Malignant Neoplasms: Statistical Leaders
Malignant tumors predominate in the incidence structure. Over recent decades, carcinoids have overtaken adenocarcinoma to take first place.
- Carcinoid tumor (Carcinoid tumour): A low-grade malignant tumor originating from enterochromaffin cells. Preferred localization is the distal ileum. The tumor intensely accumulates contrast medium. The secretion of vasoactive substances (serotonin) causes a pronounced desmoplastic reaction—mesenteric fibrosis, which leads to bowel kinking, ischemia, and obstruction. It frequently metastasizes to the liver, provoking carcinoid syndrome (flushing, diarrhea).
- Adenocarcinoma (Adenocarcinoma): An aggressive and chemoresistant tumor of the proximal sections (duodenum and jejunum). It grows predominantly radially, narrowing the lumen. On CT, it is visualized as a focal thickening with sharp, "overhanging" edges.
Lymphoma and Stromal Tumors
- Lymphoma (Lymphoma): Accounts for about 20% of primary malignant tumors. It most commonly affects the terminal ileum. A specific radiological sign is focal "aneurysmal" dilatation resulting from extensive destruction of the muscle layers. The "sandwich sign" is also encountered—confluent lymphomatous masses encasing mesenteric vessels.
- Gastrointestinal stromal tumors (GIST, GIST): Mesenchymal neoplasms arising from interstitial cells of Cajal. A key distinguishing feature is the expression of KIT (CD 117). They grow exoenterically (outward from the wall), reaching enormous sizes (sometimes >30 cm). On CT, they actively enhance with contrast and often exhibit hypodense areas of internal necrosis that show no radiopharmaceutical uptake on PET-CT.
Secondary Lesions and Benign Tumors
Secondary (metastatic) tumors are encountered in a radiologist's practice more frequently than primary ones.
- Intraperitoneal dissemination is characteristic of ovarian, gastric, and colorectal cancer. Deposits are frequently localized in the right lower quadrant due to stasis in the dependent portion of the mesentery.
- Hematogenous metastases are frequently caused by melanoma (the "bull's-eye" sign—a polypoid lesion with ulceration—is typical).
Benign tumors are rare (0.5–2%):
- Adenomas: The most common, prone to malignant transformation. On barium studies, villous adenomas resemble "cauliflower".
- Hamartomatous polyps: Occur multiple times in Peutz-Jeghers syndrome and serve as a leading lead point for intussusception.
- Lipomas: On CT, these are smooth lesions with typical fat density; on MRI, they show signal "drop-out" on opposed-phase imaging.
Capabilities of Diagnostic Imaging
The basis of modern diagnostics is CT enterography and MR enterography. These techniques significantly surpass traditional enteroclysis in evaluating the extraluminal spread of tumors and metastases.
The main limitation of MRI in this area is its relatively low spatial resolution compared to CT. Consequently, tumor nodules smaller than 5 mm may be missed. Careful visualization is critical, as the 5-year survival rate for malignant tumors has remained unchanged over the past 20 years, and only early surgical resection can improve the prognosis.
Briefly: answers to topical questions
Which genetic syndromes predispose to the development of small bowel polyps and tumors?
Several hereditary syndromes predispose to the development of small bowel polyps and tumors.
- Peutz-Jeghers syndrome (Peutz-Jeghers syndrome) is characterized by the formation of intestinal hamartomas, predominantly in the stomach and small intestine.
- Familial adenomatous polyposis (FAP) belongs to familial cancer syndromes that increase the risk of developing adenocarcinoma.
- Hereditary nonpolyposis colorectal cancer / Lynch syndrome (HNPCC) is caused by mutations in DNA mismatch repair genes, increases the risk of small bowel cancer, and accounts for 5–10% of all small bowel adenocarcinomas.
What criteria are used to assess the malignant potential risk of small bowel GISTs?
The risk of malignant potential and progression of gastrointestinal stromal tumors is assessed using several key criteria.
- Tumor size—a size greater than 5 cm is considered a sign of malignancy, at which tumors frequently invade adjacent organs and metastasize.
- Mitotic index—the number of mitoses per 50 high-power fields.
- Primary tumor location—small bowel tumors generally carry a poor prognosis.
- Presence of tumor capsule rupture—is an additional risk factor for progression.
What radiological signs are characteristic of benign small bowel tumors on barium fluoroscopy?
On barium fluoroscopy, benign small bowel tumors manifest as specific filling defects.
- Adenomatous polyps (adenomatous polyps) are visualized as intraluminal filling defects that are pedunculated (pedunculated), sessile (sessile), or intramural (intramural).
- Villous adenomas (villous adenomas) demonstrate the characteristic "cauliflower" (cauliflower) or "soap bubble" (soap bubble) sign, which is caused by the trapping of contrast media in the crevices between the tumor's multiple villous projections.
Class and exam questions
Which malignant small bowel tumors are most common?
To date, carcinoid tumors are the most frequent (up to 44%), having surpassed adenocarcinomas in incidence.
Why does a carcinoid frequently cause intestinal obstruction?
Carcinoids secrete vasoactive substances that induce a pronounced desmoplastic reaction (mesenteric fibrosis). This leads to kinking of the bowel loops and obstruction.
How to differentiate GIST from other tumors?
GISTs are characterized by exoenteric growth (a large external mass), areas of necrosis, and KIT (CD 117) receptor expression on immunohistochemistry.
What is the "sandwich sign"?
This is a radiological sign of lymphoma in which enlarged, confluent mesenteric lymph nodes densely encase the mesenteric vessels and bowel loops.
What else to study on this topic
- Radiological Patterns of Carcinoid Syndrome
- Specifics of PET-CT in Diagnosing Metastatic GISTs
- Differential Diagnosis of Tuberculosis and Crohn's Disease
- Peutz-Jeghers Syndrome and Gastrointestinal Hamartomatous Polyps
- Technique of CT and MR Enterography
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