Hydrocephalus is a common entity in pediatric neurosurgery, and treatment often encompasses a large percentage of the neurosurgical volume in a pedi-atric institution. Whether the condition has been caused by congenital etiologies, intraventricular hemorrhage, infection, or tumors, minimally invasive techniques are becoming the standard in its treatment. Minimally invasive techniques using the endoscope and image guidance have led to improved shunt placement, simplification of shunt systems, and shunt independence in select patients.

From: Minimally Invasive Neurosurgery, edited by: M.R. Proctor and P.M. Black © Humana Press Inc., Totowa, NJ

A significant development in pediatric neurosurgery during the past decade has been the evolution of neuroendoscopy and its application to the management of childhood hydrocephalus. The first endoscopic neurosurgical procedure was performed by Lespinasse, a urologist, in 1910. He used a cystoscope to fulgurate the choroid plexus in two children (1). Walter Dandy used a "ven-triculoscope" (a rigid cystoscope) to treat hydrocephalus via choroid plexus fulguration or third ventriculostomy (2), but this fell out of favor with the development of cerebrol spinal fluid (CSF) diversion catheters. However, the cerebral ventricles, when pathologically dilated, are ideally suited to neurosur-gical endoscopy. This fact, along with technological advances in optics and imaging, have brought on a resurgence in endoscopy for the treatment of pedi-atric hydrocephalus.

Armed with the endoscope as both a diagnostic and therapeutic surgical adjunct, the neurosurgeon can now fenestrate cysts and obstructing membranes. This permits the conversion of complicated shunts into more easily managed systems, and in many instances diversion of CSF can be accomplished without valve-regulated shunt systems. Advance planning of the endoscopic procedure with high-resolution neuroimaging helps to minimize potential confusion when the neurosurgeon encounters variable anatomy within the ventricular system. This can also be combined with stereotactic techniques for more precise localization when anatomy is altered by pathology.

Therapeutic procedures aimed at treating hydrocephalus with the endoscope can be divided into shunt catheter placement, membrane fenestration, and, in limited conditions, tumor resection aimed at relieving ventricular obstruction.

Many studies indicate that ventricular catheter blockage is the most common site of the shunt obstruction. Although no study has demonstrated improved shunt patency with catheter tip position (3,4), it is suggested by the fact that the most commonly found materials causing ventricular catheter obstruction are connective, glial, and granulomatous tissue. Concerning the optimal placement of the ventricular portion of a shunt system, endoscopy serves as an adjunct in that it provides an intraoperative confirmation of optimal catheter placement. This may be particularly useful in cases of multiple ventricular septations or small ventricles. Image guidance, especially employing intraoperative ultrasound, has also been responsible for improved catheter placement in ventricular shunting procedures. In very difficult cases, stereotactic image guidance or intraoperative planar imaging can also be useful. Although optimizing catheter tip position in the frontal horn may not be necessary for shunt longevity, confirmation of placement within the ventricle as opposed to a CSF cistern using these techniques has certainly prevented many reoperations.

Neonatal germinal matrix hemorrhage, as well as meningitis, usually produces a multiloculated hydrocephalus. This condition can lead to complex shunt systems and numerous shunt revisions in patients unfortunate enough to have loculated hydrocephalus. A variety of therapeutic options are available to treat multiloculated hydrocephalus, including placement of multiple shunt catheters, stereotactic aspiration, craniotomy with lysis of septations, and endo-scopic fenestrations. Unfortunately, none is entirely effective in all cases, and the treatment of these children often involves combining two or more of these techniques. Cystic membranes often collapse and scar around shunt catheters, necessitating frequent revisions or placement of additional shunt catheters, thus creating complex shunts. Stereotactic aspiration effectively decompresses the cyst, but the wall is neither devascularized nor widely fenestrated, increasing the probability for future recurrence. Craniotomy for cyst fenestration can effectively reduce the rate of shunt revisions or repeat craniotomies, although access to all loculations is not always feasible, and the procedure can be quite complex. Endoscopic cyst fenestration has been reported to provide a safe and less invasive, yet effective, therapeutic alternative without the higher rate of failure (5). The endoscope can be used through a burr hole or as an adjunct to loculated spaces during an open craniotomy. Although shunt independence is not always possible, reducing the number of shunt catheters can reduce the risk of infection and greatly simplify operative revisions at the time of a shunt malfunction.

Third Ventriculostomy

Third ventriculostomy was first performed by Dandy in 1922, and soon thereafter Mixter reported the first endoscopic third ventriculostomy (6). The introduction of shunting procedures by Holter and colleagues in the early 1950s brought about a dramatic improvement in the treatment of hydrocephalus, and thereafter third ventriculostomy and ablation of the choroid plexus fell out of vogue. Renewed interest in the technique resurfaced with improved endo-scopic technology and the realization that shunt-dependent hydrocephalus has a significant long-term morbidity including infection, need for operative revision, and increased risk of death. In 1978, Vries (7) reported the utility of the endoscopic third ventriculostomy with the use of modern instrumentation, and a second wave of interest has emerged.

