Endoscopic Pituitary Surgery

The vast majority of pituitary tumours can now be removed via the transphenoidal route (accessed through the nostrils), so avoiding the trauma of a craniotomy (opening the skull). The traditional microscopic transphenoidal technique was highly successful but has now been surpassed by endoscopic techniques that provide improved visualisation of the tumour, gland and nerves so giving the surgeon the chance to achieve greater tumour resection and to reach previously inaccessible parts of the adenomas. The endoscopic approach is a minimally invasive technique but does require particular surgical skills and equipment.

Background

The gland is approximately 12mm across and lies in a hollow in the base of the skull, beneath the brain, just behind the eyes and at the back of the nasal cavities. Above the pituitary lie the optic nerves and their junction, the optic chiasm. To each side lie the cavernous sinuses (sponge-like spaces filled with blood) that contain the passing internal carotid arteries and 3rd, 4th and 6th cranial nerves. The pituitary gland produces hormones and through these controls other glands of the body (thyroid, adrenals, gonads and kidneys). The pituitary is connected to the brain via a thin stalk, down which pass chemical messengers that direct it's hormone production.

Pituitary adenomas are benign growths arising within the pituitary gland that have a prevalence of 20 per 100,000 population and annual new presentation rate of 2 per 100,000 people. Other tumours arising in this region that are treated in a similar manner include Craniopharyngiomas, Meningiomas, Rathke's Cleft Cysts, Pituitary Cysts, Pituitary Infections and metastases. The main clinical features are visual failure (initially bitemporal field loss, followed by falling acuity and finally blindness), pituitary hormone insufficiency, acute intracranial haemorrhage and syndromes of endocrine excess (Acromegaly / Gigantism, Cushing's Disease, Hyperthyroidism). Sometimes these tumours bleed causing an acute medical emergency called Pituitary Apoplexy, with damage to the gland and adjacent nerves.

In the vast majority of cases treatment is via surgical excision, which aims to cure the tumour and preserve any remaining pituitary gland tissue. Approximately 1/3 of patients will achieve full recovery of the visual fields (about 80% improve to some extent or fully). Often the pituitary will not be functioning fully at presentation and, although the normal pituitary gland is preserved as far as possible, cure may be at the expense of increased pituitary insufficiency. Thus, peri-operative management requires joint care with a specialised Endocrinology team to provide pre-operative assessment and treatment (hormone replacement / somatostatin analogues for Acromegaly) and postoperative monitoring for diabetes insipidus and cortisol insufficiency. Full pituitary function tests are performed within 1 month following surgery. Patients are then monitored with interval MRI scanning and endocrine assessments. Hormone replacement may include any or all of; hydrocortisone, thyroxine, testosterone / oestrogen, DDAVP and growth hormone.

All patients require high definition MR imaging of the pituitary and some require specialised radiological and endocrine tests including Inferior Petrosal Sinus Sampling (IPSS) via venography. The degree of specialism, rarity and complexity of pituitary pathology means that such tumours should be managed only in centres with appropriate Endocrine, Surgical, Oncology and Radiological expertise.

Traditional Microscopic Pituitary Surgery

Traditionally 90% of pituitary adenomas and 20% of the other skull base pathologies have been operated on via the transphenoidal route (up the nose & through the nasal sinuses) with the remainder approached via Craniotomy (opening the skull and elevating a lobe of the brain). The classical transphenoidal method uses an operating microscope and submucosal strip, insertion of a bivalved retractor and wide removal of the anterior wall of the sphenoid. This provides a corridor to the pituitary fossa that is far safer than the transcranial approach but has several drawbacks: the view is restricted, instruments further obstruct the view, haemorrhage from the approach often obscures the operative field, the light at depth is dim and only tissue in the direct line of sight can be removed safely. Consequently tumour may have to be left in less accessible corners, the gland may be damaged inadvertently and complications of CSF leakage, carotid injury, intracranial haemorrhage and hypopituitarism can occur. Postoperatively the patient has bilateral nasal packs (removed after 48 hours), requires morphine analgesia for 48 hours and codeine IM for 3 days, with hospital stay of approximately 5-7 days.

The Technique of Endoscopic Surgery

Endoscopic equipment and methods provide a minimally invasive approach, improved capabilities and wider application for transphenoidal pituitary surgery. The hardware comprises long and short solid lens rigid endoscopes with light source, camera, monitor and surgical instruments. An irrigation system clears blood and debris from the lens, avoiding repeated removal for cleaning (saving time and reducing mucosal trauma). An articulated arm clamps the scope in position for the later stages where bimanual surgery is required.

