A mediastinal pseudocyst is the extension of pancreatic pseudocyst into the posterior mediastinum through oesophageal or aortic hiatus or rarely through the foramen of Morgagni. It is a rare complication of acute or chronic pancreatitis.
It can present with symptoms due to compression or complications caused by the cyst. The symptoms include dysphagia, odynophagia, chest pain, dyspnea and symptoms of pericardial or pleural effusion.
It is believed that during the acute phase of pseudocyst formation the fluid may track along the path of least resistance to gain access into the posterior mediastinum through diaphragmatic foramen and hiatus. Later in the phase, the outer wall gets organised to form a pseudocyst.
Chest radiography is not diagnostic but can reveal lower mediastinal widening, retro or para-cardiac well-defined opacity. Other associated features can be seen i.e. pleural effusion or large pericardial effusion.
Contrast-enhanced CT is one of the valuable procedure to identify the pseudocyst as well as establishing its relationship with surrounding structure. It appears as a thin-walled low attenuation peripherally enhancing cyst.
MRI-MRCP is as effective as ERCP to demonstrate the track between the peri-pancreatic cyst and the mediastinal cyst.
The differential will depend on the clinical context but as broad differential for cystic mediastinal lesions consider - other cystic mediastinal lesions.
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