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.

Layout of a neurosurgical operation theater (with modernized equipment).

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.

Displaying the ports for irrigation in endoscopic third ventriculostomy and related procedures.

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.

Endoscopic Third Ventriculostomy ( Figs. 26.2 and 26.3 )

This is the most common pediatric neuroendoscopic procedure carried out by the neurosurgeons worldwide. This procedure has almost replaced ventriculoperitoneal shunts because of the reduced incidence of postoperative complications like infections, shunt displacement, and extrusion leading to revision of the shunt and is thus associated with a very favorable outcome. The success rate ranges from 50% to 95%, with reported mortality rate of less than 1%.

Schematic diagram representing endoscopic third ventriculostomy.

Common indications: Symptomatic noncommunicating hydrocephalus (with a patent subarachnoid space), e.g., acquired aqueductal stenosis, myelomeningocele, and posterior fossa tumors with obstructive hydrocephalus. Relative contraindications include previous history of meningitis and intraventricular or subarachnoid hemorrhage (SAH). This is usually not effective in patients with ineffective and inadequate subarachnoid space, e.g., congenital and communicating hydrocephalus.

Procedure ( Figs. 26.3 and 26.4 ): Initially, a burr hole is placed at the coronal suture (Kocker point) in the midpupillary line and the dura is opened. After cannulation with the introducer sheath, the scope needs to be negotiated through foramen of Monro into the floor of anterior part of third ventricle. Then the scope is positioned in the midline and anterior to both the mamillary bodies and the underlying basilar artery apex. Continuous irrigation with facility for drainage is required for adequate visualization of the ventricular structures. Then the floor of the third ventricle is fenestrated, and the balloon catheter is repetitively inflated and deflated to widen the fenestration. The underlying ependyma and arachnoid are opened. The balloon is kept inflated for a slightly longer period for a tamponade effect to arrest any bleeding from the edges of the fenestrated opening. The CSF flow is indicated by the slow wavy movements of the margins of the fenestration. One can visualize the basilar artery through the fenestration without inserting the endoscope into the basal cisterns. This is considered as the end point for ventriculostomy.

Diagram depicting steps of endoscopic third ventriculostomy procedure.

The preoperative concerns are same as for conventional shunt procedures like signs and symptoms of noncommunicating hydrocephalus. Pediatric population falls in this category. The implications with pediatric anesthesia like securing lines, airway difficulties with enlarged head circumferences, and narrow hemodynamic reserve are important factors to be considered. Patients with increased ICP may present with headache, vomiting, confusion, and obtundation. Patients with refractory vomiting may present with signs of dehydration and other electrolyte disturbances. These need to be corrected prior to surgery. Patients who already had prior shunts should be reviewed for the type of shunt, time and site of placement, its functioning status, duration of shunt, and signs of infection. Placement of central lines carries the risk of puncture if the site of shunt is not determined in cases with prior shunts.

Intra- and postoperative considerations: General anesthesia with muscle relaxation is the preferable technique to ensure immobility and safe surgery. Inhalational induction rather than intravenous is preferred in pediatric hydrocephalic patients to accomplish smooth anesthesia and for securing an intravenous line. Securing the airway and positioning the patient play a key role in hydrocephalic patients with enlarged head. Other key elements include CVS stability and early emergence for prompt assessment of the symptoms and its relief following the surgery. Complications associated with ETV and their avoidance are already described in General Considerations . Hygroma occurs mainly in cases with severe hydrocephalus where due to sudden decrease in ICP, the thinned out parenchyma may collapse and cause hygroma.

Other optional and additional endoscopic procedures for hydrocephalus include aqueductoplasty for the management of aqueductal stenosis. In this, the closed aqueduct is opened and dilated with 3 French Fogarthy catheter. If required a stent can be placed to avoid reocclusion ( Fig. 26.5 ).

The trajectory of endoscope for endoscopic third ventriculostomy and aqueductoplasty.

