# Deeply Pigmented Reticulated Acanthoma with Sebaceous Differentiation Mimicking Cutaneous Malignancy: A Case Report and Review of the Literature

## TL;DR

A rare benign skin tumor with sebaceous features can appear deeply pigmented, mimicking skin cancer in patients with darker skin tones, leading to potential misdiagnosis.

## Contribution

This case report highlights the diagnostic challenge of pigmented reticulated acanthoma with sebaceous differentiation in patients with skin of color.

## Key findings

- A deeply pigmented skin lesion in a patient with Fitzpatrick skin type IV was diagnosed as reticulated acanthoma with sebaceous differentiation.
- The typical yellowish hue of sebaceous differentiation was obscured by heavy pigmentation, leading to initial suspicion of melanoma.
- Conservative management was chosen after biopsy confirmation, avoiding unnecessary surgery.

## Abstract

Reticulated acanthoma with sebaceous differentiation is a rare, benign skin tumor characterized by the presence of sebaceous gland cells within a net-like growth pattern. A yellowish hue, when present, may provide a clinical clue to the underlying sebaceous gland differentiation. However, in patients with darker skin tones, heavy pigmentation can completely obscure this characteristic appearance. We report a case in an elderly patient whose deeply pigmented skin lesion raised clinical concern for malignant melanoma. Microscopic examination revealed the true benign diagnosis. This case highlights an important diagnostic pitfall: in patients with skin of color, this benign tumor can masquerade as skin cancer due to excessive pigmentation. Recognizing this unusual presentation is crucial for dermatologists and pathologists to avoid unnecessary aggressive surgical treatment and to provide appropriate reassurance to patients.

Reticulated acanthoma with sebaceous differentiation (RASD) is a rare, benign cutaneous neoplasm. Its variable clinical presentation frequently mimics both benign and malignant entities, posing a significant diagnostic challenge. We report a case of pigmented RASD in a 78-year-old Malay male of Fitzpatrick skin type IV who presented with a 5-year history of an 8 × 5 mm deeply pigmented, asymmetrical nodule on the left upper back, with a 2 mm central raised area showing less pigmentation. The lesion was clinically suspicious for malignant melanoma. Histopathological examination revealed characteristic features of RASD: a broad, plate-like, reticulated and pigmented epidermal proliferation with clusters of mature sebocytes at the bases of anastomosing rete ridges. Following biopsy confirmation, the residual lesion is being managed conservatively with observation. This case demonstrates an unusual heavily pigmented clinical presentation that completely obscured the typical yellowish hue associated with sebaceous differentiation, highlighting pigmented RASD as an important diagnostic pitfall in patients with skin of color. In conclusion, RASD should be included in the differential diagnosis of pigmented cutaneous lesions, especially in patients with skin of color. Recognition of this benign entity can prevent unnecessary aggressive surgical intervention.