Virtual cisternoscopy: 3D MRI models of the cerebellopontine angle for lesions related to the cranial nerves.

ABSTRACT

This study was conducted to show that high-resolution magnetic resonance imaging (MRI) can aid in the neurosurgical approach to lesions affecting the cranial nerves (CNs) in the cerebellopontine angle (CPA). Three patients with symptomatology related to CNs VII and VIII underwent MRI examinations performed on a 1.5-Tesla Siemens MR scanner. As part of these routine examinations, the imaging technique of constructive interference in the steady state (CISS) was used to collect a volume of data through the brainstem and internal auditory canals. This high-resolution technique acquires a three-dimensional (3D) volume of data at 0.7-mm intervals. Parameters included TR 12.3/TE 5.9, number of acquisitions of 2, a matrix of 230 x 512, bandwidth of 130 Hz per pixel, and time of 840. Data were transferred to a commercially available GE workstation and reconstructed into a 3D surface-rendered model. This interactive method allows the model to be visualized from any angle, including that of a standard skull base approach of suboccipital craniotomy for access to the CPA cistern. The images shown include the CPA cistern as seen from the suboccipital surgical approach. CNs V, VII, and VIII can easily be seen in relation to the pons and petrous face. The relationship between the CNs and acoustic neuromas and skull base tumors can be evaluated. Vascular structures, which are often seen in relation to CNs VII and VIII, can be viewed in a 3D format to determine the need for microvascular decompression. Direct intraoperative photographs taken through the operating microscope confirmed the anatomic accuracy of the 3D models. Imaging used for interactive neurosurgical planning must demonstrate a high degree of anatomic detail. Virtual cisternoscopy using CISS MRI technique can achieve the required resolution. Reconstruction algorithms to create surface rendering can generate images with similar 3D anatomic detail to that seen during neurosurgical approaches to the CPA cistern.