Endoscopic Transsphenoidal Hypophysectomy

The surgical indications include pituitary neoplasms including pituitary adenomas, Rathke cleft cysts, childhood craniopharyngiomas, and hyperfunctioning pituitary adenomas like prolactinomas, adrenocorticotropic hormone (ACTH)–secreting tumors, growth hormone–secreting tumors, and nonfunctioning adenomas. Tumors of size less than 1 cm are classified as microadenomas, and those more than 1 cm are classified as macroadenomas. Endoscopy is preferred for resection of both micro- and macroadenomas, but complete resection and hormone control is achieved better with microadenomas. Prior placement of lumbar drain for CSF diversion is recommended for some cases of pituitary macroadenomas. Infusion of saline through the lumbar drain increases the ICP and aids in pushing the adenoma down and helps in achieving adequate excision of the tumor. This also helps in preventing unnecessary extradural bleeding and in the early postoperative period helps in CSF drainage in case of CSF leak. Valsalva maneuver is another method for aiding the delivery of the tumor. Monitoring and maintaining CPP at the time of application of these maneuvers is important to avoid any deleterious effects.

Types of Approach

• 1.
  

  Sublabial transseptal approach: traditional approach; for extremely large tumors and in young children wherein the endonasal corridor would be inadequate.

  
  
• 2.
  

  Endoscopic endonasal approach.

  
  
• 3.
  

  Extended endonasal techniques for anterior cranial fossa skull base tumors (menigiomas, craniopharyngiomas) or clival lesions (chordomas).

The advantages of endoscopic approach compared to open craniotomy for pituitary surgery are as follows:

• •
  

  lesser incidence of injury to optic chiasm and frontal lobes

  
  
• •
  

  lower incidence of DI

  
  
• •
  

  cosmetically more acceptable

  
  
• •
  

  clear surgical view (just like having a camera at the tip of your finger)

  
  
• •
  

  shorter hospital stay

  
  
• •
  

  a relatively short operating time

  
  
• •
  

  lesser morbidity

  
  
• •
  

  minimal postoperative pain

The endonasal approach includes nasal dissection and turbinate manipulations to reach the sella turcica through the sphenoid sinus ( Fig. 26.6 ). These structures are highly vascular, and their sympathetic tone is high. Manipulation of these structures incites a strong hemodynamic response, which in turn may lead to rapid blood loss. This is more severe with sublabial transseptal approach where it involves dissection of the sublabial, dental and septal structures. The endoscopic endonasal approach is associated with, lesser nasal, dental, and cosmetic complications and is the preferred route nowadays.

The preoperative assessment and planning depends on size of tumor, the type of endocrine disease presentation and its implications. Prolactinomas are the most common type of functional adenomas (20–30%), usually present with menstrual and sexual disorders, and hence there are no specific anesthetic implications per se. Patients with microadenomas and macroadenomas present with headache and visual loss, respectively. Rarely patients with very large tumors may present with signs and symptoms of increased ICP. Both Cushing disease and acromegaly are equally common, important, and pose unique challenge to the anesthetist for airway management, hemodynamic disturbances, and blood loss. CVS changes include hypertension, left ventricular hypertrophy, diastolic dysfunction, bundle branch blocks, ST-T changes, as well as supraventricular and ventricular ectopics. Airway changes are more common with acromegaly and include hypertrophy of mandible, enlarged tongue, and thickening of the laryngeal and pharyngeal soft tissue leading to reduction in the size of the glottis aperture. Obstructive sleep apnea (OSA) is a common feature in both acromegaly and Cushing disease. Other findings include glucose intolerance, exophthalmos, thinning of the skin, and osteoporosis in Cushing disease. Anesthetic implications include difficult intravenous cannulation, positioning of patients, difficult mask ventilation and intubation, control of blood sugars, and postoperative airway obstruction. Thyrotrophic adenomas are rare and present with signs and symptoms of hyperthyroidism and sometimes with mass effect.

A thorough functional airway assessment is essential as Mallampati (MP) grading may misguide at the time of ventilation and intubation. Indirect laryngoscopy and X-ray of the neck provide additional information regarding the airway anatomy. CVS evaluation includes detailed history, physical examination, New York Heart Association grading, electrocardiography (ECG), and echocardiography. Dobutamine stress testing is useful to evaluate the stress acceptance in patients with positive cardiac findings. Respiratory assessment is equally important for evaluating the degree of airway obstruction in patients with obesity and OSA. This includes occupational history, history of smoking, chest examination, breath holding time, pulmonary function testing, and chest X-ray. Meticulous assessment of the airway dynamics with effective diagnostic tools has a significant role in respiratory and airway management. The other focus in preoperative checkup should be the endocrinological status of pituitary hypo- or hypersecretion. Any imbalance in the hormonal status should be sought for and the patient should be started on respective hormonal therapy. Electrolyte imbalances due to mineralocorticoid levels should be optimized and corrected before surgery.

