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Parapharyngeal Space Lesion

DIFFERENTIAL DIAGNOSISCommon• Direct extension into parapharyngeal space from neoplasm

from adjacent space○ Pharyngeal mucosal space/surface → parapharyngeal

space– Nasopharyngeal Carcinoma– Squamous Cell Carcinoma, Palatine Tonsil– Non-Hodgkin Lymphoma, Pharyngeal Mucosal Space

○ Masticator space → parapharyngeal space– Sarcoma, Masticator Space– Rhabdomyosarcoma, Masticator Space

○ Parotid space → parapharyngeal space– Benign Mixed Tumor, Parotid Space– Adenoid Cystic Carcinoma, Parotid Space– Mucoepidermoid Carcinoma, Parotid Space

• Direct extension into parapharyngeal space from abscessfrom adjacent space○ Abscess, Masticator Space○ Tonsillar Abscess, Pharyngeal Mucosal Space○ Parotitis, Acute, Parotid Space

Less Common• Primary parapharyngeal space lesion

○ Pterygoid Venous Plexus Asymmetry○ Venolymphatic Malformation○ Lipoma

Rare but Important• Benign Mixed Tumor, Parapharyngeal Space• 2nd Branchial Cleft Cyst, Variant• Ranula, Diving

ESSENTIAL INFORMATIONKey Differential Diagnosis Issues• Parapharyngeal space (PPS) lesion is suprahyoid only

○ Some literature separates PPS into pre- & poststyloidcompartments

○ Using this scheme, functional differential considerationsby space can be sorted as– Prestyloid PPS = PPS (differential considerations here)– Poststyloid PPS = carotid space (not addressed here)– Carotid space masses are uncommon but displace PPS

fat anteriorly□ Considerations include vascular lesions, neurogenic

tumors, & paragangliomas (not addressed here)• Primary PPS lesions are rare

○ Intact fat plan separates mass from adjacent spaces• Displacement of PPS fat is useful to determine origin of

masses arising from adjacent suprahyoid head & neckspaces

• PPS most commonly affected secondarily by direct spreadof local malignancy or infection

Helpful Clues for Common Diagnoses• Pharyngeal mucosal space/surface (PMS) → PPS

○ PPS fat displaced laterally if mass located in PMS○ Most common etiologies are infection or malignancy

• Nasopharyngeal Carcinoma

○ CT/MR: Lateral pharyngeal recess tumor bulges intomedial PPS

○ PPS fat displaced anteriorly & medially○ Direct invasion of carotid space or bony skull base

possible• Squamous Cell Carcinoma, Palatine Tonsil

○ Induration of PPS fat & irregular margin between fat &tumor are key findings

○ CT/MR: Tumor arises in tonsillar fossa, extends laterallywith either mass effect or direct invasion of PPS

○ Tumor staged as T4 if PPS invaded• Non-Hodgkin Lymphoma, Pharyngeal Mucosal Space

○ CT/MR: Bulky PMS tumor bulges medial wall of PPS,without direct invasion

○ Homogeneous density, usually without necrosis• Masticator space (MS) → PPS

○ PPS fat displaced posteromedially for mass in MS• Sarcoma, Masticator Space

○ CT/MR: Aggressive MS tumor ± calcific matrix• Rhabdomyosarcoma, Masticator Space

○ CT/MR: Aggressive noncalcified MS tumor in child• Parotid space (PS) → PPS

○ PPS fat displaced medially– Most deep lobe parotid tumors compress &/or involve

PPS– Fascia less adherent along medial aspect of deep lobe

parotid○ When tumor is large, may be difficult to determine if site

of origin is PS or PPS○ Lesion of parotid gland can arise in, or spread to, deep

lobe of parotid & extend medially– Widening of stylomandibular tunnel characterizes

primary parotid masses extending into (prestyloid)PPS

• Benign Mixed Tumor, Parotid Space○ Benign deep lobe tumor often asymptomatic until large○ May be hard to determine if tumor is from deep lobe of

parotid or primary PPS○ CT/MR: Large, well-circumscribed mass flattening lateral

aspect of PPS• Adenoid Cystic Carcinoma, Parotid Space

○ CT/MR: Invasive parotid mass with propensity forperineural spread (CNVII)

