A large proliferating trichilemmal cyst masquerading as squamous cell carcinoma

Abstract

Proliferating trichilemmal cyst (PTC), a rare benign tumor, is a fascinating follicular neoplasm. It occurs on head and neck region of elderly women and its histologic hallmark is trichilemmal keratinization. A 70-year-old female presented to skin outpatient department with complaints of a slowly growing mass on scalp for the past 2 years. On examination, the lesion was firm, mobile, painless, and measured 6 × 5 × 3 cm and was not fixed to the underlying bone. Laboratory investigations were unremarkable. Excisional biopsy was done. Histopathology revealed well-demarcated tumor with variably sized lobules of squamous epithelium undergoing an abrupt change into eosinophilic amorphous keratin without granular cell layer (trichilemmal keratinization). PTC should be differentiated from trichilemmal cyst as it has potential for malignant transformation. Thus, complete excision is recommended for all benign proliferating variants owing to their potential for locally aggressive behavior and malignant transformation.

Giant, Bleeding, and Ulcerating Proliferating Trichilemmal Cyst, With Delayed Treatment Due to Coronavirus Outbreak: A Case Report and Review of the Literature

“…The common pilar cyst (or TC) occurs in 5-10% of the population, of which 2% become PTCs (6). PTC is often found on the scalp (1,7,8). Our literature search confirmed this, but we also found a case on the elbow, three cases on the finger, three on the mammae, one on the eyelid, and other locations as well (9)(10)(11)(12)(13)(14)(15)(16)(17).…”

“…Proliferating trichilemmal cysts (PTCs) are relatively rare tumors that may appear all over the body but most frequently on the scalp in middle-aged women (1). PTCs occur in a benign and malignant form, but the differentiation between malignant PTC and benign PTC has been debated, implying that all PTCs should be treated with the expectation that it could transform into a malignant tumor (2).…”

Congenital giant keratinous cyst mimicking lipoma: Case report and review

“…Apart from the overall malignant transformation rate, which varies from 0.033% to 9.2% in some articles,[ 18 ] to 1.5–10% in others,[ 19 ] certain other complications for these cysts are infection, Cock's peculiar tumor, abscess, cutaneous horn, which make this cyst an important diagnostic entity. [ 11 20 ]…”

The Value of Ultrasound for Differentiating Trichilemmal Cysts From Epidermoid Cysts

“…It is difficult for clinicians to identify the two entities through the naked eye. However, a TC may develop into a benign proliferative cyst or into a malignant proliferative TC, which may invade adjacent tissues or even metastasize after malignant transformation 7,8 . TC, benign proliferative TC, and malignant proliferative TC are different stages of the same disease.…”

“…However, a TC may develop into a benign proliferative cyst or into a malignant proliferative TC, which may invade adjacent tissues or even metastasize after malignant transformation. 7,8 TC, benign proliferative TC, and malignant proliferative TC are different stages of the same disease. The World Health Organization (WHO 2018) classified these three as follicular differentiated neoplasms and explained their pathological morphology as a continuum from benign to malignant.…”