Positive contrast cisternography: analysis of 1) false negative studies, 2) false positive diagnoses of acoustic neuroma.

In performing and interpreting positive contrast cisternograms, one must be aware that both false negative and false positive studies are possible. The former may be avoided by an appreciation of normal anatomical variants of the cisterns and by adequate projections. The false positive study in which a lesion other than an acoustic neuroma is found, is mainly a problem where there is non-filling of the internal auditory canal without a significant angle mass. The differential diagnosis of such lesions is discussed.