9 Obstructive Hydrocephalus
9.1 Introduction
Obstructive hydrocephalus probably has plagued humans since the beginning of human existence. Pathologic findings from the skeleton of a child dating from the period 2500 BC to 500 AD demonstrated obstructive hydrocephalus as the cause of craniofacial malformations.1 The first researchers to produce hydrocephalus experimentally in dogs were Dandy and Blackfan in 1913.2 After several attempts at treatment of this illness by different surgeons, Dandy was the first to perform a third ventriculostomy via an anterior subfrontal approach as treatment in 1922.3 Although this is a long-known disease, obstructive hydrocephalus still afflicts people, particularly children, around the world, and more commonly and intensely in the developing countries.4
Treatment options for hydrocephalus include open microsurgical procedures, shunt placement, and various endoscopic techniques. Endoscopic treatment has rapidly evolved during recent decades. Good feasibility and excellent results have promoted quick dissemination of endoscopic techniques within the neurosurgical community. In particular, endoscopic third ventriculostomy (ETV) in obstructive hydrocephalus has become a well-established surgical option. Good results in the treatment of hydrocephalus caused by brain tumors,5,6,7,8,9 aqueductal stenosis,10,11 cerebellar infarction,12 and various other causes including rare indications such as obstructive hydrocephalus due to giant basilar artery aneurysm,13 have been reported.
In this chapter, the application of the neuroendoscope in the treatment of different pathologies causing obstructive hydrocephalus, the advantages and disadvantages of the technique, and its potential risks and complications are discussed.
9.2 Pathophysiology
Recent studies and discoveries on the pathophysiology of cerebrospinal fluid (CSF) circulation disorders have created controversy over the etiology and classification of hydrocephalus.14,15,16 Hydrocephalus is classically divided in obstructive and communicating (nonobstructive) hydrocephalus. In contrast, current research data suggest that some obstruction of CSF reabsorption is present in almost every type of hydrocephalus.15,17
Most neurosurgeons use endoscopic techniques only in cases of evident obstructive hydrocephalus. However, good results have been reported on patients with normal pressure hydrocephalus treated with an endoscopic third ventriculostomy.18,19
In this chapter, the focus is set at the endoscopic treatment of obstructive hydrocephalus. Potential locations of CSF pathway obstruction (italic) and their resulting pathologic conditions are as follows (Fig. 9.1):
Within the lateral ventricle: Isolated ventricular horn.
Interventricular foramen or foramen of Monro: Dilatation of ipsilateral lateral ventricle.
Posterior part of third ventricle and cerebral aqueduct (most common): Dilatation of third and lateral ventricles.
Fourth ventricle outlets (foramina of Luschka and foramen of Magendi): Dilatation of all four ventricles.
Tentorial incisura: Blocking the passage of CSF from the infratentorial to the supratentorial compartment.20,21
The causes of obstruction are very variable and can be classified as acquired and congenital. Some acquired causes of obstruction are tumors (ventricular; e.g., frequently foramen of Monro, pineal region, posterior fossa), vascular (intraventricular hematoma, infarction, aneurysms, Vein of Galen aneurysm), infections (abscesses and/or granulomas, neurocysticercosis, ependymitis), arachnoid cysts, acquired aqueductal stenosis (adhesions following infection or hemorrhage), and supratentorial masses causing tentorial herniation. Congenital causes are: Monro foramen atrasia, aqueductal stenosis, Dandy-Walker syndrome (atresia of foramen of Magendie and foramina of Luschka), and Chiari malformation.7,12,13,22,23,24,25
9.3 Clinical Features
Interestingly, almost independently from the cause of obstruction, the symptomatology of hydrocephalus is remarkably similar among patients.23 The duration of the disease and whether the onset is acute or chronic are usually more relevant to the clinical presentation rather than the primary pathologic entity. The signs and symptoms of acute hydrocephalus are those of increased intracranial pressure and include headache, nausea and vomiting, papilledema, sixth nerve palsy, upward gaze palsy (Parinaud′s syndrome), hyperactive reflexes, ataxia, and apnea attacks syndrome. In children they include irritability, increased head circumference, bulging fontanels, spreading of cranial sutures, and enlargement and engorgement of scalp veins.8,26 Chronic ventricular enlargement symptoms include gait, cognitive, urinary disturbances, and dizziness, headache and vision problems.27 The clinical presentation is an important indicator for surgery and patient selection. Surgery is mostly indicated for patients with clinical symptoms. But, in asymptomatic patients with a progressive hydrocephalus, treatment should be considered.
