Intestinal tuberculosis
Currently, there is an increasing proportion of primary intestinal infections caused by bovine-type mycobacteria, most frequently transmitted via unpasteurized milk. The most typical localization of the process is the ileocecal region. Three main forms of the disease are distinguished: ulcerative, hypertrophic, and fibrous.
- The ulcerative form is characterized by the appearance of large circular mucosal defects with typical "ragged" edges.
- The hypertrophic form appears as a pronounced inflammatory wall thickening that stenoses the lumen. In this case, differential diagnosis with lymphoma and actinomycosis is required.
Radiological signs of intestinal tuberculosis are highly specific. The cecum assumes a conical shape, the ileocecal valve becomes gaping, and the terminal ileum dilates. Short hourglass-like strictures and transverse ulcers sharply demarcated from healthy tissue are also revealed. On CT and MRI, the key diagnostic marker is central caseous necrosis of regional lymph nodes (peripheral contrast enhancement, hypoechoic center on ultrasound).
The main challenge is to differentiate tuberculosis from Crohn's disease. Ascites, lymphadenopathy, and involvement of the peritoneal leaflets favor tuberculosis. Wall stratification, fibro-fatty proliferation, and increased vascularization are more typical of Crohn's disease.
Amebiasis and parasitic infestations
In endemic regions, up to 20% of the population are carriers of Entamoeba histolytica cysts. The invasive form of amebiasis manifests on radiographs as segmental or diffuse colitis with aphthous ulcers and a granular mucosa. A dangerous complication (about 15% of cases) is the embolic spread of the pathogen to the liver. To exclude the diagnosis, fresh stool must be examined for the presence of trophozoites.
In approximately 10% of patients, an ameboma is formed—a mass lesion composed of granulation tissue. It is localized predominantly in the cecum and colonic flexures, causing an irregular stricture that is visually virtually indistinguishable from carcinoma.
Other parasitic lesions also have their specific features:
- Chagas disease: the effect of Trypanosoma cruzi causes degeneration of the intestinal nerve plexuses, which inevitably leads to the development of megacolon.
- Schistosomiasis: the deposition of parasite eggs in the submucosa triggers a cascade of inflammatory reactions. This leads to polyp growth and, in late stages, to fibrosis, strictures, and calcification of the intestinal wall.
Lesions in immunodeficiency and diverted bowel
In AIDS patients against the background of immunosuppression, a complex of neoplastic processes and intestinal infections develops, such as cytomegalovirus (most frequently), Cryptosporidium, and Mycobacterium avium-intracellulare. These agents yield a nonspecific picture on barium enema or colonoscopy. A specific feature is the development of Kaposi sarcoma, most commonly affecting the rectum. It manifests as confluent submucosal nodules, hyperemia, and increased radiodensity of lymph nodes. Accurate imaging diagnosis is hampered by frequent mixed infections.
A specific picture is observed in diversion colitis (in a surgically diverted colon). The absence of fecal passage leads to low-grade bacterial colitis: the colon loses haustration, and its lumen narrows. MRI (on fat-suppressed T1-weighted images) reveals wall thickening, stratification, and stranding of the surrounding adipose tissue. It is important to remember that only water-soluble contrast is used for contrast studies of such segments, as barium may remain trapped in the diverted loop for years.
Acute fulminant colitis
Any inflammation of the colon (amebiasis, ischemia, Crohn's disease, salmonellosis) can progress to a fulminant stage. Most commonly, this condition complicates ulcerative colitis and is the main cause of mortality in this disease.
The process is caused by the transmural spread of inflammation. Deep ulcers penetrate into the muscle layer of the wall, destroying the neuromuscular apparatus. Toxic megacolon occurs—a sharp bowel dilation threatening perforation. The baseline criterion for the onset of this condition is an expansion of the bowel lumen by more than 5 cm against the background of deep ulcers.
The main monitoring method remains plain abdominal radiography. The images show dilation, complete disappearance of normal haustral contours, and the appearance of islands of surviving mucosa against the gas background. The role of cross-sectional imaging methods (CT, MRI, ultrasound) in assessing the depth of the lesion is steadily increasing.
Briefly: answers to topical questions
What diseases must the hypertrophic form of intestinal tuberculosis be differentiated from?
The hypertrophic form of intestinal tuberculosis must be differentiated from lymphoma and actinomycosis. In general, tuberculous involvement of the intestine also requires the exclusion of other inflammatory pathologies.
- Lymphoma—differentiated from a large exophytic mass characteristic of the hypertrophic form.
- Actinomycosis—also requires differential diagnosis in the presence of an inflammatory mass lesion.
- Crohn's disease—the main differential diagnosis for all forms of intestinal tuberculosis.
What extraintestinal complications does Entamoeba histolytica cause?
Extraintestinal complications and manifestations of Entamoeba histolytica infection include:
- Amebic liver abscess—possible with embolic spread of the pathogen; such a complication occurs in approximately 15% of cases.
- Pleuropulmonary amebiasis, including amebic lung abscess; it is usually secondary to liver involvement.
- Amebic brain abscess.
- Cutaneous amebiasis.
To differentiate intestinal tuberculosis, remember the acronym ALP: Ascites, Peritoneal involvement, enlarged Lymph nodes. If present, it is more likely tuberculosis rather than Crohn's disease.
Class and exam questions
What is an ameboma and why is it dangerous?
An ameboma is an inflammatory proliferation of granulation tissue during Entamoeba histolytica invasion. It forms a stricture with irregular contours and visually strongly resembles a malignant carcinoma.
What is the specific CT/ultrasound sign of intestinal tuberculosis?
The presence of central caseous necrosis in the lymph nodes. On ultrasound, it appears as a hypoechoic center, and on CT and MRI, it manifests as peripheral contrast enhancement.
Why is barium contraindicated in diversion colitis?
There is no normal passage of contents in the diverted bowel, due to which barium suspension can be retained in the lumen for many years. Only water-soluble contrasts should be used.
What is the radiological criterion for diagnosing toxic megacolon?
The main criterion is an expansion of the colonic lumen by more than 5 cm, loss of normal haustration, and the presence of mucosal islands against the background of deep ulcerations.
What else to study on this topic
- Radiological picture of ulcerative colitis
- Crohn's disease: differential diagnosis on CT and MRI
- Complications of amebiasis: embolization and liver abscesses
- Diagnostic imaging of gastrointestinal lymphomas
- Technique of barium enema with water-soluble contrast
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