Contrast enhanced area of posterior pituitary gland in early dynamic MRI exceeds hyperintense area on T1-weighted images.

Seventeen normal pituitary glands were studied by midline sagittal (and in one case axial) dynamic MRI before and immediately after injection of Gd-DTPA, using spin-echo sequences with a short repetition time. Images were obtained at 1 min intervals for 6 min at 1.5 T. A well-defined focal area with marked enhancement was seen in the posterior portion of the pituitary gland on the first image after injection of Gd-DTPA. The size of the early enhancing area in the posterior pituitary (EEPP) was compared with the high signal of the posterior pituitary (HSPP) on the precontrast image. The EEPP was larger than the HSPP in 10 cases (59%). The two were equal in size in seven cases (41%). The EEPP was anteriorly convex in 11 cases (65%), whereas HSPP was anteriorly convex in 4 cases (24%). We believe that EEPP closely represents the real extent of the posterior lobe. Our results support the hypothesis that HSPP may involve only a portion of the posterior pituitary.