Neurosurgery for Hydrocephalus


Background

Hydrocephalus, a condition first described by Hippocrates, is the abnormal rise in cerebrospinal fluid (CSF) volume and, usually, pressure, that results from an imbalance of CSF production and absorption.

Hydrocephalus was not treated effectively until the mid-20th century, when the development of appropriate shunting materials and techniques occurred. At the beginning of the 20th century, doctors (including urologists) attempted to introduce scopes into the ventricular system. Attempts were also made to remove the choroid plexus, which generates much of the CSF, in an attempt to treat hydrocephalus. 

Hydrocephalus research and treatment have advanced tremendously in the last 20 years. Today, the focus of hydrocephalus research is on pathophysiology, shunting (eg, new shunt materials and programmable valve design), and minimally invasive techniques of treatment. Areas of research include the following:

  • Transplantation of tissue, such as vascularized omentum, to reestablish normal CSF could be the best method for treating communicating hydrocephalus
  • Third ventriculostomies and aqueductoplasty eliminate the need for shunting in noncommunicating cases of hydrocephalus; new optics and smaller scopes are expanding this field

Pathophysiology

Hydrocephalus can be subdivided into the following three forms:

  • Disorders of CSF production - This is the rarest form; choroid plexus papillomas and choroid plexus carcinomas can secrete CSF in excess of its absorption
  • Disorders of CSF circulation - This form results from obstruction of the pathways of CSF circulation, which can occur at the ventricles or arachnoid villi; tumors, hemorrhages, congenital malformations (such as aqueductal stenosis), and infections can cause obstruction at either point in the pathways
  • Disorders of CSF absorption - Conditions such as the superior vena cava syndrome and sinus thrombosis can interfere with CSF absorption.

Some forms of hydrocephalus cannot be classified clearly. This group includes normal-pressure hydrocephalus and pseudotumor cerebri.

Etiology

The etiology of hydrocephalus in congenital cases is unknown. Very few cases (<2%) are inherited (X-linked hydrocephalus). The most common causes of hydrocephalus in acquired cases are tumor obstruction, [1trauma, intracranial hemorrhage, and infection.

Epidemiology

The overall incidence of hydrocephalus is unknown. When cases of spina bifida are included, congenital hydrocephalus occurs in 2-5 births per 1000. The incidence of acquired types of hydrocephalus is unknown.

Tanaka et al concluded that the incidence of idiopathic normal-pressure hydrocephalus was 1.4% in their study of an elderly Japanese population. [2]

Prognosis

In general, outcome is good. A typical patient should return to baseline after shunting, unless prolonged elevated intracranial pressure (ICP) or brain herniation has occurred. The neurologic function of children is optimized with shunting. Infection, especially if repeated, may affect cognitive status.

The best long-term results in the most carefully selected patients are no better than 60% in normal-pressure hydrocephalus. Few complete recoveries occur. Often, gait and incontinence respond to shunting, but dementia responds less frequently.

Often, various other neurologic abnormalities associated with hydrocephalus are the limiting factor in patient recovery. Examples are migrational abnormalities and postinfectious hydrocephalus.

In a study of responders and nonresponders to shunt surgery for idiopathic normal-pressure hydrocephalus, responders were found to have much higher preoperative pulsatile ICP than nonresponders did.



History and Physical Examination

The various types of hydrocephalus can present differently in different age groups.

Acute hydrocephalus typically presents with headache, gait disturbance, vomiting, and visual changes. In infants, irritability or poor head control can be early signs of hydrocephalus. When the third ventricle dilates, the patient can present with Parinaud syndrome (upgaze palsy with a normal vertical Doll response) or the setting sun sign (Parinaud syndrome with lid retraction and increased tonic downgaze).

Occasionally, a focal deficit, such as sixth nerve palsy, can be the presenting sign. Papilledema is often present, though it may lag behind symptomatology. Infants present with bulging fontanelles, dilated scalp veins, and an increasing head circumference. When advanced, hydrocephalus presents with brainstem signs, coma, and hemodynamic instability.

