Discussion:
Total intracranial migration of VP shunt is an extremely rare complication. The incidence of total migration of VP shunt is reported to be about 0.1-0.5% (. The migration can take place in either cranial or caudal directions. Commonly, it is usually the distal or peritoneal catheter that migrates after disconnecting into many locations such as the scalp, mouth, thorax, diaphragm, heart, pulmonary artery, chest, breast, stomach, gall bladder, liver, scrotum, colon, bladder, vagina and rectum and causing injury to the local organs . However, upward migration has been reported as well. After a thorough review of literature, we found twenty-seven cases up to date of total intracranial VP shunt migration (Table 1).
Etiology of this complication is unknown, but several factors are thought to be responsible in facilitating proximal shunt migration. It is believed that the direction of shunt migration is dependent upon the pressure gradients between cranial and peritoneal cavities. Furthermore, it is hypothesized that pediatric patients are at an increased risk due to the shorter distance between the peritoneum and cranium. This short distance and violent, uncontrolled movements of the head (windlass effect) could lead to mechanical displacement of the shunt in cranial direction (. Another possible mechanism of proximal shunt migration may be due to inadequate fixation of shunt at the distal end or detachment due to an increased rate of growth in early stages of life. In addition, thin cerebral mantle, large ventricles and wide fontanelles create an intracranial pressure close to the atmospheric pressure while abdominal pressure remains positive in comparison to the atmosphere. This creates a pressure gradient which can lead to sucking of the shunt towards cranium . Interestingly, many other case studies report patient-related factors such as malnutrition (less subcutaneous tissue for anchorage), anemia, young age, thin cortical layer, and severe hydrocephalus which could all be related to upward shunt migration . Some authors propose factors like seizures, and constipation as responsible for possible migration (. In most VP shunt insertions, a burr hole is made in the occiput providing a straight path up from the peritoneum . Although this may be the easiest mode of insertion, it may contribute to cranial shunt migration as the path is simply too straightforward. Finally, in resource poor settings like ours “Chhabra” shunt is used as it is very economical for patients. However, it has cylindrical chamber which can easily slide into the cranium (. The best approach would be a frontal burr hole instead of occipital burr hole. Further, optimum creation of subgaleal space, the firm anchoring of connector sites to the periosteum while avoiding the large dural opening and large burr holes can help prevent such complications (2).