SMALL INTESTINE (Robbins pp 802)

Tumours of the small intestine are rare, and if they occur – they are mostly benign.

Benign lesions ≫ adenomas (Robbins pp 827)

Adenomas are pretty common in the SI. They often occur at the Ampulla of Vater. They are associated with FAP. Like oesophagus and stomach, adenomas are premalignant. The adenomas resemble the ones in the colon, histologically.

Carcinoid tumours (throughout GIT) (Robbins pp 835)_

Endocrine cells are present throughout the GIT. Tumours can arise in these cells. Almost half of all SI malignancies are carcinoids. The cells of carcinoid tumours can synthesise hormones just like their normal counterparts. Carcinoids can arise anywhere from the oesophagus to the rectum. The split is: 75% = midgut origin (appendix most common), 15% = hindgut origin, 10% = foregut origin.

Ileal carcinoids are similar to appendiceal carcinoids except they have a multicentric foci. Ileal carcinoids also metastasize frequently to lymph nodes and liver. If they go to the liver, they secrete large amounts of 5HT. 5HT causes diarrhea, bronchospasm, subendocardial fibrosis, & pulmonary stenosis.

Macroscopic / Microscopic: The carcinoid tumours can occur intramurally or submucosally. They can cause polypoid like nodules on the surface. Characteristically have a yellow appearance. Rectal and appendiceal carcinoids never metastasise. Histological, all the tumour cells look alike and form clumps of cells surrounded by a delicate fibrovascular stroma.

Adenocarcinomas (Robbins pp 827)

These are pretty rare and usually present as polypoid like lesions on the surface of the duodenum. Histologically similar to adenocarcinoms of the colon.

Malignant lymphoma (Robbins pp 837)

Lymphomas usually occur at lymph nodes, but the GIT is the commonest site outside nodal areas. There are three main types of GIT lymphomas:

1) B cell tumours: B cells are present in MALT, and tumours arise here,

2) Sprue (celiac disease) associated: Arises in patients with celiac disease (malabsorption due to gluten), and is T cell origin,

3) Mediterranean lymphoma: small bowel mucosa infiltrated with plasma cells, where plasma cells make abnormal IGA heavy chains, where the variable portion is deleted. Patients may also have B cell tumours or celiac disease.

Category: Pathology Notes