Neuroendoscopy

History

The endoscope was used for the first time in the treatment of hydrocephalus by L’Espinasse in 1910. Later, Dandy pioneered this technique and was named, “the father of neuroendoscopy.” Soon, the endoscope found its place for various neurosurgical indications. The first endoscopic third ventriculostomy was reported by Mixter in 1923. After an initial large gap of 50 years, the use of neuroendoscopy unfolded in varied fields of neurosurgery like biopsy of intraventricular lesions, cyst fenestration, pituitary surgery, and treatment of hydrocephalus. Soon, the endoscope crafted its use keeping in view minimally invasive surgery through keyhole approaches.

The endoscopic concept for neurosurgery is based on the preoperative scrutiny and analysis of diagnostic images. The main advantages of keyhole neurosurgery include adequate but less invasive approach, minimal to no retraction, avoiding unnecessary exposure of the cortical surface, and sufficient enough plane to operate. These result in enhanced patient safety, reduced hospital stay, and lower postoperative morbidity and mortality. Disadvantages include narrow corridors for dissection, limited intraoperative orientation, and visual control. These can be overcome by proper preoperative planning, positioning, and precise surgical and anesthetic approach by the combined effort of both the neurosurgeon and the neuroanesthesiologist. Fig. 26.1 displays the operation room settings for a neuroendoscope procedure under anesthesia. The optimal safe and definite approach in tumor and neurovascular surgeries can be effectively controlled with the use of modern navigation tools like computed tomography (CT), magnetic resonance (MR) scan, ultrasound units, C-arm fluoroscope, and neuronavigation system.

Indications

Indications for neuroendoscopic and other minimally invasive procedures are as follows:

• 1.

  Diagnostic:

  • a.

    Anatomic surveillance: Direct endoscopic visualization can be used to reveal the site of obstruction, intraventricular tumors, and the spread of tumor.

  • b.

    Biopsy of the lesions: Biopsy of the lesions like intraventricular tumors, pineal region tumors, tumors of the optic pathways and spinal tumors.

    Advantages of neuroendoscopic biopsy includes:

    • -

      Smaller and less traumatic surgical approach

    • -

      Direct visualization and conformation of the biopsy lesion

    • -

      Ability to confirm and inspect for postbiopsy bleeding

    • -

      Decision for third ventriculostomy at the same time in patients with tumors causing obstructive hydrocephalus

• 2.

  Therapeutic:

  • a.

    Hydrocephalus: Third ventriculostomy and aqueductoplasty.

  • b.

    Marsupialization of intracranial cysts, e.g., arachnoid cysts.

  • c.

    Tumor resection: Resection of lesions such as colloid cysts with symptomatic occlusive hydrocephalus; intraventricular tumors including craniopharyngiomas, astrocytomas, and ependymomas; and brain parenchymal surgery.

  • d.

    Cerebral aneurysms and arteriovenous malformations.

  • e.

    Craniosynostosis: Endoscopic strip craniectomy.

  • f.

    Hematoma aspiration: Successful evacuation of intraparenchymal and subdural hematomas have been described, often sparing open techniques.

  • g.

    Minimally invasive deep brain stimulation (DBS) : Parkinson disease, essential tremor, psychiatric illness, and chronic pain.

  • h.

    Microdiscectomy, syringostomy, spine fusion, tumor excision, sympathectomy, and video-assisted thoracic spine surgery (VATS) : Spine disease (disc herniation, trauma, tumors, palmar hyperhidrosis and syringomyelia).

  • i.

    Percutaneous kyphoplasty and vertebroplasty.

  • j.

    Rare case of intracerebral bullet injury: Endoscopic transnasal technique was applied to remove the bullet along with skull base reconstruction for cerebrospinal fluid (CSF) infection.

Type of Approach

The site of the lesion dictates the type of approach and the position of the patient for surgery ( Table 26.1 ).

General Considerations

Neuroendoscopy has replaced conventional neurosurgical procedures in most of the centers worldwide. These keyhole procedures have shown to have lesser morbidity (5–30%) and mortality (0–1%) with better outcome. With time and advances in techniques, the anesthetic management is tailored to meet the requirements of a safe and successful surgery. The ideal goals for anesthetic management are described as follows:

• 1.

