Roentgenologic Observations Concerning Erosion of the Sella Turcica

Many observations have been made in the past which indicate that the normal sella turcica varies widely in size and shape (1–3). So great is this variation that recognition of disease based on alterations of size alone is frequently difficult and even misleading. Rasmussen (4) has shown, also, that there is no constant relation between the size of the sella and the size of the pituitary gland. This further decreases the va lue of measurements of the sella alone as an index of pituitary disease. My own experience, over a period of many years, indicates that in the past the average roentgenologist has paid too much attent ion to variat ions in the dimensions of the sella turcica and has underestimated the significance of certain basic changes in structure which will indicate the presence of disease long before measurements alone have any value. These basic changes—erosion, decalcification and destruction of bone—are intimately related to one another. They may express themselves in focal or generalized changes in contour of the sella or its related processes, depending on the type and location of the lesion. Erosion of the sella, or any of its related processes, is due to pressure from a contiguous mass, abnormal pulsation, or generalized pressure reflected from a more remote lesion. This focal or generalized pressure produces a loss of substance of the cortex of the exposed surface of the sella or contiguous processes. A certain amount of localized decalcification accompanies the pressure erosion, the degree being directly related to the sit e and severity of the associated pressure. If the pressure is of a low degree and persistent, it may be reflected only in a change in contour of a single process or of the entire sella with little evidence of decalcification, since in such cases there is a natural reparative recalcification at the site of the erosion. On the other hand, if the pressure is acute, severe, and progressive, erosion occurs rapidly without opportunity for repair by recalcification, and the picture is soon one of complete loss of bone substance, either focal or generalized. Classical examples of true decalcification of bone are seen in severe infections of the sphenoid sinus and, in varying degrees, in the presence of contiguous meningiomas. In the former, the decalcification results from the hyperemia of the walls of the sphenoid sinus which accompanies the infection, and in the latter both from hyperemia due to increased vascularity at the site of the tumor and from actual pressure by tumor cells which grow into the haversian canals of the adjacent bone. Actual invasive destruction of the sella or its related processes occurs with malignant tumors which may originate in the bony structures or may involve them secondarily by extension from a contiguous soft-tissue mass. Such changes, because of their location and extent, are usually not difficult to distinguish from erosion incident to benign lesions.