Solitary Plexiform Neurofibroma in the Urachus Associated With von Recklinghausen's Disease.

Neurofibromatosis type 1 (NF1), also known as von Recklinghausen's disease, is an autosomal dominant disorder characterized by multiple café-au-lait macules and cutaneous neurofibromas. Although neurofibromas are common in NF1, involvement of the urinary tract is rare, with the bladder being the most frequently affected site. Urachal neurofibromas are extremely rare, and their diagnosis and management remain challenging due to nonspecific imaging characteristics and their often asymptomatic presentation. We report the case of a 30-year-old man with clinical features of NF1 in whom a 5-cm mass at the bladder dome was incidentally identified on MRI performed during evaluation for spinal cord symptoms. Imaging revealed a cone-shaped mass in the urachal region, and cystoscopy showed no mucosal abnormalities. Urinalysis and urine cytology were unremarkable. A transabdominal needle biopsy confirmed the diagnosis of a neurofibroma. Given the tumor's size (>5 cm) and deep-seated location in the trunk, both known risk factors for malignant transformation, surgical excision was performed, including resection of the urachus and bilateral umbilical ligaments. Histopathological analysis confirmed a plexiform neurofibroma consistent with NF1. The postoperative course was uneventful, with no evidence of recurrence during 36 months of follow-up. This case highlights the rare presentation of a urachal plexiform neurofibroma in a patient with NF1. To reduce the potential risk of malignant transformation associated with plexiform neurofibromas larger than 5 cm and located in deep trunk regions, accurate diagnosis and timely surgical intervention are essential, even in asymptomatic cases.