Transsphenoidal Hypophysectomy Complications

Transsphenoidal Hypophysectomy

• Preoperative evaluation is crucial to identify abnormalities caused by abnormal pituitary hormone secretion or mass effect of the pituitary tumor.
• Postoperative observation is necessary to identify life-threatening complications.

Complications

• Hemorrhage is a potential complication of transsphenoidal hypophysectomy.
• Increased intracranial pressure (ICP) is a possible complication of the surgery.
• Cranial nerve palsy is a potential complication of transsphenoidal hypophysectomy.
• Diabetes insipidus (DI) is a possible complication of the surgery.
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a potential complication of transsphenoidal hypophysectomy.

Anesthesia Considerations

• Intubation by direct laryngoscopy may be difficult in 12% to 30% of acromegalic patients due to physiologic changes in the airway.

Pituitary Gland and Hypophysectomy

• The pituitary gland is located at the base of the brain in the sella turcica and consists of the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
• The anterior lobe secretes six hormones: prolactin, adrenocorticotropin, GH, follicle-stimulating hormone, luteinizing hormone, and thyroid-stimulating hormone, each by a specific cell type.
• The posterior lobe secretes vasopressin and oxytocin.
• The hormones of the pituitary influence target organs, which are affected by pathology of the pituitary gland.

Pituitary Tumors

• Almost all pituitary tumors originate in the anterior lobe, and most are benign adenomas.
• 75% of these adenomas cause an inappropriate amount of hormone secretion.
• Pituitary tumors are most commonly found in adults in their fourth to sixth decade of life and are classified by their size and functionality.
• Functioning tumors usually consist of a single cell type and secrete a single hormone, defining the disease process, such as acromegaly and Cushing disease.
• Nonfunctioning tumors do not secrete excess hormones and are usually not discovered until they are larger.

Acromegaly

• Acromegaly results from an excess production of GH when the individual develops the condition in adulthood and gigantism if the condition develops before epiphyseal closure.
• The most common cause of acromegaly is a pituitary somatotroph adenoma that releases GH.
• Excessive amounts of GH stimulate the production of IGF-1 by the liver.
• Supraphysiologic concentrations of GH and IGF-1 contribute to the signs and symptoms of the disorder, characterized by increased growth and increased carbohydrate, fat, and protein metabolism.
• The onset of the defining characteristics can evolve over 10 years before fully developing.
• Acromegaly can cause an overgrowth of the bony and soft tissues, leading to prognathism, macroglossia, and enlargement of the uvula, which can hinder ventilation and intubation.
• Other anatomic changes associated with acromegaly include thickening of the vocal cords, reduced size of the laryngeal aperture, and hypertrophy of the periepiglottic folds.
• Obstructive sleep apnea (OSA) is seen in 60% to 75% of individuals with acromegaly.
• Hypertension is seen in 30% of acromegalic patients and is commonly associated with myocardial hypertrophy.
• Diabetes mellitus is observed in 25% of these patients and can drastically affect perioperative care.

Cushing Syndrome

• Cushing syndrome results from excessive secretion of cortisol.
• The etiology of Cushing syndrome includes medications that stimulate the production of glucocorticoids, adrenal tumors, ectopic ACTH production, and Cushing disease, resulting from ACTH-secreting pituitary tumors.
• Hypersecretion of cortisol has dramatic and systemic effects on the body, including truncal obesity, redistribution of fat, proximal myopathy, osteoporosis, hypertension, left ventricular hypertrophy, hypernatremia, hypervolemia, hypokalemia, OSA, gastrointestinal reflux, glucose intolerance, insomnia, and depression.
• The diagnosis of Cushing syndrome is based on assessing free cortisol levels, which are measured in urine (>250 mcg/24 hr).

Transsphenoidal Hypophysectomy

• The treatment of choice for a well-circumscribed pituitary tumor is a transsphenoidal hypophysectomy, which accounts for approximately 20% of the intracranial surgeries done in academic institutions.
• This procedure debulks the pituitary mass and, as a result, endocrine function improves.
• Access to the pituitary gland is best achieved via the transsphenoidal approach, which minimizes surgical trauma to the brain and has the least incidence of complications.
• The surgeon is able to remove the tumor using a microscope, and imaging techniques such as fluoroscopy, ultrasound, frameless stereotaxis, three-dimensional computer-assisted neuronavigation, or MRI may be employed.
• The free space created by excision of the tumor can be packed with synthetic reabsorbing material, fat, fascia, or muscle that is harvested from the abdomen or thigh.

Transsphenoidal Hypophysectomy

• Transsphenoidal hypophysectomy is the treatment of choice for a well-circumscribed pituitary tumor.
• This procedure accounts for approximately 20% of intracranial surgeries done in academic institutions.
• The goal of the procedure is to debulk the pituitary mass, which leads to improved endocrine function.

Surgical Approach

• The transsphenoidal approach is the best way to access the pituitary gland.
• This approach can be achieved via either a sublabial or endonasal route.
• It minimizes surgical trauma to the brain and has the least incidence of complications.

Surgical Procedure

• The surgeon accesses the sella turcica by removing the inferior portion of the sphenoid sinus.
• The tumor is removed using a microscope.
• Imaging techniques employed include fluoroscopy, ultrasound, frameless stereotaxis, three-dimensional computer-assisted neuronavigation, or MRI.

Post-Excision Procedure

• The free space created by excision of the tumor can be packed with synthetic reabsorbing material, fat, fascia, or muscle harvested from the abdomen or thigh.
• The graft also seals the dura.
• The bone fragment from the floor of the sella turcica and the sphenoid sinus is packed.