• Mucoepidermoid Carcinoma, Parotid Space○ CT/MR: Invasive parotid mass; enhances, "feathery"

margins• Abscess, Masticator Space

○ Odontogenic origins; recent tooth extraction or lucencyaround molar

○ CT/MR: Pus pocket in MS; edematous muscles;induration of PPS from lateral aspect

• Direct extension into PPS from abscess from adjacent space• Tonsillar Abscess, Pharyngeal Mucosal Space

○ CT/MR: Palatine tonsil pus with surrounding edema &induration

○ Displaces PPS fat laterally if intratonsillar; abscess mayrupture laterally into PPS

• Parotitis, Acute, Parotid Space○ CT/MR: Edematous parotid gland with increased

density/enhancement

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○ Swollen, deep lobe causes mass effect on lateral wall ofPPS

○ Look for radiopaque calculus as predisposing cause○ Unilateral bacterial; bilateral viral

Helpful Clues for Less Common Diagnoses• Pterygoid Venous Plexus Asymmetry

○ Prominent venous plexus at pterygoid plates involvesPPS & MS– May simulate venous malformation– Usually more linear serpiginous than cystic

○ CECT: Asymmetric prominent venous enhancement inMS & anterior PPS near pterygoid plates

• Venolymphatic Malformation○ Common congenital suprahyoid transspatial lesion

usually presents in childhood○ Typically asymptomatic; incidental finding on imaging○ CT/MR: Can be limited, but typically involves multiple

contiguous spaces, including PPS– Appearance determined by whether lesion is primarily

venous, lymphatic, or mixed in composition– Cystic mass with T2 hyperintensity (may be uni- or

multilocular)– Lymphatic malformations are nonenhancing; venous

& venolymphatic malformations enhance– Calcified phleboliths on CT are characteristic of venous

malformation• Lipoma

○ Benign fatty tumor almost always incidental finding○ CT/MR: Enlarged but otherwise normal-appearing PPS

– Should have no soft tissue component & noenhancement

Helpful Clues for Rare Diagnoses• Benign Mixed Tumor, Parapharyngeal Space

○ Arises in PPS from ectopic salivary gland rests– Primary PPS benign mixed tumor that has no

connection to deep lobe of parotid gland– Tumor often large when diagnosed– PPS lesions "silent" & asymptomatic

○ CT/MR: Variable enhancement

– Ovoid mass typically low T1, high T2 signal on MR– If part of mass appears more aggressive or irregular,

think of malignancy arising in benign mixed tumor,"carcinoma ex pleomorphic adenoma"

• 2nd Branchial Cleft Cyst, Variant○ Primary cyst in PPS most likely branchial in origin○ CT/MR: Benign, nonenhancing cyst

– May point towards or be connected to palatine tonsil• Ranula, Diving

○ Sublingual gland retention cyst ruptures intosubmandibular space & PPS

○ CT/MR: Tail sign in sublingual space leads to SMS & PPScystic components– No fascial boundary between submandibular space &

PPS– PPS component rarest area for pseudocyst to spread

SELECTED REFERENCES1. Abt NB et al: Plunging ranula with prestyloid parapharyngeal space,

masticator space, and parotid gland extension. B-ENT. 13(1 Suppl 27):57-60,2017

2. Khatib Y et al: Venolymphatic vascular malformation of the parotid glandextending into the parapharyngeal space: A rare presentation. J OralMaxillofac Pathol. 20(2):308-11, 2016

3. Gamss C et al: Imaging evaluation of the suprahyoid neck. Radiol Clin NorthAm. 53(1):133-44, 2015

4. Abrahams JJ et al: Stylomandibular tunnel widening versus narrowing: auseful tool in evaluating suprahyoid mass lesions. Clin Radiol. 69(11):e450-3,2014

