Pathologic quiz case: cystic tumor of the left eyebrow in a 42-year-old woman. Benign cutaneous adnexal tumor with combined folliculosebaceous and eccrine differentiation.

Abstract

A 42-year-old woman presented with a cystic tumor of the skin, positioned just above the left eyebrow and measuring 4 × 4 mm; the tumor was excised under local anesthetic. Histologic sections of the excisional biopsy specimen showed a well-circumscribed lesion (Figure 1), in which eccrine tubules lined by a single central columnar layer were surrounded by a peripheral small cuboidal cell layer and contained mucinlike material adherent to an internal cuticle. In some areas, the eccrine tubules were associated with sheets of small plasmacytoid cells embedded in a chondroid matrix (Figure 2). Elsewhere, cysts containing central keratinous material were associated with a peripheral basaloid epithelial proliferation showing the formation of buds mimicking abortive anagen hair follicles. No polarizable terminal or vellus hairs were seen. Miniaturized sebaceous glands were present within these follicular structures (Figure 3). These 2 elements were geographically separate in the biopsy, but collided in the center of the lesion.What is your diagnosis?Cutaneous adnexal tumors are classified, by convention, according to the type and character of differentiation of adnexal elements identified in skin biopsies or excision specimens. For example, tumors may show follicular, eccrine, sebaceous, or apocrine differentiation. Neoplasms showing various admixtures of these different primordial elements are rare.1 Occasional cases have been reported in the literature and represent a variable admixture of folliculosebaceous, eccrine, and/or apocrine differentiation.2–7 The presence of such variable admixtures of differentiated adnexal elements poses difficulties with respect to specific classification, as in this case.The tumor we describe fits most closely with lesions described by Wong et al1 by virtue of showing an admixture of trichofolliculoma-like areas with those representing chondroid syringoma. In particular, the presence of cystic structures containing keratin and lined by mature keratinizing squamous epithelium with peripheral basaloid buds recapitulating anagen hair follicles was cognate to the morphology of a trichofolliculoma. Other differential diagnostic considerations included sebaceous neoplasms, including sebaceous adenoma, sebaceous epithelioma, trichoepithelioma, and trichofolliculoma. By showing areas of associated chondroid syringoma, our tumor demonstrates stromal foci resembling those seen in one of the cases reported by Wong et al.1 Chondroid syringoma or mixed tumor manifests tubules containing ductal epithelia surrounded by a peripheral myoepithelial investiture, which typically sprouts from the tubules into the adjacent stroma and is associated with the elaboration of a myxoid matrix. Unlike basal cell carcinoma and sebaceous epithelioma, the basaloid tumor nests in our case showed no slitlike retraction from stroma, no mitotic figures, and very few apoptotic nuclei; sebaceous epithelioma and basal cell carcinoma typically manifest all of these prototypic features.This neoplasm, a benign cutaneous adnexal tumor showing combined folliculosebaceous and eccrine differentiation, is held to reflect the pluripotent capabilities of germinative epithelium in the skin. Wong et al1 suggested an alternate diagnosis, namely “benign adnexal tumor with multi-directional differentiation,” which also seems to adequately describe this neoplasm.