Elvis J. Hermann

Laser surface scanning for patient registration in intracranial image-guided surgery

OBJECTIVE To report our clinical experience with a new laser scanning-based technique of surface registration. We performed a prospective study to measure the calculated registration error and the application accuracy of laser surface registration for intracranial image-guided surgery in the clinical setting. METHODS Thirty-four consecutive patients with different intracranial diseases were scheduled for intracranial image-guided surgery by use of a passive infrared surgical navigation system. Surface registration was performed by use of a Class I laser device that emits a visible laser beam. The Polaris camera system (Northern Digital, Waterloo, ON, Canada) detects the skin reflections of the laser, which the software uses to generate a virtual three-dimensional matrix of the anatomy of each patient. An advanced surface-matching algorithm then matches this virtual three-dimensional matrix to the three-dimensional magnetic resonance therapy data set. Registration error as calculated by the computer was noted. Application accuracy was assessed by use of the localization error for three distant anatomic landmarks. RESULTS Laser surface registration was successful in all patients. For the surgical field, application accuracy was 2.4 ± 1.7 mm (range, 1–9 mm). Application accuracy was higher for the surgical field of frontally located lesions (mean, 1.8 ± 0.8 mm; n = 13) as compared with temporal, parietal, occipital, and infratentorial lesions (mean, 2.8 ± 2.1 mm; n = 21). CONCLUSION Laser scanning for surface registration is an accurate, robust, and easy-to-use method of patient registration for image-guided surgery.

Functional magnetic resonance imaging-integrated neuronavigation: correlation between lesion-to-motor cortex distance and outcome.

OBJECTIVE:The integration of functional magnetic resonance imaging (fMRI) data into neuronavigation is a new concept for surgery adjacent to the motor cortex. However, the clinical value remains to be defined. In this study, we investigated the correlation between the lesion-to-fMRI activation distance and the occurrence of a new postoperative deficit. METHODS:fMRI-integrated “functional” neuronavigation was used for surgery around the motor strip in 54 patients. During standardized paradigms for hand, foot, and tongue movements, echo-planar imaging T2* blood oxygen level-dependent sequences were acquired and processed with BrainVoyager 2000 software (Brain Innovation, Maastricht, The Netherlands). Neuronavigation was performed with the VectorVision2 system (BrainLAB, Heimstetten, Germany). For outcome analysis, patient age, histological findings, size of lesion, distance to the fMRI areas, preoperative and postoperative Karnofsky index, postoperative motor deficit, and type of resection were analyzed. RESULTS:In 45 patients, a gross total resection (>95%) was performed, and for 9 lesions (low-grade glioma, 4; glioblastoma, 5), a subtotal resection (80–95%) was achieved. The neurological outcome improved in 16 patients (29.6%), was unchanged in 29 patients (53.7%), and deteriorated in 9 patients (16.7%). Significant predictors of a new neurological deficit were a lesion-to-activation distance of less than 5 mm (P < 0.01) and incomplete resection (P < 0.05). CONCLUSION:fMRI-integrated neuronavigation is a useful concept to assess the risk of a new motor deficit after surgery. Our data suggest that a lesion-to-activation distance of less than 5 mm is associated with a higher risk of neurological deterioration. Within a 10-mm range, cortical stimulation should be performed. For a lesion-to-activation distance of more than 10 mm, a complete resection can be achieved safely. The visualization of fiber tracks is desirable to complete the representation of the motor system.

Usefulness of intraoperative ultra low-field magnetic resonance imaging in glioma surgery.

