Pleomorphic Adenoma



Pleomorphic Adenoma


Brenda L. Nelson, DDS, MS





Key Facts


Terminology



  • Synonym: Benign mixed tumor


  • Benign epithelial tumor that shows epithelial, myoepithelial, and mesenchymal differentiation


Clinical Issues



  • Most common neoplasm of salivary gland origin


  • Parotid gland most common site


  • Slow growing


  • Minor salivary glands 2nd most frequent site affected


Macroscopic Features



  • Recurrent tumors are generally multinodular


  • Irregular mass


  • Parotid gland



    • Variably thick capsule


    • Rarely unencapsulated


  • Minor glands



    • Poorly developed to absent capsule


Microscopic Pathology



  • Innumerable cytologic and architectural patterns


  • Epithelial tissue


  • Mesenchymal-like tissue


Top Differential Diagnoses



  • Myoepithelioma


  • Basal cell adenoma


  • Adenoid cystic carcinoma


  • Polymorphous low-grade adenocarcinoma


  • Carcinoma ex-pleomorphic adenoma


Diagnostic Checklist



  • No two look alike







This tumor shows characteristic areas of tubular and ductal structures with a background of hyaline stroma. Pleomorphic adenomas show amazing microscopic diversity.






Hematoxylin & eosin shows a tumor with predominant myxoid stroma with focal epithelial structures. The ratio of epithelium and stroma can vary widely among tumors.


TERMINOLOGY


Abbreviations



  • Pleomorphic adenoma (PA)


Synonyms



  • Benign mixed tumor (BMT)


  • Mixed tumor


  • Chondroid syringoma



    • Only used if skin/dermis based primary


Definitions



  • Benign epithelial tumor that shows both epithelial and modified myoepithelial elements mixed with mesenchymal myxoid, mucoid, or chondroid appearing material



    • Significant architectural diversity rather than cytologic pleomorphism


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Most common neoplasm of salivary gland origin



      • 45-76% of all salivary gland neoplasms


      • Comprises about 75% of all major salivary gland neoplasms


      • Comprises about 40% of all minor salivary gland neoplasms


    • Approximately 3/100,000 population


  • Age



    • Wide age range



      • Peak in 4th-6th decade


      • Most common benign salivary gland tumor in children


  • Gender



    • Female > Male (slightly) in adults


    • Male > Female in children (< 18 years)


Site



  • Parotid gland most common site (approximately 80%)



    • Most commonly superficial lobe



      • Inferior (lower pole) or “tail” of parotid gland


    • Deep lobe less frequently



      • Large lesions may compromise airway


  • Minor salivary glands 2nd most common site



    • Palate



      • Most common minor salivary gland site


      • Involves junction of hard and soft palate


      • Unilateral, fixed mass (no soft tissue to allow mobility)


    • Buccal mucosa


    • Upper lip


    • Rarely affects lower lip and tongue


  • Uncommon in submandibular and sublingual glands


  • Can affect larynx, nasal cavity, ear, orbit, upper aerodigestive tract, gastrointestinal tract


  • Rarely, may develop within ectopic salivary gland tissue


Presentation



  • Usually, painless, slow-growing mass


  • Single, smooth, mobile, firm nodule



    • Rarely, a 2nd tumor is found



      • Metachronous vs. synchronous


      • May be identified concurrently with Warthin tumor


  • Mucosal ulceration is uncommon


  • Paresthesia due to nerve compression is rare finding


  • If pain is present, tumor is more likely to be infarcted Natural History


  • Slow growing


  • Asymptomatic


  • May reach enormous size if neglected


  • Uncommon malignant transformation



    • Up to 7% of cases



Treatment



  • Options, risks, complications



    • Surgical complications



      • Frey syndrome (gustatory sweating)


      • Decreased muscle control of face (if facial nerve is sacrificed)


      • Capsule disruption may result in “seeding” of tumor (increases likelihood of recurrence)


      • Enucleation only results in high recurrence rate (up to 50%)


  • Surgical approaches



    • Parotid gland



      • Superficial parotidectomy


      • Extracapsular dissection (include rim of uninvolved tissue)


      • Facial nerve preservation when possible


    • Minor glands



      • Conservative, complete surgical excision


    • Submandibular gland



      • Complete excision


Prognosis



  • Excellent long-term prognosis, although limited by recurrence and malignant transformation



    • Overall recurrence rate: Up to 2.5%, most developing within 10 years


  • Parotid gland tumors have recurrence rate as high as 8%



    • Recurrences tend to be multinodular or multifocal


  • Submandibular and minor salivary gland tumors rarely recur


  • Malignant transformation in up to 7% of cases, with the following risk factors



    • Long history of untreated tumor


    • Multiple recurrences


    • Age of patient (usually > 40 years)


    • Male gender


    • Tumors > 2 cm in greatest dimension


    • Deep lobe tumors


    • More common in parotid gland


IMAGE FINDINGS


General Features



  • Imaging provides information about exact anatomic site, extent of disease, and possible invasion or nodal metastases


  • Ultrasound or CT are complimentary and allow for image-guided fine needle aspiration



    • Excellent resolution and tissue characterization without radiation hazard, especially for superficial lobe lesions


  • MR or CT is mandatory to evaluate tumor extent and exclude local invasion



    • Unilateral mass, which shows post-contrast enhancement, has high T2 signal, and does not invade surrounding tissue planes, is most likely PA


    • MR spectroscopy may separate Warthin from PA, although not yet well accepted


  • Ultrasonography is especially valuable in children, since most tumors are benign and many are cystic or vascular (color Doppler for latter)



    • High-resolution sonography has nearly 100% sensitivity in detecting intraparotid tumors


    • Precisely outlines tumor borders


    • Can detect multiple or bilateral lesions


  • Sialography delineates ductal system but is limited in tumor assessment


MACROSCOPIC FEATURES


General Features



  • Irregular mass


  • Fibrous capsule



    • Parotid gland



      • Variably thick incomplete capsule but rarely unencapsulated


    • Minor glands



      • Poorly developed to absent


  • Cut surface homogeneous, white to white-tan


  • Recurrent tumors are generally multinodular


  • Hemorrhage




    • Secondary to FNA or previous surgical procedures


  • Infarction



    • Secondary to FNA or previous surgical procedures


Size



  • Majority between 2-5 cm


  • Rarely, may be enormous


MICROSCOPIC PATHOLOGY


Histologic Features



  • Innumerable architectural patterns



    • Solid


    • Tubular or trabecular


    • Cystic


  • Epithelial tissue shows variable morphology



    • Spindle


    • Clear


    • Squamous


    • Basaloid


    • Plasmacytoid


  • Mesenchymal-like tissue



    • Myxoid stroma


    • Myxochondroid


    • Hyaline stroma


    • Rarely lipomatous


    • Bone


  • Duct structures



    • Lined by cuboidal epithelium


    • Lined by columnar epithelium


  • Rarely, crystals are present



    • Collagenous crystalloids: Eosinophilic needle shapes arranged radially


    • Tyrosine-rich crystalloids: Eosinophilic bunted shapes arranged tubularly


    • Crystalloids resembling oxalate crystals


  • Occasionally squamous metaplasia is identified


  • Rarely necrosis


  • Rarely sebaceous cells


ANCILLARY TESTS


Cytology

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Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Pleomorphic Adenoma

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