Multimodality Imaging Overview of Common and Uncommon Solid Parotid Space Masses eEdE-139 Whitney Finke, MD, Nicholas Koontz, MD, Stephen Kralik, MD Department of Radiology & Imaging Sciences Indiana University School of Medicine Indianapolis, IN

Disclosures None

Abbreviations BMT = Benign Mixed Tumor T2WI = T2 weighted image CECT = Contrast enhanced CT Tx = Treatment DCF = Deep cervical fascia +C = Contrast enhanced EAC = External auditory canal FS = Fat-saturated MMT = Malignant Mixed Tumor NECT = Non-contrast enhanced CT PNT = Perineural tumor SCM = Sternocleidomastoid T1WI = T1 weighted image

Purpose Provide a comprehensive overview of imaging characteristics of pathology-proven common & uncommon solid parotid space masses Modalities US CT MRI FDG-PET/CT

Approach/Methods We performed a HIPAA-compliant retrospective review of our institution's electronic medical record (radiology and pathology databases) for illustrative cases of histopathologically-proven parotid masses Included cases with multimodality imaging when possible Additionally, a review of the current medical literature was performed

Findings/Discussion Introduction Anatomy Parotid space masses With permission of Amirsys-Elsevier

Introduction Largest salivary gland Superficial “lobe” Deep “lobe” 80% of glandular volume Superficial to the plane of facial nerve Overlies ramus and angle of mandible, superficial to masseter Deep “lobe” 20% of glandular volume Medial extent through stylomandibular tunnel

Parotid Space Anatomy Fascial investment Bounderies Superficial layer DCF ( ) Bounderies Superior = EAC ( ), mastoid tip ( ) Inferior = parotid tail, below angle of mandible between platysma & SCM Medial = parapharyngeal ( ) & carotid ( ) spaces Anterior = masticator space ( ) With permission of Amirsys-Elsevier

Parotid Space Contents Glandular tissue Parotid ducts Facial nerve ( ) External carotid artery ( ) Retromandibular vein ( ) Surrogate marker for CN 7 Lymph nodes ( ) Primary nodal drainage of ear, face, & scalp With permission of Amirsys-Elsevier

Parotid Masses 80% of salivary gland masses 80% benign (adults) Pediatric masses higher rate of malignancy Staging of malignant parotid masses Weighted heavily based upon size Subdivided based upon local extension Skin Soft tissues Bone Lingual or facial nerve Nodal or distant metastases

Facial Nerve Involvement CN7 involvement is a critical part of parotid mass evaluation Invasion PNT CN7 origin Image from origin nucleus to end organ Adenoid cystic most common, but seen with other malignancy With permission of Amirsys-Elsevier

Perineural Tumor a b Adenoid cystic carcinoma with PNT. (a) Axial T1WI +C FS shows enhancement along intraparotid CN7 ( ), extending along the auriculotemporal nerve ( ) connecting CN7 & V3. (b) Abnormal enhancement involves the mastoid segment of CN7 ( ) at the stylomastoid foramen and CN V3 ( ) in the masticator space.

Nodal and Distant Metastatic Disease Nodes: Poor prognostic factor Mucoepidermoid is the most common , but seen with other malignancy Distant Metastases: Very poor prognosis Evaluate lungs and bone Coronal CECT: Heterogeneously enhancing parotid mass ( ) with nodal metastases ( )

Differential Diagnosis of Primary Parotid Solid Masses Common Diagnoses: Benign Mixed Tumor Warthin Tumor Metastatic Nodal Disease Less Common Diagnoses: Mucoepidermoid Carcinoma Adenoid Cystic Carcinoma Malignant Mixed Tumor Acinic Cell Carcinoma Adenocarcinoma Ductal Carcinoma Transverse grayscale ultrasound: Benign mixed tumor

General Imaging Overview: Imaging is nonspecific. 80% benign 80% are benign mixed tumors. Look for clues to suggest malignancy such as invasive margins, perineural spread, and lymphadenopathy. FDG uptake does not always correspond with tumor grading. Ultimately biopsy and excision are needed for definitive diagnosis.

