Abstract
Advances in optics, miniaturization and surgical technique have provided a means for neurosurgeons to approach selected conditions with reduced parenchymal exposure and trauma. Neuroendoscopy can be highly effective as a minimally invasive procedure, but it is not risk free. The incidence of preventable complications can be reduced by selecting the appropriate candidate for the procedure, having the optimal instruments available and recognizing potential pitfalls in advance.
Keywords
neuroendoscopy, endoscope, brain tumor, medulloblastoma, cerebral ventricles, bleeding, hemorrhage, surgical technique
Highlights
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Complications in ventricular endoscopy are best managed by prevention.
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Comprehensive knowledge of intraventricular anatomy is essential for safe endoscopic navigation, not because the anatomy is difficult but because one sees only a small part of it at any given time.
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The endoscope has no rear-view mirror, so structures can be injured outside the endoscopic field of vision.
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In the event of intraventricular bleeding:
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Keep the endoscope focused on the site where the bleeding occurred, even if the field is obscured.
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Irrigate with a warmed solution of Ringer’s lactate.
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Be sure to keep an exit port open.
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Use an endoscopic bipolar device to coagulate a bleeding vessel when feasible.
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Leave an external ventricular drain if the bleeding cannot be controlled.
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Obtain a vascular study if there is concern about a significant arterial injury.
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Background
In recent decades, advances in optics, illumination, miniaturization, and computer technology have provided a means for neurosurgeons to approach selected conditions with reduced parenchymal exposure, manipulation, and trauma. There has been an increasing interest in the performance of endoscopic ventricular surgery to treat selected disorders such as hydrocephalus, cysts, and neoplasms. Ventricular endoscopy can be both diagnostic and therapeutic, in that the procedure is performed with minimal invasiveness.
Although ventricular endoscopy is a minimally invasive procedure, it is not risk free, and associated complications can be significant. Among the reported complications are intraventricular hemorrhage, subdural hygroma, thalamic contusions, cerebrospinal fluid (CSF) leak, and technical failures. In most cases, unexpected events can be prevented by understanding the underlying causes of the pathologies. Overall, many complications can be avoided by selecting the right candidate for the procedure, having the most appropriate instrumentation, and having a thorough knowledge of the anatomy and pathology.
Two minimally invasive procedures commonly performed using endoscopic techniques are fenestration of the third ventricular floor, known as endoscopic third ventriculostomy (ETV), and endoscopic resection of colloid cysts of the third ventricle. ETV is a powerful method for treating selected cases of noncommunicating hydrocephalus without the need for implanted shunts ( Fig. 38.1 ). Endoscopic resection of colloid cysts, when feasible, eliminates the need for brain manipulation and retraction that occur with open craniotomy.
Anatomic Insights
The ventricular endoscope is introduced into the ventricle either blindly or with the aid of image guidance. Once the endoscope is in the lateral ventricle, anatomic landmarks can be identified, including the choroid plexus, anterior septal and thalamostriate veins, and fornix. These constant landmarks guide the surgeon to the foramen of Monro, a paired structure that connects the lateral and the third ventricles. The operator can identify the mammillary bodies, tuber cinereum, and infundibular recess located on the floor of the third ventricle. In dilated ventricles, the tuber cinereum, a translucent membrane, runs from the mammillary bodies to the dorsum sellae. The surgeon can visualize the basilar apex in the interpeduncular cistern below ( Fig. 38.2 ).
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For ETV, one should use a precoronal burr hole, which should be a bit more medial in location than the conventional midpupillary line. This enables the operator to have easier access to the midline third ventricular floor using a rigid endoscope.
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For ETV, one can identify the basilar apex directly underneath the translucent floor of the third ventricle.
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For ETV, thermal energy sources should be avoided along the third ventricular floor to prevent transmitted injury to the underlying basilar artery.
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In case of massive intraventricular bleeding, the endoscopic procedure should be aborted; an emergency angiography is recommended to find the bleeding source.
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For endoscopic colloid cyst resection, the precoronal burr hole should be more anterior and lateral than that for ETV. This provides the operator with a better view of the mass at the foramen of Monro. Image guidance can be helpful for this approach.
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If problems are encountered during endoscopic colloid cyst resection, the procedure can be easily converted to a microsurgical approach.
Risk Factors
Ventricular endoscopy can be challenging in patients presenting distorted ventricular anatomy. For instance, anatomic variations are commonly seen in patients with hydrocephalus and myelomeningocele, including a vertically oriented third ventricular floor, thickened massa intermedia, and hindbrain descent. Therefore careful analysis of the preoperative magnetic resonance imaging (MRI) study is helpful in planning the surgical procedure.