Preoperative Evaluation

• Preoperative evaluation of a patient with a pituitary tumor should include evaluation of prolactin concentration, thyroid function test, and MRI.
• MRI is superior to CT scan for differentiating soft tissues and identifying microadenomas.
• In-depth evaluation should be performed based on target organs affected, such as musculoskeletal, cardiovascular, and respiratory systems.

Neurological Abnormalities

• Functional tumors rarely extend beyond the sella turcica and seldom produce symptoms by mass effect.
• Nonfunctional tumors are usually not diagnosed until they impinge on adjacent structures outside the sella.
• Pituitary tumor is the most common cause of bitemporal hemianopsia due to its proximity to the optic chiasm.
• Cranial nerve palsy can result from compression of cranial nerves III, IV, V, and VI in the cavernous sinuses.
• Increased ICP due to the tumor mass can cause headache, papilledema, and altered level of consciousness.

Anesthetic Implications of Acromegaly

• Anatomic airway abnormalities in acromegaly include narrow glottic opening, thickened laryngeal cartilages, and soft tissue hypertrophy.
• Laryngeal stenosis, subglottic narrowing, and vocal cord paralysis can result from recurrent laryngeal nerve stretching.
• Prognathism, macroglossia, and hypertrophy of the lips and epiglottis can make airway management challenging.
• 12%-30% of acromegalic patients may be difficult to intubate by direct laryngoscopy.
• Glottic or subglottic involvement can be suspected if hoarseness, stridor, or OSA is observed.
• Alternative airway management strategies such as awake intubation may be necessary.
• Using a smaller endotracheal tube than expected can help avoid soft tissue trauma, bleeding, and subsequent edema.

Transsphenoidal Hypophysectomy

Intraoperative Period

• Patient positioning requires access to the upper lip and nose, so the operating table and patient are rotated 180 degrees.
• Patient's head is slightly elevated and secured in a headrest, increasing the potential for venous air embolus.
• Surgeon stands to the left of the patient, so patient's head is turned to the left.
• Endotracheal tube is secured to the left side of the mouth and taped to the patient's cheek or lower lip.

Cardiovascular Abnormalities in Acromegaly and Cushing Disease

• Half of all untreated acromegalic patients die before the age of 50, primarily due to cardiac disease.
• Acromegaly is characterized by left ventricular hypertrophy, increased cardiac output and stroke volume, and diastolic dysfunction.
• ECG abnormalities include bundle branch block, ST-segment depression, and T-wave abnormalities.
• Cushing disease is associated with hypertension (80% of patients) and diastolic blood pressure > 100 mm Hg (50% of patients).
• Cushing disease also presents with ECG abnormalities, such as high-voltage QRS complexes, inverted T waves, and left ventricular hypertrophy.

Anesthetic Considerations for Cushing Disease

• Obstructive sleep apnea is present in over half of all patients with Cushing disease.
• Hyperglycemia frequently occurs, so intraoperative blood glucose assessment is necessary.
• One-third of patients with Cushing disease exhibit exophthalmos, which increases the risk of corneal abrasions.
• Thinning skin due to hypercortisolism leads to superficial veins, making vascular cannulation difficult.
• Pathologic fractures occur in approximately 20% of patients due to osteoporosis, so careful positioning and padding are vital.
• Protein catabolism leads to muscle hyper-metabolism, resulting in weakness, and requires adjustment of muscle relaxant medication.
• Hypokalemia should be corrected preoperatively to avoid cardiac effects and skeletal muscle weakness.

Anesthetic Complications during Transsphenoidal Hypophysectomy

• Inadequate muscle relaxation can lead to patient movement, causing cranial nerve damage, optic chiasm injury, or vascular injury.
• Internal carotid artery damage can result in massive hemorrhage, requiring deliberate hypotension during surgical repair.
• Blood loss may be significant if the tumor is large or involves the suprasellar region.
• Valsalva maneuver may be requested to assess for cerebrospinal fluid (CSF) leak, which may require packing the sella turcica with autologous fat.

Anesthetic Considerations for Transsphenoidal Hypophysectomy

• Blood entering the stomach during surgery can cause emetic effects, so orogastric suctioning is necessary to remove it before emergence.
• An oral airway should be placed before emergence to encourage mouth breathing, as the nasal cavity is packed.
• Awake extubation is preferred, especially if ventilation and intubation were difficult, and can be done using an endotracheal tube changer if necessary.
• Pharyngeal suctioning before emergence helps avoid excessive stimulation and coughing.
• Intravenous lidocaine can be administered to blunt hyperreactive airway reflexes during emergence.
• A postoperative assessment of neurologic status should be performed quickly, facilitated by using short-acting drugs like propofol and remifentanil.

Importance of Neurologic Examination Postoperatively

• A comprehensive neurologic examination is necessary to evaluate the involvement of structures near the surgical site, such as the internal carotid arteries, cranial nerves, and optic chiasm.
• Complications may include carotid artery spasm, cranial nerve damage, and visual changes, which may require immediate direct assessment using CT, MRI, or reexploration.

Postoperative Complications with Delayed Onset

• Neuroendocrine abnormalities, such as diabetes insipidus (DI) and syndrome of inappropriate antidiuretic hormone (SIADH) secretion, may not be detectable immediately after surgery.
• DI occurs in approximately 25% of patients and is usually transient, requiring fluid and electrolyte replacement and administration of vasopressin.
• Urinary catheter placement can help assess urinary output for DI.
• Assessing the patient for fluid draining into their throat, frequent swallowing, or continuous drainage can indicate a CS leak.
• Nausea and vomiting occur in nearly 40% of neurosurgical patients and can have detrimental consequences on increased ICP.
• Prophylactic antiemetic medication should be incorporated into the plan of care.
• Hypopituitarism can occur, requiring corticosteroid administration to avoid acute adrenal crises if plasma cortisol levels decrease significantly.