Imaging description

In a hiatal hernia, the stomach protrudes into the chest through the esophageal hiatus of the diaphragm. The stomach is an intraperitoneal organ, and so herniation of the stomach through the diaphragm is inevitably accompanied by herniation of the adjacent peritoneal recesses [1]. In a patient with a hiatal hernia and ascites, this can lead to ascitic fluid filling the peritoneal recesses around the herniated stomach in the chest, resulting in a fluid collection in the posterior mediastinum above the esophageal hiatus that has been termed “mediastinal ascites” (Figure 7.1) [2]. The anatomy of peritoneal herniation in hiatal hernia is such that fluid first accumulates to the left of and anterior to the esophagus and later surrounds the esophagus bilaterally.

Importance

On CT or MRI, mediastinal ascites may simulate fluid-filled mediastinal pathology such as a foregut cyst, mediastinal abscess, necrotic tumor, or pancreatic fluid collection [1].

Typical clinical scenario

Mediastinal ascites can occur in any patient with ascites and a hiatal hernia. My experience is that it occurs primarily in older patients with large volume ascites due to ovarian cancer or cirrhosis.

Differential diagnosis

The primary distinction is between true fluid-filled pathology in the posterior mediastinum and mediastinal ascites. Identification of a hiatal hernia and continuity of the thoracic fluid with intra-abdominal ascites are helpful signs in making the correct diagnosis [1, 2]. Rarely, the omentum alone can be herniated through the esophageal hiatus, resulting in a fatty mass above the diaphragm [3, 4]. Such an omental hernia can also be associated with a mediastinal ascites (Figure 7.2). Diagnostic findings in omental herniation include a fatty bilobed mass in the posterior mediastinum that is in continuity with subdiaphragmatic fat and contains omental blood vessels passing through the esophageal hiatus.