The most important tests done prior to surgery are the radiology tests.
This is usually the first investigation undertaken for a suspected pituitary tumour. A lateral view of the skull often shows an enlarged pituitary fossa and may shows signs of erosions. This radiograph is still of great importance in the planning of surgery.
The current imaging technique of choice is the CT scan. CT scans are extremely valuable in the diagnosis of macroadenomas, but are less so in the diagnosis of microadenomas. The cut off size between good surgical correlation to CT findings seems to be adenomas of above 6mm in diameter
The advent of this relatively new imaging technique has improved the imaging of suprasellar and parasellar extensions of the pituitary. The advantages of the MRI scan is that it is able to demostrate an intact sellar diaphragm, the presence of a haemorrhage in the pituitary, and for measuring the changes of adenoma size after medical treatment.
This test is used for the localisation of ACTH-secreting tumours when current radiological techniques have failed. This test can be used to accurately distinguish pituitary and ectopic sources of ACTH causing Cushing's syndrome. The principle of the test is to sample the blood from the petrosal sinuses draining the pituitary gland, to compare the levels of ACTH with those found in the peripheral blood. A petrosal:peripheral ratio of > 2, indicating excess ACTH from the pituitary, is necessary to diagnose Cushing's disease with confidence. Accuracy can be improved using CRH stimulation to exaggerate the difference.