# Folliculosebaceous Cystic Hamartoma With Unusual Mucinosis: A Report of a Rare Case

## TL;DR

This paper reports a rare case of a skin lesion with unusual mucin deposits, expanding the known histopathological features of folliculosebaceous cystic hamartoma.

## Contribution

The paper presents a novel histopathologic variant of folliculosebaceous cystic hamartoma with mucinosis, previously unreported in the literature.

## Key findings

- A unique variant of folliculosebaceous cystic hamartoma with mucin deposits in sebaceous lobules was identified.
- This case expands the histological presentation of folliculosebaceous cystic hamartoma.
- The finding suggests a possible unknown pathologic mechanism of mucin deposition in this condition.

## Abstract

We report a case of a clinically indistinct pink papule on the midline upper back of a 77-year-old woman. Histopathological examination of the lesion revealed a unique variant of folliculosebaceous cystic hamartoma (FSCH) characterized by mucin deposits in sebaceous lobules. FSCH is a rare lesion involving a cystically dilated follicle surrounded by sebaceous glands embedded within a stromal matrix composed of mesenchymal features. Follicular mucinosis is an uncommon inflammatory disorder typically presenting as benign, idiopathic lesions in children or mycosis fungoides-associated lesions in adults. A literature review revealed no previously reported cases of FSCH involving mucinosis of our knowledge to date, making this a novel and clinically relevant histopathologic variant. This case expands the histological presentation of a rare lesion and highlights the importance of careful examination in differentiating between similarly presenting dermatological conditions. Additionally, this novel finding suggests the possibility of an unknown pathologic mechanism of mucin deposition in FSCH, warranting further research.