9.4 Diagnosis and Neuroimaging
Even though computed tomography (CT) is the initial neuroimaging test obtained, magnetic resonance imaging (MRI) is the preoperative imaging of choice for all patients with obstructive hydrocephalus. It usually leads to the diagnosis of hydrocephalus, allows the differentiation of obstructive from communicating hydrocephalus, and frequently enables the physician to find the exact location of the obstruction, which permits detailed operative planning. The routine T1- and T2-weighted MR images should be obtained in all three planes (axial, coronal, and sagittal) so that an accurate study of each case can be performed. Special sequences, such as multiacquisition steady-state free precession (SSFP), inversion recovery turbo spin-echo (IR-TSE) and cine phase-contrast (cine PC) MRIs are also important to answer some questions. The SSFP MRI images permit the recognition of thin membranes that may eventually disturb normal circulation of CSF (Fig. 9.2). The IRTSE and cine PC-MRI sequences in the sagittal plane are interesting for the investigation of the CSF flow.6
When analyzing the preoperative images before surgery, special attention should be given to the following 7:
The underlying pathology leading to hydrocephalus (e.g., tumor, congenital malformation, infection, etc.).
Site and nature of CSF obstruction (e.g., compression of the aqueduct or aqueduct stenosis, etc.).
Position of the basilar artery in relation to the floor of the third ventricle and the extension of the prepontine space (e.g., third ventriculostomy).
Patency of the cerebral aqueduct (e.g., cases of obstruction of both foramina of Monro).
Potential problems with the surgical approach (e.g., narrow foramen of Monro, anatomical variations, large intraventricular blood clot or tumor, etc.).
If a rigid endoscope is used, an optimal site for placing the bur hole for combined procedures (e.g., third ventriculostomy and tumor biopsy, third ventriculostomy and blood clot evacuation, etc.) and a preview of the endoscopic trajectory that will be performed.
If a flexible endoscope is used, the standard precoronal bur hole is recommended.
Detailed preoperative analysis of MR and/or CT images is mandatory to identify the cause of obstructive hydrocephalus. The most important underlying pathologies and their imaging features are considered in the following.
9.5 Indications for Endoscopic Treatment
The indication for an endoscopic treatment is highly influenced by a patient′s demographics (for example, an adult or a pediatric patients, residence in a developed nation or a third world country, etc.) and the personal preference and experience of the neurosurgeon. In the authors’ experience, obstructive hydrocephalus caused by intraventicular or paraventricular tumors is the most frequent indication for an ETV, followed by an aqueductal stenosis, intraventicular and paraventricular hemorrhage, communicating hydrocephalus, and various malformations (Table 9.1).28
9.5.1 Space-Occupying Lesions
Tumor masses within or adjacent to the ventricular system frequently cause obstructive hydrocephalus. Tumors in the lateral ventricle are mainly subjected to direct surgical removal, so endoscopic restoration of CSF circulation is less frequent. In the authors’ experience, about two-thirds of the lesions that undergo an endoscopic CSF circulation restoration are located in the third ventricle and about one-fourth in the posterior fossa. In general, any tumor of the brain may obstruct the CSF circulation, particularly masses of the pineal gland and gliomas of the tectum.5 Besides tumors, other space-occupying lesions such as giant basilar artery aneurysms, cavernous hemangiomas, and Vein of Galen aneurysms have also been found to cause obstructive hydrocephalus.7,13,29
After identification of the mass lesion and its relationship to the adjacent structures, it is important to decide whether a direct tumor resection or prior restoration of CSF circulation via an endoscopic treatment is favored. Whether or not endoscopic CSF restoration prior to tumor resection improves shunt-free patient outcome is a matter of debate.
