Normal pituitary gland: 2. Microscopic anatomy-CT correlation.

Pituitary microadenomas may present with subtle or no mass effect. They may appear lucent, dense, or heterogeneous on computed tomographic (CT) images. The normal pituitary gland may also have a nonhomogeneous CT appearance with intermingled lucent and dense areas. This heterogeneity is related in part to microscopic variation within the anterior and posterior lobes. Thirteen autopsy specimens of the pituitary gland were examined by coronal CT and histologically sectioned in similar coronal planes. The CT-lucent and CT-dense areas of the anterior and posterior lobes were correlated with corresponding areas on microscopic examination. To determine the effects of contrast infusion during CT, density measurements of lucent and dense areas in the anterior lobes of 26 normal contrast-enhanced pituitary glands in vivo were compared with density measurements of adjacent vascular structures at the time of scanning. Microscopic features corresponding to increased CT density in the anterior lobe included increased tissue compactness and increased cellular granularity, both of which usually occurred together in areas composed of tightly compacted and heavily granulated acidophilic cells. Conversely, microscopic features corresponding to decreased CT density in the anterior lobe included decreased tissue compactness and decreased cellular granularity, both of which frequently occurred together in areas containing chromophobic and/or mildly to moderately granulated basophilic cells. The degree of contrast enhancement within the anterior lobe appeared primarily to depend on vascularity, which in turn often depended on the degree of tissue compactness. In the posterior lobe, CT-lucent areas appeared to correspond to less compact and/or less vascular neurohypophyseal tissue.