  Maintenance of adequate anesthesia and relaxation to provide an immobile patient. As the surgery proceeds along narrow neurovascular corridors, bucking during surgery may lead to devastating irreversible injuries.

• 2.

  Monitoring of hemodynamics and cerebral perfusion pressure (CPP) to avoid ischemic insults

• 3.

  The anesthetist should be experienced enough to detect and manage any perturbations in hemodynamics and CPP.

• 4.

  Avoid nitrous oxide (N ₂ O) as this has shown to diffuse into and expand the ventricular air bubbles and increase the chances of pneumocephalus.

• 5.

  Emergence should be rapid enough for prompt neurologic assessment

• 6.

  Wherever possible, intraoperative potentials and cranial nerve electromyograms should be used for monitoring; it requires modification and titration of anesthetic drugs.

• 7.

  Minimize the intra- and postoperative complications by continuous monitoring of neurological deterioration, hemodynamics, and intracranial pressure (ICP) with timely interventions.

Preoperative Checkup

The preanesthetic checkup is same as for conventional craniotomy, crafted as per the disease state. Detailed history and evaluation of neurological, cardiovascular (CVS), respiratory, and other systems should be done. The surgical candidates range from small infants with craniosynostosis and hydrocephalus to moribund elderly patients coming for kyphoplasty and vertebroplasty. Counseling of the patient regarding the procedure, regarding conversion of the procedure to conventional craniotomy and its outcome, and pertaining to the disease needs to be done preoperatively. The nothing by mouth guidelines need to be strictly adhered to. Hydrocephalic patients and patients with pituitary adenomas usually have delayed gastric emptying time. Gastric motility agents like metoclopramide may play a role in preventing regurgitation and its complications. Prolonged vomiting leading to electrolyte abnormalities are common and need to be addressed and optimized prior to surgery. Premedication drugs are prescribed in accordance with the Glasgow Coma Scale (GCS) and cardiorespiratory status of the patient. The ones with sedative properties, e.g., benzodiazepines and opioids, should be avoided in patients with depressed consciousness. A thorough and meticulous assessment of airway and peripheral veins is essential in obese patients as well as those with Cushing disease and hydrocephalus. Proper titration of anesthetic drugs for maintenance, adequate relaxation, vigilant monitoring, and good recovery without any respiratory compromise are the key anesthetic elements for a good surgical outcome.

Intraoperative Concerns

Airway management: This is a concern mainly in patients with hydrocephalus, craniosynostosis, Cushing disease, and obesity. Proper planning either awake or with spontaneous ventilation should be done in cases of difficult airway. This requires meticulous attention to the airway and availability of difficult airway cart and personnel without jeopardizing the adequacy of CPP.

All intra- and periventricular endoscopic procedures are usually performed under continuous irrigation. The main purpose of irrigation is first to allow adequate visualization by expanding the collapsed ventricles and second by maintaining the PIN (pressure inside neuroendosope) above the venous pressure to tamponade the venous and to some extent the arterial bleeding. The balanced electrolyte solution composition quite close to CSF and decreased incidence of complications compared to normal saline is the guiding force behind Ringer lactate (at a temperature of 36–37°C) being the choice of irrigating fluid in neuroendoscopic procedures. This should be kept at a height of 100 cm. The flow of the irrigation fluid is controlled with a foot switch. Fig. 26.2 displays the inlet and outlet port for irrigation in endoscopic third ventriculostomy and related procedures. Use of normal saline is associated with postoperative increases in body temperature, delayed awakening, dyselectrolytemia, and changes in CSF composition. Volume of normal saline used rather than the duration of procedure correlated with these changes. The paramount step is to make sure that the outflow channel is not closed or kinked to avoid hazardous increase in ICP and further aggravating the ischemic insult. Some neurosurgeons advocate limited use of irrigating solutions wherever required to reduce the incidence of complications associated with irrigation. Other problems related to the particular lesions, its surrounding structures, and the type of approaches will be discussed in detail in the management of specific lesions.

