Assoc. Prof. Emma Duncan
Royal Brisbane and Women's Hospital, Brisbane.
Craniopharyngiomas are benign (non-cancerous) tumours arising in the area of the pituitary gland – usually above and behind the gland. They are extremely rare (around 1 person in a million present with this problem each year, so that about 20 cases will present each year Australia-wide). About half of all cases present in children less than 16 years of age, and between 6 and 13% of all intracranial (“brain”) tumours in children are due to craniopharyngiomas.
These tumours have a variable behaviour: they can be very slow growing but sometimes they can be more aggressive and grow quite quickly.
Craniopharyngiomas can be very variable in their structure – from mainly solid tumour to a mix of solid and cystic (fluid-filled) parts to mainly cystic. The fluid in the cysts can be oily, resembling engine oil, or can be shimmering with cholesterol crystals. The tumour often shows areas of calcification, which may be detected even on a plain skull x-ray.
Rathke’s cleft cysts are also uncommon benign growths, usually within the pituitary gland itself, and are a subset of the craniopharyngiomas. Rathke’s cleft cysts contain oily fluid within the cyst wall and do not usually have much solid structure otherwise. It is uncommon for them to cause symptoms.
The pituitary gland is made up of two parts – the anterior (front) and posterior (back). These two parts arise from separate areas in the developing foetus – the anterior part grows upwards from the roof of the mouth (from Rathke’s pouch) and the posterior part grows downwards from parts of the brain. These two parts then fuse together to form the pituitary gland. However, sometimes this developmental process is disturbed or imperfectly completed, and it is thought that this is what causes craniopharyngiomas and Rathke’s cleft cysts to develop.
Many of these tumours are asymptomatic. However, when symptoms develop, these are usually due to pressure and disturbance of the function on surrounding structures, particularly the pituitary gland and the hypothalamus. Pressure on the brain and obstruction to the fluid system can cause a build up of cerebrospinal fluid (CSF) within the brain (called hydrocephalus) and patients may develop headaches, nausea and vomiting. Pressure on the optic nerves may cause loss of vision. Pressure on the pituitary gland or on the pituitary stalk that carries signals to the pituitary gland from the hypothalamus may cause a loss of secretion of the hormones normally produced by the pituitary gland (see section on pituitary tumours for details of this).
As growth hormone and the gonadotrophins (LH and FSH) are important for normal growth and pubertal development, children may have growth retardation and pubertal delay. In adults, partial or complete pituitary insufficiency may result (see section on pituitary tumours for details of this this). Craniopharyngiomas may also affect the hypothalamus (which lies above the pituitary gland). As the hypothalamus controls secretion of the normal pituitary hormones from the pituitary gland, pituitary deficiency (hypopituitarism) may result (see section on pituitary tumours regarding this also). The hypothalamus also controls some behaviours, such as eating, drinking and sleeping, and influences memory and temperature control. Patients may be excessively sleepy and forgetful, may have marked overeating (hyperphagia) and obesity, may not complain of thirst, even when they have large fluid losses, and may overheat in the summer months or after exercise.
Once a tumour is suspected clinically due to symptoms and signs such as visual loss, headache, or loss of pituitary function, a scan of the head with an MRI scan (magnetic resonance imaging) or a CT scan (computerised tomography) will usually diagnose the lesion. Sometimes it can be difficult to differentiate these tumours from other tumours in the pituitary region. However, if a combination of cysts and solid elements is seen, or if there is evidence of calcification in the tumour, it suggests that the tumour might be a craniopharyngioma. If a clearly cystic lesion is seen within the pituitary fossa, it might suggest a Rathke’s cleft cyst.
These tumours often require surgery. The type of surgery depends on many factors, including the size of tumour, the site of the tumour, and the involvement of other structures that the tumour is invading or pressing on. Hydrocephalus may require a shunt to be inserted to drain CSF from the brain to the abdomen, thereby relieving the pressure in the brain. Occasionally, some cysts can be drained without more extensive surgery; this procedure can be repeated if the fluid re-accumulates. However, craniopharyngiomas usually require removal, either a trans-sphenoidal operation (through the nose) or a craniotomy (through the bone of the skull).
Before surgery, it is important that the pituitary function is carefully assessed so that any deficient essential hormones are replaced before proceeding to surgery.
The surgeon often has to balance complete removal of a craniopharyngioma against ensuring minimal damage to the underlying brain and other important structures. This means that in some cases a complete removal may not possible without unacceptable side-effects and brain damage. Therefore, in adults radiotherapy is almost always offered after surgery for a craniopharyngioma, to control the growth of any residual tumour. In children, radiotherapy is often offered after surgery but this depends on the age of the child. Although Rathke’s cleft cysts can reoccur, their surgical management may be more simple and radiotherapy is not always offered to these tumour types.
After surgery and/or radiotherapy, the function of the pituitary gland is reassessed carefully and deficient hormones replaced.
Unfortunately, it is not uncommon for craniopharyngiomas to regrow, and patients may require further therapies, most commonly surgery and/or irradiation. The exact number of patients who have recurrent disease is hard to quantify as it depends upon the type of initial therapy (for example, whether the surgeon tried to remove it completely or only partially; whether radiotherapy was given after the first operation; etc.). Overall, around a third of patients with initial surgery and radiotherapy will need further management; more than half of those with partial removal will need further management. Craniopharyngioma cysts that have undergone drainage can re-accumulate; sometimes the cysts can be drained again without the need for more radical surgery. Rathke’s cleft cysts usually do not re-accumulate or require radiotherapy.
As these tumours can grow back after many years, and as the long term results of radiotherapy can affect the function of the pituitary and the brain, it is imperative that patients with craniopharyngiomas and Rathke’s cleft cysts are followed up lifelong, usually by an endocrinologist and a neurosurgeon.
Updated: March 2013