Peritoneal echinococcosis

Imaging findings of peritoneal echinococcosis

During contrast-enhanced computed tomography (CT), peritoneal echinococcosis (Peritoneal Hydatidosis) is visualized as a massive multilocular cystic lesion localized in the abdominal cavity.

Key radiological signs:

• Honeycomb sign (honeycomb appearance). Within the main mother cyst, multiple small daughter cysts are clearly defined. It is they that give the lesion a specific septated appearance.
• Rim calcification. A very characteristic feature is the calcification of the capsule along the edge of the lesion (rim calcification), indicating the chronic nature of the parasitic process.

Differential diagnosis: Mesenteric panniculitis and Sclerosing mesenteritis

When identifying lesions and consolidations in the abdominal cavity, the diagnosis is differentiated from rare inflammatory lesions of the adipose tissue of the small bowel mesentery (less commonly, the colon). This is a spectrum of a single disease of unknown etiology, which may be triggered by surgery, trauma, lymphoma treatment, autoimmune, or oncological processes. Clinically, the process is often asymptomatic or accompanied by non-specific pain, diarrhea, and weight loss. The prognosis is predominantly favorable, with the possibility of self-resolution.

The disease is divided into two forms depending on the predominant pathological process:

1. Mesenteric panniculitis (predominance of fat necrosis and inflammation):
2. On CT, it is visualized as a heterogeneous fatty mass with well-defined margins at the root of the mesentery (usually in the left upper quadrant).
3. The mass envelops the mesenteric vessels, forming a zone of low density around them — the halo sign (halo).
4. Bowel loops are not involved in the process, but may be displaced.
5. The combination of these features forms the picture of a misty mesentery (misty mesentery).
6. On MRI (T2-weighted images), a hypointense capsule is identified, which enhances with contrast after gadolinium administration.

1. Sclerosing (retractile) mesenteritis (predominance of fibrosis):
2. On CT, it appears as an infiltrative soft-tissue mass with radiating spicules (strands). It can mimic carcinoid or fibromatosis. Calcifications are often visible in the necrotic center.
3. On MRI, the predominance of fibrous tissue produces a characteristic low signal on both T1-weighted and T2-weighted images.

Mesenteric lymphadenitis and Non-inflammatory mesenteric oedema

For completeness in abdominal imaging, it is important to consider other conditions that alter mesenteric attenuation:

Mesenteric Lymphadenitis (Mesenteric Lymphadenitis) On contrast-enhanced coronal CT scans, a pronounced cluster of enlarged lymph nodes is identified, localized predominantly in the right iliac fossa. This process is very frequently combined with thickening of the terminal ileum wall.

Non-Inflammatory Mesenteric Oedema (Non-Inflammatory Mesenteric Oedema) A secondary condition characterized by a diffuse increase in the density of all mesenteric adipose tissue on CT (or signal alteration on MRI). Due to edema, normal, previously well-delineated mesenteric vessels are visualized extremely poorly along their path to the bowel loops. It occurs in the setting of systemic pathologies:

• Hypoalbuminemia and liver cirrhosis;
• Nephrotic syndrome;
• Right-sided heart failure;
• Mesenteric ischemia, vasculitis, or prior trauma.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathogenesis of daughter cyst formation in echinococcosis
• Differential diagnosis of the «misty mesentery» sign
• Association of mesenteric panniculitis with lymphoproliferative diseases
• Causes of terminal ileum wall thickening
• The role of excisional biopsy in the diagnosis of mesenteric pathologies

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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