Intraperitoneal cerebrospinal fluid pseudocyst. A rare complication of ventriculoperitoneal shunt

Background
Since 1905, the abdominal cavity has been used for absorption of cerebrospinal fluid in patients with hydrocephalus (1). Abdominal pseudocyst is an uncommon complication in its use. We report a case of a patient with a subhepatic cerebrospinal fluid (CSF) pseudocyst after a ventriculo-peritoneal (V-P) shunt insertion.
Case report
A 31-year-old female, had undergone a V-P shunt for hydrocephalus. One year after operation she was readmitted to our department because of low-grade fever, poor appetite, light headache, abdominal and back pain. She had no history of malignancy, pancreatic or liver disease. Physical examinations showed sensitivity on right abdominal flank and a low-grade body temperature (37,9ºC). No malfunction of V-P shunt was also noted. Laboratory examinations revealed elevations in the white blood cell count (15.200/ml), C-reactive protein levels (8.6 mg/dl), erythrocyte sedimentation rate (85 mm/h), AST levels (14 U/l) and alanine aminotransferase levels (15 U/l), amylase levels (37 U/l), LDH (258 U/l), CPK (39 U/l), g-GT (17 U/l), Ht (39.4 %), Hb (14.6 g/dl). The pregnancy testing was negative. CSF studies showed no abnormal findings. A plain X-ray of the abdomen showed that the tip of the V-P shunt was located in the right upper quadrant. The ultrasonographical (US) evaluation of the abdomen allowed for recognition of a well defined, cystic mass lesion with internal echogenicity and volume of 50 cm3, in the recessus hepatorenalis (fig. 1).
In aim of differential diagnosis an abdominal CT scan was performed, showing a no enhanced cystic mass with homogenous low attenuation in the Morrison's recess measuring approximately 5, 5 x 4 x 6 cm. The peritoneal tip of the V-P shunt seemed to be located within the mass lesion (fig. 2). Follow-up brain CT revealed no enlargement of the ventricular size. An abdominal pseudocyst as a complication of the V-P shunt was highly suspected. A distal externalization of the peritoneal catheter without excision of the pseudocyst was performed. CSF culture demonstrated a Staphylococcus epidermis infection and adequate antibiotic treatment was administrated. The previous symptoms improved 4 weeks later and a new catheter was placed intraperitoneally in a different quadrant. The postoperative course was uneventful.

Discussion
The peritoneal cavity offers a large surface area of tissue and is the most common site of CSF absorption in hydrocephalus treatment The presence of an intraperitoneal catheter can initiate various common complications, such as tube disconnection, blockage of the shunt tip, infection, bowel obstruction, and perforation (2). Uncommon complications that are described include subphrenic abscess, small-bowel perforation with secondary formation of a cerebrospinal-enteric fistula, untreatable cerebrospinal fluid ascites, migration of the tip of the shunt to distant locations, such as intrathoracic or subphrenic areas and protrusion of the shunt from the anus (3, 4, 5).
Among uncommon complications is the formation of an abdominal CSF pseudocyst, which was first described by Harsh in 1954 (6). This is a rare, but important complication in patients with a V-P shunt insertion. Incidence of abdominal pseudocyst ranges from 1-4.5% (7).
Several predisposing factors for this complication have been suggested, including infection, multiple shunt revisions, obstruction or dislodgement, peritoneal reaction to stranger body reject, but the pathophysiology is still unknown (7). However, the abdominal inflammatory process is accepted widely as a hypothesis for the formation of an abdominal pseudocyst (1, 7, 8). We also suggest that chronic inflammation or subclinical peritonitis is a predisposing factor for this complication. The infection rate has been reported to be from 17 to 80% and S. epidermis and Staphylococcus aureus are the most commonly cultured micro-organisms (7, 8).
CSF- pseudocysts are seen as a thin-walled cystic mass around the shunt tip. Microscopically, the wall of pseudocysts consists of fibrous tissue without epithelial lining and is filled with CSF. Debris is identified in the majority of the fluid collections (1). They can either move freely within the peritoneal cavity or adhere to small-bowel loops, the serosal surface of solid organs, and the parietal peritoneum.
The time interval from the last shunting procedure to the development of an abdominal pseudocyst ranges from 3 weeks to 10 years (9).
The most frequent symptoms and signs of abdominal pseudocysts are abdominal pain (63%), abdominal distension (37%), abdominal tenderness (31%) and abdominal mass (29%) (10). In a review of fourteen cases, children mainly complained of symptoms of elevated intracranial pressure, such as headache and nausea and adults predominantly suffered local abdominal signs (1).
US or CT scan pose the definitive diagnosis. US are the method of choice in the evaluation of the pseudocyst and other complications at the distal end of the V-P shunt (1, 8).
Imaging findings may show a large fluid-filled collection containing debris and the V-P shunt catheter close to the walls (11). Besides, the double echo of the catheter walls may produce the so-called railroad sign within the pseudocyst (1). Furthermore, a CT scan of the abdomen provides the definitive diagnosis, especially when abdominal pseudocyst is not defined by US (10, 11).
If infection is suspected, many authors suggest that it is essential: To place a temporary extraventricular device, to remove the peritoneal shunt tube and to administer adequate antibiotics (8, 11, 12). It is not clear, if the pseudocyst wall is to be excised or not (8, 11, 12). After confirming negative cultures of the CSF, a new distal catheter may be replaced in the right atrium or intraperitoneally in a different quadrant (8, 11, 12).
Excision or repositioning of the shunt tip with minimally invasive laparoscopic techniques is also performed. This technique in the setting of a no infected pseudocyst has proved to be safe, with results comparable to those of a conventional open surgical technique (13). Percutaneous drainage (CT-guided or sono-guided) of the pseudocyst can be both diagnostic and therapeutic (14). Recurrences are rare, especially under appropriate medical treatment of infection (1).
In differential diagnoses of abdominal cystic mass, one has to consider the following clinical entities: metastatic disease from the brain through V-P shunt, cyst of mesentery or omentum, small bowel duplication cyst, seroma, lymphocele, cystic teratoma, cystic spindle cell tumour, cystic lymphangioma, pancreatic pseudocyst, biloma, urinoma and abdominal abscess (1, 9). Abdominal abscess, biloma, urinoma and pancreatic pseudocyst most frequently mimic a pseudocyst in a post-traumatic patient.

Conclusions
Abdominal CSF pseudocyst is an uncommon complication of V-P shunts, thus remaining clinically important for early recognition and treatment in patient management. An awareness of this complication is necessary in creating an index of suspicion for the primary care physician whose patients harbor a V-P shunt and demonstrate abdominal symptoms.

References
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