5. Gupta M et al: A rare parapharyngeal space branchial cleft cyst. BMJ CaseRep. 2013, 2013

6. Kato H et al: Imaging findings of parapharyngeal space pleomorphicadenoma in comparison with parotid gland pleomorphic adenoma. Jpn JRadiol. 31(11):724-30, 2013

7. Varoquaux A et al: Retrostyloid parapharyngeal space tumors: a clinician andimaging perspective. Eur J Radiol. 82(5):773-82, 2013

8. Ohmann EL et al: The utility of fine needle aspiration to identify unusualpathology in a parapharyngeal mass. Am J Otolaryngol. 32(1):82-4, 2011

9. Tang LL et al: Prognostic value and staging categories of anatomicmasticator space involvement in nasopharyngeal carcinoma: a study of 924cases with MR imaging. Radiology. 257(1):151-7, 2010

10. Babbel RW et al: The parapharyngeal space: the key to unlocking thesuprahyoid neck. Semin Ultrasound CT MR. 11(6):444-59, 1990

(Left) Axial T1WI MR shows anonkeratinizing EBV(+)nasopharyngeal carcinomafilling the pharyngeal mucosalspace st. The parapharyngealspace and prevertebralmuscles st are invaded by thetumor. (Right) Coronal T1WIMR in the same patient revealscarcinoma st in thenasopharyngeal mucosalspace invading laterally intothe right parapharyngealspace . Note the normal leftparapharyngeal space fat st.

Nasopharyngeal Carcinoma Nasopharyngeal Carcinoma

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Parapharyngeal Space Lesion

(Left) Axial CECT shows alarge palatine tonsil squamouscell carcinoma (SCCa) invadingposterolaterally into theparapharyngeal space st.Note the fatty triangle of thenormal contralateralparapharyngeal space .(Right) Axial CECT in the samepatient demonstrates thepalatine tonsillar SCCainvading the sublingual spacest and lateral parapharyngealspace . Bilateral malignantlevel II nodes st are alsonoted.

Squamous Cell Carcinoma, Palatine Tonsil Squamous Cell Carcinoma, Palatine Tonsil

(Left) Axial CECTdemonstrates a bulky,bilateral nasopharyngeal non-Hodgkin lymphoma bulginginto both parapharyngealspaces st. The "feathery"appearance on the leftsuggests invasion of theparapharyngeal space. (Right)Axial CECT in the same patientshows the mass nearlyobliterating the leftparapharyngeal space st.

Non-Hodgkin Lymphoma, PharyngealMucosal Space

Non-Hodgkin Lymphoma, PharyngealMucosal Space

(Left) Axial CECT shows amasticator spaceosteosarcoma withdestruction of the mandibleand extension through themaxillary sinus wall st. Notemild mass effect on theparapharyngeal space .(Right) Axial bone CT in thesame patient demonstrates"sunburst" malignantperiosteal changes st ofosteosarcoma.Parapharyngeal spacecompression , from lateralto medial, is characteristic of amasticator space tumor.

Sarcoma, Masticator Space Sarcoma, Masticator Space

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(Left) Axial T1 MR shows alarge masticator spacerhabdomyosarcoma st in a 7-year-old boy. Theparapharyngeal space fat is displaced medially and ispartly effaced. Note thenormal-appearing leftparapharyngeal space fat .The right parotid gland is alsoinvaded by tumor st. (Right)Axial T2WI MR reveals a largerhabdomyosarcoma in themedial masticator space,destroying the mandible .The mass displaces andinvades the parapharyngealspace st.

Rhabdomyosarcoma, Masticator Space Rhabdomyosarcoma, Masticator Space

(Left) Axial T1WI MR shows alarge, deep parotid tumor stwith effacement of thepterygoid muscles, airwaycompromise, and mass effecton the soft palate st. Theparapharyngeal space ismarkedly flattened anddisplaced medially but notinvaded. (Right) Coronal T1WIMR in the same patientconfirms a thin, hyperintensefat stripe, supporting that theparapharyngeal space isstretched over the mass butnot invaded.

