Pituitary Surgery

Mr Wang is one of two neurosurgeons in Victoria who has undergone specific overseas training in endoscopic trans-sphenoidal pituitary surgery. The benefits of the endoscopic trans-nasal approach includes improved illumination and visualisation, the ability to “look around corners” with angled endoscopes potentially allowing greater tumour removal, as well decreased nasal trauma and a more rapid post-surgical recovery to the patient.

What is the Pituitary Gland?

pituitary

The pituitary gland is the dominant regulator of the hormonal status of the body. It secretes eight important hormones that are involved in the body’s stress-response, growth and development, sexual and reproductive functions and general well-being. The pituitary gland is primed to respond to minute changes in hormone levels by increasing or decreasing output of a specific hormone in response to certain triggers including infections, stress, pregnancy etc.

Where is the Pituitary Gland?

The pituitary gland is situated at the based of the brain. It is an extension of the neural tracts of the brain and comprises an anterior and posterior part, both of which are important in the control of hormone levels in the body. Specifically, the pituitary gland is situated about 10-12 cm backwards from the tip of the nose towards the brain in the direct trajectory of the nasal cavity. Another way to localise it is about 6-7cm directly backwards from directly between the eyes. It is around 1cm in size and is surrounded on each side by the carotid arteries and cavernous sinuses containing the 3rd, 4th, 5th and 6th cranial nerves which control the movement of eyes and facial sensation, and above by the optic nerve and chiasm which controls vision.

What can go wrong with the Pituitary Gland?

Problems with the pituitary gland may present in several ways due to hormonal imbalance, or abnormal growth. Most pituitary disorders can be treated with medically, however if there is a pituitary tumour present then surgery may be required.

The majority of pituitary tumours are benign. This means they are not cancers and treatment is usually highly successful. Pituitary tumours may be functioning (hormone secreting) or non-functioning (non-hormone secreting). They may be micro-adenomas (less than 1cm) or macro-adenomas (more than 1cm). The most common pituitary tumour is the non-functioning macro-adenoma.

Non-functioning Macro-adenoma

These tumours may present is several ways. The first is by increased pressure on the normal pituitary tissue surrounding the adenoma resulting in hypo-pituitarism. This means that the normal pituitary tissue does not function normally resulting a lack of circulating hormones such as cortisol, growth hormone, sex hormones and thyroid hormones. The second is by direct mass-effect on the surrounding structures of the pituitary fossa. As the optic chiasm sits directly above the pituitary gland, the most common clinical effect will be for a gradual loss of the peripheries of ones’ visual fields, culminating in tunnel vision or even blindness. Pressure on the sides of the pituitary fossa may also result in blurring or double vision.

Functioning Pituitary Tumours

Pituitary tumours may over-secrete hormones resulting in changes in body shape, facial features and significant risks to important organs such as the heart, lungs and bowel. Untreated functioning pituitary tumours may result in a decrease in life expectancy.

The most common functioning pituitary tumour is a prolactinoma. Thankfully this is also the easiest to treat and the mainstay of treatment is medical, using tablets such as cabergoline or bromocriptine. Prolactinomas may result in amenorrhea (no periods), galactorrhea (abnormal lactation/nipple discharge) and infertility and there is no risk to the heart or lungs with prolactinomas. A small percentage of people with prolactinomas may require surgical treatment due to failure of the medications to shrink the tumour, or an individual severe intolerance to the various tablets used to treat prolactinomas medically. It is important to understand that small rises in the blood levels of prolactinomas does not always mean you have a pituitary tumour. In fact the most common cause of an elevated prolactin is due to medications such as anti-depressants. Abnormal stress may also result in an elevated prolactin level in the absence of a pituitary tumour.

The second most common functioning pituitary tumour is a growth hormone secreting tumour. Excess growth hormone results in gigantism in the adolescent, or acromegaly in the adult. This results in a gradual increase in size of the hands, feet and head and may be evident by increasing glove/shoe/hat sizes. It is common for this gradual increase not to be evident to the patient and their family series of photographs spanning 6-7 years are reviewed. Enlargement of the heart and respiratory passages may also occur resulting in cardiomyopathy and obstructive sleep apnoea. The gastrointestinal system may be affected with bleeding and the development of cancers of the large bowel. It is for these reasons that treatment for acromegaly is vital as untreated acromegaly will result in a decrease in life expectancy of 7-8 years. Treatment may include a combination of surgery, medical therapy and radiotherapy. Trans-sphenoidal surgery is usually the first-line treatment for growth hormone secreting tumours and has a success rate of about 70% in resulting in biochemical remission for acromegalics.

