Presentation
Patient presented with a long standing history of cough, increasing chest pains and low grade fevers. A left sided chest tube was placed and subsequently removed prior to the HRCT chest scan, after it was noted on plain film to be mal-positioned.
Patient Data
There is extensive air density seen in the soft tissues of the anterior, lateral and posterior chest wall, dissecting into the deep soft tissue and muscle planes, and which extends superiorly and inferiorly to involve the left neck and left lateral abdominal wall, respectively. The emphysema even crosses over to the right side at the level of the thoracic inlet.
Within the lung fields, there is a large, well defined, cystic lesion measuring 16 cm (AP) x 9 cm (Trans) x 19 cm (CC) seen in the left lung, occupying almost the entire lung field. Within the dependant portion of this lesion, there is a heterogeneous, serpiginous or onion peel like nodule density. This is representative of the spin or Cumbo sign of detached or ruptured hydatid cyst membranes.
Pleural reaction posteriorly, as well as lung atelectasis medial to the cyst, are also seen, in keeping with the rupture.
Surrounding the hydatid cyst there are multiple smaller cystic cavities interspersed with areas of severe panlobular interstitial emphysema. Midline shift to the right is also seen, likely secondary to mass effect.
The right lung field is unaffected.
The arrows in the annotated slices above point to the pathway created by introduction of the left chest tube (red arrow), the disruption of the skin and subcutaneous soft tissues (green arrow) which is representative of the incision site, and the overlying wound dressing (blue arrow).
Case 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.