The normal suprasellar subarachnoid space in computed tomography.

Changes in visibility or configuration of the suprasellar cistern are often the only signs on a CT scan of a patient with a juxtasellar expansion. Normal variations of this subarachnoid space on a CT scan are side for anatomical and technical reasons. The ability to differentiate between normal and abnormal in this area is essential in interpreting computed axial tomograms. To determine normal variants of the suprasellar cistern, 456 consecutive standard tomograms interpreted as normal were reviewed. The cistern was visible in 73.7% of the scans and the shape of the cistern was found to be either hexagonal (71.5%) or tetragonal (28.5%). The visible content of the cistern included the anterior part of the third ventricle (55.5%), the optic nerves and/or chiasm (52%) and the dorsum sellae (34.9%). The content of the cistern could not be accurately defined in 24.8% of the scans. In about one-fourth of the scans the suprasellar subarachnoid space was not visualised at all. If any doubt exists as to the visibility and configuration of the suprasellar cistern when there is a clinical suspicion of a juxtasellar tumour, additional investigations must be performed.