The effectiveness of third ventriculostomy is highly dependent on patient selection. The ideal candidate is a patient with adolescent- or adult-onset aque-ductal stenosis, with a predicted response rate of 80-90% (8,9), Because most hydrocephalus patients do not fit this category, the decision must be made on a patient-by-patient basis. Inherent in this decision is the consideration of what constitutes a success, which in turn is dependent on the initial indications for the procedure. In newly diagnosed hydrocephalus, the desired effect of treatment is the abatement or reversal of symptoms caused by increased intracranial pressure and reduction in ventriculomegaly. However, for third ventriculostomy it is interesting that symptoms may resolve without a significant change in ventricular size (10). Whereas this may seem counterintuitive, as normalization of ventricular size often seems a sign of successful treatment in a shunted patient, there are definite advantages in maintaining enlarged ventricles in a patient with chronic ventriculomegaly. For instance, the physiological drainage offered by third ventriculostomy seems to reduce the rate of subdural formation seen when these same patients with chronic ventriculomegaly are shunted.

A second group of patients who benefit from third ventriculostomy are those who are already shunted but have had shunt-related complications, such as fre quent obstructions, difficulty in achieving the proper intracranial pressure dynamics, and shunt infections. The goal in this population may be to make them less shunt-dependent, or to minimalize the malfunction rate, or to free them from shunts altogether. Patients with noncommunicating hydrocephalus, who are known to decline rapidly with life-threatening symptoms when their shunt fails, may be aided by third ventriculostomy even if they remain shunt dependent. Conversion of noncommunicating to communicating hydro-cephalus gives a much larger CSF reserve and can thereby make shunt failures in these same individuals a less urgent surgical imperative, with less chance of a morbid outcome.

Beyond selection of appropriate patients based on underlying disease and age considerations, other practical issues should be addressed. The preopera-tive image of choice is the magnetic resonance imaging (MRI). This modality allows for a more accurate assessment of third ventricular anatomy (i.e., width of the floor, attenuated floor, and bulging down into the interpeduncular cistern). Several contraindications to third ventriculostomy exist. Owing to the possibility of intraoperative bleeding, patients who have received prior brain radiation therapy may be at greater risk from endoscopy. Patients with fungal basal meningitis are poor candidates secondary to thickening of the floor and obliteration of the interpeduncular cisterns. The preoperative MRI may identify vascular abnormalities involving the basilar apex, thereby obviating endo-scopic exploration. Patients with grossly abnormal anatomy, such as severely involved Chiari II syndromes, may be at an increased risk because of the inability to identify anatomical landmarks (11).

The complication rate of third ventriculostomy has not been clearly defined, although it is considered to be low in experienced hands. Jones et al. (12) attempted 103 third ventriculostomies and had a 6% complication rate, with no mortalities reported. Numerous isolated complications have been reported following endoscopic third ventriculostomy, including scalp abscesses, ataxia, drowsiness, hypothalamic damage (i.e., SIADH, DI, aberrant temperature regulation), cardiac arrest, injury to the basilar artery (i.e., catastrophic hemorrhage, pseudoaneurysm formation, and stroke), and visual impairment.

Implanted Shunts

Some recent advances in shunt technology have led to more minimally invasive approaches to hydrocephalus in select patients. Adjustable valves serve as a good example. Although they do not seem to have affected shunt failure rates (13), there are two definite patient populations in whom these valves have allowed for fewer surgical procedures. The first includes those with severe ven-triculomegaly, who generally need a higher pressure valve early on to prevent overdrainage and subdural formation, but a lower pressure later on as the ventricles decrease in size to allow for adequate drainage. The second involves those with slit ventricle syndrome, in whom gradually turning the valve pressure up has allowed for progressive dilation of the ventricles over time.

Since most shunt failures are proximal blockages of the ventricular catheter, percutaneous clearance of the ventricular catheter has recently been employed as a method of avoiding shunt surgery at the time of a failure. Two methods, one involving endoscopic exploration of the catheter itself combined with coagulation to clear the blockage, and the other being ultrasonic disruption of the blockage, are both currently under investigation (14,15), In both cases the catheter is entered percutaneously, without a skin incision. Success rates have been reported comparable to those for open surgical exchange of the catheter.

Laparoscopic assisted placement of the distal shunt, into either the pleura or the peritoneum, is another way in which minimally invasive techniques are aiding in the treatment of hydrocephalus (16).

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