Predictive value of hippocampal MR imaging-based high-dimensional mapping in mesial temporal epilepsy: preliminary findings.

BACKGROUND AND PURPOSE: We objectively assessed surface structural changes of the hippocampus in mesial temporal sclerosis (MTS) and assessed the ability of large-deformation high-dimensional mapping (HDM-LD) to demonstrate hippocampal surface symmetry and predict group classification of MTS in right and left MTS groups compared with control subjects. METHODS: Using eigenvector field analysis of HDM-LD segmentations of the hippocampus, we compared the symmetry of changes in the right and left MTS groups with a group of 15 matched controls. To assess the ability of HDM-LD to predict group classification, eigenvectors were selected by a logistic regression procedure when comparing the MTS group with control subjects. RESULTS: Multivariate analysis of variance on the coefficients from the first 9 eigenvectors accounted for 75% of the total variance between groups. The first 3 eigenvectors showed the largest differences between the control group and each of the MTS groups, but with eigenvector 2 showing the greatest difference in the MTS groups. Reconstruction of the hippocampal deformation vector fields due solely to eigenvector 2 shows symmetrical patterns in the right and left MTS groups. A "leave-one-out" (jackknife) procedure correctly predicted group classification in 14 of 15 (93.3%) left MTS subjects and all 15 right MTS subjects. CONCLUSION: Analysis of principal dimensions of hippocampal shape change suggests that MTS, after accounting for normal right-left asymmetries, affects the right and left hippocampal surface structure very symmetrically. Preliminary analysis using HDM-LD shows it can predict group classification of MTS and control hippocampi in this well-defined population of patients with MTS and mesial temporal lobe epilepsy (MTLE).

Comparison of Scientific Calipers and Computer-Enabled CT Review for the Measurement of Skull Base and Craniomaxillofacial Dimensions.

Traditionally, cadaveric studies and plain-film cephalometrics provided information about craniomaxillofacial proportions and measurements; however, advances in computer technology now permit software-based review of computed tomography (CT)-based models. Distances between standardized anatomic points were measured on five dried human skulls with standard scientific calipers (Geneva Gauge, Albany, NY) and through computer workstation (StealthStation 2.6.4, Medtronic Surgical Navigation Technology, Louisville, CO) review of corresponding CT scans. Differences in measurements between the caliper and CT model were not statistically significant for each parameter. Measurements obtained by computer workstation CT review of the cranial skull base are an accurate representation of actual bony anatomy. Such information has important implications for surgical planning and clinical research.

Three-dimensional localization: from image-guided surgery to information-guided therapy.

Image-guided surgery has become the standard of care for intracranial procedures. However, significant development is required before the benefits of this technology are brought to the majority of patients undergoing surgery. This article categorizes the areas wherein progress is needed, and indicates recent advances that may form the basis for the broad acceptance of this exciting technology. Emphasis is placed on a technique whereby preoperative imaging can be updated using low-resolution intraoperative imaging to reflect changes in anatomy caused by surgery, and on transforming image-guided surgery to information-guided therapy, in which diverse sources can be brought to bear at the time of greatest possible benefit, when the patient's anatomy is exposed for therapeutic intervention.

Mesial temporal sclerosis and temporal lobe epilepsy: MR imaging deformation-based segmentation of the hippocampus in five patients.

In five patients with mesial temporal sclerosis, the authors verified the precision and reproducibility of hippocampal segmentations with deformation-based magnetic resonance (MR) imaging. The overall percentage overlap between automated segmentations was 92.8% (SD, 3.5%), between manual segmentations was 73.1% (SD, 9.5%), and between automated and manual segmentations was 74.8% (SD, 10.3%). Deformation-based hippocampal segmentations provided a precise method of hippocampal volume measurement in this patient population.

Shape analysis of hippocampal surface structure in patients with unilateral mesial temporal sclerosis.

