Method evolution: from enema to CT
Cross-sectional imaging techniques (cross-sectional techniques) have become the gold standard, though conventional techniques are still used in surgical practice.
- Water-soluble contrast enema (Water-soluble contrast enema). Solutions (e.g., Gastrografin) are used to assess anatomy in real time, check anastomosis integrity, visualize fistulas, or rule out mechanical obstruction. The main danger is the risk of perforation due to fluid overdistension of the bowel.
- Double-contrast barium enema (Double-contrast barium enema). A method using a barium suspension and gas insufflation. In modern diagnostics, it is considered outdated for detecting cancer and polyps, having been completely superseded by tomography.
- Computed tomography (CT). Can be performed with intravenous, oral, or targeted rectal contrast enhancement. Normally, the intestinal wall thickness does not exceed 3 mm, and the paracolic fat appears homogeneous.
CT colonography and virtual endoscopy
CT colonography (CT colonography, CTC) is an examination of the large intestine pre-distended with gas. The method is practically comparable to endoscopy in detecting large neoplasms.
A key preparation step is faecal tagging (faecal tagging). The patient ingests a contrast agent that imparts high X-ray attenuation to residual contents, helping to avoid overdiagnosis.
How to distinguish a polyp from artifacts on CT:
- Fecal masses. Have heterogeneous density due to internal gas bubbles and shift when the patient is repositioned (prone or supine). A true polyp is fixed and has a soft-tissue structure.
- Lipomas. Appear as polyps on 3D reconstruction, but their specific fatty density is clearly visible on flat 2D images.
- Inverted diverticulum. Mimics a protrusion into the bowel lumen, but the presence of gas inside the lesion on 2D images reveals its true nature.
Imaging findings in specific pathologies
Proper visualization allows for an accurate assessment of the extent of involvement in systemic and acute diseases.
- Neutropenic enterocolitis (typhlitis). Ultrasound and CT show a markedly thickened cecum. Decreased contrast enhancement of the wall indicates ischemia or necrosis, which is a predictor of perforation. Generalized ascites is frequently detected.
- Cystic fibrosis (Cystic Fibrosis). Patients often develop distal intestinal obstruction syndrome (DIOS), the equivalent of meconium ileus with fecal impaction in the right colon. Ileocolic intussusceptions, strictures (fibrosing colonopathy), and appendiceal enlargement without wall thickening or periappendiceal inflammation are also characteristic.
- Abdominal trauma. In hemodynamically stable children, CT is the modality of choice (the liver is most commonly injured). To reduce high radiation exposure, a split-bolus contrast technique (split bolus) is used to obtain arterial and portal venous phases in a single scan.
Hereditary polyposis syndromes
A number of genetic disorders are associated with a high risk of colorectal cancer (CRC). Tumor masses in these syndromes can reach enormous sizes.
| Syndrome | Features of pathogenesis and imaging | Oncology risks |
|---|---|---|
| Lynch (HNPCC) | DNA mismatch repair gene mutations. Tumors are more frequently located in the proximal segments. Cancer develops early (average age 45). | CRC (up to 85%), endometrial cancer, small bowel cancer, renal pelvis cancer |
| Peutz-Jeghers | Mucocutaneous pigmentation, large gastrointestinal hamartomas on a stalk prone to bleeding. | Gastrointestinal, ovarian, pancreatic, and breast cancers |
| Turcot | Association of colorectal adenomas with CNS tumors. | Primary brain tumors |
The "3-2-1" rule for diagnosing Lynch syndrome: 3 relatives with associated cancer, 2 consecutive generations, 1 tumor diagnosed under the age of 50 (and 1 affected individual is a close relative of two others).
Class and exam questions
Can barium enema still be used for cancer screening?
No, in modern clinical practice this method is considered obsolete. It has been entirely replaced by CT colonography for detecting polyps and cancer.
What is the danger of water-soluble contrasts in bowel strictures?
Such agents are hyperosmolar. If the fluid moves proximal to the obstruction, it will draw water into the lumen, overdistend the bowel, and potentially trigger perforation.
How to distinguish a polyp from food residue or stool on virtual colonoscopy?
Fecal masses change position when the patient is turned and have heterogeneous density. For greater accuracy, oral stool tagging is used, which renders the contents radiopaque (bright on CT).
How does the appendix appear on ultrasound in cystic fibrosis?
Due to thick mucus stasis, it is increased in diameter, but the wall is not thickened, and periappendiceal inflammation is absent (unless complicated by superimposed acute appendicitis).
What else to study on this topic
- Rare forms of polyposis: Cowden syndrome, Cronkhite-Canada syndrome, juvenile and serrated polyposis.
- Extra-intestinal abdominal manifestations of cystic fibrosis (pancreatic cystosis, hepatic steatosis).
- Application of computer-aided detection (CAD) systems as a "second reader" in CT colonography.
- Pelvic MRI anatomy: visualization of the mesorectal fascia and fat.
- Contrast-enhanced ultrasound in blunt abdominal trauma.
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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