RESUMEN
INTRODUCTION: Proliferating trichilemmal cysts (PTCs) are rare benign neoplasms originating from the follicular isthmus. They can undergo trichilemmal keratinization and malignant degeneration to form epidermoid carcinoma. They occur on the scalp in more than 90% of patients and are more common in elderly women. PRESENTATION OF CASE: A 56-year-old woman complained of perianal discomfort upon sitting. She presented with a perianal nodule of approximately 3 cm in diameter that had exhibited slow and progressive growth over 8 years. After surgical excision of the lesion with safety margins, histopathological examination showed that it was a proliferating trichilemmal cyst in the perianal region. DISCUSSION: There are no reports in the literature on PTC in the perianal region. The location with the highest prevalence is the scalp; other sites of occurrence are the neck, trunk, underarms, pubis, vulva, lower and upper limbs, upper lip, and gluteal region. CONCLUSION: The development of PTC in the perianal region is an exceptional occurrence, and when it does occur, surgical treatment should always be indicated because of the risk of malignant degeneration to form epidermoid carcinoma.
