Giant Endometrioma of the Canal of Nuck Mimicking a Vulvar Mass: A Rare Case and Narrative Review

Background: Endometriosis of the canal of Nuck is an extremely rare manifestation of extrapelvic endometriosis that may mimic common groin pathologies such as inguinal hernia or hydrocele, often leading to diagnostic difficulty and delayed recognition. Case Presentation: We report the case of a 29-year-old nulliparous woman who presented with a gradually enlarging painless swelling in the right vulvar region over eight months. Physical examination revealed a large cystic mass measuring approximately 15 × 10 cm involving the right vulva and inguinal area with displacement of the clitoris and vaginal introitus. Ultrasonography demonstrated a well-defined cystic lesion with internal echoes, while magnetic resonance imaging revealed a hemorrhagic cystic lesion along the course of the canal of Nuck without peritoneal communication. Surgical exploration identified a cystic mass adjacent to the round ligament containing characteristic “chocolate-like” fluid. Complete excision of the lesion was performed. Histopathological examination confirmed endometrioma of the canal of Nuck. The postoperative course was uneventful, and the patient remained asymptomatic with no evidence of recurrence during three years of follow-up. Conclusion: Although rare, canal of Nuck endometriosis should be considered in the differential diagnosis of inguinal or vulvar masses in women of reproductive age. Early recognition with appropriate imaging and complete surgical excision allows accurate diagnosis and excellent outcomes. To our knowledge, this case represents one of the largest canal of Nuck endometriomas reported in the literature and highlights the diagnostic challenges posed by atypical presentations without cyclic symptoms.