interpretation of panoramic radiographs

Australian Dental Journal 2012; 57:(1 Suppl): 40–45

doi: 10.1111/j.1834-7819.2011.01655.x

Interpretation of panoramic radiographs

S Perschbacher*

*Department of Radiology, Faculty of Dentistry, The University of Toronto, Ontario, Canada.

ABSTRACT

Panoramic radiography has become a commonly used imaging modality in dental practice and can be a valuable diagnostictool in the dentist’s armamentarium. However, the panoramic image is a complex projection of the jaws with multiplesuperimpositions and distortions which may be exacerbated by technical errors in image acquisition. Furthermore, thepanoramic radiograph depicts numerous anatomic structures outside of the jaws which may create additional interpretationchallenges. Successful interpretation of panoramic radiographs begins with an understanding of the normal anatomy of thehead and neck and how it is depicted in this image type. This article will describe how osseous structures, soft tissues, air spacesand ghost shadows contribute to the final panoramic image. A systematic and repeated approach to examining panoramicradiographs, which is recommended to ensure that critical findings are not overlooked, is also outlined. Examples ofchallenging interpretations, including variations of anatomy, artefacts and disease, are presented to illustrate these concepts.

Keywords: Dental radiology, orthopantomograph.

INTRODUCTION

Panoramic radiography has become a commonly usedimaging modality in dental practice and can be avaluable diagnostic tool in the dentist’s armamentar-ium. However, the panoramic image is a complexprojection of the jaws with multiple superimpositionsand distortions which may be exacerbated by technicalerrors in image acquisition. Furthermore, the pano-ramic radiograph depicts numerous anatomic structuresoutside of the jaws which may create additionalinterpretation challenges. Successful interpretation ofpanoramic radiographs begins with an understandingof the normal anatomy of the head and neck and how itis depicted in this image type. This article will describehow osseous structures, soft tissues, air spaces andghost shadows contribute to the final panoramic image.A systematic and repeated approach to examiningpanoramic radiographs, which is recommended toensure that critical findings are not overlooked, is alsooutlined. Examples of challenging interpretations,including variations of anatomy, artefacts and disease,are presented to illustrate these concepts.

Anatomy of a panoramic radiograph

Although it is obvious that a panoramic radiographdepicts the teeth and jaws in a single convenient view, it

may be less clear how the other structures of the headand neck become captured on the image. It is oftenthese superimposing hard and soft tissues and airwaysthat create confusing shadows which cause challengesin interpretation.

The panoramic perspective

The first step in understanding panoramic anatomy is toappreciate the perspective from which each part of theimage is presented. Because the image is captured by anX-ray tube which rotates around the patient’s head,rather than from a stationary source, this perspectivechanges from the posterior regions of the jaws to theanterior area. The right and left posterior parts of theimage represent lateral views, looking at the patientfrom the side; the anterior part of the image representsan anterior-posterior view, looking at the patient fromthe front (Fig. 1). The entire panoramic image isanalogous to a composite of portions of two lateraland one anterior-posterior skull views, except withoutas many superimpositions.

Osseous anatomy

With the panoramic perspective in mind, the osseousstructures of the maxillofacial region can be reviewed.The structures around the posterior maxilla, which

40 ª 2012 Australian Dental Association

Australian Dental JournalThe official journal of the Australian Dental Association

include the sphenoid, zygomatic and temporal bones,are likely the least familiar for many dental practitio-ners but contribute an important part of the panoramicimage. The pterygoid plates of the sphenoid bonearticulate with the posterior wall of the maxilla and,together, form the pterygomaxillary fissures (Fig. 1aand b). The zygomatic processes of the maxilla arethick buttresses of bone extending laterally from themaxilla bilaterally and are seen as J-shaped shadowssuperimposed over the maxillary sinuses (Fig. 1c). Theyarticulate with the zygomatic bones which, in turn,articulate with the zygomatic processes of the temporalbones to form the zygomatic arches (Fig. 1d). Thezygomatic arches can be followed posteriorly to wherethe temporal bones form the superior components ofthe temporomandibular joints (Fig. 1e). Sometimes themastoid processes of the temporal bones, containingmultiple radiolucent air cells, are imaged posterior andinferior to the temporomandibular joints (Fig. 1f).Occasionally, the mastoid air cells may extend anteri-orly and pneumatize the roof of the temporomandib-ular joint (Fig. 2). This is a normal anatomic variationbut may seem to mimic pathology due to the multiloc-ular appearance produced. The lateral and inferiororbital rims of the orbits are seen as thick, curved,linear radiopaque structures superior to the maxillary

