Faculty Bibliography

Coregistration of different modality imaging serves to increase the ease and accuracy of stereotactic procedures. In many cases, magnetic resonance (MR) stereotaxis is supplanting computerized tomography (CT). The advantages of increased anatomical detail and multiplanar imaging afforded by MR, however, are offset by its potential inaccuracy as well as the more cumbersome and less available nature of its hardware. A system has been developed by one of the authors by which MR imaging can be performed separately without a stereotactic fiducial headring. Then, immediately prior to surgery, a stereotactic CT scan is obtained and software is used to coregister CT and MR images anatomically by matching cranial landmarks in the two scans. The authors examined this system in six patients as well as with the use of a lucite phantom. After initially coregistering CT and MR images, six separate anatomical (for the patients) and eight artificial (for the phantom) targets were compared. With coregistration, in comparison to CT fiducial scans, errors in each axis are less than or equal to 1 mm using the Cosman-Roberts-Wells system. In fact, the coregistered images are more accurate than MR fiducial images, in the anteroposterior (p = 0.001), lateral (p < 0.05), and vertical (p < 0.03) planes. Three-dimensional error was significantly less in the coregistered scans than the MR fiducial images (p < 0.005). The coregistration procedure therefore not only increases the case of MR stereotaxis but also increases its accuracy.

Recent studies documenting the efficacy of carotid endarterectomy (CEA) in selected patients provide further impetus for developing noninvasive techniques to evaluate carotid occlusive disease. Eliminating the morbidity due to preoperative angiography would further refine the treatment of this condition. Recent improvements and greater experience with magnetic resonance angiography (MRA) of extracranial vessels have increased the accuracy of this technique. We present our experience using MRA in combination with duplex ultrasonography as the primary mode of preoperative evaluation for CEA. Fifty-two patients referred for CEA underwent these two studies. In 47 patients (90%), significant stenosis (> 70%) was unambiguously identified on both ultrasound and MRA. Forty-one of these patients underwent CEA on the basis of these studies alone, without conventional angiography. In all of these cases, significant stenosis was identified at the time of surgery (100%), and CEA was performed without difficulty or complications. In five cases (9.6%), the MRA and ultrasound findings did not concur exactly. In three of these cases, the interpretation of the two studies differed with respect to the severity of stenosis; in the others, one of the studies was indeterminate. These patients underwent conventional angiography before surgery. Our experience suggests that the combined use of MRA and ultrasonography affords an accurate noninvasive evaluation of carotid occlusive disease sufficient for surgical planning in most cases.

The regeneration of lesioned axons is critically influenced by the local microenvironment. In this study, semipermeable polymer tubes were used to provide a defined microenvironment in vivo to analyze the regeneration of dorsal root axons under various conditions in the adult rat. Cut dorsal root fibers grew across a 2.7 mm gap within enclosed polymer tubes by 4 weeks. The pattern of axonal outgrowth was dramatically influenced by mechanical factors such as the inner surface topography of the polymer tube. Tubes containing various molecular and cellular substrates were also used to study their effect on dorsal root regeneration.

The damaged spinal cord has only a limited capacity for anatomical and functional recovery. However, a growing body of experimental work is demonstrating a potential for enhanced axonal regeneration and recovery following injury. Important pathophysiologic processes are discussed, along with strategies designed to improve outcome through the reconstruction of damaged pathways and the modulation of the spinal cord's response to the primary injury.