S4751 Recurrent Gastrointestinal Bleeding in a Patient With Ganglioneuromatosis Overlying a Rectal Mesenteric Plexiform Neurofibroma

Introduction: Neurofibromatosis Type 1 (NF1) is a disorder characterized by the presence of neurofibromas, or benign nerve sheath tumors, in various parts of the body including the skin, abdomen, and chest. Patients with NF1 may also have concurrent diffuse ganglioneuromatosis, a lesion made up of both nerve sheath and ganglion cells. While 10-25% of NF1 patients have gastrointestinal (GI) involvement, they are most often asymptomatic. We present a rare case of lower GI bleeding secondary to a rectal plexiform neurofibroma overlaid by ganglioneuromatosis, managed successfully with surgery. Case Description/Methods: A 29-year-old man with intellectual and developmental disability, NF1, and hemorrhoids presented for evaluation of painless bright red blood per rectum (BRBPR) occurring intermittently for the past year. A year ago, he was initially diagnosed with internal hemorrhoids and symptoms improved with conservative measures. Colonoscopy and endoscopic ultrasound done 5 months prior identified an intramural rectal tumor located 0.5 cm from the anal verge, covering 75% of the circumference and extending to the submucosa. At the time, pathology was consistent with a neurogenic/nerve sheath tumor. Since then, he experienced increased frequency and quantity of BRBPR, occurring up to 5 times a day despite soft stools every 3 days. Due to his worsening symptoms, the patient was seen by colorectal surgery and underwent outpatient transanal resection of the rectum with complete removal of the lesion, with no acute surgical complications. Pathology revealed extensive ganglioneuromatosis of the large bowel with an underlying associated plexiform neurofibroma that stained positive for SOX10. Post operatively he had resolution of bleeding and improvement in frequency of bowel movements. Discussion: Neurofibromas can be classified as localized, diffuse, or plexiform. Plexiform neurofibromas have intertwined nerve bundles and no ganglion cells, differentiating this growth from our patient’s ganglioneuromatosis. The plexiform subtype is found in approximately 30% of patients with NF1, is pathognomonic for NF1, and harbors the greatest potential for malignant transformation. As both neurofibromas and ganglioneuromas are generally asymptomatic, they are often monitored closely. Frequent clinical monitoring is crucial in NF1 patients with colorectal tumors given high risk of malignant transformation, particularly if they have clinical symptoms, as early intervention will decrease overall mortality risk.