Though the lateral skull x-ray will show gross changes of the sella turcica indicating a pituitary space occupying lesion or show suprasellar calcification suggesting a suprasellar craniopharyngioma, the MRI is the imaging technique of choice for demonstrating an intra- or suprasellar mass. In addition, the MRI when used with gadolinium enhancement can show the relation of the supra- and para-sellar tumor extension to neural tissue. In this respect the MRI is clearly superior to the CT, which can be useful in those patients in whom the bony structures of the skull base need to be examined. Unlike CT however, MRI will not show the calcification associated with craniopharyngioma. Digital or MRI angiography can show vascular abnormalities, i. e. intrasellar aneurysms (see chapter 4, Radiology of the Hypothalamus and Pituitary).

Since changes in vision are often early signs of tumor progression, ophthalmological investigations are useful in the primary diagnosis as well as during follow up. Goldmann perimetry is most frequently performed to document visual field defects though computerized perimetry (Octopus) is more reliable. Sometimes visual evoked potentials (VEP) can be helpful in demonstrating lesions located along the optic pathways. VEPs may be useful in discriminating simple compression from severe demyelinating lesions of the optic pathways.

Full evaluation of pituitary function is needed in all patients with a pituitary hypothalamic tumor (7). The latter can often not be preformed by measuring basal hormones only. Thus, stimulation tests may be required (table 5), (38)). These tests are designed to assess target gland function and pituitary hormone reserve, ie. for hypopituitarism.

Tests which asses the hypothalamic-pituitary-target gland axis, particularly adrenal axis are most important. The insulin hypoglycaemia test, which stimulates ACTH, GH, and PRL secretion, is still the gold standard for testing anterior pituitary function (39). However, this test should not be performed in patients more than 65 years of age, or those with coronary disease, uncontrolled hypertension or epilepsy, because of the high risk of complications.

The short synacthen test with 250 mcg ACTH 1-24 is used in many centres as an alternative to the IST. There is still debate about the accuracy of this test, its sensitivity and positive and negative predictive value. (39.1). This has again been addressed in a large retrospective survey from UK and deemed to be a safe reliable replacement test for the IST (39.2). With excellent long-term predictive accuracy for assessment of the hypothalamic – pituitary – adrenal axis this test should now replace the IST, although it cannot assess growth hormone reserve for which other tests are required.

Stimulation of the anterior pituitary with a combination of all releasing hormones is almost as effective as the hypoglycaemia test, though this global test is at present very labor intensive and is not often necessary. Patients with pituitary tumors and hypopituitarism (no rise during insulin hypoglycaemia and subnormal target gland hormone levels) who have a normal hormone rise after administration of releasing hormones usually have stalk compression. In contrast, patients with pituitary tumors unresponsive to releasing hormones, often normalize their pituitary function after removal of the pituitary mass (9). Impingement on the pituitary stalk or hypothalamic involvement is also indicated by hyperprolactinemia and diabetes insipidus. Tests for diabetes insipidus are frequently indicated in patients with suprapituitary masses and not uncommonly in NFPA patients after pituitary surgery, especially when urine volume exceeds 3 litres/day.

The classical triad pointing to a hypothalamic lesion is hyperprolactinemic anterior pituitary failure, diabetes insipidus and visual field defects (Tab. 6).

In addition to the measurement of pituitary hormones during stimulation tests (table 5) target gland hormones (thyroid, adrenal and sex hormones) need to be measured. (Table 7)

For example the pituitary thyroid axis can be assessed by free T4 and TSH levels. In those institutions where TSH is the single screening test of thyroid function it is essential to request free Thyroxine level. The pituitary gonadal axis can be assessed by testosterone, oestradiol and basal gonadotrophin levels and the GnRH stimulation test is reserved for those patients in whom fertility induction with pulsatile GnRH is contemplated.

Posterior pituitary function is evaluated by measuring daily urine output and serum and urine osmolality, and is tested formally by the water deprivation/desmopressin test. Often partial diabetes insipidus becomes manifest only after appropriate hydrocortisone substitution therapy in ACTH deficient patients.

In patients with intra, supra- and para-sellar tumor, PRL must be measured. When serum PRL-concentration is over 5000 mU/l, the diagnosis is most likely a prolactinoma. Moderately elevated serum PRL in the presence of a large space occupying lesion is often due to stalk compression rather than a true prolactinoma, but this cannot be excluded. When measurement of PRL is performed by immunoradiometric assay high PRL-levels may be missed due to the "hook effect" (40). Thus, a macroprolactinoma may be diagnosed as a NFPA, which would have serious therapeutical consequences. This can be avoided when the serum samples are measured in several dilutions.

TRH stimulation test with measuring of ? -subunits and gonadotropins may be of importance in classifying endocrine inactive adenomas as silent gonadotropinomas (see table 5). However, a TRH-test should not be done in a patient with a macroadenoma, because of serious side effects which have been reported, i. e. pituitary apoplexy, sudden visual loss, etc. (41). beta -hCG and alpha -fetoprotein in the peripheral circulation or the CSF may help to identify a suprasellar mass as a germ cell tumor (28).

Pituitary hypothalamic space occupying lesions need to be treated, either by surgery, radiotherapy or both. In special situations medical therapy may be indicated.

A more complex problem is presented by the accidentally discovered pituitary mass (incidentaloma). Clinical judgement is needed not only in determining the extent of evaluation but also in respect to therapy and follow-up. In the absence of visual field abnormalities and endocrine dysfunction, initial periodic follow-up is indicated (MRI scan at 12 month intervals) in order to detect whether the tumor will develop into a larger space occupying lesion. Limited information suggest that this will occur rarely in patients with microadenomas but in up to 25% of larger tumors (1).

Since patients with pituitary or hypothalamic tumors are rarely cured completely or at least harbor one or several hormonal deficits needing substitution therapy, lifelong follow-up of these patients is warranted.