SURGICAL TREATMENT OF HYDROCEPHALUS
The treatment of hydrocephalus depends on the etiology and factors such as the patient’s age, comorbidities, and anatomy. When hydrocephalus is secondary to a tumor or cyst blocking CSF outflow pathways, tumor removal or cyst fenestration may suffice. Most patients with communicating or obstructive hydrocephalus, however, require a CSF diversion procedure to compensate for impaired absorption or blockage. Successful CSF diversion procedures can halt progressive ventricular dilation and elevation of intracranial pressure and can frequently lead to improvement in neurologic function. CSF diversion can be accomplished by endoscopic procedures that bypass an obstruction or by insertion of a shunt to move CSF to an alternate site for absorption into the bloodstream.
Transient hydrocephalus can be temporarily treated with an external ventriculostomy or lumbar drain. These temporary drainage systems allow constant monitoring of the amount and character of CSF drainage, which can be quite helpful in patients with a limited neurologic examination. For obstructive hydrocephalus, the CSF diversion must occur above the blockage. In preterm infants, temporary treatment of symptomatic hydrocephalus is achieved with a ventriculosubgaleal shunt that drains the CSF into a subgaleal pocket or into a ventricular access device that has a reservoir to tap to remove CSF. Once the preterm infant achieves an adequate size, a more permanent CSF diversion procedure is performed, if needed.
Endoscopic procedures for CSF diversion include endoscopic third ventriculostomy (ETV), cyst fenestration, choroid plexus coagulation, and other procedures. The success of these procedures depends on multiple factors, including patient selection and specific anatomic details. The primary benefit of endoscopic procedures is the avoidance of implantation of shunt components that may later malfunction, become infected, or induce shunt dependence. Endoscopic procedures for CSF diversion can have late failure, and all patients after endoscopic procedures continue to require chronic neurosurgical supervision similar to patients with shunts.
The most common shunt system used is a ventriculoperitoneal shunt with a valve. Shunt components are made from Silastic material, and some are antibiotic-impregnated to decrease the risk of infection. The ventricular catheter tip is targeted to the frontal horn of a lateral ventricle from either a frontal or parieto-occipital trajectory. As the catheter exits the skull in the subcutaneous space, it is connected to a valve. Some surgeons use an intervening reservoir. The goal of the valve is to minimize overdrainage and subsequent collapse of the ventricular system and formation of life-threatening subdural hematomas. Various types of valves have been devised; none among them has been proved superior in a well-designed multicenter trial. Shunt tubing can also contain a valve at the distal tip. The subcutaneous distal shunt tubing is inserted into the peritoneal cavity, where the peritoneum absorbs the CSF back into systemic veins. Adequate tubing is placed in infants to decrease the chance that a lengthening procedure will be required. Alternate distal tubing sites include the right atrium or the pleural cavity. Lumboperitoneal shunts are used in select patients. Occasionally, it is necessary to obtain CSF from a patient with a shunt or to inject antibiotics or chemotherapy into the ventricular system instead of via a lumbar puncture. Rarely, contrast material may also be injected to identify loculations within the ventricular cavity. Any manipulation of a shunt by a non-neurosurgeon should be performed only in direct collaboration with a neurosurgeon.
The long-term success of the CSF diversion procedure depends upon the continued patency of the shunt or endoscopic opening. Failure of an endoscopic fenestration can lead to the same symptoms and signs of neurologic decline as a shunt failure. Once shunted, patients who may have previously absorbed a portion of their CSF may become completely dependent on the shunt for CSF diversion. The clinical presentation of a patient with failure of the CSF diversion procedure may or may not mimic the symptoms at the time of the diagnosis of hydrocephalus and initial treatment. The symptoms and signs of failure and period of illness may depend on the type of failure, the etiology of hydrocephalus and the patient’s age. The most common cause of shunt malfunction is proximal catheter occlusion. Many patients with CSF diversion failure will present with recurrence of ventriculomegaly. Of importance, 10% to 20% of children presenting with a shunt malfunction will have no apparent change in the ventricular size compared with a baseline imaging study.