Trichoblastomas Mimicking Basal Cell Carcinoma: The Importance of Identification and Differentiation

Abstract

Trichoblastoma is a rare, slow-growing, benign cutaneous tumor derived from follicular germinative cells. Trichoblastoma commonly appears as an asymptomatic, symmetrical, well-circumscribed, skin-colored to brown or blue-black papule or nodule. It may appear clinically and histologically similar to basal cell carcinoma, making its diagnosis challenging. Even on dermoscopy, it is challenging to differentiate trichoblastoma from basal cell carcinoma. In practice, it is important to differentiate the two, because the choice of treatment and resulting prognosis differ between the lesions. Surgical biopsy to analyze histopathological and immunohistochemical differences is the gold standard for diagnosing and differentiating trichoblastoma from basal cell carcinoma. Trichoblastoma typically has a favorable prognosis, with a low incidence of recurrence, progression or association with malignancy. This paper provides a review of the epidemiology, clinical presentation, dermoscopy, histology, immunochemistry, treatment, and prognosis of trichoblastoma.

Keywords: basal cell carcinoma; follicular germinative cells; trichoblastoma.

Figure 1. Nodular (large) trichoblastoma

The large nodules are crowded and mostly solid (red arrow), but some are punctuated by an infundibulocystic structure that contains corneocytes (blue arrow). Follicular germlike structures are wedded often to a follicular papilla. Some neoplastic cells are necrotic, as evidence by pyknosis and karyorrhexis (green arrow). (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 415. Copyright Ardor Scribendi. All rights reserved)

Figure 2. Retiform trichoblastoma

Follicular germinative cells arranged in nodules (red arrow). A second population of neoplastic cells, presumably modified germinative ones, is arrayed in reticulations (blue arrow). At the periphery of cords of reticulations are attempts at formation of follicular germs (green arrow). (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 524. Copyright Ardor Scribendi. All rights reserved)

Figure 3. Cribriform (trichoepithelioma) trichoblastoma

Fibroepithelial units separated from one another by clefts. The epithelial component is made up of follicular germinative cells arranged in a sieve-like pattern (red arrow), and the nonepithelial component is composed of fibrous tissue that is richly fibrocystic and resembles perifollicular sheath (blue arrow). The germs are in contiguity with a follicular papilla. Some aggregations are continuous with a preexisting infundibulum. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 535. Copyright Ardor Scribendi. All rights reserved)

Figure 4. Racemiform trichoblastoma

Constituted of aggregations that vaguely resemble bunches of grapes (red arrow). Although the stroma is typical of several types of trichoblastoma (e.g., small nodular, large nodular, and cribriform), that is, like embryonic perifollicular sheath (blue arrow), the germlike protuberances are not accompanied by a follicular papilla. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 588. Copyright Ardor Scribendi. All rights reserved)

Figure 5. Columnar trichoblastoma (desmoplastic trichoepithelioma)

May be confused with a microcystic adnexal carcinoma because of the small and large infundibulocystic structures, columns of epithelial cells that emanate from cystic structures, and depth of extension of neoplastic cells. Unlike microcystic adnexal carcinoma, however, this desmoplastic trichoepithelioma is associated with aggregations of follicular germinative cells (red arrow) and with well-defined follicular bulbs (blue arrow) and rudimentary papillae. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 601. Copyright Ardor Scribendi. All rights reserved)

Figure 6. Adamantinoid trichoblastoma

Aggregations of follicular germinative cells; some structures resemble follicular germs and papillae (red arrow); and pale-staining, delicate, richly fibrocystic connective tissue (blue arrow) enveloping aggregations of germinative cells simulate perifollicular sheath. The trichoblastoma is adamantinoid because the findings within aggregations closely resemble stellate reticulum of adamantinoma. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 486. Copyright Ardor Scribendi. All rights reserved)

Figure 7. Trichofolliculoma

A central infundibulocystic structure (red arrow) from which emanate smaller infundibula, from which, in turn, radiate numerous abnormal vellus follicles (blue arrow) that are surrounded by a characteristic stroma that resembles perifollicular sheath (green arrow). (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 151. Copyright Ardor Scribendi. All rights reserved)

Figure 8. Trichoadenoma.

Numerous infundibulocystic structures positioned close to one another (red arrows). Every cystic structure contains cornified cells arranged in lamellae, and are linked to one another by their lining that seems to have merged one with the other (blue arrow) or by short columns of squamous epithelium. The stroma is like that of the normal peri-infundibular dermis (green arrow), not at all like that of the perifollicular sheath. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 211. Copyright Ardor Scribendi. All rights reserved)

Figure 9. Verruca vulgaris with tricholemmal differentiation (tricholemmoma)

Warts with tricholemmal differentiation (cells of hyperplastic infundibula, not neoplasia of tricholemmal cells – i.e., cells of the outer sheath) in bulbous infundibula are known conventionally as tricholemmomas, but, in reality, they are not neoplasms, but hyperplasias of infundibular epithelium (red arrow) induced by papillomavirus. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 273. Copyright Ardor Scribendi. All rights reserved)

Figure 10. Tumor of follicular infundibulum

The infundibulum and the epidermis consist of nearly identical epithelium (red arrow); not so the isthmus. The character of the cells within the anastomosing proliferation can be seen to differ from those within epidermis and infundibula. The isthmic cells that constitute tumor of follicular infundibulum (blue arrow) have less cytoplasm and less prominent intercellular bridges than those of epithelium of epidermis and infundibulum. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 317. Copyright Ardor Scribendi. All rights reserved)

Figure 11. Pilar sheath acanthoma

From contiguous widely dilated infundibula filled with cornified cells emerge bulbous aggregations composed of isthmic epithelium (red arrow). Those aggregations are arrayed in a radial fashion, and some extend in depth to the level of skeletal muscle (blue arrow). Sebaceous ductal structures can be seen in the aggregation of the isthmic epithelium (green arrow). Sebaceous ductal differentiation is an expected finding in pilar sheath acanthoma. (Adapted with permission from Ackerman A, Reddy V, Soyer H. Trichoblastoma. In: Ackerman A, Reddy V, Soyer H, editors. Neoplasms with Follicular Differentiation. New York: Ardor Scribendi; 2001. p. 331. Copyright Ardor Scribendi. All rights reserved)