A 44-year-male presented with progressive dyspnoea for 6 months, dry cough and chest discomfort for 3 months. His chest radiograph and computed tomographic (CT) thorax features, as shown here (Figures 1 to 5), were typical characteristic of a hydatid cyst.

Hydatid disease (echinococcosis) is a parasitic disease known to affect humans and other mammals. Four Echinococcus species have been identified: Echinococcus granulosus, E. multilocularis, E. vogeli and E. oligarthus.

E. granulosus has a worldwide prevalence particularly in regions where cattle-rearing is common. E. multilocularis mainly occurs in central Europe, northern parts of Europe, Asia, and North America. E. vogeli and E. oligarthus are not so common and their prevalence is limited to Central and South America.

Although echinococcosis may involve any organ, liver (in 75% of cases) and lungs (in 5–15% of cases) are most frequently affected. Most of the lesions may grow until picked up on imaging modality or become large enough to compromise the functions of host organ.1

Plain radiographs are useful in localising the lesions, and in cases with pulmonary disease, floating membrane in cyst (or water lily sign) is of high diagnostic value. Ultrasonography is a useful initial diagnostic technique; cysts with a visible split wall inside, septated cysts, or those with a honeycomb pattern are pathognomonic. CT scans usually show cyst(s) with fluid having water attenuation (3-30 HU).2 The matrix represents hydatid fluid containing membranes of broken daughter cysts, scolices, and hydatid sand.

Membranes may appear within the matrix as serpentine linear structures, a finding that is highly specific for hydatid disease (water lily sign). Multilocular cysts manifest as well-defined fluid collections in a honeycomb pattern with multiple septa—a spoke wheel pattern.

Serological diagnosis include detection of anti-Echinococcus antibodies IgG using indirect haemagglutination test or enzyme-linked immunosorbent assay.

Usual treatment of echinococcosis includes chemotherapy using albendazole and/or mebendazole along with surgical removal of the cysts whenever feasible though multi-organs or vital organ involvement makes surgery impractical.

Author information: Prem Parkash Gupta, Professor, Respiratory Medicine; Krishan B Gupta, Senior Professor, Respiratory Medicine; Dipti Agarwal, Assistant Professor, Physiology; Postgraduate Institute of Medical Sciences, University of Health Sciences, Rohtak, India

Correspondence: Professor Prem Parkash Gupta, Professor, Respiratory Medicine, Postgraduate Institute of Medical Sciences, University of Health Sciences, Rohtak, India. Email: gparkas@yahoo.co.in