The third most common functioning pituitary tumours is a ACTH secreting tumour. This results in Cushing’s disease which is an elevated circulating blood level of cortisol or steroid. Excess steroid levels result in central obesity of the trunk and facial features. Other effects include unstable diabetes, heart failure, osteoporosis, mood swings and easy bruising. Like growth hormone secreting tumours, an untreated ACTH secreting tumour will result in a decreased life-expectancy. Treatment again includes a combination of surgery, medical therapy and radiotherapy.

Finally, other functioning pituitary tumours may include TSH or FSH secreting tumours. The mainstay of these tumours is surgery and radiotherapy.

How are pituitary tumours treated?

Treatment of pituitary disorders involves a multi-practitioner approach with the co-ordination between the endocrinologist, pituitary neurosurgeon, neuro-radiologist, neuro-ophthalmologist and neuro-anaesthetist. In general the diagnosis of a pituitary tumour involves static blood tests and a MRI of the brain to identify the tumour. Occasionally dynamic blood testing may be required. This is particularly so for the diagnosis of functioning tumours and may involve the collection of serial blood or urine samples after application of oral or intravenous stimulation substances. Annual visual fields and MRI scans may be scheduled to monitor non-functioning pituitary tumours.

Medical treatment

The endocrinologist is vital in the management of pituitary tumours regardless of whether it is a functioning or non-functioning tumour. They are responsible for replacing any hormone deficiencies identified during blood testing, or following surgery. Medical management of functioning pituitary adenomas include the use of dopamine agonists (for prolactinomas), somatostatin analogues or GH receptor antagonists (for acromegaly) or steroid synthesis inhibitors (for Cushing’s disease). These treatments are co-ordinated by the endocrinologist. The endocrinologist is also vital in the post-operative period should trans-sphenoidal surgery have been performed for the pituitary tumour, particularly to ensure that adequate hormone replacement and fluid balance is adhered to in the first few weeks after surgery.

Surgical treatment

Endoscopic trans-sphenoidal surgery is surgical approach of choice for pituitary adenomas. The indications for surgery in pituitary tumours include progressive growth of a non-functioning adenoma, compressive signs and symptoms (visual field deficits, double vision), or functioning tumours with an obvious pituitary adenoma on MRI scans. Surgery is aimed at debulking of a non-functioning pituitary tumour, or complete removal of the functioning pituitary tumour resulting in normalisation of the hormone secreted.

Endoscopic trans-sphenoidal surgery allows improved illumination and visualisation of the pituitary tumour. It allows the surgeon to look around corners using angled endoscopes as opposed to the traditional microscopic approaches. The endoscopic trans-sphenoidal approach also allows other pituitary region lesions such as craniopharyngiomas, Rathke’s cleft cysts and other tumours to be safely treated. The use of this “keyhole” approach also has many benefits in terms of post-operative pain and recovery. Minimal transient nasal trauma is suffered by the patient with no post-operative nasal packing employed.

Who performs pituitary surgeries?

It has been repeated shown that a specialist pituitary neurosurgeon is vital in obtaining good surgical results. All neurosurgeons are exposed to trans-sphenoidal pituitary surgeries during their training but very few have undergone further training in this approach. It is important that the pituitary neurosurgeon is not only trained in trans-sphenoidal surgeries, but also has an understanding of the complex hormonal interactions of pituitary tumours and the post-operative management of these. Some neurosurgeons will work in combination with an ENT surgeon to assist them with the endoscopic approach to the pituitary region.

What are the complications of endoscopic trans-sphenoidal pituitary surgeries?

Rare but major risks (less than 0.1% risk; case dependant):

  • Carotid artery injury resulting in strokes
  • Blindness from optic nerve/chiasmal injury
  • Death

More common and treatable risks (5-10% & case dependent):

  • Bleeding (nasal & tumour bed)
  • Infection (sinusitis, abscess, meningitis etc.)
  • CSF leak & pneumocephalus
  • Pituitary dysfunction & need for hormone replacement: usually transient, but can be permanent
  • Diabetes insipidus & SIADH
  • Residual tumour (case dependent)
  • Need for further surgery & adjuvant radiotherapy
  • Other medical complications (respiratory, cardiovascular etc.)