The Role of NMR Imaging in the Diagnosis and Management of Acoustic Neuroma

Nuclear magnetic resonance (NMR) scans of 15 patients with acoustic neuroma are compared with the results of computed tomography (eT). The absence of signal from bone has meant that the images are unaffected by artifacts and that small intra-canalicular tumors can be visualized. The multi planar facility of NMR is emphasized as this allows precise assessment of both tumor volume and its relationship to the ventricular system, brainstem, and tentorial hiatus. The different appearances pro-duced by alternative scan sequences are illustrated and the possibility of predicting the physical constitution from scan ap-pearances is discussed. Acoustic neuroma is the most common extraaxial tumor in the posterior fossa and is by far the most frequently occurring tumor in the cerebellopontine angle, accounting for 92 % in a series reported by Valvassori in 1969 [1]. The most common clinical presentation is progressive unilateral sensorineuronal deafness; if the tumor is large, this may be accompanied by brainstem involvement and increased intracranial pressure. Materials and Methods In a combined total of over 500 cranial examinations at the Nottingham and Hammersmith medical centers, 20 patients were clinically suspected to be harboring cerebetlopontine angle mass lesions. Of these, 15 proved to have an acr)ustic neuroma; there was one case each of glioma and epidermoi j, and the other three had completely normal examinations at CT, Nl,m, and meatography. Most acoustic neuromas were larger than 2 cm in at least one dimension; only two were 1 cm or less. In Nottingham the scanning was performed with a Picker resistive system operating at a main fi eld strength of 0.15 tesla and employing a steady-state free precession (SSFP) sequence where the r '~sulting image contrast was given by p x T, / T2. At Hammersmitn Hospital the scanning was performed by a Picker superconduc ting system with a main field strength of 0.15 tesla and employing a variety of pulse se-quences; this report considers inversion recovery images reflecting predominantly T, and spin-echo images reflecting predominantl