Bladder Melanosis: Clinicopathologic Insights Into a Rare Mimic of Malignant Melanoma.

Melanosis of the urinary bladder (melanosis vesicae) is a rare condition where dark, velvety patches are seen on the bladder mucosa during cystoscopy. With fewer than 30 cases reported to date, it remains an exceptionally rare finding. The condition is often associated with symptoms like urinary urgency or incontinence. Microscopically, the diagnosis is confirmed by the presence of melanin granules within urothelial cells and lamina propria macrophages. Although the exact cause is unknown, melanosis is considered benign. However, its clinical importance lies in the need to distinguish it from primary or metastatic malignant melanoma. It must also be differentiated from other forms of bladder pigmentation, such as hemosiderin or lipofuscin deposition. Because it can mimic a malignancy, urologists and pathologists must be aware of this entity to avoid an incorrect diagnosis of cancer. This report describes a case of melanosis vesicae in a 26-year-old male with spina bifida who presented with lower urinary tract symptoms and a suspected bladder tumor. The clinicopathologic features and a review of the current literature are provided.