sinuses (Fig. 1g). Each infraorbital canal may be seen asthin parallel cortices, extending inferiorly and mediallyfrom the floor of the orbit (Fig. 1h). The inferiorturbinates of the nasal fossa create surprisingly largeshadows across a large portion of the maxillary sinuses(as seen from the lateral perspective). They are also seenin the middle part of the image on either side of thenasal septum (seen from the anterior perspective)(Fig. 1i). The hyoid bone, which is normally seeninferior to the mandible, may create confusion when itbecomes superimposed over the inferior border becauseof patient positioning (Fig. 1j).

Fig 1. Top – composite photograph depicting the osseous anatomy of the maxilla and surrounding bones from the panoramic perspective. Theanterior region is viewed from the front while the posterior regions are viewed from the side. Bottom – a panoramic radiograph divided to match theregions represented by the photograph above. a and black dotted outline = pterygoid plate; b = pterygomaxillary fissure; c = zygomatic processof maxilla; d = zygomatic arch; e = temporal component of temporomandibular joint; f = mastoid process of temporal bone (not imaged inpanoramic radiograph); g = lateral and inferior orbital rim; h = infraorbital canal; i and white dotted outline = inferior concha ⁄ turbinate;

j = hyoid bone.

Fig 2. Mastoid air cells are seen bilaterally where they have pneu-matized the articular processes of the temporal bones creating

rounded, radiolucent loculations (black arrows). This is a variation ofnormal anatomy.

ª 2012 Australian Dental Association 41


Soft tissues and air spaces

The osseous structures of the maxillofacial region aresurrounded by the soft tissues of the face, neck and oralcavity. These soft tissues create indistinct radiopaqueshadows which superimpose over the osseous anddental structures. The external nose may be seen overthe apices of the maxillary incisors with the ala curvinglaterally from the midline (Fig. 3a). The soft tissues ofthe external ear are often seen superimposed over themandibular condyle with the earlobe forming arounded radiopacity posterior to the ramus (Fig. 3b).The largest intraoral shadow is created by the tongue,whose dome-shaped image occupies a large proportionof the panoramic radiograph (Fig. 3c). In the posteriorparts of the radiograph, the posterior region of thetongue may have a more irregular surface due to thelingual tonsils (Fig. 3d). The epiglottis can often be seenas a thin finger-like projection extending from theposterior tongue, below the angles of the mandible(Fig. 3e). The soft palate is seen from a lateralperspective on both sides of the panoramic image asan oval or inverted tear-drop shape extending off thehard palate (Fig. 3f). Its inferior surface is superior andapproximately parallel to the tongue.

The upper airway includes the nasal fossa, oral cavityand pharynx, all of which are imaged on the panoramicradiograph as radiolucent passages. These radiolucen-cies may be confused for bone destroying pathology orfractures (Fig. 4). The nasal fossa is seen in the midline,superiorly, and extends bilaterally across the region ofthe maxillary sinuses (Fig. 3,1). Posteriorly, it opensinto the nasopharynx. The nasopharynx is seen poster-ior to the maxilla and superior to the soft palate(Fig. 3,2). It is continuous with the oropharynx inferi-orly, which occupies the region anterior to the cervicalspine and posterior to the tongue (Fig. 3,3). The oralcavity may be seen as a variably-sized radiolucent stripbetween the superior surface of the tongue and thepalate (Fig. 3,4). The increased radiolucency of the oralcavity may obscure the roots of the anterior teeth due tooverexposure. This effect may be minimized by havingthe patient place his or her tongue flat against the palateduring imaging. The oral orifice, or space createdbetween the upper and lower lips, may be seen as a‘kiss-shaped’ radiolucency over the crowns of themaxillary and mandibular incisors (Fig. 3,5). Havingthe patient close his or her lips around the bite-stick canprevent overexposure of this area.

