Deflating abdominal pseudocyst causing temporary normalization of ventriculoperitoneal shunt malfunction

Ventriculoperitoneal shunt (VPS)-related abdominal pseudocyst (APC) is a rare cause of shunt malfunction. Variable VPS function due to APC has not been described before. A 21-year-old male with hydrocephalus and bilateral VPS presented with a right-sided shunt malfunction. After a routine abdominal ultrasound (US), that proved to be unremarkable, the patient had a clinical and radiological improvement followed by a relapse. An abdominal computed tomography scan subsequently showed an APC around the peritoneal catheter tip. Laparoscopic intervention on the APC cured the shunt malfunction. We believe that the APC emptied during the compression involved while performing the abdominal US. The pseudocyst collapse led to missing it on the abdominal US and explains the short-lived clinical and radiological improvement. We introduce the concept of APC-related variable VPS function, discuss the possible mechanisms by which the pseudocyst deflated, and make suggestions toward this diagnostic problem. Key Messages: A collapsible abdominal pseudocyst could result in a variable ventriculoperitoneal shunt function. Starting the abdominal ultrasound examination over the location of the peritoneal catheter tip may overcome the collapse. Contrasted computed tomography is superior to ultrasound in diagnosing the pseudocyst.