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Pituitary surgery

Pituitary tumours are the third most common intracranial tumour and transsphenoidal surgery is the commonest approach for management, with lower overall complication rates comparable with conventional transcranial surgery

Anatomy

The sphenoidal sinuses form the inferior and anterior walls, and this anatomical relationship is used to approach the pituitary gland in transsphenoidal resections.

The dorsal sella of the sphenoidal bone forms the posterior walls.

The lateral walls are closely related to the cavernous sinuses, internal carotid arteries (ICAs) and cranial nerves III to VI.

These structures are at risk of damage by pathology or during surgery, potentially causing massive haemorrhage, stroke or cranial nerve palsies

Compromise to the optic apparatus, typically in the context of a postoperative sella haematoma, is rare, with a reported rate of 0.4–1.2%, but requires an emergency return to the operating theatre

Physiology

Epidemiology

Pituitary tumours account for 10–15% of all adult brain tumours, with a prevalence of 16.7%

Most pituitary adenomas (PAs) are benign, slow-growing tumours with a poorly understood aetiology

Pituitary carcinomas are extremely rare, accounting for less than 0.2% of all pituitary tumours

Classification:

• size

  • 10mm → macroadenoma

  • <= 10mm → microadenoma
• hormonal secretion
  • non-functioning (36-54%)
  • functioning (46-64%)
    • PRL
    • GH
    • ACTH
    • thyrotropin

Presentations

• local mass effect
  • headache
  • visual change
    • bitemporal hemianopia
    • ↓ visual acuity
• hormonal
  • hyposecretion ∵ pituitary gland compression
    • panhypopit
    • DI
    • (rarely) pituitary apoplexy from haemorrhage / infarction into gland
      • ↓consciousness
      • headache
      • visual defect
  • hypersecretion
• incidental / asymptomatic

Acromegaly

Excessive GH production after epiphyseal closure → acromegaly
tumours occurring before puberty → gigantism

Soft tissue and bony expansion complicate airway management, caused by

• kyphoscoliosis,
• prognathism,
• macrognathia,
• macroglossia,
• pharyngeal and laryngeal tissue hypertrophy
• rarely recurrent laryngeal nerve palsy
  25% of patients with acromegaly develop associated thyroid goitres, causing tracheal compression

expect difficult Airway esp. w/ evidence of laryngeal involvement e.g. HOV, dysnpoea, snoring
→ discuss awake intubation

Comorbidities:

• refractory hypertension,
• left ventricular hypertrophy,
• ischaemic heart disease,
• cardiomyopathy,
• biventricular dysfunction,
• arrhythmias,
• impaired glucose tolerance or overt diabetes mellitus
  OSAS has been observed in up to 80% of patients with acromegaly and may be associated with a difficult airway and right heart failure

Patients with clinically severe OSAS or acromegaly-related high output heart failure may warrant preoperative somatostatin analogue therapy to reduce anaesthetic and surgical risks caused by excess GH production

Cushing's

Commonly observed features are

• central Obesity
• GORD
• metabolic disturbances,
• cardiovascular disease (e.g. hypertension and left ventricular hypertrophy)
• DM
  Other considerations:
• proximal myopathy + obesity complicate airway Mx & ventilation
• prothrombotic state

Prolactinoma

Prolactin-producing adenomas are the commonest pituitary tumours, manifesting as galactorrhoea, secondary hypogonadism, menstrual disturbances in females or erectile dysfunction in males

Surgical approaches

transsphenoidal approach is currently the standard for surgical management of PAs

The endoscopic technique is the gold standard technique for transsphenoidal resections.

Intraoperative computer-assisted navigation and guidance aids the surgeon, particularly for revision surgeries or anatomical mapping.

Intra-op

Principles of neuroanaesthesia should be observed throughout, including

• induction of anaesthesia with minimal cardiovascular disturbance,
• optimal cerebral perfusion and oxygenation,
• meticulous haemodynamic control,
• readiness to manage intraoperative complications
• smooth emergence from anaesthesia.

