Although not strictly a procedure that involves the gastrointestinal tract, placement of ventriculoperitoneal (VP) shunts may cause problems that manifest themselves in the abdomen. VP shunts are usually placed to decompress hydrocephalus due to both benign and malignant conditions. Complications may be related to migration of the shunt catheter with or without subsequent infection, abnormal fluid collections, spread of neoplasm, and other miscellaneous mechanical problems.
When a VP shunt is placed in the abdomen, it is not sutured in place. Therefore it can migrate. Since the catheter is nonreactive, fibrous tissue does not form about its tip, leading to some complications discussed later. When the catheter does shift in position, it may migrate through various intra-abdominal passageways, perforate hollow viscera, or penetrate solid ones. An example of the first type is passage via a patent processus vaginalis resulting in a scrotal hydrocele . Another congenital anomaly associated with tube migration was a patent foramen of Bochdalek . In this instance, a patient developed a hydrothorax filled with cerebrospinal fluid (CSF) as the catheter transitted from the abdomen to the chest across the abnormal pleuroperi-toneal communication. In another instance, the tip of the shunt catheter migrated through the foramen of Winslow, resulting in a CSF collection within the lesser sac . The latter was detected on a scintigraphic examination.
Perforation, even through the thick wall of the stomach, may occur during placement of the shunt catheter  or many months later . Perforation through the colonic wall has resulted in a VP shunt presenting per rectum during defecation . The shunt was subsequently removed via a sigmoidoscope.
Multiple cases of liver [49-52] or even splenic  abscesses have been reported. These have an appearance similar to other pyogenic abscesses except for the presence of a VP shunt in the abdomen or liver proper. Liver lesions were described at CT imaging as a hypodense cyst with multiple septations. On sonography the lesion was cystic with internal echoes and septations, and the shunt tip was seen within the pseudocyst . In all cases the shunt catheter had to be externalized, the abscess drained, and systemic antibiotics used to treat the infection. In at least one case a perforation of the colonic wall by the VP shunt catheter led not to an abdominal infection but retrograde spread to the head . This resulted in an E. coli meningitis.
In rare instances, fibrous tissue may form around the abdominal portion of the ventriculoperitoneal shunt. As CSF continues to drain into the abdomen, it may be encapsulated by the fibrous tissue without an epithelial lining . This gives rise to a peritoneal pseudocyst or CSF pseudocyst, also anecdotally called a CSF'oma (Fig. 1.17). These occur in slightly less than 2%  or as many as 4.5% of all shunts , developing as soon as 3 weeks postoperatively . Predisposing factors for their development include previous shunt placement [55,57] and infection . Following VP shunt placement, intraperitoneal surgery, either open  or laparoscopic , may lead to an increased incidence of pseudocyst formation.
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