Brown Umbilical Nodule: A Case of Primary Cutaneous Endometriosis.

Background: Endometriosis is a common condition in which endometrial glands and stroma are implanted outside the uterine cavity. Rarely, the skin can be involved. Case Presentation: We describe a case of a 41-year-old woman who presented to the dermatology clinic complaining of a brown umbilical nodule with slight erythema. It was occasionally painful and hemorrhagic. She denied a history of endometriosis and abdominal surgeries. A shave biopsy of the nodule was consistent with a diagnosis of cutaneous endometriosis. The patient was referred to her gynecologist for further evaluation and treatment. Conclusion: This unique case demonstrates primary cutaneous endometriosis in the umbilicus of a female patient. Cutaneous endometriosis can be classified as primary or secondary. Primary cutaneous endometriosis is rarer and has an unclear etiology, developing seemingly spontaneously without history of surgical interventions. Secondary cutaneous endometriosis typically arises within surgical scars following abdominal operations, which is believed to be a result of iatrogenic implantation of endometrial cells. Definitive treatment involves surgery. This case highlights the importance of considering cutaneous endometriosis in the differential diagnosis of a female patient with painful and intermittently hemorrhagic skin nodules.