Airway

presence of acromegaly increases the risk of a difficult airway four-to five-fold

Oral intubation with a reinforced tracheal tube placed away from the operative site is preferred

The mouth and pharynx can be packed to prevent bleeding into the glottis and entry of blood into the stomach, which may precipitate PONV

SGA

• controversial
• Pros
  • ↓ laryngeal stimulation thus cardiorespiratory responses
• Cons
  • risk of airway contamination / aspiration

nasal preparation

• beware of arrhythmogenic & hypertensive effects from agents used

I.V. TXA at induction has been shown to minimise bleeding and improve surgical field quality

Monitoring

Foley: indicated in complex cases or if DI anticipated
A line

• frequent haemodynamic change
• proximity to carotid arteries / cavernous sinus

Central venous catheterisation is rarely required unless cardiovascular compromise is present, but wide-bore i.v. access is recommended

Patients are placed supine with a 20–30° head-up tilt to improve venous drainage

Conduct of anaesthesia

meta-analysis demonstrated that TIVA was associated with reduced blood loss and improved surgical visualisation compared with an inhalation anaesthetic technique. However, neither method has shown to be superior in affecting quality of postoperative recovery

For resection of large and invasive adenomas, a lumbar drain can be inserted at the beginning of surgery to minimise CSF leak, by reducing the pressure at the site of surgery and allow the injection of sterile 0.9% saline to promote the visibility of suprasellar tumours through transmission of pressure in the CSF column. However, there is limited evidence to support this practice

The surgical team may request the anaesthetist to perform a Valsalva manoeuvre to

• improve visualisation of tumours with suprasellar extensions,
• check for CSF leaks
• ensure adequate haemostasis

The surgical team should also inform the anaesthetic team if CSF leak is present, as this limits the ability to maintain a 30° head-up tilt after surgery.

Analgesia

TSS not typically painful and can be managed with simple analgesics, combined with short-acting opioids for breakthrough pain.

Non-steroidal anti-inflammatory drugs are generally avoided because of concerns over bleeding.

Preventing PONV is crucial, as vomiting and retching can increase venous and intracranial pressures, increasing the risk of bleeding and can also unmask previously unidentified CSF leak

Abx

Current best evidence shows that prophylactic antibiotics do not significantly alter the rates of postoperative meningitis or sinus infections

Steroid

Perioperative steroid replacement practices vary and there is no unifying guidance.

Anaesthetists should be familiar with local protocols and it is essential that endocrinologists are involved

Complications

Major complication rare

most commonly venous bleeding & CSF leaks

Venous bleeding is generally well controlled by pressure application, haemostatic agents or additional reverse Trendelenburg

Prompt intraoperative repair of CSF leaks is essential given the potential for serious complications, such as meningitis and pneumocephalus.

Repair techniques use autologous fat or fascia grafting from the thigh or abdomen to fill the sella turcica, or use synthetic materials such as Surgicel.

If there is an anticipation autologous tissue may be required, the thigh and abdomen should be prepared at the beginning of surgery.

Injury to the ICA, although rare, is one of the most serious and potentially fatal complications of TSS

Venous air embolism is a rare complication

Extubation

remove throat pack

suction clear airway

Patients at the greatest risk of airway-related complications are those with acromegaly, class III or above obesity or sleep apnoea; these patients may benefit from extubation over a ventilation catheter or solid intubating stylette

The aims for smooth emergence for anaesthesia are to

• ↓ coughing,
• ↓ bleeding,
• prevent dislodgement of the fat graft,
• ↓ CSF leak
• prevent airway catastrophes

Early reintubation or insertion of a supraglottic device should be considered if airway compromise occurs post extubation, as excessive positive pressure with facemask ventilation may precipitate CSF leaks, pneumocephalus and bleeding.

There are no clear guidelines or consensus regarding the use of continuous positive airway pressure (CPAP) after surgery in patients with OSA.

Current practice avoids CPAP where possible to minimise risks of

• CSF leak,
• tension pneumocephalus
• meningitis.

Post-op

Regular observations for visual and neurological changes are required in the immediate postoperative period to detect any deterioration indicating a life-threatening emergency

The most frequent postoperative complications are CSF rhinorrhoea and DI

To reduce the risk of postoperative CSF leak, patients are given stool softeners and asked to avoid straining and nose-blowing for up to 6 weeks after surgery

Central transient DI usually develops in the first 24 h. Early identification is necessary, by monitoring for signs and symptoms, fluid balance, urine and serum osmolarities and electrolytes

Other potential complications include

• epistaxis,
• sinusitis,
• meningitis,
• hypopituitarism,
• cranial nerve palsies,
• visual impairment,
• cerebral ischemia,
• stroke
• hydrocephalus.

References

Anaesthesia for Pituitary Surgery - BJA Ed