6.2.8\ Shunt-Associated Infections

6.2.8.1\ Discussion

Shunt-associated infections may be classified as proximal or distal, and it is important to image both ends of the shunt system in suspected cases of infection. Proximal ventricular shunt-­associated infections mainly include ventriculitis (ependymitis) and meningitis. Cerebritis and abscess are less common complications. Overall, the incidence of VP shuntassociated infection ranges from 2% to 40% per shunting procedure. Distal shunt-associated infections include cellulitis and subcutaneous and intra-abdominal abscesses, which can be

readily demonstrated on CT (Figs. 6.40 and 6.41). Intra-abdominal and subcutaneous abscess related to the ventricular catheter appear as rim-enhancing fluid collections with surrounding fat stranding on CT. The most common causative organisms are

Staphylococcus aureus and epidermidis. On imaging, ventriculitis can manifest as periventricular enhancement and restricted diffusion associated with intraventricular layering debris (Fig. 6.42). Treatment generally consists of removal of the entire shunt device, an interim period of external ventricular drainage and antibiotic therapy, and eventual replacement of the shunting device at a different site.

Fig. 6.40  Ventriculitis. Axial FLAIR (a), DWI (b), and ADC map (c) show layering debris with restricted diffusion­ in the occipital horns of the bilateral lateral ventricles­ . Axial T1-weighted post-contrast axial MRI

(d) show diffuse enhancement along the walls of the bilateral lateral ventricles. There are also bilateral cererbral convexity subdural fluid collections, left larger than right

Fig. 6.41  Cellulitis and subcutaneous abscesses. Axial CT image (a) shows extensive skin thickening and subcutaneous stranding along the path of the lumboperitoneal shunt. Subsequent axial CT image obtained after removal of the device (b) shows development of multiple rimenhancing fluid collections along the prior shunt tract. Staphylococcus aureus was cultured from the wounds

Fig. 6.42  Intraperitoneal abscess. Axial contrast-­ enhanced CT image of the pelvis (a) shows an abscess in the midpelvis (arrow). Axial CT of the abdomen (b) shows externalization of the distal end of the ventriculoperitoneal shunt. The tip of the catheter exits the skin of the right lower quadrant (arrow)

6.2.9\ Shunt Malposition

and Migration

6.2.9.1\ Discussion

Proper positioning of shunt catheters within the ventricles can be challenging particularly in patients with small ventricles. It has been reported that suboptimal ventriculoperitoneal shunt positioning occurs in about 25% of cases and that in about 8% of cases, the catheter tip is located entirely outside the ventricular system, either too far proximal or distal. Catheter malposition can compromise cerebrospinal fluid drainage and lead to injury of brain parenchyma and associated symptomatology (Fig. 6.43).

Distal shunt catheter migration has been reported to occur in many different locations, including into the scrotum, vagina, heart, lungs/ pleura, rectum, and abdominal wall, among others. Retraction into the abdominal wall can lead to the formation of a pseudocyst within the subcutaneous tissues (Fig. 6.44). Migration of the distal shunt into the rectum must be preceded by bowel perforation. Bowel and liver perforation by VP shunt catheters are rare occurrences (Fig. 6.45). Imaging is useful to localize the migrated shunt device components and associated complications. Management may include laparotomy with catheter removal and replacement into another absorptive site.

Fig. 6.44  Bowel perforation. Frontal radiograph (a) shows coiling of a VP shunt catheter in the midabdomen. The catheter then courses in the pelvis and projects in the

rectum/anus region (arrow). Axial CT images (b, c) show the catheter within the left colon and rectum (arrows) (Courtesy of Nina Klionsky, MD)

Fig. 6.45  Catheter liver puncture. The patient presented with worsening neurological status after attempted ventriculoperitoneal shunting at another institution. Axial CT image of the head (a) shows marked verntriculomegaly

despite recent ventricular shunt insertion. Axial CT image of the abdomen (b) shows the distal portion of the catheter within the liver parenchyma, surrounded by a small amount of cerebrospinal fluid (arrow)