Benign Mixed Tumor AKA: Pleomorphic Adenoma Pathology: Interspersed epithelial, myoepithelial, & stromal cellular components Tx: Surgical Resection Recurrence seen with surgical seeding 15% malignant transformation Axial T2WI shows a boscillated, hyperintense mass involving both the superficial and deep lobes of the left parotid gland.

Benign Mixed Tumor Most common salivary gland tumor: 80% of parotid gland tumors >80% involve the superficial lobe <1% are multifocal Axial T2WI: BMT in the deep parotid lobe Image courtesy of R Wiggins

BMT Seeding Post-Parotidectomy Recurrent BMT along the course of the parotid duct. (a) Axial T1WI, (b) Axial T2WI, (c) Axial T1WI+C demonstrates T1 hypointense ( ), T2 Hyperintense ( ), mildly enhancing masses along the parotid duct ( ).

Malignant Mixed Tumor 2 Types: Carcinoma-ex-pleomorphic adenoma: Malignant degeneration of one of the cell lines in a BMT. Carcinosarcoma: multiple malignant cell lines (<70 reported cases) Patients present with a rapidally enlarging, long- standing parotid mass. Early: Indistinguishable from BMT Late: aggressive, infiltrating parotid mass. T1WI+C: homogenously enhancing mass with invasion into the stylomastoid foramen.

Malignant Mixed Tumor a b Malignant mixed tumor with invasion into the masseter and sternocleidomastoid muscle. (a) Longitudinal greyscale ultrasound shows a hypoechoic parotid mass ( ). (b) Axial CECT shows a heterogeneous mass in the superficial parotid ( ) with invasion into the SCM ( ) and masseter ( ).

Warthin Tumor Smoking associated Arises from salivary- lymphoid tissue 2nd most common benign parotid tumor 2-10% of parotid tumors Most common parotid tail mass 20% multifocal 30% cystic component FDG and Tc avid Tx: excision (<1% malignant transformation) Axial CECT: hyperenhancing masses in the bilateral parotid tails.

Warthin Tumor a b Warthin Tumors. (a) Longitudinal greyscale ultrasound shows a hypoechoic, partially cystic mass in the parotid tail ( ). (b) Axial FDG-PET/CT in a different patient shows an FDG avid mass in the parotid tail ( ).

Mucoepidermoid Carcinoma Most common primary parotid malignancy 30% salivary gland malignancies 50% in parotid Most common salivary gland malignancy in children. 44% have nodal metastases Tx: resection + radiation, and possible neck dissection Coronal CECT: heterogeneously enhancing, partially cystic mass in the parotid tail

Mucoepidermoid Carcinoma b c Mucoepidermoid carcinoma in patient with history of prior left superficial parotidectomy for Warthin Tumor. (a) Axial T2WI shows a cystic mass in the parotid bed that has invaded through the anterior wall of the EAC ( ). (b) Axial T2WI more inferiorly shows cystic masses in the residual superficial lobe and the deep lobe, with characteristic T2 hypointense regions ( ). (c) Axial T1WI+C shows involvement of the deep parotid lobe ( ). 65-year-old male with metastatic periauricular SCCa.

Adenoid Cystic Carcinoma 2nd most common parotid malignancy 2-6% parotid gland tumors 33% present with facial pain and/or paralysis Look for PNT along V3 or the facial nerve Metastasizes to the lungs and bone. Tx: parotidectomy and radiation. Poor long term prognosis (up to 20 year late recurrence) Axial FDG-PET image shows an increased radiopharmaceutical uptake in the left parotid mass.

Adenoid Cystic Carcinoma b c 65-year-old male with metastatic periauricular SCCa. Adenoid cystic carcinoma of the deep lobe of the parotid gland, with extension into the superficial lobe. (a) Axial T1WI shows a T1 hypointense mass ( ). (b) Axial T2WI shows a heterogeneous, primarily hyperintense mass ( ). (c) Axial T1WI+C shows enhancement of the mass ( ). The irregular margins and infiltrative appearance suggest a higher grade malignancy.