Other laboratory studies include complete blood count, electrolytes, sugar, coagulation studies, calcium levels, and other metabolic functions. Hormonal assay includes thyroid panel, serum cortisol, ACTH, insulinlike growth factor 1, testosterone, luteinizing hormone, follicle-stimulating hormone, α subunit, and prolactin. Exact location, size, and extent of the tumor are identified with CT and MRI of the brain for a tailored surgical approach.

Preoperative medications like thyroid, corticosteroid medications, and other replacement hormones should be continued till the day of surgery. Thyroid hormone replacement sometimes may precipitate adrenal crisis in patients with impaired ACTH reserve. Diabetes is a very common abnormality seen in patients with acromegaly and Cushing disease. Electrolyte abnormalities and glucose levels should be optimized before taking up the patients for surgery. In patients with OSA and deranged spirometry, ABG analysis helps in evaluating the respiratory reserve. Longer acting sedatives should be used with caution in patients with significant upper airway obstruction, OSA, and in cases with raised ICP. Counseling regarding postoperative nasal packing and mouth breathing should be done wherever indicated.

Intraoperative considerations : Proper planning and availability of difficult cart and personnel are essential factors for successful airway management without any catastrophes. Use of small-caliber endotracheal tubes (ETTs) with continuous monitoring of cuff pressure may decrease the incidence of postoperative upper airway obstruction. Flexometallic tubes are preferred to avoid kinking and further compromise of CPP. South pole Ring Adair and Elwyn tube provides ample surgical operating field. Antisialogogues are administered to decrease the secretions for awake fiber-optic intubation if planned and during positioning. Throat packs soaked with normal saline are used to avoid spillage of blood and secretions into the trachea. This should be tagged and its placement, and removal should be notified in the anesthesia chart.

Hemodynamic perturbations are common with endoscopic manipulation of the nasal cavity. Different drugs and strategies are used to attenuate this response. Nasal application of xylometazoline drops is performed 10–15 min before induction to vasoconstrict the nasal mucosa. Infiltration of the nasal mucosa with local anesthetic drugs before incision; β-blockers like metaprolol and labetolol; vasodilators like nitroglycerine and sodium nitroprusside; supplemental opiate administration; propofol; and dexmedetomidine are used to maintain stable hemodynamics during the procedure. Bilateral maxillary nerve and infraorbital nerve blocks are found to be effective adjuncts for hemodynamic stability and perioperative analgesia.

Ultra-short-acting drugs like propofol and remifentanil and inhalational agents with low blood gas solubility like sevoflurane are drugs of choice for early recovery and immediate neurologic assessment. Narcotics should be used with caution in the intraoperative period to avoid airway perils in acromegalic patients and in patients with OSA and upper airway obstruction. Adequate muscle relaxation is achieved with vecuronium, atracurium, or cis -atracurium. Inadequate relaxation during surgery could lead to CSF leak, visual loss, and injury to major vessels.

The surgery is done in supine with slight head up position and head tilted a little toward the opposite side. This reduces venous engorgement, minimizes bleeding, and provides a proper aligned approach to the sellar region. Careful padded positioning is done to avoid pathological fractures.

Monitoring: American Society of Anesthesiologists (ASA) standard monitoring is advocated. Invasive monitoring is mandatory in patients with uncontrolled hypertension and impaired cardiorespiratory reserve. Use of β-blockers and vasodilators for achieving controlled hypotension mandates continuous monitoring of ABP. Selection for the site of placement of an arterial cannula is important as ulnar artery is compromised in 50% cases of acromegalic patients with carpal tunnel syndrome. CVP monitoring will guide fluid therapy, especially in suspected cases of antidiuretic hormone deficiency. Depth of anesthesia and neuromuscular junction monitoring will guide the titration of anesthetic drugs for hemodynamic stability and an early recovery. Visual evoked potential monitoring may be useful but very cumbersome to use and is extremely sensitive to anesthetic drugs. Close monitoring of urine output, serum osmolality, glucose, and electrolyte will help in early identification of complications like DI and hyperglycemia.

