24.1 Benign Small Bowel Tumors

Adenomas, leiomyomas and lipomas are the three most frequently discovered primary tumors of the small intestine. Hamartomas, fibromas, angiomas and neurogenic tumors are much less common. As a general rule, benign tumors are least common in the duodenum and increase in frequency toward the ileum. Benign tumors often remain asymptomatic and are usually found incidentally.

Symptomatic benign tumors present primarily with obstructive features, giving rise to intermittent colicky abdominal pain or complete bowel obstruction. Bleeding may occur, particularly from leiomyomas that ulcerate centrally. Intussusception occurs with polypoid distal lesions.

Adenocarcinomas, lymphomas, leiomyosarcomas and carcinoids are the most common primary small bowel malignant tumors. Metastatic cancer to the small intestine occurs rarely in patients with melanoma, breast cancer and lung cancer. Primary adenocarcinomas occur in the duodenal and proximal jejunum as annular lesions, narrowing the lumen and presenting with the signs and symptoms of obstruction. Leiomyosarcomas are evenly distributed along the small bowel. Symptoms are similar to those of adenocarcinoma - i.e., crampy abdominal pain and bleeding. Lymphoma of the small bowel must be carefully evaluated to determine whether the tumor has originated in the small intestine (primary lymphoma) or whether the small bowel is involved by a diffuse systemic lymphoma. Primary lymphoma of the small intestine is usually a histiocytic lymphoma. The lymphoma is most often proximal and presents with abdominal pain, weight loss, malabsorption, perforation and anemia. There is an increased incidence of primary lymphoma in patients with long- standing celiac disease or immunodeficiency states and in renal transplant patients receiving chronic immunosuppressive therapy.

A specific form of malignant lymphoma called immunoproliferative small intestinal disease occurs in people of Mediterranean descent. It is characterized by proliferation of mucosal B cells and has a high incidence of a-heavy chain paraproteinemia. It typically involves the duodenum and proximal jejunum, presenting with diarrhea and malabsorption.