The MR contribution after CT demonstration of supratentorial mass effect without additional localising features.

The contribution of magnetic resonance (MR) imaging was retrospectively evaluated in 24 patients in whom CT demonstrated a supratentorial mass effect without significant additional localising features. Using a combination of T1-weighted inversion recovery (IR) and T2-weighted spin echo sequences, the MR images localised the lesion with greater precision than CT in 80% of cases. Areas of contrast enhancement were visible on the IR images in five of nine (56%) patients assessed after intravenous gadolinium-diethylenetriamine pentaacetic acid, where no comparable enhancement was seen on CT. Twenty of the 24 patients subsequently underwent surgery; eight had biopsies and 12 had resections. Magnetic resonance accurately predicted the site of the tumour in all these patients. Three of the remaining four cases were treated with radiotherapy on the basis of the MR findings without a tissue diagnosis being sought. Magnetic resonance produces better localization than CT and provides a sound basis for further diagnostic and therapeutic procedures.