Pulmonary hydatid infection is a common manifestation of hydatid disease.

For a general discussion, and for links to other system specific manifestations, please refer to the article on hydatid disease. 

Epidemiology

The lung is the second most common site of involvement with Echinococcus granulosus in adults after the liver (10-30% of cases), and the most common site in children ¹. The coexistence of liver and lung disease is present in only 6% of patients ².

Clinical presentation

When pulmonary hydatid cysts rupture and communicate with bronchioles, patients expectorate what is described as 'grape skin'-like material ⁷.

Pathology

Thoracic involvement may occur via ¹:

• transdiaphragmatic route (0.6-16% of cases of hepatic disease)

• haematogenous spread

Although Echinococcus granulosus presents commonly with unilocular cysts, Echinococcus multilocularis and Echinococcus vogeli may cause alveolar and polycystic echinococcosis.

Radiographic features

CT

Generally, chest CT scan features include ²:

• solitary cystic lesion up to 20 cms in diameter

• multiple cystic lesions, unilateral or bilateral

• lower lobe predominant

• no calcification, (low CO₂ in lung inhibits calcium precipitation ¹⁰)

Uncomplicated cysts are characterised by:

• round or oval masses with well-defined borders

• enhancement after contrast injection

• hypodense content relative to the capsule

Complicated cysts may show:

• meniscus sign or air crescent sign

• cumbo sign or onion peel sign

• water-lily sign

• consolidation adjacent to the cyst in case of a ruptured cyst

MRI

• T1: hypointense

• T2: hyperintense

The cyst capsule is hypointense on T2 weighted images (hypointense rim sign), isointense on T1 weighted images, and shows mild contrast enhancement. The folded membranes within cysts are T2-hypointense ⁸.

Ultrasound 

Double-layered wall in univesicular cysts and a double-layered septum in cases of multivesicular cysts (wall sign) ⁹

Other less common thoracic hydatid manifestations include invasion of the mediastinum ⁴, pericardium, pleura, chest wall ⁵, cardiovascular system, or inferior vena cava ⁶.