Endoscopic Third Ventriculostomy (ETV)

By far the most commonly performed intraventricular neuroendoscopic procedure is ETV for hydrocephalus.^{3, 4} Indications include primary congenital anomalies such as aqueductal stenosis (narrowing of the duct connecting the third ventricle to the fourth ventricle), meningomyelocele/Chiari malformation and idiopathic causes, obstruction secondary to pineal tumors, aqueductal stenosis secondary to tectal gliomas, and cisternal arachnoid cysts. ETV is also used as a viable and efficacious alternative to treat cases of obstructive hydrocephalus, previously treated by ventriculoperitoneal shunting, that present with a shunt failure. The burr hole in the skull is typically placed at the same location where the ventriculoperitoneal (VP) shunt would be inserted (lateral to the right sagittal suture and anterior to the coronal suture in the midpupillary line). An endoscope is placed through the burr hole into the frontal horn of the lateral ventricle, through the foramen of Monro into the third ventricle, and then directed toward the anterior floor of the third ventricle. An opening is created in the floor of the third ventricle posterior to the infundibular recess, which creates a bypass within the brain allowing the CSF to drain, avoiding the placement of a ventricular peritoneal shunt. Figure 15.1 demonstrates the endoscopic and schematic view of the anatomy of the foramen of Monro and the anterior translucent floor of the third ventricle. Figure 15.2 illustrates the different surgical steps in performing ETV and Figure 15.3 the fenestration of the third ventricular floor using Fogarty occlusion balloon (Edwards, Irvine, CA) or NeuroBalloon (Integra, Saint-Priest, France) catheters with view into the prepontine cistern.^{3, 4}

Preoperative Issues

Much of the preoperative considerations and anesthetic care is dictated not by the specific endoscopic procedure but by the patients’ conditions including age, weight, baseline neurological status, underlying disease process, associated medical illnesses, and current state of health.⁵ Patients may range in age from preterm newborns to adolescents. Some patients presenting for ETV may have had prior shunt placements with shunt systems extending from the ventricles to the peritoneal/pleural cavity or the right atrium or central vascular locations. The need for repeated surgical procedures secondary to malfunction or infections can result in added morbidity to the patient. A standard preoperative workup should address the patient’s systematic illnesses as well as the current underlying primary disease process (e.g., intraventricular hemorrhage). Preoperative evaluation must be focused on the neurological status; for example, patients with hydrocephalus or a primary lesion resulting in obstruction of CSF pathways may present with symptoms of increased ICP. Patients with prolonged vomiting may have significant dehydration and/or electrolyte abnormalities, requiring correction prior to the surgical procedure. Associated medical illnesses especially cervical spine abnormalities, syndromes, and current medication regimen might influence the perioperative anesthesia planning. As these procedures have a potential for blood loss, our current practice includes laboratory testing for the majority of these patients (including coagulation and a type and cross). Preoperative medication (e.g., benzodiazepines) may not be required or desired because of potentially associated problems such as presence of intracranial hypertension and/or altered mental status and the need for postoperative rapid awakening to expedite a neurological examination. Treatment with anticonvulsants or other therapeutic agents should usually be continued during the perioperative period, and pharmacological interactions with neuromuscular blocking agents have to be taken into account and appropriately monitored.⁶

Intraoperative Management

The intraoperative anesthesia care should be guided by the fact that endoscopic intraventricular neurosurgical interventions are short, noninvasive procedures performed in supine position without neurosurgical head pins. For the majority of these semielective procedures, intravenous induction or inhalational induction represent equally good options. However, for urgent indications, such as the presence of increased ICP, nausea, and vomiting, a modified rapid sequence induction should be taken into account. Endotracheal intubation is required secondary to the muscle relaxation needed to prevent patient movement during the delicate intraventricular surgical maneuvers. Ventilation must be carefully controlled, especially in small infants when the proportionate increase in dead space along with small tidal volumes may cause end-tidal CO₂ to underestimate PaCO₂, resulting in hypercapnia and associated alterations in ICP. Anesthesia monitoring includes the standard monitors (electrocardiogram, pulsoxymetry, capnography, noninvasive blood pressure). An arterial line and central line are usually not required except in the presence of serious comorbidities. Often a second access of a peripheral vein is advisable. In case of central line placement, VP/ventriculoatrial shunt locations need to be explored to avoid unintended puncture of the peripheral shunt tubing. For maintenance anesthesia, in our practice, the combination of an inhalation anesthesia (without nitrous oxide) and wound infiltration with local anesthetics (at the site of the burr hole at the beginning of the procedure) aiming to minimize the administration of opioids is sufficient. The burr hole approach creates minimal postoperative pain, so small doses of short-acting narcotics and acetaminophen are satisfactory. The anesthetic goals should focus on intraoperative immobilization, cardiovascular stability, control of ICP and preservation of cerebral blood flow, and rapid emergence for early neurologic examination. After emergence from anesthesia, the surgical team will perform the first neurological examination in the operating room (OR). Thereafter, the patient is moved to the postanesthesia care unit (PACU) and thereafter to the ward with frequent follow-up neurological examinations.