The most common intraoperative complications include hypertension and reflex bradycardia. Uncontrolled hypertension may result with intravascular injection of adrenaline leading to unopposed alpha effect in patients with β-blockers. Due to the close vicinity of ICA, cranial nerves III–VI, and optic canal to the pituitary, injury or compression to these structures is common. Injury to ICA may occur leading to massive bleeding and sometimes death. Others include CSF leak, DI, VAE, hyperglycemia and electrolyte disturbances. At the end of the surgery, Valsalva maneuver is applied to see for any CSF leak and reconstructed with fat if detected. Injection of air or saline into the thecal space and permissive hypercapnia are obsolete now and were used previously to delineate the tumor for better surgical dissection and excision. Use of N ₂ O is avoided in such situations as it expands the air bubble and increases the chance of pneumocephalus.

Emergence: Smooth and early recovery with adequate return of protective airway reflexes is essential for the assessment of visual deterioration and to minimize coughing, thus decreasing the incidence of bleeding. The oropharynx should be suctioned properly and throat pack removed without failure. Adjunct airway devices can be used for obligate nasal breathers and in patients who develop laryngospasm postoperatively. Some patients with upper airway obstruction may benefit from tracheal extubation in seated position.

Postoperative considerations and complications: Vigilant monitoring is required in the postoperative period for vital signs, analgesia, bleeding and airway problems, respiratory dynamics, electrolyte and fluid balance, and neurological and visual deterioration. Some physicians withheld the administration of dexamethasone postoperatively with regular monitoring of serum cortisol levels. Steroids are restarted once symptoms of adrenal insufficiency appear with a serum cortisol level of <2 μg/dL. Early respiratory complications include postoperative airway obstruction, laryngospasm, and sometimes leading to negative pulmonary pressure edema. Others include epistaxis, pain, nausea and vomiting, and aspiration. Multimodal analgesia with short-acting opioids, patient-controlled analgesia, and blocks are effective. Nausea and vomiting may have a deleterious effect on cerebral dynamics. Antiemetics, e.g., ondansetron and palonosetron are effective in controlling the nausea and vomiting. Blood pooled in the pharynx and stomach during surgery may result in regurgitation and aspiration. Acute hematoma or apoplexy is a rare but disastrous complication. Patients present with sudden blindness, ophthalmoplegia along with loss of consciousness (LOC) and hypotension. This requires immediate surgical intervention. Neuroendocrine complications include temporary and permanent DI, SIADH, hypopituitarism, as well as visual and cranial nerve dysfunction. Other complications include rhinological changes, glucose and electrolyte disturbances, CSF rhinorrhea, sphenoidal sinusitis, and meningitis. Injury to ICA may lead to formation of carotid cavernous fistula and pseudoaneurysm.

Endoscopic-Assisted Skull Base Surgery

Endoscopic skull base surgery presents a distinctive challenge to the neuroanesthesiologist. The varied indications include tumors of the anterior and middle cranial fossa, pituitary tumors and its surrounding structures, as well as tumors and cranial nerves of the posterior cranial fossa. Minimal invasiveness and maximal assertive and aggressive management of these tumors with this approach has major influence on the patient outcome and recovery. The key requisites of endoscopic skull base surgery are selecting a surgical corridor that causes minimal manipulation of the surrounding structures and reduces the risk of complications. Types of approach include:

• 1.
  

  Extended endoscopy and endoscopic endonasal approach has already been discussed.

  
  
• 2.
  

  Endoscopic supraorbital approach is successfully used for excision of the tumors of the anterior cranial fossa, meningiomas, craniopharyngiomas, and supra- or parasellar extensions of pituitary tumors and esthesioneuroblastomas.

  
  
• 3.
  

  Endoscopic retrosigmoid approach is indicated for tumors of the posterior cranial fossa, e.g., acoustic neuromas and meningiomas, and also for microvascular decompression of trigeminal nerve.

Image-guided neuronavigation system plays an important role in identifying the limits of the lesional excision and other surrounding structures if encased and sheathed by the tumor. Contraindications for the extended transsphenoidal approach includes involvement of the optic canal and encasement of the third cranial nerve.

