The diaphragma sellae: its relationship to the configuration of the pituitary gland.

One hundred sphenoid bones that were removed at autopsy from patients without apparent pituitary disease and with histologically normal pituitary glands were examined. In 46 specimens the diaphragma sellae was complete. The majority showed convex downward bowing below the diaphragmatic line in both the lateral and frontal planes while the remainder were straight, corresponding to the diaphragmatic line. In only one specimen was the diaphragma sellae convex upward in both planes. These findings suggest that upward displacement of the diaphragma sella as seen of coronal and sagittal computed tomography (CT) may provide early evidence of an expanding pituitary lesion. Twenty of 54 defective specimens had a defect that was larger than 80% of the length of the diaphragma sellae. There was a correlation between the size of the defect and the depth of the intrasellar cistern that resulted from the downward extension of the suprasellar cistern. Such variations may lead to confusion in CT interpretation. The pituitary infundibulum was at or behind the level of the midpoint of the diaphragma sellae in all specimens. In the presence of a defect, the infundibulum usually retained its relationship to the posterior rim of the defect, and therefore when the defect was large the infundibulum was found adjacent to the dorsum sellae.