Acinic Cell Carcinoma 3rd most common primary parotid malignancy (~15%) 2nd most common pediatric parotid malignancy. Indistinguishable from other low grade malignancies. May have cystic areas. 3% bilateral. Tx: Excision and radiation Mean age 44, younger than most parotid masses a/w prior radiation 5-17% parotid malignancies Axial CECT shows an ill-defined, centrally necrotic and peripherally enhancing mass within the left parotid gland.

Acinic Cell Carcinoma a b c Acinic Cell Carcinoma (additional images from patient seen on previous slide). (a) Transverse grayscale ultrasound shows a hypoechoic mass in the left parotid gland ( ). (b) Axial PET CT shows an FDG avid mass in the left parotid gland ( ). (c) Axial T1WI+C shows a peripherally enhancing mass with central necrosis that involves the superficial and deep lobes of the parotid gland, and extends into the stylomastoid foramen ( ).

Adenocarcinoma NOS 9% of total salivary gland malignancies. 28-50% are in parotid Usually present with painful, rapidly enlarging mass Tx: Parotidectomy and radiation Axial T2WI shows an irregular T2 hyperintense mass in the superficial and deep lobes of the left parotid gland Image courtesy of K Mosier.

Salivary Ductal Carcinoma Pathology: Similar to invasive ductal carcinoma of the breast. Uncommon, extremely aggressive malignancy Perineural spread is common Cervical nodal metastasis in 70% Distant metastasis to lung, bone, brain Axial CECT shows an ill defined enhancing mass in the superficial and deep lobes of the left parotid gland, with extension into the stylomandibular tunnel

Salivary Ductal Carcinoma b 65-year-old male with metastatic periauricular SCCa. Salivary ductal carcinoma. (a) Axial CECT shows an irregular, enhancing mass in the superficial and deep lobes of the left parotid gland. ( ). (b) Coronal CECT shows enhancing cervical lymphadenopathy ( ).

Squamous Cell Carcinoma Rare 0.1-0.5% parotid tumors 3-10% malignant parotid tumors Squamous metaplasia develops secondary to chronic inflammation Must exclude metastatic disease from skin Metastasizes to regional nodes, lungs, and liver. Axial CECT shows an ill defined enhancing mass in the right parotid gland with areas of necrosis. Patient had a history of long standing chronic sialadenitis

Non-Hodgkin Lymphoma Nodal: Primary nodal Systemic 1-8% involve parotid Primary parenchymal Mucosa associated lymphoid tissue type (MALT) Rare, 2-5% of parotid malignancies Infiltrative mass Axial T1WI shows an infiltrative hypointense solid mass in the superficial parotid.

Non-Hodgkin Lymphoma a b c Non-Hodgkin lymphoma. (a) Axial CECT demonstrates enlarged nasopharyngeal lymphoid tissue ( ) and enlarged and necrotic intraparotid lymph nodes ( ). (b & c) Coronal CECT demonstrate enlarged and necrotic cervical lymphadenopathy ( ). The necrotic appearance of the lymph nodes suggests an aggressive vs. partially treated lymphoma.

Intraparotid Nodal Metastases 4% of all parotid neoplasms 1st order nodal station for skin SCC and melanoma from scalp, ear, and face. Systemic metastases are rare. Evaluate for extracapsular extension and perineural spread. Axial CECT shows abnormally enlarged intraparotid lymph nodes.

Intraparotid Nodal Metastases b c Melanoma Nodal Metastases. (a) Axial T1WI image shows multiple abnormally enlarged right intraparotid lymph nodes ( ). (b) Axial NECT and (c) Axial FDG PET images show enlarged ( ) FDG avid ( ) right intraparotid lymph nodes.

Conclusion: Imaging is nonspecific. Look for clues such as invasive margins, perineural spread, lymphadenopathy, and multifocality. 80% benign 80% are benign mixed tumors. Invasive margins suggest a more aggressive tumor. Ultimately biopsy and excision are needed for definitive diagnosis.

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