may remove bone around teeth without affecting the teeth,there may be a tendency to include a malignant lesion in the differentialdiagnosis. However, maintenance of some lamina dura and thelack of an invasive periphery and bone destruction should be enoughto remove this category of diseases from consideration.The diagnosis relies primarily on radiographic and surgical observationsbecause the histopathologic aspects are not characteristic.These lesions occasionally heal spontaneously. A biopsy and analysisof a healing cyst may falsely indicate the presence of an ossifyingfi broma or fi brous dysplasia because of the formation of new immaturebone ( Fig. 21-32 ).364 PART V RADIOGRAPHIC INTERPRETATIONManagementThe customary treatment is a conservative opening into the lesion andcareful curettage of the lining; this usually initiates bleeding and subsequenthealing. Spontaneous healing has been reported. Periodicfollow-up radiographic examinations are advisable, especially if thepatient declines treatment. These lesions can recur but it is rare.