Magnetic resonance imaging of hypophysis
I.-V. Malla Huesh
Hypothalamic-pituitary diseases represent with wide variety of symptoms in regard with changes in the endocrine function. Magnetic resonance imaging has a crucial role in detecting the morphologic appearance in physiologic conditions, malformative diseases and acquired pathologies. The MR-imaging is established as the method of choice in assessing and précising the changes in the hypothalamic-pituitary axis. The pituitary gland is a complex structure with an important role in the homeostasis of the organism even though it is so small? It is surrounded by bony structures, vessels, nerves and the brain parenchyma. It consists of three parts – anterior called – adenohypophysis, posterior – neurohypophysis and pituitary stalk. The anterior part comprises about 75% of the gland. Computed tomography (CT) has a limited role in detecting the pituitary gland. It is mainly used in cases of elevated intracranial pressure due to suspected apoplexy. The gland’s small size, relation to other structures and its soft tissue characteristic make it an accessible region of interest for detecting with MR-imaging. The lack of ionizing energy and the technical advances in the MR-methods are responsible for the creating images with better spatial resolution and signal to noise ratio. The examination is carried out on a standard protocol. It is important that thin slices are executed in sagittal and coronal planes. Performing a sequence, regarding the brain parenchyma is essential, since many malformations of the pituitary gland are associated with other congenital conditions. The examination starts with a T1W sequence to assess the normal anatomic condition of the gland. The intensity of the adenohypophysis is compared to the one in the pons. It is hypointense, whereas the neurohypophysis is hyperintense, due to the lipid neurosecretory granules transported along the hypothalamic-pituitary axis. Т2W-images in coronal plane are used to evaluate the hypothalamus, pituitary stalk, optic chiasm, olfactory nuclei and sulci. FLAIR – sequences with its advantage in suppressing the signal from the cerebrospinal fluid is useful in case of meningeal involvement in hypophysitis. DWI is essential in case of ischemia, apoplexy and associated necrotic changes. Contrast medium application is not compulsory, but it increases the sensitivity of the method, especially in young patients. The contrast used is Gadolinium, applied according to the body weight. After contrast application the gland enhances homogeneously. MR-methods made are responsible for throwing light upon the normal images of the pituitary gland from the neonatal patients to adults, explaining the malformative and rare conditions, leading to disturbances in the hypothalamicpituitary axis. The most common reason for pathologic conditions in the hypothalamic-pituitary axis remain the adenomas. MRimaging is the method of choice to rule out a suspected formation in the sellar area. Small adenomas with size around 3mm are now detectable with the use of equipment with high strength of magnetic field. Authors agree on the fact the secreting and nonsecreting adenomas need a thorough MR-follow up in time, especially the nonsecreting ones that are usually detected accidentally. In the era before the multislice diagnostic imaging the pathologies in the hypothalamic-pituitary axis were difficult to assess. The introduction of the new methods of investigation made the diagnosis of such conditions achievable. Magnetic resonance imaging is convenient, informative and clinically applicable for detecting hypothalamic-pituitary axis. However there is no agreement how the MR-protocol should be carried out. MR with high magnetic field is an essential tool in obtaining images with better quality, higher diagnostic value and the opportunity for performing sequences in thin slices and reconstructions in different planes.
Key words: MAGNETIC RESONANCE IMAGING. HYPOPHYSIS. 3 TESLA