A standard OR layout, including adequate positioning of the equipment and view of the monitors, must be carefully considered. To facilitate surgical exposure and surgical access to the patient, the patient and bed are often turned 90° to 180°. The anesthesia team and equipment are usually situated on the left side of the patient. The surgical team is positioned directly around the head of the patient, observing the video monitors, which are located at the foot of the patient while navigating the endoscope. Importantly, the OR table must be absolutely immobile when the endoscope is maneuvered inside the ventricular system.

Avoidance of Complications and Postoperative Concerns

Prevention of intraoperative complications requires control of ICP and irrigation pressures, and mastery of the intraventricular anatomy to minimize tissue trauma. Despite the minimally invasive nature of these procedures, acute bradycardia and other cardiovascular complications may occur. During the procedure, there is a constant flow of irrigation solution (normal saline or lactated Ringer’s solution) through the endoscope to irrigate the ventricular space. These irrigation fluids should be warmed to body temperature, as cold fluid can cause bradycardia and hypothermia. The difference in chemistry between CSF and irrigation fluid may cause toxic reactions such as meningitis, fever, headache, and an increased cell count.^{7, 8} Normal saline irrigation may cause CSF acidosis, and use of lactated Ringer’s has been reported to result in postoperative increased potassium serum levels.⁹ Acute increases in ICP will occur if egress of the irrigating fluid is not maintained, mandating a constant evaluation of the amount of fluid infused and the amount retrieved. Otherwise, a Cushing-type response may result with refractory hypertension and tachycardia/bradycardia as an indicator of impaired brain perfusion and/or stimulation of the preoptic area,^{10, 11} which require vigilant recognition and correction to prevent serious and potentially irreversible injury. The development of neurogenic pulmonary edema after vigorous intraventricular irrigation may be another acute intraoperative complication requiring postoperative ventilation and treatment in the intensive care unit (ICU).¹² Intraoperative acute bradycardia might occur during the process of fenestration through a thickened third ventricular floor (reported up to 41%), which is mostly self-resolving with cessation of the surgical stimuli.¹³

Occasionally bleeding may occur during intraventricular endoscopic procedures.¹⁴ The scope must then be maintained within the field and continuous irrigation with warm irrigation fluid generally stops the bleeding. Cauterization may be attempted if a bleeding site can be identified and a ventricular drain may be left in place along the endoscopic tract to allow for drainage of the intraventricular hemorrhage in rare cases if mild bleeding persists. If the bleeding is catastrophic, rapid conversion to open craniotomy has to be considered.

The importance of mastering the intraventricular anatomy and landmarks is paramount to limiting complications.¹⁵ The endoscope is navigated along the desired trajectory through the foramen of Monro; care should be taken to avoid injury to the fornix, which might result in transient memory loss, personality changes, and injury to cranial nerves III and VI. Lateral entry can result in injury to the hypothalamus entailing endocrine problems such as syndrome of inappropriate antidiuretic hormone, diabetes insipidus, secondary amenorrhea, loss of thirst, seizures, or trancelike states. Fenestration along the anterior floor risks injury to the pituitary, and fenestration posteriorly risks injury to the mammillary bodies and brainstem. Injury to the basilar artery, the most feared surgical complication, might cause hemorrhage, formation of a pseudoaneurysm, or stroke, and may even result in intraoperative death.

A report of 368 patients with an average age of 6.5 years over a 15-year period (1989–2004) from multiple Canadian centers cited a complication rate of 14%, with the most common complications being CSF leak 3.6%, meningitis 2.8%, hemorrhage 1.4%, hypothalamic injury 1.4%, cranial nerve injury 1.4%, seizure 1.4%, and other 1.4%.¹⁴

After an uneventful surgical procedure, the majority of patients can be discharged with apnea monitoring from the PACU to the ward when the patient is fully awake, the neurological exam is at baseline, and the PACU course is uneventful. Patients should be monitored for signs of central nervous infections, and if clinically indicated, monitoring of serum electrolytes might be warranted.