Pseudoazygos lobe caused by lymph node pneumatocele

In patients with AIDS, the relatively high incidence of pulmonary tuberculosis places them at risk for more severe esophageal tuberculosis (including fistula formation), and tuberculous esophagitis in the setting of AIDS may be more common than had been thought. Tuberculous esophageal fistulae have long been described and are well known. Air tracking from the esophagus into a mediastinal lymph node is very rare and reported previously to collect in small pockets in either of two patterns: irregular (or "amorphous") or peripheral and curvilinear. Complete filling of a large lymph node by air has not previously been reported. Reported here is a case of tuberculous mediastinal lymphadenopathy in an AIDS patient in whom CT scans demonstrated fistula development between a large lymph node and adjacent esophagus; this was accompanied by total replacement of the apparently necrotic content of the node with air, surrounded by the relatively thin, smooth, residual wall of the node. A lymph nodal pneumatocele was thereby created, which has not been previously described, and is the first feature of this case. On frontal chest radiography, the lateral wall of the lymph nodal pneumatocele produced an appearance falsely akin to an azygos fissure, creating the second feature: a previously unreported cause of false appearance of an azygos lobe. It is important to consider tuberculosis when a fistula to the esophagus is demonstrated in an AIDS patient, to be aware that even a large lymph node may "shell out" entirely in that setting, and not to confuse the final resulting appearance with the normal variant it may resemble.