Normal-pressure hydrocephalus has a very distinct symptomatology. The patient is older and presents with progressive gait apraxia, incontinence, and dementia. This triad of symptoms defines normal-pressure hydrocephalus.


Imaging Studies

Computed tomography (CT) of the head delineates the degree of ventriculomegaly and, in many cases, the etiology. When performed with contrast, it can show infection and tumors that cause obstruction. It also helps with operative planning. Ventricles are usually dilated proximal to the point of obstruction. Ventriculomegaly can be an early sign of neurodegeneration in normal-pressure hydrocephalus. [4In pseudotumor cerebri, CT findings are usually normal.

Magnetic resonance imaging (MRI) of the head is waaranted in most, if not all, congenital cases of hydrocephalus. (See the images below.) This delineates the extent of associated brain anomalies (eg, corpus callosum agenesis, Chiari malformations, disorders of neuronal migration, and vascular malformations). Some tumors (eg, midbrain tectal gliomas) can be detected only with this study. T2-weighted images can show transependymal flow of cerebrospinal fluid (CSF). Perfusion and diffusion MRI can help select appropriate patients for surgical treatment of idiopathic normal-pressure hydrocephalus. [5]

Noncommunicating obstructive hydrocephalus caused Noncommunicating obstructive hydrocephalus caused by obstruction of foramina of Luschka and Magendie. This MRI sagittal image demonstrates dilatation of lateral ventricles with stretching of corpus callosum and dilatation of fourth ventricle.
Communicating hydrocephalus with surrounding Communicating hydrocephalus with surrounding "atrophy" and increased periventricular and deep white-matter signal on fluid-attenuated inversion recovery (FLAIR) sequences. Note that apical cuts (lower row) do not show enlargement of sulci, as is expected in generalized atrophy. Pathologic evaluation of this brain demonstrated hydrocephalus with no microvascular pathology corresponding with signal abnormality (which likely reflects transependymal exudate) and normal brain weight (indicating that sulci enlargement was due to increased subarachnoid cerebrospinal fluid [CSF] conveying pseudoatrophic brain pattern).

Fetal and neonatal cranial ultrasonography is a good study for monitoring ventricular size and intraventricular hemorrhage in the neonatal intensive care unit (NICU) setting. Certainly, it is worthwhile to perform other imaging studies before treatment.

Lumbar Puncture

Lumbar puncture can be used to measure intracranial pressure (ICP), but it should only be performed after imaging studies rule out an obstruction. A diagnostic high-volume lumbar puncture in normal-pressure hydrocephalus can assist in making decisions regarding shunting. Spinal fluid can show the type and severity of infection (see Meningitis).


Approach Considerations

Most cases of symptomatic hydrocephalus must be treated before permanent neurologic deficits result or neurologic deficits progress.

When an etiologic factor is known, hydrocephalus can be treated with temporary measures while the underlying condition is treated. Examples of temporary treatment measures are ventriculostomy until a posterior fossa tumor is resected or lumbar punctures in a neonate with intraventricular hemorrhage until the blood is absorbed and normal cerebrospinal fluid (CSF) absorption resumes.

Few cases of hydrocephalus should not be treated. Cases in which treatment should not be implemented include the following:

  • Patients in whom successful surgery would not affect the outcome (eg, a child with hydranencephaly)
  • In ventriculomegaly of senescence, patients who do not have the symptom triad
  • Patients with ex-vacuo hydrocephalus - This is merely the replacement of lost cerebral tissue with CSF; because no imbalance in fluid production and absorption exists, it technically is not hydrocephalus
  • Patients with arrested hydrocephalus - In this rare condition, the neurologic status of the patient is stable in the presence of stable ventriculomegaly; the diagnosis must be made extremely carefully, because children can present with very subtle neurologic deterioration (eg, slipping school performance) that is difficult to document
  • Patients with benign hydrocephalus of infancy - Neonates and young infants with this condition are asymptomatic, and head growth is normal; computed tomography (CT) shows mildly enlarged ventricles and subarachnoid spaces

