FOLLICULOSEBACEOUS CYSTIC HAMARTOMA OF THE ORAL MUCOSA: CLINICOPATHOLOGIC ANALYSIS OF 3 CASES OF AN UNCOMMON ENTITY

Abstract

Objective Folliculosebaceous cystic hamartoma (FSCH) represents an unusual type of cutaneous hamartomatous proliferation, manifesting clinically as an asymptomatic, slow-growing papulo-nodular lesion that most commonly affects the facial skin, primarily around the nose. Microscopically, FSCH is composed of infundibular structures with numerous radiating sebaceous lobules embedded in a mesenchymal stromal component. Despite the nomenclature, significant cystic dilatation is observed in Results Three FSCH cases were identified in the archives of the Oral and Maxillofacial Pathology Laboratory, University of Minnesota between 2008-2017 with M:F ratio=2:1 and mean age =42.3 years (age range: 27-61 years). All cases were located in the buccal mucosa and presented as painless, submucosal nodules of long duration measuring 0.6-1.5 cm. No previous history of skin graft in the area of the lesions was reported and none of the patients had a clinically identifiable syndrome. Histopathologically, oral FSCHs showed aggregates of variable number of rudimentary follicular structures and sebaceous lobules. Occasionally, the sebaceous glands were radially arranged and attached to small in size infundibular structures featuring rare microcystic changes, or were scattered in the deeper portions of the oral mucosa. The pilosebaceous units were immersed in a dense, focally desmoplastic, connective tissue stroma with variable amounts of mature adipocytes and vessels. Piloerector muscles were present in 2 out of 3 FSCHs, while inflammation was generally absent. Conclusions Oral FSCH is an infrequent lesion which can be misdiagnosed as ectopic Fordyce granules or other sebaceous neoplasms. Similar to a subgroup of cutaneous FSCH, oral lesions fail to show prominent cystic formation. Notably, a predilection for the buccal mucosa is reported. Whether oral FSCH represents late developing stage of trichofolliculoma remains unknown.