6 December 2007 – Case of the Week #103
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Case of the Week #103
An 86 year old man had a stable parotid mass for 20 years, which was excised. On gross examination, there was a 3 cm well circumscribed tan nodule and a smaller, 7 mm brown-red nodule.
What is your diagnosis?
Sebaceous lymphadenoma and small oncocytoma / oncocytic nodule
Sebaceous lymphadenoma is a rare, benign tumor with nests and islands of bland epithelium composed in part of sebaceous elements, in a prominent lymphoid stroma. Over 90% occur in or near the parotid gland. It is not usually diagnosed prior to excision (Acta Otorhinolaryngol Ital 2007;27:144).
On gross examination, there is a solid or cystic, well circumscribed, tan-yellow mass, up to 3 cm, with variable encapsulation. Microscopically, there are nests and islands of benign squamous cells, often lining a cyst. The epithelial nests have focal areas of sebaceous differentiation. The background is a prominent lymphoid infiltrate, often with germinal centers. There may be an associated foreign body reaction, collections of histiocytes or oncocytic change.
Fine needle aspiration shows a mixed population of large and small lymphocytes, plasma cells and occasional tingible body macrophages. There are also 3 dimensional, cohesive aggregates of epithelial cells, often with cytoplasmic vacuoles characteristic of sebaceous differentiation, surrounded by layers of basaloid cells (Acta Cytol 2004;48:551)
The differential diagnosis includes normal sebaceous glands (present in 10% of parotid glands but not forming a mass), Warthin’s tumor and low grade mucoepidermoid carcinoma. Warthin’s tumor has prominent cysts and lymphoid stroma, but the cysts have a bilayered oncocytic epithelium, not present in sebaceous lymphadenoma. However, sebaceous lymphadenoma may have collections of oncocytes or a distinct oncocytic nodule, as in this case, and both tumors may arise from salivary duct inclusions within a parotid lymph node (AJCP 1980;74:683).
Low grade mucoepidermoid carcinoma may also be cystic, and contains epithelial islands and mucinous cells that may resemble sebaceous glands. However, in mucoepidermoid carcinoma, the epithelial islands, ducts and cysts tend to be haphazardly distributed with variable shapes and sizes. There is usually infiltration of connective tissue or parenchyma, and the cells have some atypia. Mucin stains are positive within the cells, in contrast to sebaceous lymphadenoma.
Excision of sebaceous lymphadenoma is curative, with no recurrences. Only rarely does it undergo malignant transformation (Eur Arch Otorhinolaryngol 2006;263:940)
Nat Pernick, M.D., President
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