Monitoring: Beat-to-beat measurement of heart rate (HR) is a very essential monitor to detect any bradyarrhythmia/tachyarryhthmia, which are very commonly encountered in these procedures. The frequent perturbations in hemodynamics and its resultant effect on cerebral ischemia warrants the use of arterial blood pressure (ABP) and ICP monitoring for effective detection and intervention apart from the routine monitoring of saturation by pulse oximetry (SpO ₂ ) and end tidal carbon dioxide (etCO _​2 ) analysis. Continuous core body temperature monitoring is essential to maintain normothermia, especially in patients undergoing intraventricular procedures and endoscopic strip craniectomy. Monitoring of urine output, glucose, arterial blood gas (ABG) findings, and electrolytes will guide the fluid management.

PIN is commonly used as a surrogate monitor for ICP in neuroendoscopic procedures. The reliability of PIN is increased if the electronic tip sensor is placed at the distal end of the rinsing channel of the endoscope. The values are either over- or underestimated if measured at the inlet or outlet of the rinsing channel. Transcranial Doppler (TCD) and telemetric medicine are alternative indirect techniques for detecting changes in ICP. It is recommended that the CPP for these procedures be maintain above 40 mmHg at any given point of time. Normovolemia is maintained with continuous monitoring of systolic pressure variation (SPV) and central venous pressure (CVP) wherever indicated. In patients with specific cardiac disease or dysfunction, pulmonary arterial catheter (PAC) or continuous cardiac output (CCO) monitoring like flotrac are preferred.

Monitoring for detection of venous air embolism (VAE) like transesophageal echocardiography (TEE) and Doppler would be helpful in cases in which VAE is expected. Bispectral index (BIS) or entropy monitoring is used to assess the depth of anesthesia. Specific neurophysiological monitorings like cranial nerve electromyograms, motor evoked potentials (MEPs), brain stem auditory evoked potentials (BAEPs), and somatosensory evoked potentials (SSEPs) are useful to guide the surgical procedure and prevent further neurologic injury.

Choice of anesthetic agents: General anesthesia with adequate muscle relaxation is the key note for a noiseless surgery. Coughing or bucking in a patient with head fixed by Mayfield clamp can lead to injury to vital structures, e.g., fornix, hypothalamus, brain stem, internal carotid artery (ICA), basilar artery, and spinal cord. Scalp block, specific nerve blocks, or local anesthetic infiltration at the pin site would attenuate the hemodynamic response to placement of clamp and surgical procedure. Antisialogogues are administered preoperatively to decrease the secretions associated with positioning. Both intravenous agents and inhalational agents < 1 minimum alveolar concentration (MAlC) can be used without any adverse effects for induction and maintenance for these procedures. Maintenance of etCO ₂ within normal limits avoids the cerebral vasodilatory and vasoconstricting effects. Short-acting opioids like remifentanil and fentanyl and nondepolarizing muscle relaxants like rocuronium, atracurium, and cis -atracurium are preferred for easy reversibility and prompt assessment of the neurological status. The risk of VAE and increased ICP warrants the avoidance of N ₂ O. Longatti et al. has shown that in selected cases endoscopic surgery can be successfully done under local anesthesia. Attenuation of sympathetic response may provide a bloodless field especially in endoscopic sublabial transsphenoidal hypophysectomy. Intraoperative monitoring of evoked potentials and cranial nerve electromyogram requires the titration of intravenous drugs with or without inhalational agents and avoidance of neuromuscular blocking drugs. Normovolemia is maintained with normal saline as the fluid of choice. Preventive measures for hypothermia need to be considered in the form of warm irrigation fluids, proper in-line drainage system, and warming blankets. Intraoperative steroid replacement is mandatory for steroid-dependent patients. Prophylactic administration of antiemetics, anticonvulsants, and analgesics with a combination of short-acting opioids and paracetamol are helpful for a painless and smooth recovery. Nonsteroidal antiinflammatory drugs are contraindicated because of hemostatic concerns.