Structural hippocampal magnetic resonance (MR) imaging-based analysis is helpful in the diagnosis and treatment of mesial temporal epileptic seizures. Computational anatomic techniques provide a framework for objective assessment of three-dimensional hippocampal structure. We applied a previously validated technique of deformation-based hippocampal segmentations in 20 subjects with documented unilateral mesial temporal sclerosis (MTS) and temporal lobe epilepsy. Using composite images, we then measured shape differences between the epileptogenic, smaller hippocampus, and contralateral hippocampus. Final shape differences were projected on the contralateral "normal" side. We calculated results for the left MTS group (10 patients) and right MTS group (10 patients) separately. Both groups showed similar regions of maximal inward deformation in the affected hippocampus, which were the medial and lateral aspect of the head, and posterior aspect of the tail. These results suggest that there are specific three-dimensional patterns of volume loss in patients with mesial temporal epilepsy.

Magnetic resonance imaging deformation-based segmentation of the hippocampus in patients with mesial temporal sclerosis and temporal lobe epilepsy.

We compared manual and automated segmentations of the hippocampus in patients with mesial temporal sclerosis. This comparison showed good precision of the deformation-based automated segmentations.

Acellular dermal allograft for sellar reconstruction after transsphenoidal hypophysectomy.

Obliteration of the sphenoid sinus using fat is often used after transsphenoidal hypophysectomy. The morbidity of this approach includes donor site complications, fat necrosis, and delayed mucocele formation. As obliteration with fat is intended to prevent cerebrospinal fluid (CSF) leakage, an alternative for this technique would be techniques used for CSF rhinorrhea repair. Instead of sinus obliteration, these defects are repaired with fascial autografts, which are unfortunately associated with donor site complications. To avoid sinus obliteration and donor site complications, we have reconstructed the sella with acellular dermal allograft in lieu of sinus obliteration. Transsphenoidal hypophysectomy was performed under combined microscopic and endoscopic visualization. For closure, the sellar anterior wall was reconstructed with acellular dermal allograft, septal cartilage/bone autograft, and fibrin glue. The sinus mucosa was then draped over the reconstruction and held in place with microfibrillar collagen hemostat slurry. The sphenoid sinus was not obliterated. Postoperatively, all patients underwent serial nasal endoscopy. Thirteen patients underwent the procedure as described for removal of pituitary adenoma. Postoperative discomfort and pain were minimal. Intraoperative CSF leaks were identified in five patients; none of these patients experienced a postoperative CSF leak. The microfibrillar collagen hemostat was cleared by sphenoid mucociliary clearance. One patient developed acute sphenoid sinusitis several weeks after surgery; this patient did not develop meningitis. One postoperative CSF leak occurred in an obese patient, in whom an intraoperative CSF leak was not identified; this leak resolved with bedrest and delayed lumbar drainage alone. Sellar reconstruction with acellular dermal allograft may eliminate the need for sphenoid sinus obliteration after transsphenoidal hypophysectomy. Acellular dermal allograft sellar reconstruction ultimately provides for an aerated, functioning sphenoid sinus without increased CSF leak risk or potential donor site morbidity.

Triple-technique (MR imaging, single-photon emission CT, and CT) coregistration for image-guided surgical evaluation of patients with intractable epilepsy.

Ictal and interictal single-photon emission CT (SPECT) play an increasingly important role in the surgical evaluation of patients with epilepsy. We present a method of coregistration of MR, SPECT, and CT images to correlate structural data (MR imaging), blood flow changes (SPECT), and location of subdural electrodes (CT) for patients undergoing image-guided surgical treatment of epilepsy. MR-SPECT root mean square (rms) mismatch distances were 2.1 to 2.5 mm, and MR-CT rms mismatch distances were 1.0 to 4.5 mm. Coregistration assisted in image-guided placement of subdural electrodes and in surgical resection of the suspected epileptogenic focus.

Image-guided surgical techniques for infections and trauma of the central nervous system.

