[Chiasmatic syndromes-diagnostic possibilities with computerized tomography (CT)]

The normal suprasellar subarachnoid space (so-called "suprasellar hexagon") and its content are fairly well demonstrated by CT. Abnormal appearance (obstruction, stenosis, asymmetry) of this space is always suspect of a suprasellar space occupying lesion. Enhancing (intravenous application of iodine containing contrast medium) helps to delineate the exact tumor extension. The point of origin--important for deciding on the nature of a lesion--is often difficult to determine. The CT-pattern itself is not specific for a certain kind of tumor. We have observed a typical chiasmatic syndrome with all meningiomas of the tuberculum sellae, with 75% of the chromophobe adenomas and with 50% of the craniopharyngiomas. Absence of this syndrome was due to high position of the tumor (craniopharyngiomas) or to parasellar extension of the lesion (chromophobe adenomas). Diagnosis of recurrent tumor is difficult; it must be based on the post-operative CT-examination. Chiasmatic syndromes not due to the pressure effect of a space occupying lesion (i.e. chiasmatic syndromes of vascular, toxic or degenerative origin) can not be assessed directly by CT.