General Considerations
General Anatomy and Parts
The pituitary gland is a small organ that sits underneath the base of the brain and immediately above the back of the nose (on top and behind of one of the nasal sinuses called the sphenoid sinus) in a pocket within the skull called the pituitary fossa or sella turcica (since it reminded early anatomists of a Turkish saddle).
Its location is explained by the fact that the front two thirds of the gland (the anterior lobe) develops in the embryo from the roof of the nose and the back one third (the posterior lobe) from the brain itself, with a small cleft known as Rathke’s cleft in between.
The posterior lobe remains connected to the brain by the pituitary stalk. The gland is surrounded by a rich collection of blood vessels and is bordered on each side by the cavernous sinuses through which run the carotid arteries on their way to supply the brain with blood and a variety of nerves that help move the eye and control sensation in the face.
Immediately above the sella in the “suprasellar cistern” the optic nerves run back from the eye to the brain, meeting together in the middle and forming the optic chiasm. There is therefore a log jam of important structures in the immediate vicinity of the pituitary gland that may become involved in various disease processes.
Dr Brennan is highly trained and experienced in the surgical treatment of conditions of the brain including brain tumours and pituitary tumours.
Rathke’s Cleft Cyst
The normal space between the anterior and posterior lobes of the pituitary is referred to as Rathke’s cleft and is a leftover of the extension from the mouth and nose in the embryo forming the anterior pituitary known as Rathke’s pouch. In some situations the cells which line this space may secrete fluid leading to the formation of a cyst, either in the cleft itself or elsewhere if some of these leftover cells are “trapped” as the gland develops. Although these cysts may not change at all over time, in other cases the cysts may gradually expand as more and more fluid is secreted by these cells. In this way, although the lesions are not in fact true tumours, the increase in size of the cyst may lead to problems of mass effect as described above for pituitary tumours. In this setting surgery may be needed to drain the fluid and debride the cyst wall.
Craniopharyngioma
Like Rathke’s cleft cysts these lesions are not true tumours but may behave as such due to their tendency to gradually get larger and compress and insinuate themselves around the structures in the suprasellar cistern and base of the brain. They are thought to arrive from cells that started as part of Rathke’s pouch but undergo partial changes into a more aggressively growing cyst. They can occur in many locations in or around the pituitary, as well as higher up towards the brain and even within the fluid compartments of the brain itself. They occur more commonly in children in the first decade of life although a different subtype can occur in adults most commonly in the fifth decade. They often require combinations of treatment such as surgery, medications, and sometimes radiotherapy.
Rarer lesions
- Other primary tumours such as granular cell tumour and the very rare malignant pituitary carcinoma.
- Meningioma (arising off the lining of the sella),
- Other cysts such as arachnoid cysts and so called “inclusion cysts” such as dermoid and epidermoid cysts
- Metastases (e.g. from breast cancer or lung cancer)
- Germ cell tumours (particularly germinomas in children)
- Infections (pituitary abscess)
- Medical conditions with inflammation (such as lymphocytic hypophysitis, sarcoidosis, etc).
Workup and Investigations
The optimal management of pituitary lesions more often than not requires a team approach between a number of different medical specialists, both before, during, and after treatment.
A careful and thorough assessment is needed to determine what might be going on and help decide on the best treatment options. Most patients can expect to need to have an MRI scan as the key radiological test to sort out the anatomy involved, often supplemented by CT scan particularly if surgery may be needed. Visual function can be assessed by physical examination including the visual fields, visual acuity, and by looking into the back of the eye with an ophthalmoscope. Often, this is supported by review by an ophthalmologist (a doctor specialising in diseases of the eye). The function of the pituitary gland can be checked with a variety of blood tests most often with the help of an endocrinologist (a doctor specialising in diseases of hormones and metabolism). In more complex cases additional hormone assessment may be needed from urine collections and on some occasions inpatient tests done in hospital to challenge the pituitary and measure its responses (sometimes via a type of angiogram referred to as petrosal venous sinus sampling). Not all of these tests will be required in every case and each patient needs an approach tailored to their on individual issues.