The value of image-guided stereotactic systems is directly dependent on the ease and speed of their use. In the past, most stereotactic techniques were complicated and timely to set up; thus, they were used exclusively for either resecting neoplasms or for neurologic function. However, current systems equipped with advanced registration techniques are much simpler and faster to employ, and indications for their use are rapidly increasing. We describe an advanced image-guided navigation system and provide examples of its successful use in neurosurgical treatment of central nervous system infection and trauma.

Therapeutic Intervention Scoring System used in the care of patients in pentobarbital-induced coma to determine nurse-patient ratios.

BACKGROUND: Critical care patients generally require extensive interventions, thereby consuming a large percentage of healthcare resources. Induced pentobarbital coma for the management of increased intracranial pressure is one such intervention, required to maintain patient stability. Quantification of these interventions, as well as the amount of nursing work required, has not been addressed in the literature. OBJECTIVE: To use the Therapeutic Intervention Scoring System to analyze and quantify how interventions affect nurse-patient ratios in the management of patients in pentobarbital coma for refractory increased intracranial pressure. METHODS: The medical records of patients with subarachnoid hemorrhage from aneurysmal rupture and subsequent increased intracranial pressure, in whom pentobarbital coma was salvage therapy, were reviewed retrospectively. The Therapeutic Intervention Scoring System was used to quantify the number of interventions required before, during, and after coma induction. The data were analyzed and daily Therapeutic Intervention Scoring System scores correlated with serum pentobarbital levels. Typically, a critical care nurse can manage a patient caseload of 40 to 50 Therapeutic Intervention Scoring System points. By quantifying the interventions, the score reflected the amount of care required to manage the patient in barbiturate coma. RESULTS: The intensity of interventions correlated with the level of coma, length of time in coma, and associated complications. CONCLUSIONS: The scores indicated the intensity of interventions used in pentobarbital coma and the use of resources. Nursing care and complications involved with this therapy were quantified and nurse-patient ratios were established.

Clinical applications of frameless stereotactic devices in neurotology: preliminary report.

Conventional stereotactic surgery has been utilized primarily for intracranial neuro-surgical procedures. Despite their utility, head-frame systems are restrictive and often inconvenient, thus they have not proved applicable for neurotologic surgery. Recently frameless stereotactic navigational systems have been developed that employ three-dimensional digitizers to transform the coordinates in surgical space to the corresponding image space, without the employment of head frames. This allows the determination of position of a surgical instrument in real time during surgery, and its display on video-projected computed tomography or magnetic resonance imaging scanned images. This preliminary report focuses upon an optoelectric referenced frameless stereo-tactic system, the NeuroStation, as it relates to minimally invasive neurotologic surgery. Clinical applications, limitations, and future directions are discussed, and three representative surgical cases are presented. This device has potential as an adjunctive navigational tool for certain neurotologic procedures.

Presurgical localization of functional cortex using magnetic source imaging.

The boundaries of somatosensory cortex were localized noninvasively by means of a large-array biomagnetometer in six patients with mass lesions in or near eloquent cortex. The results were used by neurosurgeons and neurologists in preoperative planning and for reference in the operating room. The magnetic source imaging (MSI) localizations from somatosensory evoked potentials were used to predict the pattern of phase reversals measurable intraoperatively on the cortical surface, providing a quantitative comparison between the two measures. The magnetic localizations were found to be predictive in all six cases, with the two sets of localizations falling within an 8-mm distance on average. Somatosensory localizations using MSI offer accuracy in localizing somatosensory cortex stereotactically and in depicting its relationship to lesions. Such data are valuable preoperatively in assessing the risks associated with a proposed surgical procedure and for optimizing subsequent minimum-risk surgical strategy.

Frameless stereotactic ultrasonography: method and applications.