OBJECTIVE The aim of this study was to demonstrate the usefulness of a mobile, intraoperative 0.15-T magnetic resonance imaging (MRI) scanner in glioma surgery. METHODS We analyzed our prospectively collected database of patients with glial tumors who underwent tumor resection with the use of an intraoperative ultra low-field MRI scanner (PoleStar N-20; Odin Medical Technologies, Yokneam, Israel/Medtronic, Louisville, CO). Sixty-three patients with World Health Organization Grade II to IV tumors were included in the study. All patients were subjected to postoperative 1.5-T imaging to confirm the extent of resection. RESULTS Intraoperative image quality was sufficient for navigation and resection control in both high- and low-grade tumors. Primarily enhancing tumors were best detected on T1-weighted imaging, whereas fluid-attenuated inversion recovery sequences proved best for nonenhancing tumors. Intraoperative resection control led to further tumor resection in 12 (28.6%) of 42 patients with contrast-enhancing tumors and in 10 (47.6%) of 21 patients with noncontrast-enhancing tumors. In contrast-enhancing tumors, further resection led to an increased rate of complete tumor resection (71.2 versus 52.4%), and the surgical goal of gross total removal or subtotal resection was achieved in all cases (100.0%). In patients with noncontrast-enhancing tumors, the surgical goal was achieved in 19 (90.5%) of 21 cases, as intraoperative MRI findings were inconsistent with postoperative high-field imaging in 2 cases. CONCLUSION The use of the PoleStar N-20 intraoperative ultra low-field MRI scanner helps to evaluate the extent of resection in glioma surgery. Further tumor resection after intraoperative scanning leads to an increased rate of complete tumor resection, especially in patients with contrast-enhancing tumors. However, in noncontrast- enhancing tumors, the intraoperative visualization of a complete resection seems less specific, when compared with postoperative 1.5-T MRI.

Stereotactic Biopsy in Gliomas Guided by 3-Tesla 1H-Chemical-Shift Imaging of Choline

Objective: To investigate chemical-shift imaging (CSI) to guide stereotactic biopsy of the choline ‘hot spot’ in cerebral lesions suggestive of low-grade glioma. Methods: Nine patients with hyperintense lesions on T2-weighted images of standard magnetic resonance imaging without contrast enhancement underwent advanced magnetic resonance studies. These studies included 3-dimensional T1-weighted sequences with contrast enhancement and 2-dimensional 1H-CSI spectroscopy at 3 T. Signal intensity maps with relative signal intensities for choline were generated. The region with the highest choline signal intensity (the hot spot) was chosen as the target for stereotactic biopsy. The histopathological results were correlated with the increase in choline. Results: All spectroscopic data were of sufficient quality. In 5 instances the neuropathological diagnosis was grade II glioma, according to the WHO classification, and in 4 instances it was grade III glioma. According to the CSI criteria, all grade III gliomas and 4 of the 5 grade II gliomas were classified correctly. One grade II glioma was overestimated by CSI as a high-grade glioma. Conclusion:1H-CSI-guided stereotactic biopsy may offer advantages as compared to conventional stereotactic biopsy. The biopsy of the choline hot spot in suggestive low-grade gliomas may help to identify focal points of higher tumor malignancy independent of contrast enhancement.

Electromagnetic-guided neuronavigation for safe placement of intraventricular catheters in pediatric neurosurgery

OBJECT Ventricular catheter shunt malfunction is the most common reason for shunt revision. Optimal ventricular catheter placement can be exceedingly difficult in patients with small ventricles or abnormal ventricular anatomy. Particularly in children and in premature infants with small head size, satisfactory positioning of the ventricular catheter can be a challenge. Navigation with electromagnetic tracking technology is an attractive and innovative therapeutic option. In this study, the authors demonstrate the advantages of using this technology for shunt placement in children. METHODS Twenty-six children ranging in age from 4 days to 14 years (mean 3.8 years) with hydrocephalus and difficult ventricular anatomy or slit ventricles underwent electromagnetic-guided neuronavigated intraventricular catheter placement in a total of 29 procedures. RESULTS The single-coil technology allows one to use flexible instruments, in this case the ventricular catheter stylet, to be tracked at the tip. Head movement during the operative procedure is possible without loss of navigation precision. The intraoperative catheter placement documented by screenshots correlated exactly with the position on the postoperative CT scan. There was no need for repeated ventricular punctures. There were no operative complications. Postoperatively, all children had accurate shunt placement. The overall shunt failure rate in our group was 15%, including 3 shunt infections (after 1 month, 5 months, and 10 months) requiring operative revision and 1 distal shunt failure. There were no proximal shunt malfunctions during follow-up (mean 23.5 months). CONCLUSIONS The electromagnetic-guided neuronavigation system enables safe and optimal catheter placement, especially in children and premature infants, alleviating the need for repeated cannulation attempts for ventricular puncture. In contrast to stereotactic techniques and conventional neuronavigation, there is no need for sharp head fixation using a Mayfield clamp. This technique may present the possibility of reducing proximal shunt failure rates and costs for hydrocephalus treatment in this age cohort.

