3.1.1 General Considerations in Pediatric Patients

The child awaiting surgery will be anxious and may benefit from anxiolytic premedication. Excessive fasting will increase distress and cause dehydration and should be avoided. NPO (nil per os) guidelines should encourage drinking clear liquids until 2 hours before surgery. Blood loss is well tolerated until severe, and hypotension is a late sign of volume depletion.

3.1.2 Anatomical Considerations of Pediatric Skull Base Surgery

The sphenoid bone is solid at birth. Pneumatization is not complete until puberty. ¹ The pediatric neurosurgeon must drill through a variable amount of solid sphenoid bone to reach the sella turcica. ¹ Size considerations generally limit the fully endoscopic endonasal approach to children older than 3 to 4 years. The internal carotid arteries and cavernous sinus are in the middle skull base; any surgery in this area risks massive bleeding. ²

3.1.3 Common Lesions

Craniopharyngioma, Rathke’s cleft cyst, and pituitary adenoma are typical pediatric skull base lesions. ¹ Multiple Endocrine Neoplasia 1 (MEN 1) causes both pituitary adenoma and hyperparathyroidism. ³

3.1.4 Mass Effect of Skull Base Tumors

Skull base tumors can compress the third ventricle, causing hydrocephalus and elevated intracranial pressure (ICP). ⁴ Pressure on the optic chiasm leads to visual defects. ⁴ Compression of the pituitary can cause hyposecretion of one or more pituitary hormones and cause hypothyroidism, growth failure, secondary adrenal insufficiency, or diabetes insipidus (DI). ²

3.1.5 Pituitary Hormone Excess

Pituitary adenomas may secrete excess hormones. The most common is prolactinoma, which is usually medically managed and does not impact anesthetic care significantly. ⁴

Adrenocorticotropic hormone (ACTH) excess causes Cushing’s disease, with many anesthetic implications. ⁴ The patient may have central obesity, with increased risk of gastroesophageal reflux disease (GERD) and aspiration. The Cushingoid face may impede mask ventilation. Hypertension is common, as is hyperglycemia. The skin is easily torn; care with tape and positioning is essential. Mild obstructive sleep apnea (OSA) is also common. ⁴

Excess growth hormone may cause gigantism in a child or acromegaly in the teenager. Acromegaly causes macroglossia, hypertrophied pharyngeal tissue, and laryngeal stenosis; both OSA and difficulty with intubation are common. Hyperglycemia and hypertension are also common. ² Thyroid-stimulating hormone (TSH) hypersecretion is rare in the pediatric population. ⁴

3.1.6 Laboratory Investigations

Electrolytes should be assessed. Hyponatremia may occur with overzealous DI therapy, hypernatremia from undertreated DI. Hypercalcemia may occur with MEN 1. Hyperglycemia is common in Cushing’s disease, and hypoglycemia occurs with ACTH deficiency. ³

A type and screen, complete blood count, and coagulation studies should be checked due to the risk of massive intraoperative bleeding from large vascular structures. ⁴

Pituitary functional assessment includes serum cortisol, ACTH, TSH, insulin-like growth factor 1 (IGF-1), and prolactin level. Any hormonal deficiency should be replaced. ⁴

3.1.7 Imaging

MRI and CT are performed to evaluate hydrocephalus, invasiveness of lesion, compression or encasement of vital structures, and also as a component of neuronavigation. ¹

3.1.8 The Morning of Surgery

The patient with a hypopituitarism should continue the hormone replacement therapy (including glucocorticoid stress dosing). ⁴

Physical examination should look for signs of Cushingoid facies or acromegaly, which may cause difficult mask ventilation or intubation, respectively. ² Lethargy, emesis, and papilledema suggest elevated ICP, which may warrant rapid sequence intubation. ³

Premedication can be useful after ruling out elevated ICP. Midazolam 0.5 mg/kg orally will facilitate parental separation, ease anxiety, and enhance patient compliance. Glycopyrrolate may be given for antisialagogue activity if difficult airway is anticipated.

3.2.1 Induction

The endonasal endoscopic approach to skull base surgery avoids the potential injury caused by brain retraction and other complications associated with a transfrontal craniotomy. ⁵ This technique can be performed in children as young as 3 to 4 years, below which the naris is too small to allow successful instrumentation.

The choice between inhalation and intravenous induction can be jointly decided between the parent, child, and anesthesiologist, provided that ICP is not elevated. Unless the child has acromegaly or Cushing’s disease, airway management is routine. A cuffed endotracheal tube is mandatory to prevent significant aspiration of blood and secretions from the nasal cavity. Two large bore peripheral intravenous catheters should be placed because of the risk of bleeding.

If the patient has hypopituitarism, stress dose glucocorticoids should be administered.

3.2.2 Monitoring

In addition to routine anesthesia monitors, the patient should also have continuous arterial blood pressure monitoring, first, to assist in monitoring extreme hemodynamic fluctuations, second, because of the risk of sudden massive blood loss, and, third, to monitor electrolytes in the event of DI. A Foley is essential because the patient may be receiving mannitol and also to monitor urine output because of the risk of DI. A central venous pressure (CVP) is generally not necessary.

3.2.3 Positioning

The patient will be positioned supine with head elevated approximately 30°, with the head slightly extended and turned to the left. The head is secured in a Mayfield clamp. The operating room table is then rotated 90° away from the anesthesiologist. The endotracheal tube should be well secured to prevent displacement during surgical manipulation. A throat pack is placed by the surgeon to help keep blood out of the stomach and lungs.

Maintenance of anesthesia may be accomplished by volatile agent alone, total intravenous anesthesia (TIVA), or more commonly a combination of the two. If the patient has elevated ICP, then TIVA is preferred. ⁶

TIVA is easily accomplished using continuous infusion of propofol and remifentanil. TIVA also has the advantage of less postoperative nausea.

Visual evoked potentials (VEP), although not routine, are occasionally monitored to help preserve the integrity of the visual pathway. TIVA may increase the predictive value of VEP changes. ⁷

Neuromuscular blockade is routinely used to prevent potentially disastrous patient movement.

The surgeon will begin preparing the nasal cavity with lidocaine and epinephrine to induce vasoconstriction. This may cause tachycardia and hypertension. This temporary problem can be treated by increasing the depth of anesthesia.

The surgeon may elect to place a lumbar spinal drain to detect (with intrathecal fluorescein) and decrease the incidence of cerebrospinal fluid (CSF) leak in select patients with high-risk settings. ⁸ Newer surgical closure techniques have greatly reduced the likelihood of the CSF leak. ⁹

Antibiotic prophylaxis must provide coverage for gram-positive bacteria frequently found on the nasopharynx.

Normocapnia is ideal to prevent pituitary retraction upward and out of the sella turcica. Blood pressure should be maintained at preinduction levels. Hypotension may result in cerebral ischemia, while hypertension will increase the likelihood of bleeding.