FINAL DIAGNOSIS: SEBACEOUS LYMPHADENOMA
DISCUSSION Sebaceous lymphadenoma is a rare benign tumor composed of mature solid or gland-like sebaceous elements surrounded by a lymphoid stroma. McGavran et al. first applied the term sebaceous lymphadenoma to this tumor in 1960. Clinically, this is a slow-growing, asymptomatic neoplasm almost exclusively reported in the parotid gland. A single case has been reported in the anterior midline of the neck. Most patients are 50 years or older at the time of diagnosis, with an age range of 25 to 89 years. Men and women are almost equally affected.
Grossly, the tumors are well-circumscribed or encapsulated and have ranged from 1.5 to 6.0 cm in greatest dimension. On cross section, they present as yellow, tan or gray masses with a solid or microcystic surface. Lesions occurring as solitary cysts are uncommon. Microscopically, they are composed of variably sized and shaped groups of sebaceous cells, salivary ducts and cysts in lymphoid background, the latter often demonstrating lymphoid follicles with germinal centers and subcapsular sinuses.
The pathogenesis of this lesion and nature of the lymphoid tissue in this lesion is controversial. One theory proposes that the sebaceous lymphadenoma appears to arise from ectopic salivary gland tissue entrapped in lymph nodes during embryogenesis. This observation is based on the fact that the ectopic salivary gland tissue in intraparotid or periparotid lymph nodes is a common finding. Additionally the presence of sebaceous differentiation in some of the intranodal salivary gland inclusions and demonstration of a fibrous capsule with sinuses, lymphoid follicles and germinal centers in most of the tumors, support the presence of an underlying lymph node component. Accepting this lymph node-salivary gland inclusion theory, one can explain the histogenetic relationship between these and several other parotid gland lesions. It is possible that parotid gland tissue entrapped within lymph nodes may undergo cystic degeneration to become a lymphoepithelial cyst, sebaceous differentiation to become a sebaceous lymphadenoma or sebaceous lymphadenocarcinoma, or oncocytic differentiation to become a Warthin's tumor. However, there are some examples of Warthin's tumor and sebaceous lymphadenoma in which the lymphoid component does not appear to represent nodal tissue. It is possible that the lymphoid component represents a secondary, reactive response to the epithelial proliferation as seen in other parotid gland tumors. This phenomenon was referred as tumor-associated lymphoid proliferation.
Sebaceous lymphadenoma may be mistaken for a low-grade mucoepidermoid carcinoma, especially on a small biopsy specimen. Mucin, if present, is confined to the ductal epithelial cells and ductal lumens in sebaceous lymphadenoma, and is never present in the sebaceous cells. A foreign body giant cell reaction is also more commonly observed in sebaceous lymphadenoma than in mucoepidermoid carcinoma.
The treatment for sebaceous lymphadenoma is a complete surgical excision.