Ventriculoperitoneal shunt migration into the pulmonary artery

BackgroundVentriculoperitoneal (VP) shunting is the most common form of treatment for hydrocephalus. Complications of VP shunts may occur anywhere along their course from the cerebral ventricle to the peritoneal cavity. Rare complications such as migration of the peritoneal catheter into the stomach, gallbladder, urinary bladder, vagina, liver, bowel, colon, and diaphragm have been described in the literature.MethodsIn this review of the literature we discuss the rare but serious event of migration of the distal catheter of a ventriculoperitoneal shunt (VP shunt) into the pulmonary artery. We present an additional patient with a special emphasis on minimally invasive treatment.ResultsThe patient’s postoperative course was uneventful, and a postoperative plain X-ray of the chest and abdomen confirmed appropriate placement of the new distal catheter intraperitoneally.ConclusionIt is useful to consider alternative nonsurgical techniques for percutaneous intravascular foreign body retrieval. Many different percutaneous techniques have been described. Rare complications of percutaneous intravascular foreign body retrieval may include transient cardiac arrhythmia, fragmentation of the foreign body, or migration of the foreign body to a different location. A multidisciplinary discussion and approach is pivotal to treating this extraordinarily rare complication.

Effect of apolipoprotein E genotype on the outcome after anterior cervical decompression and fusion in patients with cervical spondylotic myelopathy

OBJECT The authors examined a possible association between apolipoprotein E (APOE) gene polymorphism and the outcome after anterior microsurgical decompression in patients with cervical spondylotic myelopathy (CSM). METHODS The authors conducted a prospective study of 60 consecutive patients (40 men, 20 women) with CSM who underwent anterior microsurgical decompression. The patients ranged in age from 26 to 86 years (mean 61.5 +/- 14.6 years). Neurological deficits were classified according to the modified Japanese Orthopaedic Association Scale. Mean follow-up was 18.8 +/- 4.6 months and APOE genotyping was carried out by isolation of DNA from venous blood samples. The APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and polyacrylamide gel electrophoresis of digested fragments. Categorical variables were analyzed with the chi-square test, continuous data with the Mann-Whitney U-test, and for multiple groups with the Kruskal-Wallis H-test. A backward stepwise binary logistic regression analysis was performed to determine the effect of APOE in a multivariate model. RESULTS Of the 60 patients with CSM, 35 (58.3%) improved and 25 (41.7%) did not improve or suffered deterioration (no-improvement group). In the improvement group 5 patients (8.3%) possessed the epsilon4 allele compared with 16 patients (26.7%) in the no-improvement group (p = 0.002, OR 3.3, 95% CI 1.7-6.1). In a multivariate model, the occurrence of the epsilon4 allele was a significant independent predictor for no improvement after anterior decompression and fusion (p = 0.004, OR 8.6, 95% CI 5.1-20.6). CONCLUSIONS The results of this study show that APOE gene polymorphism influences the short-term outcome of CSM patients after surgical decompressive and stabilizing therapy in the way that the presence of the APOE epsilon4 allele is an independent predictor for a no improvement. The presence of APOE may explain in part the different responses to operative therapies in patients with cervical myelopathy.

