Diagnosis of the Pituitary Tumour
Pituitary tumours are often diagnosed casually while performing a brain imaging test. The ideal imaging test to assess a pituitary tumour is a nuclear magnetic resonance scan, which can evaluate the type of pituitary tumour, the size, and the relationship with the neighbouring structures.
When the presence of a pituitary tumour is confirmed, blood tests are performed to determine the pituitary production of hormones, as well as the peripheral ones, and to assess if there is any hormonal deficiency or over-production.
In the case of hormonal over-production by a functioning adenoma, the clinical picture usually suggests the hormone that is being produced in excess, and for this reason a more complete initial analytical study is performed. It is also recommended to perform a complete ophthalmological assessment.
Tests to diagnose a pituitary tumour
Blood tests. In the study of pituitary function, it is essential that the blood specimen is collected under certain conditions in order to be able to correctly evaluate the different hormones. The blood is drawn first thing in the morning as the production of hormones varies throughout the day (circadian rhythm). Occasionally, it may be necessary to take samples in the afternoon or at night to evaluate the circadian rhythm. In general, the analysis of blood is sufficient, but if a Cushing’s disease is suspected or it needs to be ruled out, it is often necessary to obtain a 24-hour urine specimen and/or nocturnal saliva specimens.
Function tests. They are used to study a possible excess or deficiency in hormone production. Hormone deficiencies are evaluated using stimulation tests. A stimulating factor is injected or a physical stimulation is induced with thirst or exercise, and blood specimens are obtained over a period time in order to see the hormonal response to this stimulation. In general, they are well tolerated and are usually performed as an outpatient. In the case of suppression tests, a hormone over-production is assessed. After a few hours, a blood specimen is drawn in order to measure the hormonal response.
Brain magnetic resonance (MR) scan. It is the technique of choice. It does not use radiation, unlike computed tomography (CT), and it is based on the movement of atoms produced by the magnetic fields created. With these movements, an image is reconstructed of the inside of the brain where the pituitary is found. Contrast is normally used, and any associated side effects are very uncommon. It is not recommended (contraindicated) in pregnant women, carriers of metal implants, and cases of claustrophobia.
Computed axial tomography (CAT) scan. It is an alternative to the MR scan but it produces a less precise image of the pituitary. It takes less time, does not cause claustrophobia, and uses radiation.
Petrosal sinus catheterisation. It is employed in patients with corticotropin (ACTH) producing tumours, with the aim of locating the origin of the production (generally at pituitary level, but in some cases at an ectopic level). To do this, some fine tubes are inserted into the groin and are positioned at both sides of the pituitary, in the petrosal sinuses. After an injection of the stimulating hormone ACTH, simultaneous specimens are obtained from both sides and from a distant vein at various times, and it is evaluated if the ACTH production is at pituitary level or in another location.
Ophthalmology Assessment. Due to the proximity with the optical path, there may be changes in the visual field, even going unnoticed by the patient. For this reason, it is important to make an ophthalmology assessment, especially when the tumour is in contact with the optic chiasm. To do this, a direct examination of the retina is performed by means of back-of-the-eye (fundus) with prior dilation with drops, and a campimetry that enables its visual field to be sketched. An optical coherence tomography (OCT) is also performed, in order to obtain an image of the retina and assess any damage.
Genetics study. This is done when a familial type is suspected, either due to a family history or due to the form of presentation of the pituitary tumour or other symptoms presented. This is done by analysing a blood specimen.
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