Radiological Diagnosis

HYDATID CYST - RIGHT LUNG - PRE AND POST RUPTURE

Patient was unable to lie down in supine position due to bouts of cough and expectorations, hence C.T.Scan Chest was done in prone position. C.T.Scan Chest revealed a large cavitatory lesion, with air-fluid level and floating membranes (Water Lilly Sign). Patchy consolidation is also seen in the left lower lobe. A radiological diagnosis of Ruptured Hydatid Cyst - Right Lung was given. Laboratory and operative findings confirmed the above diagnosis.

Hydatid disease (echinococcosis) is caused by a tapeworm, either Echinococcus granulosus or E. Alveolaris, the later being more uncommon and restricted in distribution. Humans are accidental hosts and acquire infection by ingesting ova form fomites or contaminated water and by direct contact with dogs. Cysts develop in the lung, or less commonly in the mediastinum, and may be ruptured (2/3rd) or unruptured (1/3rd) at the time of presentation.

The Radiological findings with unruptured pulmonary cysts are one or more homogeneous, roughly spherical or oval, sharply demarcated mass lesions [Figure - 1]. They range in size from 1 to 1 Ocms and occur particularly in the mid and lower zones. About 20% are multiple. The intrapulmonary masses are of soft tissue density and almost never calcify, unlike mediastinal lesions.

Cysts rupture is usually associated with secondary infection and may occur into the airways or pleural space. Acute symptoms often develop when cyst rupture occur and frequently precipitate presentation. There are three layers to the wall, two in the cysts itself (endo and ecto cysts) and a third derived from the surrounding lung (pen, cyst). If the two inner layers remain intact, communication results in a ring opacity containing a rounded homogeneous density. The radiographic appearance is that of an intracavitary body, and resembles a meniscus sign. Should there be disruption of the inner layers, complex cavitary lesions will result with one or more of the following radiographic features: 1. An air-fluid level, 2. A floating membrane (Water Lilly Sign, Camalote Sign Figure No.3) 3. A double wall 4. An essentially dry cyst with crumpled membranes lying at its bottom (rising sun sign, serpent sign) 5. A cyst with all its contents expectorated (empty cysts sign). Secondary infection of a Hydatid Cyst may produce a lung abscess with or without surrounding consolidation, C.T. & M.R.I demonstrates a number of these features better than Chest Radiograph. Rupture into the pleural spaces causes an effusion or if there is additional airway communication a hydropneumothorax.[5]