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15 June 2016 - Case of the Week #392

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Case of the Week #392

Clinical history:
A 54 year old man presented with painless swelling over the left half of his upper lip for the past 10 years. There was no history of trauma, fever, cigarette smoking or tobacco chewing. His intraoral examination revealed a single, mobile, irregular, nodular, 3 cm swelling. The lesion was excised.

Gross description:
A single, vaguely nodular soft tissue mass measured 3.2 x 3 x 1.5 cm. Cut surface showed a well circumscribed and thinly encapsulated greyish white to tan solid mass with multiple microcystic spaces filled with granular yellowish material.

Gross images:

External surface

Cut surface

Cytology images - fine needle aspiration cytology:

Calcified material

Squamous cells

Eosinophilic globules

Keratinous material

What is your diagnosis?

Pleomorphic adenoma of upper lip with florid squamous metaplasia and multiple keratocysts with adipocytic differentiation


Micro images:

Squamous metaplasia

Keratin granuloma

Conventional area

Adipocytic metaplasia

Keratinous cyst with lamellar keratin

Pleomorphic adenoma (PA) is a benign tumor of salivary glands which originates from the myoepithelial and intercalated duct cells. This tumor is common in the major salivary glands (85% occur in the parotids), and the most common sites involving minor salivary glands are the palate, followed by the upper lip.

Cytology smears showed clusters of bland ductal epithelial cells and scattered banal appearing spindle cells in a fibrillary chondromyxoid background. Imprint cytology showed epithelial and spindle cells arranged in a chondromyxoid background with many globules composed of acellular eosinophilic material and many singly scattered squamous epithelial cells along with keratinous and calcified material.

Histopathology showed a well circumscribed and thinly encapsulated nodular mass composed of epithelial and stromal components within a fibrillary chondromyxoid matrix with extensive areas of squamous metaplasia. There were multiple cystic spaces filled with lamellar keratinous material. Foci of giant cell reaction and extensive adipocytic differentiation were noted. Increase in mitosis / atypical mitotic figures were not appreciated.

Histologically, these tumors show great diversity, attributable to the myoepithelial cell component (Adv Anat Pathol 2004;11:69). Myoepithelial cells are capable of dedifferentiation and metaplasia (Am J Pathol 1985;119:33), and hence play a vital role in determining the morphology of the tumor. Metaplastic changes can involve both the epithelial and stromal components. Epithelial metaplastic changes include squamous, sebaceous, oncocytic and clear cell transformation of the luminal cell layer. The stroma can contain chondroid, myxoid, chondromyxoid and hyaline elements, and very rarely osseous and adipose tissue. Adipocytic differentiation is considered uncommon (J Laryngol Otol 1992;106:50), except in cutaneous sites.

Complete excision is recommended for preventing recurrence and malignant transformation, and prognosis after complete excision is excellent. Carcinoma ex-pleomorphic adenoma arising from untreated pleomorphic adenoma occurs in up to 3% of minor salivary gland tumors (Soames: Oral Pathology, 4th ed, 2005). The recurrence rate of PA is estimated to be 3.4% after 5 years and 6.8% after 10 years (Cancer 1984;54:1620) and is almost always a result of incomplete surgical resection (Med Oral Patol Oral Cir Bucal 2008;13:E582).

Discussion edited by: Dr. Jennifer R. Kaley, University of Arkansas for Medical Sciences (USA).
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