The diaphragma sellae: its relationship to normal sellar variations in frontal radiographic projections

Recognition of prolactin-secreting microadenomas has led to renewed interest in normal variations in sellar contour that may mimic pathologic changes. A study of sphenoid bones obtained at autopsy from 100 patients who had histologically normal pituitary glands was done to determine the relationship between the diaphragma sellae and variations in the floor of the sella turcica, as seen in frontal radiographs. Nineteen of 46 (41%) sphenoid bones with a complete diaphragm had a floor that was convex downward with a depth range of 1-2 mm. Thirty-one of 54 (57%) sphenoid bones with a defective diaphragm had a floor that was convex downward with a depth range of 0.5-6 mm. A positive correlation existed between the presence of a defect in the diaphragma sellae and the depth of the central depression of the floor, and also between the depth of any resulting intrasellar cistern and the depth of the central depression. Eight bones with large defects in the diaphragma sellae showed great convex downward bowing of the floor with a central depression of greater than 2 mm in each case. Despite a histologically normal pituitary gland, a defect in the diaphragma sellae may lead to expansion of the bony contour of the sella turcica.