Dr C Hamilton-Wood
Consultant Radiologist, Royal Devon and Exeter Healthcare NHS Trust

Before the advent of these techniques, imaging the pituitary was difficult and often unsatisfactory. Plain films gave only an assessment of the bony sella (space) in which the Pituitary gland sits, but could not show the gland itself.

Some information was derived from invasive and now obsolete techniques using air injected through a lumbar puncture approach.

With CT (Computer-Assisted Tomography), and subsequently MR (Magnetic Resonance), it became possible to obtain images of both the normal and abnormal pituitary gland. Both these techniques are made possible by the combination of advanced imaging and the arrival of modern computer technology, and together they have made an enormous impact on diagnosis and monitoring techniques.

In a CT scanner, data is acquired as a set of individual measurements. A thin X-ray beam traverses the area of the body to be examined, and the effects of the interaction between the X-ray beam and all the tissues in its path are recorded, and this produces a measurement.

This measurement is repeated many times and the data obtained is then processed by the computer leading to the reconstruction of an image of the tissues being examined.

CT scanning, therefore, revolutionised the ability of radiologists to image the pituitary gland, but it should be remembered that the machine still subjects the patient to X-radiation and there is a limitation on the number of angles from which the images can be taken.

With the arrival of Magnetic Resonance Imaging (previously known as Nuclear Magnetic Resonance) some of the problems involved in using X-rays have been overcome and, indeed, MR as it is now called, has shown some clear advantages over CT scanning.

The physics of MR is extremely complex, but in essence the patient is placed in a very strong and homogenous magnetic field (Fig 1). A radio wave is sent in, interacts with the protons of water nuclei of which there are a great many in the human body, and as a result of this interaction, or resonance, the protons emit a radio signal which is picked up and used for the reconstruction of the MR image.

Fig 1. A modern MR machine showing the position of
the patient in its cavity, the long axis of which
relates to the direction of the magnetic field.

MR imaging is associated with some distinct advantages over CT and these include much higher resolution (the ability to resolve or separate two closely related structures), and a much higher contrast between tissues.

As a result, MR scanning can show, sometimes in exquisite detail, very small structures, and differentiate between structures of different physical characteristics.

In addition it does not use any X- or other potentially harmful irradiation, and may even supply useful information regarding the characteristics of flow within blood vessels, which are included in the slices examined during the study.

MR scanning, however, must be used judiciously, and it should be remembered that because of the very strong magnetic fields employed, any patient with metallic foreign bodies (especially in the eye), and those patients with metal surgical clips particularly in brain surgery, as well as those patients with pace-makers and metallic heart valves, should never undergo an examination in an MR scanner as the metal contents of these structures could be adversely effected, and indeed fatalities have been recorded as a result of imprudent use of an MR scanner in such patients.

In the context, therefore, of previous surgery, great care should be take in determining the exact nature of that surgery and whether or not para-magnetic clips were used. It may be necessary to resort to a plain radiograph to determine whether any such clips are present, and great care exercised if any are noted.

In the space of only 20 years, the ability of the radiologists to image the pituitary gland has been revolutionised by the appearance first of CT and subsequently MR; it is now possible not only to see the normal pituitary gland (Fig 2) and display this information in any plane considered diagnostically desirable, but it is also possible (with no known biological hazard) to demonstrate and follow-up abnormalities of the pituitary gland (Fig 3) which can give very important information to the Endocrine Physician and Surgeon, as well as to patients and their families.