Medical Therapy

Medical therapy is usually a temporizing measure. In transient conditions (eg, sinus occlusion, meningitis, or neonatal intraventricular hemorrhage), medical therapy can be effective, [6 as follows:

  • Acetazolamide (25 mg/kg/day in three doses) - Careful monitoring of respiratory status and electrolytes is crucial; treatment beyond 6 months is not recommended
  • Furosemide (1 mg/kg/day in three doses) - Again, electrolyte balance and fluid balance must be monitored carefully
  • Lumbar punctures - In neonates recovering from intraventricular hemorrhage, serial lumbar punctures can, in some cases, resolve hydrocephalus; if possible, this is the preferred method of treatment

Removal of the underlying cause usually resolves hydrocephalus.

Surgical Therapy

As performance of CSF diversion (most often ventriculoperitoneal shunting) has increased in frequency, so has awareness of the pitfalls of the procedure. There has been a resurgence of interest in third ventriculostomies. [789]

Preparation for surgery

Make every effort to identify the cause of hydrocephalus before considering a diversion procedure. Do not consider an indwelling distal catheter in patients with active infection or high CSF protein (>150 mg/dL). Obtain some idea of brain compliance in order to select the optimum valve pressure and decide if the pressure-programmable valve should be used. Use a single dose of preoperative prophylactic antibiotics.

Operative details

Third ventriculostomy

Reserve third ventriculostomy for obstructive cases in patients who have normal or near-normal CSF absorptive capacity. Use a blunt instrument to penetrate the floor of the third ventricle. Sharp instruments or lasers can cause vascular injury. Leaving a clamped drain in place postoperatively might be prudent. The burr hole placed on the coronal suture allows a straight trajectory to the foramen of Monro. Stereotactic guidance is not needed if endoscopic techniques are used.

Ventriculoperitoneal shunting

Ventriculoperitoneal shunting is by far the most common procedure for CSF diversion. The abdomen should be able to absorb the excess spinal fluid. Either of two major locations for the burr holes is typically used. The ventricular catheter can be placed more reliably from the (right) frontal approach. Some surgeons still prefer parieto-occipital catheters. The proximal catheter tip should lie anterior to the choroid plexus in the frontal horn of the lateral ventricle when the parieto-occipital approach is used. Certain landmarks and measurements are used, as per neurosurgical texts.

In difficult cases, stereotactic placement may be an option.

In a study of patients who underwent ventriculoperitoneal shunt surgery for idiopathic normal-pressure hydrocephalus, cerebral perfusion was found to recover promptly in 62.5% of patients (10 of 16). Perfusion increased in the whole brain in three patients, in the right cerebral hemisphere in one, and in the separate cerebral regions (frontal, parietal, temporal, cerebellum, cingulate gyrus) in six. Perfusion improvement was predominantly observed in the frontal lobes: the right frontal lobe in three cases and the left frontal lobe in three. [10]

In another study of patients who underwent ventriculoperitoneal shunt surgery for hydrocephalus, the overall shunt failure rate necessitating shunt revision was 46.3%, and the majority of shunt revisions occurred during the first 6 months after shunt placement. The shunt revision rate was significantly higher in pediatric patients (17 years): 78.2% vs 32.5%. [11]

Ventriculoatrial shunting

Ventriculoatrial shunting is usually the first choice for patients who are unable to have distal abdominal catheters (eg, those with multiple operations, recent abdominal sepsis, known malabsorptive peritoneal cavity, or abdominal pseudocyst). [12 The procedure carries more risk. Long-term complications are more serious (eg, renal failure and great vein thrombosis). Fluoroscopic guidance is necessary to prevent catheter thrombosis (short distal catheter) or cardiac arrhythmias (long distal catheter).

Other shunts

Reserve ventriculopleural shunting for patients with failed peritoneal and atrial shunts.

