The differential diagnosis for a sellar mass includes:
- Pituitary Adenoma
- Internal Carotid Artery Aneurysm
- Optic Nerve Glioma
- Cavernous Sinus Thrombosis
The key is to learn about the anatomical relationships. Whilst performing surgery it is important to be able to identify key structures, and avoid the big vessels the carotid and the basilar artery being one!
Anterior: Sphenoid Sinus
Posterior: Midbrain and Basilar Artery
Inferiorly: Sphenoid Sinus
Laterally: Cavernous Sinus
Superiorly: Optic Chiasm
Keep Note of the Lamina Terminalis this will be of note in the future with its relationship with the 3rd ventricle (floor)
Tumours of the Pituitary Gland are generally benign occurring from the anterior portion of the gland
They were previously classfied according to the microscopic appearance:
- Eosinophilic cells- Prolactin and GnRH. Acromegaly can be caused by co-secretion with prolactin.
- Basophilic cells- ACTH, TSH, FSH,LH
- Chromophobe cells- Non-FUnctioning
They are classified whether they are microadenoma (<1cm) or macroadenoma (>1cm)
Presentation of Pituitary Tumours
- Present with headaches, visual field defects
- Hydrocephalus- with compression of the 3rd ventricle (if vertical compression onto the hypothalamus) that forms the floor of the 3rd ventricle
- Elevated Prolactin due to either secreting prolactinoma or due to the Pituitary stalk effect.
- Pituitary Apoplexy
- Hypersecretion e.g GH secreting tumour Acromegaly
Growth Hormone Hypersecretion
Growth Hormone is stimulated by GnRH. Note that GnRH release is pulsatile and hence is not measured in the blood tests. Acromegaly causes a number of distinct features and characteristics that can be learnt in endocrinology.
Hyperglycaemia should suppress GH secretion and hence the glucose tolerance test can be used as a diagnostic aid.
Measuring Prolactin is essential because this can be managed medically and SHOULD NOT BE FORGOTTEN.
Prolactin inhibits GnRH that stimulates FSH and LH and hence prolactinoma can cause amennorrhea/infertility. Galactorrhea is another symptom.
Other causes of hyperprolactinoma include:
Hypothyrodism (TRH Stimulates Prolactin)
Anti-psychotics (dopaminergic drugs)
Hypothalamic lesions e.g craniopharyngioma or Pituitary stalk syndrome. Prolactin is under tonic control via Hypothalamus or raised intra-sellar pressure prevents dopamine from inhibiting prolactin therefore raising prolactin levels.
Cushings syndrome is generally caused by an adrenal adenoma, ectopic ACTH secretion (e.g malignancy) but in rarer circumstances pituitary adenoma. Excessive hypersecretion from ACTH produces Cushings Disease which displays symptoms of Cushings syndrome. In order to suppress ACTH secretion these patients require high dose dexamethasone to suppress cortisol by>50%.
Note patients with excessive ACTH secretion may present with hyperpigmentation due to increased alpha-MSH secretion a precusor of pre-opiomelanacortin.
Large tumours may cause destruction of pituitary function leading to pan-hypopituitarism. The important aspect of this is the order in which the hormones tend to be affected
- Growth Hormone and Gonadotrophins tend to be affected first
In order to distinguish which hormones have been affected a combined pituitary stimulation test can occurr:
- GH: Insulin Tolerance Tesrt
- ACTH: Short Synthacten Test
- GnRH injection
- TRH injection (will stimulate both thyroxine and prolactin)
Assessment of a Patient with Pituitary Mass
- The usual blood tests that are essential as stated below- a full pituitary screen
- Visual Fields Assessment
- MRI of Pituitary- extent of the tumour to the optic chiasm
- Bedside Visual Field and Perimetry
Complications of Trans-Sphenoidal Surgery
- Hormonal Imbalance including hypopituitarism, diabetes insipidus
- Empty Sella Syndrome- chiasm retracts into the evacuated sella
- Hydrocephalus- 3rd ventricular obstruction, or tumour oedema
- CSF Leakage- causing meningitis and cerebral abscess
- Air entering the cranial cavity- called Pneumocephalus again acts as a resevioir for bacteria to enter the cranial cavity
- Carotid Artery Rupture
- Damage to structures in the Cavernous Sinus
The Posterior Pituitary stimulates the secretion of ADH. If there is a lack of anti-diuretic hormone post-operatively you will find the patient will become excessively thirsty and the urine output will significantly increase.
The hallmark of diagnosing diabetes insipidus:
Urine Specific Gravity <1.005 (decreased solutes in urine)
Urine Osmolality of <200mosmoles
Sodium may be normal or high
Increased Urine Output (>1 litre over every 4 hours is significant)
These patients can be given desmopressin importantly. They should also have endocrinology input and daily UEs till stable
The following information is based upon the Society for Endocrinology guidelines who have provided a fantastic PDF on the management of pituitary apoplexy.
This is a medical emergency that can lead to catastrophe. For your level at medical school, it can be defined as haemorrhaging or infarction into the tumour within the pituitary gland. This can often be accompanied by extra-ocular palsies (most commonly 3rd nerve palsy cavernous sinus involvement) and rapidly progressive visual failure (bi-temporal hemianopia)
Pituitary apoplexy can present in the sameway as a Sub-Arachnoid Haemorrhage with fever, neck stiffness and photophobia.
- Severe onset headache with the exclusion of a sub-arachnoid haemorrhage and meningitis
- Pre-existing pituitary mass
- Neuro-opthalmic symptoms
This medical emergency can be triggered by hypertension, surgery, pregnancy, trauma, pituitary dynamic studies and coagulopathies
Management Includes the following:
- Blood tests: FBC, U’E, LFT’s, Coagulation, T4,TSH,IGF1-,GH, Cortisol, LH,FSH, testosterone (men) and oestrodiol (females) and don’t forget Prolactin
- MRI Pituitary (sensitive in 90% of patients). If MRI contra-indicated than this requires CT Pituitary
- CT Head excludes SAH
- Bedside Visual Perimetry
- Hydrocortisone Injection 100mg IV stat bolus followed every 6 hourly if haemodynamically unstable, visual field deficit, deteriorating conscious levels.
- Urgent referral to the Neurosurgical and Endocrine team
Early operative management is required if significant visual field deficit, deteriorating consciousness. This is often by trans-sphenoidal surgery- which is done in conjunction with ENT Surgeons.