NF1 and neurofibroma: GI tract tumors in NF-1 occur most frequently followed by thoracic tumors, arterial involvement, and endocrine tumors.[3, 4] Abdominopelvic involvement is primarily extraperitoneal in NF-1.[5] GI tract involvement includes neurofibromas within the liver, mesentery, retroperitoneum, stomach, the small and large bowel, and the rectum.