Benign Mixed Tumor, Parotid Space Benign Mixed Tumor, Parotid Space

(Left) Axial T1 C+ FS MR showsan enhancing, invasive,recurrent tumor in the parotidgland st with extension intothe parapharyngeal space in a patient previously treatedfor parotid adenoid cysticcarcinoma. Parapharyngealfat has been replaced bytumor. (Right) Coronal T1 C+FS MR in the same patientdemonstrates a deep lobetumor extending into theparapharyngeal space .There is also perineural tumorst along the 3rd division ofthe trigeminal nerve at theforamen ovale.

Adenoid Cystic Carcinoma, Parotid Space Adenoid Cystic Carcinoma, Parotid Space

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(Left) Axial CECT of high-grademucoepidermoid carcinoma ofthe parotid st shows focalcalcifications st at the tumorcomponent involving the deeplobe. Parapharyngeal fat isdisplaced medially .Compare to normalparapharyngeal fat on right. (Right) Abscess of themedial pterygoid muscle ,causing effacement & medialdisplacement ofparapharyngeal space fat st,is shown on axial CECT. Notenormal right parapharyngealfat . Inflammatorystranding extends to the deeplobe of the parotid .

Mucoepidermoid Carcinoma, Parotid Space Abscess, Masticator Space

(Left) Axial CECT in a patientwith a 2-week history oftonsillitis shows pus in theparapharyngeal space witha large, adjacent, inflamedpalatine tonsil st andassociated masticator spacephlegmon st. (Right) AxialCECT in the same patientreveals an inferior palatinetonsil abscess st causingextensive submandibularspace cellulitis andparapharyngeal andmasticator space abscess (notshown).

Tonsillar Abscess, Pharyngeal MucosalSpace

Tonsillar Abscess, Pharyngeal MucosalSpace

(Left) Axial CECTdemonstrates asymmetricenlargement andenhancement of the rightparotid gland st. There isstranding in the subcutaneousfat and increased density inthe right parapharyngealspace fat from associatededema. (Right) Axial CECTdemonstrates a prominentasymmetric left pterygoidvenous plexus as racemoseenhancement in the deepmasticator st and anteriorparapharyngeal space.

Parotitis, Acute, Parotid Space Pterygoid Venous Plexus Asymmetry

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(Left) Axial CECT in a patientwith violaceous oropharyngealmucosa shows a tissue densityvenous malformation withphleboliths, involving thepharyngeal mucosal st andparapharyngeal space.(Right) Axial T2WI FS MRreveals a high-signalvenolymphatic malformationthat fills the parapharyngealspace and ipsilateralretropharyngeal space st. Thetransspatial nature, fluidsignal, and shape all suggestvenolymphatic malformation.

Venolymphatic Malformation Venolymphatic Malformation

(Left) Axial CECTdemonstrates a lipoma in theparapharyngeal space . Thislipoma extended inferiorly andinvolved the submandibularspace (not shown). (Right)Axial CECT shows an ovoidbenign mixed tumor stcentered in theparapharyngeal space. Notethe sharp delineation between the deep lobe of theparotid gland and the tumor,indicating that the lesionarose in the parapharyngealspace and not in the deep lobeof the parotid gland.

LipomaBenign Mixed Tumor, Parapharyngeal

Space

(Left) Axial NECT reveals anovoid, low-density cyst in theright parapharyngeal space, deep to the palatine tonsilst. This is a rare example of a2nd branchial cleft cystprojecting superiorly into theparapharyngeal space. (Right)Axial CECT reveals a fluid-density lesion st in the leftparapharyngeal space. Thissuperior extension of a divingranula is confirmed on inferiorimages, defining the ranularsublingual space origin (notshown).

2nd Branchial Cleft Cyst, Variant Ranula, Diving