Ruptured pulmonary hydatid cyst

Discussion:

Subcutaneous or surgical emphysema often occurs in the chest wall secondary to a malpositioned chest tube. This is not a life threatening complication and will resolve given time. Clinically may be perceived as crepitus of the soft tissues on the affected side. It is also known as surgical emphysema due to the dissection of the air into the deep soft tissues and intramuscular planes.

In this case, the underlying pulmonary pathology is that of a ruptured (complicated) cyst from a pulmonary hydatid infection. This is the second most common site of hydatid disease after the liver (hepatic hydatid cyst), and may infect the lungs through either transdiaphragmatic or hematogenous spread. Concurrent infection in both the liver and the lungs however, is rare. In this case, the liver is visualized and has normal parenchyma. 

These hydatid cysts can grow very large and can be uni or multiloculated. They can also have odd shapes and rupture (as in this case) due to pressures from adjacent broncho-vascular structures, as well as the continuous production of hydatid fluid and increase in intracystic pressure. The imaging characteristics of these cysts include various radiological signage devised to help with its diagnosis, including the Cumbo/ Onion peel/ Double arch sign seen here.

It is worth noting that patients with underlying pleural pathology (such as in this case where the adjacent hydatid cyst causes pleural reaction) may be prone to malpositioning of a chest tube due to the chronic pleural inflammation.

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