In stereotactic neurosurgery, computed tomography (CT) and magnetic resonance (MR) images are registered in a coordinate system defined with respect to the skull. By intraoperatively tracking the coordinate position of a surgical instrument, various displays can be formed which show the position of the instrument in the MR and/or CT images. However, the accuracy of this display varies because intracranial structures may shift or warp from their position prior to surgery. Ultrasonic imaging systems provide real-time images of the brain, but structures in these images are difficult to interpret because the images are based on ultrasonic echoes. A method has been developed for the real-time registration of these images. With this registration, software continuously updates a corresponding image constructed from the set of MR and/or CT images used for guidance. By developing this second view of the structures in the ultrasound image, the surgeon can easily interpret the ultrasound image, and it becomes possible to determine the extent of the intra-operative structure shift between the two images.

The NeuroStation--a highly accurate, minimally invasive solution to frameless stereotactic neurosurgery.

The NeuroStation is an image-guided neurosurgery workstation designed to deliver frameless stereotaxy within an ergonomic, integrated surgical environment. Generally, stereotaxy can provide the neurosurgeon with important intra-operative localization information using diagnostic images such as computerized tomography (CT) or magnetic resonance imaging (MRI). To date, however, stereotaxy has not been widely accepted by neurosurgeons due to the procedural difficulties of incorporating conventional stereotaxy. The NeuroStation addresses the problems of conventional stereotaxy through the use of frameless stereotactic methods wherein state-of-the-art instrumentation and computer innovations allow: a) standard surgical instruments to be used as the localization device; b) multipoint registration methods in place of frame-based registration; and c) real-time interactive surgical localization. The NeuroStation can thus be transparently integrated into the neurosurgical procedure providing the neurosurgeon with image-guidance for surgical planning, biopsies, craniotomies, endoscopy, intra-operative ultrasound, radiation therapy, etc.

An accurate and ergonomic method of registration for image-guided neurosurgery.

We have developed a system for accurately and conveniently achieving surgical registration for image-guided neurosurgery, based on alignment and matching of patient forehead contours. The system consists of a contour digitizer that is used in the operating room to acquire patient contours, editing software for extracting contours from patient image data sets, and a contour-match algorithm for aligning the two contours and performing data set registration. Initial tests of the individual portions of the system have found each to be robust; we are in the process of refining the design of the optical digitizer in order to further automate the procedure as well as provide increased accuracy.

Variables affecting the accuracy of stereotactic localization using computerized tomography.

Stereotactic localization using computerized tomography (CT) is increasingly employed to guide neurosurgical procedures in crucial areas of the brain such as the brain stem. This technique allows the surgeon to resect a lesion in its entirety while sparing critical areas of the brain. Thus, the parameters used for scanning should be selected for maximum accuracy. While the small pixel size of CT scanners suggests a high degree of precision in localization, there have been few systematic studies of this accuracy. The authors have studied the amount of error in localization created by variables such as CT scan thickness, interscan spacing, size of lesion, and method of computation when using the Brown-Roberts-Wells (BRW) stereotactic system. Over 1000 CT scans were made of a phantom composed of spheres of differing diameter and location. The CT slice thickness was varied from 1.5 to 5.0 mm, and interscan spacing was varied from 0.5 to 3.0 mm. The coordinates of the center of the spheres were calculated independently using the laptop computer supplied with the unit and also by a stereotactic computer which automatically calculates the center of the fiducials. The actual BRW coordinates of the sphere center were obtained using the phantom base and were then compared to the computer-calculated coordinates to determine error in localization. Variables with a significant effect on error included the scan thickness, interscan spacing, and sphere size. The mean error decreased 23% as the scan thickness decreased from 5.0 to 1.5 mm and 45% as the interscan spacing decreased from 3.0 to 0.5 mm. Mean error was greatest for the smallest sphere sizes. The two computational methods did not differ in error. This study suggests that, for critical areas of the brain or for small lesions, a scan thickness of 1.5 mm and interscan spacing of 0.5 mm should be employed.