9.5.2 Membranous Aqueductal Stenosis
Several diseases may be responsible for stenosis of the cerebral aqueduct. Dilatation of lateral and third ventricle is typical. Gliosis, or forking, of the cerebral aqueduct—dividing it into two blind-ending sacs—may be a cause of stenosis. Some other anatomical obstacles, such as aqueductal webs, septa, and diaphragms may also obstruct the flow through the third ventricle. Sagittal MRI is very important to distinguish an extrinsic mass compression from an intrinsic aqueductal abnormality. CSF flow studies may also help in the diagnosis of an aqueductal stenosis. Interstitial edema has a high intensity on a FLAIR (fluid-attenuated inversion recovery) MRI and may be present in the periventricular zone.29
9.5.3 Clots and Synechiae
Trauma or infections may also be the cause of ventricular system obstruction. Clot formation by fibrinous tissue may be responsible for obstruction of the cerebral aqueduct or fourth ventricle outlets. Meningitis or ventriculitis may develop fibrous adhesions and disturb the CSF flow through the third ventricle, for example. Cysticercal cysts in patients with intraventricular neurocysticercosis may also be the cause of an obstruction of the ventricular system in different sites.25,29,30 All these obstructions frequently can be identified on MRI studies.
9.5.4 Hemorrhages and Hematomas
Hemorrhages with intraventricular extensions may also lead to obstructive hydrocephalus and endoscopic treatment has been reported.24,31,32 Trauma, acute subdural and epidural hematomas, and parenchymal bleeding in the posterior fossa may also be a cause of obstruction of the ventricular system.29 The careful study of the images and the understanding of where the CSF congestion problem is, will help in selecting the right therapeutic alternative (endoscopic or not) in these cases.
9.5.5 Cerebellar Infarction
Massive cerebellar infarction may provoke acute hydrocephalus by compression and obliteration of the fourth ventricle by mass effect. Endoscopic treatment of this pathology via a third ventriculostomy has been described with good results in the literature. CT scans are suitable for diagnosis and planning the operation in these cases.12 However, endoscopic treatment is limited to the rare case where even with blockage of CSF circulation, there is still enough space provided in the posterior fossa without brainstem compression for the endoscope to pass.
9.5.6 Trapped Ventricles
Trapping of the temporal horn may occur when flow of CSF from the anteroinferior extension of the lateral ventricle is blocked. Sole trapping of the third ventricle is rare and an ependymal or arachnoid cyst or a third ventricle squamous papillary craniopharyngioma should then be considered in the differential diagnosis. Simultaneous occlusion of the cerebral aqueduct and of the foramen of Luschka and of Magendie may result in a trapped fourth ventricle. Most frequently, trapping of the fourth ventricle is associated with shunt overdrainage. In this situation, with production of CSF by the choroid plexus and expansion of this chamber, compression of the brainstem and cerebellum result in the classic symptoms of posterior fossa hypertension.29
9.6 Treatment
The first step before treatment of obstructive hydrocephalus is understanding the underlying disease. Through a careful imaging examination, recognition of the cause of the CSF obstruction, and interpretation of the clinical presentation, the best possible treatment choice can be made for the patient. Whether to restore the CSF pathway directly or to create a bypass to the subarachnoid space by ETV can be determined. In cases in which the anatomy is not clear or the ventricles are very small, a neuronavigation system may be used to help during the approach; for example, to identify the ideal entry point and to identify intraventricular structures and the ideal area for performing the perforation. However, brain shift may be an issue after CSF release.6 Different endoscopic treatment options are available depending on the needs of each case. Some of the endoscopic surgical alternatives for obstructive hydrocephalus follow.
9.6.1 Septum Pellucidum Fenestration (Fig. 9.3 and Fig. 9.4)
For the septum pellucidum fenestration to function, the contralateral foramen of Monro has to be patent or one lateral ventricle needs to be draining through shunting. The ideal fenestration point should be individually chosen depending on the anatomy. In chronic cases, a restricted region of the septum is usually thin and less vascularized and is best for a blunt perforation. The opening of the septum should be ~ 1 cm in diameter.6,33
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