Trichilemmal Cysts With Divergent Ductal Differentiation: A Series of 4 Cases

[Main Types of Cysts in Dermatopathology: Part 1]

Cystic structures represent one of the most common findings in dermatopathology. These encompass both cystic tumors and pseudocysts resulting from the accumulation of certain substances, such as mucin. In a two-part series (of which this is the first part), we have reviewed the principal types of cysts and pseudocysts that may be observed in cutaneous biopsies, examining their histopathological features and primary differential diagnoses. This first part encompasses infundibular cysts, eruptive dermoid cysts, pigmented follicular cysts, pilonidal cysts, tricholemmal cysts, milium cysts, hybrid cysts, bronchogenic cysts, as well as steatocystoma, hydrocystoma, and comedones.

Trichilemmal cysts with proteinaceous material: A potential diagnostic pitfall

BACKGROUND

Cysts of the skin are observed frequently and their diagnoses are generally straightforward. However, atypical cystic lesions for which differentiation is indistinct have been noted.

METHODS

We examined five cases of trichilemmal cyst with proteinaceous material (TCPM), which required differentiation from sweat duct/gland tumors. We investigated the histopathological findings of TCPMs and evaluated the immunohistochemical expression of cytokeratin (CK) 10, CK13, CK17, CK19, CD8, and CD117. Immunohistochemical analysis was performed on the five TCPMs, 10 trichilemmal cysts (TCs), five clear cell hidradenomas, five poroid hidradenomas, and cutaneous normal adnexa.

RESULTS

Apoptotic cells were present in the cyst wall with a small amount of keratin or calcification in the cavity of TCPMs. The TCPMs and TCs were negative for CK19 and CD117, whereas clear cell hidradenoma and poroid hidradenoma were positive for CK19 and CD117. The restricted positivity for CK10 was detected in the suprabasal layers of the cyst walls of TCPMs and TCs. The immunostaining patterns of TCPMs and TCs were similar to those of normal follicular isthmus.

CONCLUSIONS

The histopathological findings with characteristics of TCs and a panel of immunohistochemical antibodies including CD117, CK19, and CK10 contributed to a correct diagnosis of TCPM. This article is protected by copyright. All rights reserved.