# Case report: Congenital Bednar tumor with pregnancy-associated growth and pain: a diagnostic pitfall with blue nevus-like features

## TL;DR

A rare congenital tumor was misdiagnosed as a blue nevus but was correctly identified as a Bednar tumor after showing growth and pain during pregnancy.

## Contribution

This case report presents a rare congenital Bednar tumor with pregnancy-associated growth and pain, emphasizing diagnostic challenges.

## Key findings

- A congenital pigmented lesion was misdiagnosed as a blue nevus but was identified as a Bednar tumor.
- Histopathology showed spindle cell proliferation with melanin and CD34 positivity, confirming the diagnosis.
- The case underscores the need to consider Bednar tumors in congenital lesions with interval growth or symptoms.

## Abstract

Bednar tumors are rare pigmented variants of dermatofibrosarcoma protuberans (DFSP), accounting for less than 5% of DFSP cases. We report a rare case of a congenitally pigmented lesion that progressively enlarged during pregnancy and developed pain. A 32-year-old woman presented with a blue-black nodule on her right shoulder, which had been present since birth and was initially misdiagnosed as a blue nevus. Histopathological analysis revealed spindle cell proliferation in a storiform pattern with focal melanin pigment. Immunohistochemistry showed strong CD34 positivity and negative S100 staining, consistent with Bednar tumors. This case highlights the importance of considering Bednar tumors in the differential diagnosis of congenital pigmented lesions, particularly those showing interval growth or symptoms.