Gastrointestinal ❯ Small Bowel Tumor
CT Protocol for Small Bowel Tumor
| Problem | Evaluation of the patient with suspected small bowel tumor. This may be based on findings from a prior CT scan, clinical symptoms or presentation (weight loss, GI bleed) or clinical history. |
| Protocol | The key to the protocol which requires oral and IV contrast is to be able to detect small tumors that have a range of appearances and can be subtle. Ideally if I am lloking for a suspected small bowel tumor I will do dual phase imaging with arterial phase imaging at 30-35 seconds, and venous phase imaging at 70 seconds from the start of contrast injection. Oral contrast is ideal and there are advantages to positive oral or neutral oral contrast agents. If I was looking for adenocarcinoma or lymphoma than positive contrast would be ideal especially for subtle infiltrating tumors. For vascular tumors including carcinoid tumors water as a neutral agent is ideal to detect the enhancement of these lesions. Water is also ideal if you are also looking for a suspected GI bleed. Post processing with coronal and sagittal imaging is ideal and 3D mapping with MIP and VRT is also valuable. Scan protocols need both thin and thick section CT (.75nmm and 3mm) with the thin section CT ideal for the MPR/3D mapping. |
| Pearls | Small bowel tumors may be challenging to detect when they are small. Some helpful hints include; 1. The key is good small bowel distension. This makes it easier to see the tumors whether they are vascular or not. The patterns of tumors will vary whether you are dealing with adenocarcinoma, lymphoma, GIST tumors, carcinoid tumors or metastases 2. In addition to looking at the bowel one should carefully analyze the mesentery and omentum for signs or primary disease or spread of disease. With small bowel lymphoma large mesenteric nodes are not uncommon. With carcinoid tumors a mass in the mesentery with desmoplastic reaction is common. The primary tumor in carcinoid is also usually vascular as is the mesenteric mass. 3. GIST tumors are common in the duodenum. Carcinoid tumors are usually in the ileum but duodenal carcinoids do occur. Lymphoma is more common in the distal small bowel and adenocarcinoma in the proximal small bowel. 4. Duodenal GIST tumors may be large and simulate pancreatic cancer 5. GIST tumors commonly bleed while metastases are more commonly involved with intussuceptions. This is especially true with melanoma 6. Review of images in coronal plane is critical to detect small lesions that are not obstructive 7. Lymphoma has many CT patterns ranging from solitary to multiple masses, tumor infiltration with encasement and bulky tomors. Ulceration is not uncoomon 8. Careful attention to the liver and spleen may also be helpful in defining the various small bowel tumors. 9. Metastases to small bowel often simulates primary small bowel tumors. 10. Transition sites in small bowel can be due to strictures but also could be a sign of bowel infiltration by tumor |