Torkildsen shunts or internal shunts are straight tubes that communicate to CSF spaces without a valve. Their effectiveness and long-term efficacy have not been established.

Lumboperitoneal shunts are used in communicating hydrocephalus, especially if ventricles are small. Pseudotumor cerebri is the classical indication of this method of shunting. A positional valve is helpful because it turns off the flow of CSF when the patient is upright, thereby preventing overdrainage headache. [13]

A meta-analysis by Rasul et al suggested that endoscopic three-dimensional ventriculostomy was more beneficial than a shunt procedure in patients with a noncommunicating hydrocephalus. [14]

Postoperative Care

After a third ventriculostomy, observation in the intensive care unit (ICU) is advised.

In patients with high brain compliance, gradual assumption of the upright position and slow mobilization may reduce the incidence of early subdural hematoma formation.

Plain radiographs of the entire hardware system confirm good position and serve as excellent baseline studies for the future. Postoperative CT is used to document ventricular size (see Long-Term Monitoring).

Wounds should remain dry for at least 3 days postoperatively, until epithelialization has occurred.

In patients with pleural shunts, perform an early postoperative chest radiograph to ensure adequate absorption of fluid. Large effusions can occur in short periods, and respiratory problems can ensue.

If the patient has no clinical indicators of ventriculitis, CSF sampling from extraventricular drains should be performed once every 3 days; this reportedly decreases the incidence of ventriculitis. [15]

Complications

The most common complications differ, depending on the type of shunt and the underlying pathophysiology.

Infection is the most feared complication in young patients. The overwhelming majority of infections occur within 6 months of the original procedure. Common infections are staphylococcal and propionibacterial. Early infections occur more frequently in neonates and are associated with more virulent bacteria (eg, Escherichia coli). Infected shunts must be removed, CSF must be sterilized, and a new shunt must be placed. Treatment of infected shunts with antibiotics alone is not recommended, because bacteria can be suppressed for extended periods and resurface when antibiotics are stopped.

Subdural hematomas occur almost exclusively in adults and children with completed head growth. The incidence of subdural hematomas can be reduced by slow postoperative mobilization and perhaps by avoidance of rapid intraoperative ventricular decompression. This allows for brain compliance reduction. Treatment consists of drainage and may necessitate temporary occlusion of the shunt.

Shunt failure is mostly due to suboptimal proximal catheter placement. Occasionally, distal catheters fail. Infection should be suspected if the distal catheter is obstructed with debris. Abdominal pseudocysts are synonymous with low-grade shunt infection.

Overdrainage is more common in lumboperitoneal shunts and manifests with headaches in the upright position. In most cases, overdrainage is a self-limiting process. However, revision to a higher-pressure valve or a different shunt system occasionally may be necessary. A positional valve that closes when the patient is upright is also available.

Slit ventricle syndrome is an extremely rare condition in which brain compliance is unusually low. It mostly occurs in the setting of prior ventriculitis or shunt infection. The patient may develop high pressures without ventricular dilatation. The slit ventricle syndrome does not imply overdrainage, and the symptoms usually are those of high pressure rather than low pressure. Most experts also agree that slit ventricles predispose the patient to a higher incidence of ventricular catheter failure.

Repeated ventricular blockage by the coapted ventricular wall may be helped by performing a subtemporal decompression that creates an artificial pressure reservoir and induces slight reenlargement of the slit ventricle.

Long-Term Monitoring

Remove stitches by 2 weeks after the surgical procedure.

Perform CT for baseline at 2-4 weeks after surgery.

Monitor all children with shunts every 6-12 months. Carefully monitor head growth in infants. Check distal tubing length with plain radiographs when the child grows. Appropriate specialists should carefully assess child development.

What happens to ventricular size in patients who have a third ventriculostomy or Torkildsen shunt is not known. Other methods of assessment of patency must be used, such as magnetic resonance imaging (MRI) flow studies and clinical evaluations (eg, detailed funduscopic examinations).

In patients with pseudotumor cerebri, visual acuity and fields should be monitored by the appropriate specialist.