Endoscopes differ from surgical microscopes in that the light is transmitted to the tip of the scope, close to the surgical target and adjacent to the instruments providing significantly better illumination at depth. In addition the scopes give a wide-angled view and are manufactured with 0o, 30o, or 70o side-viewing lenses to see around corners. These features provide the surgeon with a highly magnified, bright, wide and detailed view of the anatomy with little surgical trauma and consequently little haemorrhage. Nasal packs are not required; the patient can breathe and smell normally and is discharged in 24-48 hrs as routine. Thus, the endoscopic technique has the advantages of reduced mucosal trauma, less bone removal, improved tumour removal, greater preservation of the residual pituitary gland and fewer complications than the traditional method. For more complex cases the endoscopes can readily be combined with Neuronavigation, providing real-time tracking of the endoscope tip relative to the patient's MRI studies.

The Extended Endoscopic Transphenoidal approach is used for tumours traditionally approached via craniotomy (such as craniopharyngiomas and meningiomas). This involves extending the bone removal into the skull base and dissecting the tumour from the nerves and vessels without retracting the brain at all. This is safer and carries much lower morbidity than craniotomy with early recovery and discharge. However, this is technically demanding and requires special equipment and advanced endoscopic skills. A further challenge with these operations is the difficulty of sealing the CSF-containing membranes at completion and so they always require a fat graft and pack, and sometimes a lumbar drain also. Thus with advanced endoscopic techniques the need for craniotomy in these tumours can be reduced substantially and completeness of resection improved.

Literature Review

Endocrine Outcomes

Mr Dorward has conducted a full review of the medical literature on endoscopic pituitary surgery, published as "Dorward N.L Endocrine outcomes in Endoscopic Pituitary Surgery: A Literature Review Acta Neurochirurgica: Volume 152, Issue 8 (2010), Page 1275." This study compared the combined endoscopic outcome data with similar microscopic series and revealed that for the majority of tumours the endoscopic results were at least equal to the microscopic results, as were complications. For functioning macroadenomas however, the study revealed that the endoscopic techniques achieves significantly better results.

NICE Conclusions for Endoscopic Pituitary Surgery

a) Tumour Clearance

On review of the available literature NICE concluded that "endoscopic transsphenoidal pituitary adenoma resection resulted in comparable surgical outcomes to conventional surgery" and this is generally accepted. However, the comparative studies do each demonstrate improvement in microadenoma cure rates compared to conventional surgery. Enhanced visualisation and the ability to view at acute angles within the pituitary fossa are expected to reduce the rate of residual adenoma resulting in a better overall cure rate.

b) Duration of Surgery

Few direct comparative studies have been published. The only high class paper to address operation time showed a significant reduction for endoscopic surgery compared with the conventional method. The study reveals that the operating time was initially similar and fell steadily with surgical experience with endoscopic equipment.

c) Nasal Packs

For conventional transsphenoidal surgery nasal packs are left in situ for 2 days to ensure mucosal adherence to nasal cartilage. There is attendant discomfort, blockage and pain on removal. Packs are not required in endoscopic surgery, as the mucosa is not stripped. This results in substantially reduced discomfort and a better overall experience. This may be particularly advantageous for acromegalic patients with respiratory obstruction and sleep apnoea due to tongue enlargement.

d) Post-operative Pain

There are no controlled studies with statistical analysis of pain scores in both techniques. However, the studies available have all commented on an apparent reduction in pain for the endoscopic group. The reduced hospital stay (see below) provides strong supportive evidence for this. In his own series Mr Dorward has found a significant reduction in morphine usage after endoscopic pituitary surgery compared with conventional surgery.

e) Hospital Stay

In their randomised controlled study comparing traditional and endoscopic pituitary surgery Cho & Liau demonstrated a statistically significant reduction in hospital stay for the endoscopic group. White et al similarly showed a statistically significant reduction and many cohort studies have shown a non-significant reduction. There are no studies showing the opposite effect. In their overview NICE gave the durations of stay as 2-5 days (median 3.5 days) for endoscopic surgery and 4-10 days (median 7 days) for conventional surgery, while Cappabianca and Jho have found 50% of patients stay just 1 night with the endoscopic method.

Safety

Complication Rates

No study has been published showing a higher complication rate with endoscopic methods and many studies have now been published that show lower complication rates for this technique, with a statistically significant reduction in nasal complications found by White et al. NICE commented that "the complication rate of endoscopic transsphenoidal pituitary adenoma resection is less than that of conventional surgery".

Benefits for the patient

  • Minimally invasive (no facial swelling / sinus pain)
  • No nasal packing
  • No nasal scar
  • Improved tumour removal
  • Reduced complications
  • Reduced post operative analgesia
  • Reduced hospital stay
  • Improved patient outcome