The presentation of these skull base tumors depends on the location, mass effect, and vicinity of the nerves. Common signs and symptoms include imbalance, weakness of the arms and legs, headaches, double vision, numbness, weakness or pain in the face, hoarseness, and pain due to stretching of the nerves. MR imaging and CT scan provides detailed picture of the location of the tumor and the surrounding brain, nerves, muscles, and bony changes, and cerebral angiography about the surrounding vessels and dictates the approach. Other specific investigations include audiogram, neuro-ophthalmology, and endocrinology evaluation. Due to the vicinity of the cranial nerves, cranial nerve electromyograms/BAEP/SSEP are used to avoid any injury. The goals of anesthetic management include maintenance of an optimal depth of anesthesia to avoid patient movement during periods of intense stimulation, while at the same time permitting neurophysiological monitoring, especially in those undergoing excision of posterior cranial fossa tumors. Supraorbital approach involves muscle dissection and does not disrupt sensory nerves, hence muscle relaxation is not contraindicated and physiological monitoring is not necessary. The preferred anesthetic regimen is total intravenous anesthesia (TIVA) with propofol and short-acting opioids like fentanyl and remifentanil. Inhalational agents > 1 MAlC are avoided as they interfere with BAEPs and muscle relaxants where cranial nerve or brain stem monitoring is mandatory (posterior cranial fossa lesions). In patients undergoing supraorbital frontal approach for tumor excision phenytoin should be started and maintained.

Special care must be given to secure the patient’s airway. Armored ETTs and oral Guedel airways are used to prevent biting of the tube at the time of neurophysiologic monitoring. The preferred position for endoscopic retrosigmoid approach is lateral oblique position (Park Bench position), which is challenging. Other intraoperative complications include injury to vascular structures like ICA, cavernous and superior hypophyseal arteries (anterior cranial fossa tumors), basilar sinus and intracavernous carotid artery (posterior fossa lesions), cranial nerves (optic nerve, Vidian nerves, abducens nerve), and injury to brain stem. Inadequate hemostasis is another important challenge. Monopolar cautery is avoided specifically because of its potential injury to the olfactory nerve fibers and smoke formation leading to decreased vision when working in the sphenoid sinus close to neurovascular structures. Other complications include incomplete tumor removal and DI. Emergence from anesthesia should be quick for an early neurologic assessment and at the same time smooth enough to avoid subcutaneous CSF collection around the eye. The postoperative complications include CSF leakage, cranial nerve palsies, hypopituitarism, DI, brain stem injury, bacterial meningitis, epileptic seizures, sphenoid sinus mycosis, and respiratory complications. Proper and adequate training in these techniques, identification, and management of the challenges encountered are essential to reduce the morbidity and mortality.

Endoscopic Tumor Excision/Cyst Fenestration

Indications: This procedure is mainly indicated for excision of intraventricular tumors of second or third ventricle with soft consistency, <2–3 cm diameter, moderate to low vascularity, associated hydrocephalus, and low-grade histologically. A systemic review by Barber et al. has shown that presence of a cystic tumor component and use of neuronavigaion techniques are significantly associated with lesser complication rates. Endoscopic fenestration is the first line of management of intracranial cysts. The tumors and cysts that are amenable for endoscopic excision are:

• 1.
  

  Colloid cysts,

  
  
• 2.
  

  Subependymal giant cell astrocytoma,

  
  
• 3.
  

  Exophytic low-grade gliomas into the ventricles,

  
  
• 4.
  

  Central neurocytoma and small choroid plexus tumors,

  
  
• 5.
  

  Intraventricular craniopharyngiomas,

  
  
• 6.
  

  Pineal tumors, and

  
  
• 7.
  

  Intraventricular cysts like epidermoid cysts, pineal cysts, and arachnoid cysts.

Disadvantages:

• 1.
  

  Time consuming because of piecemeal-fashioned removal of the tumor mass.

  
  
• 2.
  

  Frequent obscuration of vision even if minimal bleeding occurs.

The site of approach depends upon the site of tumor.

Successful management of colloid cysts has been reported in 60–90% of cases with neuroendoscope. In some cases like pineal tumors and tumors associated with hydrocephalus, it also helps in sampling the tumor, CSF for tumor markers and cytologic studies, to inspect the intraventricular cavities for nodules missed with MR imaging, and to treat hydrocephalus at the same time. Endoscopic fenestration of the arachnoid cyst includes fenestration of the cyst into the subarachnoid or intraventricular system. Fig. 26.7 depicts the supraorbital keyhole approach for excision of craniopharyngiomas and its cosmetic advantages.

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