Ghost shadows

Ghost shadows are shadows of structures imaged whenthey are not within the focal trough. Because thesestructures are outside the plane of focus, they appearincreasingly magnified and blurry. For example, when

the left side of the mandible is being imaged, the film orsensor is positioned close to this side. However, the X-ray source is positioned on the right side of the patientand the beam must pass through the right mandible inorder to image the left side. Because the right side is at agreater distance from the film, its image is enlarged andindistinct. Hence there is a ghost shadow of the rightmandible seen superimposed, in a slightly superiorposition and a reversed orientation, over the leftmandible. Of course, the same is true for the contra-lateral side (Fig. 5a). The cervical spine may be seen infocus on a panoramic radiograph on the most posteriorparts of the image. However, a ghost shadow of thecervical spine is formed when the anterior teeth areimaged because the X-ray beam originates from behindthe patient’s head. This shadow may obscure a clearview of the anterior region of the jaws (Fig. 5b). Havinga patient stand as tall as possible with his or her cervicalspine extended maximally helps minimize this super-imposition. Foreign objects, such as earrings or facialjewellery, may also create ghost shadows which canobstruct visualization of the underlying anatomy if theyare not removed (Fig. 6).

Fig 3. Panoramic radiograph with major soft tissue structures (a–f)and airways (1–5) traced. a = external nose; b = external ear;

c = tongue; d = lingual tonsils on posterior tongue; e = epiglottis;f = soft palate; 1 = nasal fossa; 2 = nasopharynx; 3 = oropharynx;

4 = oral cavity; 5 = oral orifice.

Fig 4. The air shadow of the oral cavity may create a thin radiolucentline superimposed over the mandibular ramus, which may be mistakenfor a fracture if not properly identified (open black arrows). Carefulexamination of the periphery of the radiograph is done to avoidmissing findings in the tissues surrounding the jaws. An elongated

styloid process (black arrow) and submandibular calcification (whitearrow), most likely representing a submandibular gland sialolith, are

detected in this patient.


S Perschbacher

An approach to reading panoramic radiographs

The interpretation of a panoramic image follows thesame principles as with any other image or imageseries. A systematic and repeated process is used toensure that all significant findings are identified. Anobserver cannot count on abnormalities to presentthemselves. Rather, one must be vigilant in assessingall anatomic structures to ensure they are presentand normal. In the systematic approach recom-mended here the osseous structures and surroundingsoft tissues are assessed first. Second, the alveolarprocesses are examined. Finally, the teeth areevaluated.

Osseous structures and surrounding soft tissues

Compared to intraoral radiographs, the panoramicimage depicts a much larger area of anatomic structuresof the oral and maxillofacial region. More time willtherefore be required to assess these structures, thoughonce a routine is established a practitioner will find thatthis becomes a quick and natural process. It is critical tohave a good understanding of the normal anatomy inorder to identify the presence of any abnormalities. It isuseful to compare the left and right sides of the imagewhen deciding if a finding is normal, since structures

appearing bilaterally are generally anatomic. Compar-ing the left and right sides may also allow detection ofany asymmetries that may be indicative of disease or adevelopmental condition.

The following steps are an example of an approach toanalysing the complex projection of the anatomicstructures on a panoramic radiograph:1. Assess the periphery and corners of the image

• Start here to avoid zoning in on the teeth andneglecting important findings in the tissuessurrounding the jaws (Fig. 4).

• Structures that may be seen in this area includethe:

– orbits– articular processes of the temporal bones (at the

temporomandibular joints)– cervical spine– styloid processes– pharynx– hyoid bone.

2. Examine the outer cortices of the mandible• Trace the periphery of the bone starting at one

spot and completing a circuit which includes:– anterior and posterior rami– coronoid processes– condyles and condylar necks– inferior border.• Look for continuity and evenness of the cortices

(Fig. 7).3. Examine the cortices of the maxilla

• This includes the posterior and medial walls andfloor of each maxillary sinus.

• While examining the posterior wall of the sinus,also look at the:

– zygomatic process of the maxilla– pterygomaxillary fissure

Fig 5. The ghost shadows produced by the contralateral mandible (a)and cervical spine (b) are traced on this panoramic radiograph. Theshadows of these structures are indistinct because they are so far

outside the focal trough when imaged.

Fig 6. Earrings worn by this patient during image acquisition havecreated ghost shadows. The right earring is seen superimposed over theleft maxillary sinus (white arrow) and the left earring is projected over

the right zygomatic arch (black arrow).

Fig 7. Careful examination of this panoramic radiograph reveals thatthe inferior cortex of the mandible is not seen clearly on the left side,compared to the right. Assessment of the bone pattern also revealsincreased trabecular bone density in the posterior left mandible. Thishas caused the mandibular nerve canal to appear relatively more

prominent. The path of the nerve canal is also altered in a superiordirection. These findings are consistent with fibrous dysplasia. Thisimage cannot portray the buccal-lingual expansion that is character-

istic of this condition.