Stereotactic guidance should be considered for patients with small ventricles and distorted anatomy. It improves the accuracy of the surgical approach and minimizes trauma. Frameless stereotactic localization can be useful for planning the surgical trajectory precisely, from the entry point to the target site, thus minimizing the risk of injury to the superior sagittal sinus and emissary veins. Such a maneuver can potentially reduce the risk of neural and vascular injuries during ventricular endoscopy.
Poor intraoperative visibility is an important risk factor for ventricular endoscopy complications. It can be caused by a murky CSF or bleeding. In cases of massive bleeding from injury of major vessels, the procedure must be interrupted; an emergency angiographic study is recommended to find the bleeding source.
Prevention of Complications
Complications in ventricular endoscopy can be avoided by identifying preventable adverse events such as distorted intraventricular anatomy and inadequate endoscopic instruments. Surgical complications may result in increased morbidity, length of hospital stay, and hospital costs for the patient. Here we describe how to prevent adverse events during the performance of ventricular endoscopy.
Preoperative Prevention
Instrumentation
In neurosurgery, there are two types of endoscopes: the flexible fiber-optic and the rigid rod-lens scope. The flexible scope has the advantage of steerability and maneuverability, although the imaging quality is not as clear as that provided by the rigid scope. The operator should properly synchronize the endoscope with the camera so that the true anatomic orientation correlates with the orientation seen on the screen. Rarely, a piece of the endoscope lens can break off into the ventricle and may need to be retrieved. The use of thermal energy sources, such as laser instruments, should be avoided on the floor of the third ventricle due to the risk of basilar artery injury.
Perioperative Prevention
Vascular Injury
Intraventricular bleeding from small subependymal vessels is the most frequent hemorrhagic complication in ventricular endoscopy. It is usually caused by the endoscopic instrumentation and can be easily managed by gentle irrigation or coagulation of the bleeding source using the endoscopic bipolar device.
On the other hand, hemorrhage from larger vessels can significantly impair operative visibility. Generous irrigation with Ringer’s lactate solution should be attempted. In that case, one should be certain that an exit port in the endoscope sheath is open, thus preventing the increase of intracranial pressure. In severe cases of hemorrhage, one may need to leave an external ventricular drain in place. Angiography may be necessary to identify a pseudoaneurysm, which may require endovascular repair.
For ETV procedures, minimal bleeding may arise around the edges of the ventriculostomy after deflation of the balloon catheter. Often this injury can be controlled by tamponade after reinflating the balloon. The most fearful complication in ETV is injury of the basilar artery or its perforators, a life-threatening injury. Its prevalence is reported to be about 1% of cases. One tries to avoid basilar artery injury by fenestrating the floor of the third ventricle anteriorly, as close to the dorsum sellae as possible. Injuries to the anterior cerebral or pericallosal arteries have been reported infrequently during ETV.
Neural Injury
Neural injury can occur anywhere along the endoscope trajectory. Investigators report the overall rate of neural injury between 3% and 4%. Most serious injuries occur in the deep structures surrounding the ventricles, including contusions of the fornices, mammillary bodies, hypothalamus, thalamus, brainstem, and cranial nerves. The risk of these lesions increases in cases of structural anomalies, such as a small foramen of Monro.
Investigators have reported intraocular hemorrhage secondary to an acute increase of intracranial pressure (ICP) due to obstruction of the outflow channel by debris, blood clot, or kinking of the tubes. Such acute increase of ICP results in bradycardia and tachycardia during intraventricular irrigation. Cardiac instability can cease if the inciting factors are corrected, such as by releasing the irrigation fluid. Other described neurologic complications after ventricular endoscopy include hemiparesis, transient third and sixth cranial nerve palsies, speech delay, and transient personality changes.
For endoscopic treatment of arachnoid cysts, the most common complication is bleeding obscuring the endoscopic view. Therefore one should coagulate the arachnoid vessels in the entry zone of the endoscope to prevent bleeding. For anatomic orientation, the middle cerebral artery is the main landmark in arachnoid cysts of the sylvian fissure. In this case, the cystocisternostomy should be performed between the carotid artery and the oculomotor nerve. There is an increased risk of injury of the oculomotor nerve and posterior communicating and anterior choroidal arteries.
For the resection of colloid cysts, the removal of the cyst capsule from the roof of the third ventricle can be challenging ( Fig. 38.3 ). If the cyst wall is firmly adherent to the roof, there is an increased risk of venous bleeding when the removal of the cyst capsule is attempted. In those cases, cyst wall remnants should be coagulated using bipolar coagulation devices and left in place.
