UBP 3.5 (Short Form): Neuro – Transphenoidal Hypophysectomy

Question 1

What general concerns do you have for this case?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 1

In general, my concerns for this case include the following:

1. hemodynamic lability and risk of end organ ischemia associated with chronic hypertension;
2. the risk of cerebral ischemia secondary to a reset autoregulation curve, hemodynamic lability, air embolism, and/or increased ICP with suprasellar extension of the tumor;
3. the increased risk of aspiration associated with GERD, diabetes mellitus (autonomic neuropathy), and bromocriptine (may cause gastroparesis);
4. the potential for difficult airway management associated with acromegaly (the patient is taking bromocriptine and octreotide), obesity, and OSA;
5. the potential for endocrinologic conditions, such as –
   
   • Cushing’s disease,
   • panhypopituitarism,
   • acromegaly,
   • hyperthyroidism, and
   • diabetes insipidus; and
6. the risk of procedure-related complications, such as –
   
   • massive hemorrhage,
   • air embolism,
   • arrhythmias,
   • high spinal, and
   • cranial nerve damage.

Question 2

What do you think of this patient’s complaints?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 2

This patient’s complains of headache, blurred vision, and rhinorrhea are consistent with parasellar extension of the pituitary tumor, with expansion of the sella (headache), compressing the optic chiasm (blurred vision), and inferior extension of the adenoma (rhinorrhea).

Compression of adjacent structures is usually associated with larger, nonfunctional macro-adenomas that are greater than 1 cm in size.

However, since this patient is taking bromocriptine and octreotide, I would suspect that his pituitary tumor is functional, with the excessive secretion of growth hormone leading to acromegaly.

Because hormone-secreting lesions cause noticeable systemic effects, they are often diagnosed earlier, prior to the onset of the compression-related signs and symptoms associated with larger non-functioning tumors (i.e. nausea, vomiting, headache, visual disturbances, rhinorrhea, apoplexy, panhypopituitarism, and hydrocephalus).

The most common functional pituitary adenoma is a prolactinoma, which is associated with amenorrhea, galactorrhea, and infertility.

Other pituitary adenomas secrete excessive amounts of

• ACTH, leading to Cushing’s disease (truncal obesity, abdominal striae, hypertension, and hyperglycemia);
• growth hormone, leading to acromegaly (HTN, insulin resistance, visceromegaly, osteoporosis, skeletal overgrowth, and soft-tissue overgrowth); and
• TSH, leading to hyperthyroidism (this is rare).

Question 3

What is the physiologic function of the pituitary gland?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 3

The anterior pituitary is responsible for the synthesis, storage, and secretion of the six following tropic hormones:

1. adrenocorticotrophic hormone (ACTH), which stimulates the adrenal cortex secretion;
2. prolactin, which stimulates the secretion of breast milk and inhibits ovulation;
3. human growth hormone, responsible for body growth;
4. thyroid-stimulating hormone (TSH), which stimulates thyroid secretion and growth;
5. follicle-stimulating hormone (FSH), responsible for ovarian follicle growth in females and spermatogenesis in males; and
6. luteinizing hormone, which stimulates ovulation in females and testosterone secretion in males.

The anterior pituitary also secretes beta-lipotropin, which contains the amino acid sequences of several endorphins that bind to opioid receptors.

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The posterior pituitary stores and secretes two hormones that are initially synthesized in the hypothalamus and transported to the posterior pituitary.

These two hormones are:

1. antidiuretic hormone (ADH), which promotes water retention and regulates plasma osmolarity, and
2. oxytocin, which causes uterine contraction and the ejection of breast milk

Question 4

Why is this patient taking Bromocriptine? Octreotide? What is the mechanism of these drugs?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 4

Bromocriptine is used to treat the excessive secretion of both prolactin and growth hormone from functional pituitary tumors.

It is a synthetic dopamine-2 receptor agonist that inhibits the secretion of both growth hormone and prolactin, bringing their levels down sufficiently to improve symptoms in many patients.

Since this patient is also being treated with Octreotide, a drug not often utilized in the treatment of a functional prolactinoma, I suspect that he is receiving these medications to treat acromegaly.

Octreotide is a somatostatin analogue that inhibits the release of growth hormone and may actually shrink the size of pituitary tumors.

Question 5

How is the diagnosis of acromegaly made?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 5

The diagnosis of acromegaly is based on an initial clinical suspicion, due to the presence of several characteristic manifestations, and confirmed by biochemical testing.

The characteristic manifestations of acromegaly include –

• skeletal overgrowth (large body, hands, and feet; prognathism),
• soft tissue overgrowth (large lips, tongue, epiglottis, and vocal cords),
• recurrent laryngeal nerve paralysis (secondary to stretching caused by overgrowth of surrounding structures),
• peripheral neuropathy (secondary to trapping caused by the overgrowth of surrounding tissue),
• visceromegaly,
• glucose intolerance,
• osteoarthritis,
• osteoporosis,
• hyperhidrosis, and
• skeletal muscle weakness.

Biochemical tests used to confirm the diagnosis include –

• measurement of serum IGF-I (the most reliable test since it is less variable throughout the day),
• measurement of serum growth hormone (varies from hour-to-hour with exercise, sleep, and food ingestion), and the
• performance of an oral glucose tolerance test (in acromegalic patients, the serum GH levels remain above 2 ng/mL within two hours of ingesting 75 g of glucose).

Question 6

What general anesthetic concerns would you have in someone with Acromegaly?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 6

My primary concern in patients with acromegaly is the potential for difficult airway management.

• Distorted facial anatomy (difficult mask fit),
• enlargement of the tongue and epiglottis (predisposition to upper airway obstruction & impaired visualization during laryngoscopy),
• overgrowth of the mandible (prognathism),
• a narrowed glottis opening (may require smaller endotracheal tube),
• enlarged nasal turbinates (may inhibit nasal passage of an airway), and
• recurrent laryngeal nerve paralysis may all compromise airway management.

Other than the airway, my concerns would include and increased incidence of – coronary artery disease and the risks associated with hypertension, cardiomegaly, congestive heart failure, obstructive sleep apnea (mask ventilation, postoperative apnea, and inadequate pain control), diabetes mellitus, and peripheral neuropathy (positioning).

Question 7

Would you require an echocardiogram prior to starting the case?

(A 34-year-old, 98 kg, male presents for transphenoidal resection of a pituitary adenoma in the sitting position. He complains of progressive headache, blurred vision, and rhinorrhea over the last 3 months. Past medical history is significant for hypertension, GERD, obstructive sleep apnea (OSA), and diet controlled diabetes mellitus. His medications include: propranolol, hydrochlorothiazide, omeprazole, octreotide, and bromocriptine. Vital signs: HR = 54, BP = 140/62 mmHg, RR = 18, Temp = 37.1 °C, Hgb = 12.1 gm/dL.)

Answer 7

Given the increased risk of venous air embolism during intracranial procedures performed with the head above the level of the heart, I would prefer to perform –

a bubble study with precordial echocardiography or transesophageal echocardiography to rule out a patent foramen ovale, which would place him at risk for paradoxical embolism to the coronary or cerebral circulations (bubble studies could also be performed with a transcranial Doppler).

If he had a patent foramen ovale, the sitting position is relatively contraindicated and I would discuss alternative patient positioning with the surgeon.

In addition to identifying this risk, an echocardiogram may prove helpful in identifying any cardiac pathology resulting from his hypertension or obstructive sleep apnea.