- The thin radiopaque lines produced by thesestructures run roughly parallel to the posterior wall ofthe maxillary sinus, and may be confused with it.Destructive disease affecting the maxillary sinus mayerode the posterior wall, which can be easily missed ifall three lines are not identified (Fig. 8).4. Examine the zygomatic bones and arches

• Follow where they extend posteriorly from thezygomatic processes of the maxilla to thetemporal bones.

5. Assess the internal density of the maxillary sinuses• Compare left and right sides.• Opacification is most commonly a sign of

inflammatory disease but could be a sign ofmore serious pathology.

6. Assess the structures of the nasal cavity and thepalates

• Examine the nasal floor ⁄ hard palate and con-chae extending horizontally along both sidesof the image.

• Examine the nasal septum in the midline.• Note the soft palate seen bilaterally extending

from the posterior aspect of the hard palateand into the oropharynx.

7. Examine bone the pattern of the maxilla andmandible

• Assess the density and pattern of the trabeculaefor abnormalities (Fig. 7).

• Keep in mind that some metabolic conditionsmay present with a generalized alteration inbone pattern and therefore comparing leftand right sides may not be helpful.

• In the mandible examine the size, position,cortication and symmetry of the:

– inferior alveolar nerve canals– mandibular foramina– mental foramina.

Alveolar processes and teeth

The spatial resolution of a panoramic image is muchlower than intraoral radiographs, making detailedassessment of the alveolar processes and teeth moredifficult. Nonetheless, full evaluation is required toavoid missing disease. These structures should beviewed in a systematic manner. A sequence from theposterior of the first quadrant to the posterior of thefourth quadrant in a clockwise direction, repeated foreach finding to be evaluated, is recommended.

The following steps are suggested as an approach tothis part of the interpretation: (1) assess the crestal boneposition of the alveolar processes to identify anyperiodontal bone loss; (2) examine the periodontalligament spaces and lamina duras around each toothfor signs of inflammatory disease; (3) don’t forget toexamine the follicles and papillae of developing teethfor anything affecting their size, position or corticalboundaries. These changes could be indicative ofdeveloping pathology; (4) evaluate the teeth for pres-ence ⁄ absence ⁄ eruptive or positional abnormalities, car-ies, inadequate restorations, calculus, developmental oracquired abnormalities.

Interpretation of pathology on panoramicradiographs

The panoramic radiograph is especially useful whenexamining regions of the jaws which cannot be imagedwith intraoral radiographs, such as the temporoman-dibular joints and third molar regions. Due to distor-tion and a limited two-dimensional view, the temporo-mandibular joint cannot be assessed in detail, however,a general overview is provided which allows majorabnormalities to be ruled out. When a lesion in the jawsneeds to be studied, it is important to be able toexamine its entire boundary, which may be bestachieved on a panoramic image. Usually the location,periphery and shape, internal density and effects on thesurrounding structures of lesions in the jaws can beappreciated on panoramic images. However, thismodality is limited by the numerous superimpositionsprojected on the image, especially in the maxillary sinusand palate regions, and by its inability to demonstratemedial-lateral changes (Fig. 7). Advanced imaging,such as computerized tomography, cone beam comput-erized tomography or magnetic resonance imaging maybe required to provide multidimensional views tosupplement the information obtained from a panoramicradiograph.

CONCLUSIONS

Panoramic radiographs have many useful applicationsin dentistry but require diligence on the part of the

Fig 8. Examination of the cortical lines in the posterior maxillaryregions of this image would allow the observer to detect that the

posterior wall of the left maxillary sinus is absent (open black arrowsindicate where the cortex should be seen). This destruction was caused

by a malignancy within the sinus. The white lines formed by thezygomatic process of the maxilla and posterior boundary of the

pterygomaxillary fissure, which should be assessed at the same time asthe posterior wall of the maxilla, are still visible.


S Perschbacher

observer to examine the image thoroughly. For thisreason, a systematic approach is recommended for theinterpretation of this image type. Understanding theperspective of the anatomy on a panoramic radiographas well as the many superimpositions and distortionsproduced will help the practitioner to be more success-ful at this task.

Address for correspondence:Dr Susanne PerschbacherDepartment of Radiology

Faculty of Dentistry124 Edward Street

TorontoOntario M5G 1G6

CanadaEmail: [email protected]



interpretation of panoramic radiographs

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