and Abnormal Internal Auditory Canal

MR performed with thin, contiguous sections has replaced CT for the study of the cerebellopontine angle and for diagnosis of acoustic neuromas. In our experience large acoustic neuromas are well seen in all pulse sequences. Tumors with small extracan-alicular components are seen in the T1- and spin-density-weighted sequences whereas purely intracanalicular lesions are often visualized only in the T1-weighted images. Small acoustic neuromas producing thickening of the nerve are easily recognizable in narrow internal auditory canals but may be missed in large canals because of partial volume averaging. Since further enhancement of the signal intensity of tumors can be obtained by IV injection of paramagnetic agents, we foresee the use of such agents in the near future in the diagnosis of acoustic neuromas. Until recently, CT has been the study of choice for assessing the internal auditory canal and diagnosing acoustic neuromas [1). Extracanalicular lesions larger than 8-1 0 mm are clearly demonstrated on CT scans obtained after infusion of iodinated contrast media. The diagnosis of intracanalicular and small extracanalicular tumors requires a more invasive approach; namely, the injection in the subarachnoid space by lumbar puncture of gaseous or opaque material. MR imaging performed with thin, contiguous sections has opened a new ap-proach, which in our view, and that of other authors [2-6). has replaced CT for the diagnosis of cerebellopontine angle tumors. The main advantage of MR is the opportunity it provides to diagnose tumors of any size without ionizing radiation, in a noninvasive manner with multiplanar display. The availability in the near future of paramagnetic agents such as gadolinium OPT A [7, 8) for tumor enhancement will improve the detection of acoustic neuromas and other cerebellopontine tumors