Parasitic lung diseases

Pulmonary echinococcosis

Pulmonary involvement in echinococcosis is most commonly presented by single (solitary) cysts, although in 10% of cases they can be multiple or bilateral. Less commonly, the echinococcal cyst is localized in the mediastinum, heart, or pulmonary arteries. The clinical presentation of the pulmonary form is often non-specific, and the main dangers are associated with the disruption of the integrity of the lesion walls. Aggressive invasion into the pulmonary and bronchial arteries can provoke massive hemoptysis and profuse hemorrhage.

Radiological findings depend on the state of the parasitic lesion:

• Intact (unruptured) cysts: visualized as one or more spherical (oval) homogeneous masses with sharp margins, causing a local mass effect.
• Ruptured cysts: form a complex cavitary lesion due to the disruption of internal membranes. They are often accompanied by secondary infection, abscess formation, pleural effusion (upon rupture into the pleura), or hydropneumothorax (upon communication with the airways).

Specific radiological signs of rupture:

1. Air crescent sign — an accumulation of gas at the periphery of the cyst, visually resembling a mycetoma.
2. Presence of a fluid-gas level within the cavity.
3. Water lily sign (or floating lily sign) — a rounded shadow of the detached chitinous membrane floating on the surface of the fluid inside the lesion.
4. Double-wall sign.
5. Rising sun sign (snake sign) — a dry cyst where the shrunken membranes settle to the bottom.
6. Empty cyst sign — determined if the patient has completely coughed up the intracystic contents.

Trematodiases: paragonimiasis and schistosomiasis

Two important representatives of the trematodiases group affecting the respiratory system have fundamentally different pathogenesis and radiological patterns.

Paragonimiasis is caused by the lung fluke (Paragonimus westermani). Infection occurs alimentarily — by eating raw or poorly cooked freshwater crustaceans. In the early stage, juvenile forms migrate through tissues, and in the late stage, cysts form around the parasite.

• The imaging pattern is characterized by bilateral changes: areas of consolidation, nodules, as well as tubular, ring-like, and linear opacities.
• A frequent CT finding is a combination of focal pleural thickening and subpleural linear strands extending to a peripheral necrotic nodule.
• Differential diagnosis: involvement of the upper lobes mimics tuberculosis, while the lower lobes mimic bronchiectasis.

Schistosomiasis (caused by Schistosoma) causes chronic granulomatous inflammation of the pulmonary arterioles in the lungs.

• The pathological process leads to obliterating arteriolitis, which in turn causes pulmonary arterial hypertension and the development of cor pulmonale.
• A possible complication is a pulmonary artery aneurysm.
• Radiographs and CT scans (especially with 3D reconstruction) clearly show pronounced dilatation of the pulmonary artery trunk. Schistosomiasis should always be suspected in patients from endemic regions presenting with signs of pulmonary hypertension.

Other parasitic chest infections

In addition to echinococcosis and trematodiases, specific radiological changes are caused by other pathogens:

• Dirofilariasis (infection is often associated with contact with dogs) manifests as fever, cough, and chest pain. Radiography shows ill-defined opacities, most commonly in the lower lobe of the right lung. CT reveals multiple scattered bilateral pulmonary nodules surrounded by a characteristic ground-glass halo.
• Strongyloidiasis (Strongyloides stercoralis) presents as a massive invasion (hyperinfection) in immunocompromised patients (e.g., with AIDS). The CT picture includes multiple focal areas of consolidation and ground-glass opacities.
• Toxocariasis is characterized by fever, cough, weight loss, and tachypnea. Radiologically, a diffuse micronodular pattern in the lungs is typical for it.
• Chagas disease / Trypanosomiasis manifests with chest pain and regurgitation. The main CT finding is a significantly dilated esophagus with intraluminal contents, air bubbles, and a fluid level, along with accompanying pleural effusion.
• Disseminated cysticercosis in the thorax is often asymptomatic and diagnosed as an incidental finding on a chest X-ray showing multiple calcified cysticerci in the chest wall muscles.

Briefly: answers to topical questions

What else to study on this topic

• Evaluation of 3D reconstructions and volume rendering in pulmonary trunk enlargement.
• Imaging findings of eccentric filling defects in the aorta and pulmonary vessels.
• Differential diagnosis of the diffuse micronodular pattern in the pulmonary parenchyma.
• Clinical and radiological correlations in hyperinfection syndrome against the background of immunodeficiency states (AIDS).

Other topics in the «Chest Radiology» section

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