Complications: Both bradyarrhythmias and tachyarrhythmias with hemodynamic perturbations are common during neuroendoscopy. Bradycardia and hypotension occurs due to stimulation of the preoptic area. This occurs due to stretching of this area during perforation of the floor of the third ventricle for ETV. Similarly, tachycardia and hypertension occur due to stimulation of the posterior hypothalamus. These hemodynamic changes usually are the presenting features of preischemic events occurring either with an increase in ICP or during endoscopic manipulation. Atypical Cushing response (tachycardia with hypertension) is also seen. Tachycardia is attributed to compression of hypothalamus due to dilated third ventricle and hypertension due to high-speed fluid irrigation or due to kinking of the outflow tube. These are self-limiting and resolve with the reduction of ICP. The last action needs to be reversed whenever there is bradycardia or asystole. The audible levels of the cardiac monitor need to set at a higher level along with noise control in the theater to detect bradycardia or asystole in time. Maintaining normothermia, controlled rate of irrigation at 10 mL/min, and proper and adequate drainage of the irrigation are important requisites to prevent cardiac disturbances.

Electrolyte disturbances are commonly seen both intraoperatively and postoperatively. This was attributed mainly to the type of irrigating fluid and in some cases to hypothalamic dysfunction. Hypokalemia and hypernatremia with acidosis have been reported with normal saline irrigation and hyperkalemia with Ringer lactate irrigation.

Hypothermia is a common complication following continuous irrigation and wet drapes, sometimes compounded with hypothalamic injury. This can be avoided to some degree with use of in-line drainage system, prewarmed irrigation fluids, and warm blankets.

Vascular injury, e.g., injury to basilar artery, ICA, superior hypophyseal artery, posterior cerebral artery, small artery in the interpeduncular cistern, large ependymal veins, and sinuses occurs during manipulation, leading to bleeding. Excessive bleeding may result in conversion to emergency craniotomy for effective control. The incidence of VAE with neuroendoscopy varies between 0.35% and 4%. Other rare but disastrous injuries can occur to paraventricular structures like fornix, basal ganglia, hypothalamus, and brain stem. Most of them present with transient symptoms related to hypothalamic injury like dysphagia, amenorrhea, loss of thirst, diabetes insipidus (DI), drowsiness, decreased insulinlike growth factor 1, and electrolyte disturbances in the postoperative period. Other complications related to positioning have already been discussed. The specific complications related to the pathodiagnosis will be described in specific situations later.

Postoperative Considerations

The common postoperative complications include delayed awakening, neurological deterioration, convulsions, hyperkalemia, confusion, memory loss, transient papillary dysfunction, and hemiplegia. Delayed awakening may occur due to raised ICP, acidosis following normal saline irrigation, and hypothermia. Titration and selection of short-acting agents are required for early recovery and prompt neurologic assessment. Sometimes patients may present with transient fever. This is attributed to the aseptic irritation of the ependyma or due to manipulation of the hypothalamus. Injury to the surrounding neural structures dictated by the site of tumor and type of approach is common, e.g., third cranial nerve, abducens nerve, optic canal, and chiasm. Injury to vascular structures may later present as aneurysms in the postoperative period. Other complications include transient herniation syndromes, hemiparesis, bleeding, syndrome of inappropriate antidiuretic hormone (SIADH), and acute subdural hematoma. The last of these complications can be avoided by preventing drainage of large amounts of CSF from the ventricles. Closed monitoring in an intensive care unit, early detection of any adverse event, and timely intervention are very essential tools in the postoperative management of patients undergoing endoscopic procedures. Pneumocephalus following neuroendoscopy may result in impaired consciousness and delayed awakening. This can be avoided by midline positioning of the head with a burr hole placed at the superior point, minimal loss of CSF, proper irrigation, and flushing of the air bubbles and avoidance of N ₂ O. Late complications include chronic subdural hematoma, hygroma, delayed blockade of the ventriculostomy stoma leading to refractory increased ICP, as well as central nervous system infections like meningitis, ventriculitis and death.