Figure 1.17. CSF'oma. Sagittal (A) and transverse (B) scans of the midabdomen show a sonolucent structure with a slightly echogenic wall, consistent with a CSF'oma. The debris-coated VP shunt is well seen inside this pseudocyst. (Courtesy of R. Wachsberg, MD, Newark, NJ)

The presence of a pseudocyst may be associated with either local abdominal signs or symptoms or related to increased intracranial pressure [55]. According to most authors, abdominal signs and symptoms predominate in children [56-58], although one study also included increased intracranial pressure among the clinical presentations [55]. The same authors also stated that abdominal signs and symptoms predominate in adults.

The diagnosis of a CSF pseudocyst is made most often on ultrasound [55-57]. A sonolucent mass may be identified in the area of a palpated abnormality. Sizes of up to 2L have been reported [59]. Treatments include shunt revision and repositioning [55-58,60]. Aspiration of the pseudocyst contents can be performed under CT [58] or ultrasound guidance [56,60] or intraoperatively (with or without cyst wall resection) [55,56,58-61]. In one series of 27 patients, 15 of the abdominal CSF pseudocyst resolved spontaneously [60].

Infection rates of the pseudocyst may range as high as 77% in children under the age of 4 years [60]. Overall, the infection rate is approximately 30% [55,60]. No difference in the imaging characteristics between infected and sterile pseudocysts has been described.

Just as the shunt catheter can act as a conduit for abdominal flora to reach the central nervous system, so can central nervous system neoplasms seed down the shunt catheter to enter the peritoneal cavity. This complication arises on average approximately 17 months after shunt surgery, and the patients often die (73%) [62,63]. The time from the diagnosis of the abdominal symptoms to the patient's demise was only 2 months [62]. Germinomas were the most common lesion in pediatric patients over the age of 10 years, while in the under-10-year-old group medulloblastomas were the most common primary lesion [62].

Unusual mechanical problems related to the presence of the catheter itself have also been reported. The VP shunt in the abdomen may accidentally be detached from the intracranial portion and retract into the abdomen (Fig. 1.18). In another case, a VP shunt catheter formed a knot

Figure 1.18. Broken VP shunt. Supine film of the abdomen shows a long fragment of a VP shunt catheter that had become detached from the more proximal portion. It lies folded back upon itself in the supravesical region.

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