Automated Fiducial Marker Detection for Patient Registration in Image-Guided Neurosurgery

Objective: The registration of applied fiducial markers within the preoperative data is often left to the surgeon, who has to identify and tag the center of each marker. This is both time-consuming and a potential source of error. For this reason, the development of an automated procedure was desirable. In this study, we have investigated the accuracy of a software algorithm for detecting fiducial markers within the navigation data set. The influence of adjustable values for accuracy and threshold on the sensitivity and specificity of the detection process, as well as the time gain, was investigated. Patients and Methods: One hundred MP-RAGE MRI data sets of patients with different pathologies who were scheduled for image-guided surgery were used in this study. A total of 591 applied fiducial markers were to be detected using the algorithm of the software VVPlanning 1.3 (BrainLAB, Heimstetten, Germany) on a Pentium II standard PC. The size value of a marker in the y-direction is called “accuracy” and depends on the slice thickness. “Threshold” describes the gray level above which the algorithm starts searching for pixel clusters. The threshold value was changed stepwise on the basis of a constant “accuracy” value. The “ccuracy” value was changed on the basis of that threshold value at which all markers were detected correctly. Results: The time needed for automatic detection varied between 12 s and 25 s. An optimum value for adjustable marker size was found to be 1.1 mm, with 8 undetected markers (1.35%) and 7 additionally detected structures (1.18%) out of 591. The mean gray level (Threshold) for all data sets above which marker detection was correct was 248.9. The automatic detection of markers was good for higher gray levels, with 11 missed markers (1.86%). Starting the algorithm at lower gray levels led to a decreased incidence of missed markers (0.17%), but increased the incidence of additionally detected structures to 27.92%. Conclusion: The automatic marker-detection algorithm is a robust, fast and objective instrument for reliable fiducial marker registration when used with optimum settings for both threshold and accuracy.

Large intramedullary abscess of the spinal cord associated with an epidermoid cyst without dermal sinus. Case report.

An intramedullary abscess of the spinal cord (IASC) represents a rare disease associated with a potentially devastating outcome. Few cases involving children suffering from an IASC have been reported in the neurosurgical literature. In the majority of the reported pediatric cases there were either congenital abnormalities, such as a dermal sinus, or signs of local infections leading to a secondary hemopoietic spread. The authors report the case of an 18-month-old girl with an extensive IASC associated with an epidermoid cyst extending from T-11 to S-2 without evidence of a dermal sinus or history of clinically apparent systemic infection. To their knowledge, this is the first case report of an IASC without a condition facilitating either direct contamination via a dermal sinus or hemopoietic spread from an infectious focus outside the central nervous system. Signs and symptoms, the clinical course, and imaging features are discussed and the relevant literature is reviewed.

Combined transventricular and supracerebellar infratentorial approach preserving the vermis in giant pediatric posterior fossa midline tumors.

OBJECTIVE Giant pediatric midline tumors of the posterior fossa involving the fourth ventricle and the tectal region are difficult to approach and present a high risk of postoperative neurological deficits. Children with sequelae such as cerebellar mutism and ataxia experience a compromise in their quality of life. Here, we present our combined transventricular and supracerebellar infratentorial approach to avoid complications of vermian splitting. METHODS The combined transventricular and supracerebellar infratentorial approach described here was used in a total of four pediatric patients. A medial suboccipital craniotomy with opening of the foramen magnum and resection of the C1 lamina was performed with the patient in the semisitting position. The tumor mass filling the fourth ventricle was removed via a transventricular telovelar route through the foramen of Magendie, preserving the vermis. The rostral tumor portions in the peritectal region extruding up to the thalami were exposed and resected via an infratentorial supracerebellar route to preserve the venous drainage of the cerebellum. RESULTS There were no new neurological deficits postoperatively. Two patients had low-grade astrocytomas, and two patients had malignant tumors. Complete tumor resection was achieved in two patients, and near-total tumor removal in the two others. CONCLUSION The combined transventricular and supracerebellar infratentorial approach offers a unique possibility of safely removing giant pediatric midline tumors. Splitting of the cerebellar vermis is not necessary for removal of such tumors.