Infundibulocystic Structures and Prominent Squamous Metaplasia in Sebaceoma-A Rare Feature. A Clinicopathologic Study of 10 Cases

The authors describe 10 cases of sebaceoma that manifested prominent infundibulocystic structures in all cases and, additionally, conspicuous squamous metaplasia in 6 neoplasms. All tumors occurred on the scalp or the face (2 cases lacked clinical information) and presented as a solitary lesion, measuring from 5 to 20 mm. The patients' age ranged from 22 to 89 years. The main component of all tumors was small, uniform basaloid cells (immature sebocytes) intermixed with mature sebocytes clearly arranged in nodules, classifying the lesions as a sebaceoma. In all neoplasms, the tumor cells showed organoid growth patterns of sebaceoma, including rippled, sinusoidal/labyrinthine, and carcinoid-like, occurring alone or in combination. Additionally, numerous infundibulocystic structures were readily noticed and were either distributed multifocally or unilocular within the tumors. In some cases, they were segregated from the main tumor bulk. The authors posit that these structures, which are different from both sebaceous ductal differentiation and squamous metaplasia, represent an authentic follicular differentiation. The infundibulocystic features (combined with squamous metaplasia), when prominent and in a limited biopsy specimen, may cause a confusion with trichoadenoma or even microcystic adnexal carcinoma.