Imagerie normale de la région hypothalamohypophysaire

Exploring the sellar region is nowadays based on magnetic resonance imaging (MRI). The main advantages of MRI are its high sensitivity for the study of tissues, a three-dimensional approach, the low impact of the original bone artifacts and its safety. Because it's a small structure, the pituitary remains difficult to explore. The acquisition technique is dominated by the spin-echo T1- and T2-weighted sequences; the two key parameters are a thin section thickness (<3 mm) and a high matrix (512). Sequences with gadolinium injection should not be systematic. Dynamic imaging MRI is sometimes useful, but is less decisive than it was with CT. It is important to recognize the key artifacts that might disrupt the study of the pituitary region: vascular artifacts, magnetic susceptibility artifacts, flow of cerebrospinal fluid artifacts and partial volume effect. It is in the field of exploration of the hypothalamic-pituitary axis that MRI began to reveal its functional imaging capabilities. The high T1 signal intensity of the posterior pituitary lobe reflects a normal functional state, indeed. Physiological changes of the anterior pituitary lobe are also observed: hypertrophy and T1-hyperintensity of the anterior lobe during the first months of life, adolescence (especially in girls), during pregnancy and in the postpartum, reflect intense secretory activity at these moments.