Clinical and histological data from 8 trichilemmal carcinomas are reviewed. The tumors occurred mainly on sun-exposed skin of the face of elderly people as small solitary, frequently ulcerated nodules. Histologically, they consisted of multilobulate, infiltrative growths, connected to the epidermis and pilosebaceous structures and showing features reminiscent of the outer root sheath of the hair follicle. The presence of lobules of clear, glycogen-rich cells with peripheral palisading, hyaline basement membranes, trichilemmal keratinization, and abortive follicular sheaths and the absence of ductal or acinar differentiation allow distinction from other clear cell tumors of the skin. Although the histological picture suggests a high-grade malignant neoplasm, trichilemmal carcinoma has an indolent course. No recurrence or metastases have been observed.

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Benign follicular tumors comprise a large and heterogeneous group of neoplasms that share a common histogenesis and display morphological features resembling one or several portions of the normal hair follicle, or recapitulate part of its embryological development. Most cases present it as clinically nondescript single lesions and essentially of dermatological relevance. Occasionally, however, these lesions be multiple and represent a cutaneous marker of complex syndromes associated with an increased risk of visceral neoplasms. In this article, the authors present the microscopic structure of the normal hair follicle as a basis to understand the type and level of differentiation of the various follicular tumors. The main clinicopathological features and differential diagnosis of benign follicular tumors are then discussed, including dilated pore of Winer, pilar sheath acanthoma, trichoadenoma, trichilemmoma, infundibuloma, proliferating trichilemmal cyst/tumor, trichoblastoma and its variants, pilomatricoma, trichodiscoma/fibrofolliculoma, neurofollicular hamartoma and trichofolliculoma. In addition, the main syndromes presenting with multiple follicular tumors are also discussed, namely Cowden, Birt-Hogg-Dubé, Rombo and Bazex-Dupré-Christol syndromes, as well as multiple tumors of follicular infundibulum (infundibulomatosis) and multiple trichoepitheliomas. Although the diagnosis of follicular tumors relies on histological examination, we highlight the importance of their knowledge for the clinician, especially when in presence of patients with multiple lesions that may be the cutaneous marker of a cancer-prone syndrome. The dermatologist is therefore in a privileged position to recognize these lesions, which is extremely important to provide further propedeutic, appropriate referral and genetic counseling for these patients.

Although typical naked sarcoid granulomas are the most common features of cutaneous sarcoidosis, the dermatopathologist must be aware of possible atypical findings, which are more common than previously expected, because of the differential diagnosis with other causes of cutaneous granulomas, namely infectious diseases.

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