Keisuke Maruyama, Kyousuke Kamada, Masahiro Shin, Daisuke Itoh, Yoshitaka Masutani, Kenji Ino, Masao Tago and Nobuhito Saito
No definitive method of preventing visual field deficits after stereotactic radiosurgery for lesions near the optic radiation (OR) has been available so far. The authors report the results of integrating OR tractography based on diffusion tensor (DT) magnetic resonance imaging into simulated treatment planning for Gamma Knife surgery (GKS).
Data from imaging studies performed in 10 patients who underwent GKS for treatment of arteriovenous malformations (AVMs) located adjacent to the OR were used for the simulated treatment planning. Diffusion tensor images performed without the patient's head being secured by a stereotactic frame were used for DT tractography, and the OR was visualized by means of software developed by the authors. Data from stereotactic 3D imaging studies performed after frame fixation were coregistered with the data from DT tractography. The combined images were transferred to a GKS treatment-planning workstation. Delivered doses and distances between the treated lesions and the OR were analyzed and correlated with posttreatment neurological changes.
In patients presenting with migraine with visual aura or occipital lobe epilepsy, the OR was located within 11 mm from AVMs. In a patient who developed new quadrantanopia after GKS, the OR had received 32 Gy. A maximum dose to the OR of less than 12 Gy did not cause new visual field deficits. A maximum dose to the OR of 8 Gy or more was significantly related to neurological change (p < 0.05), including visual field deficits and development or improvement of migraine.
Integration of OR tractography into GKS represents a promising tool for preventing GKS-induced visual disturbances and headaches. Single-session irradiation at a dose of 8 Gy or more was associated with neurological change.
Kyousuke Kamada, Tomoki Todo, Yoshitaka Masutani, Shigeki Aoki, Kenji Ino, R.T., Akio Morita and Nobuhito Saito
There is continuous interest in the monitoring of language function during tumor resection around the fron-totemporal regions of the dominant hemisphere. The aim of this study was to visualize language-related subcortical connections, such as the arcuate fasciculus (AF) by diffusion tensor (DT) imaging–based tractography.
Twenty-two patients with brain lesions adjacent to the AF in the frontotemporal regions of the dominant hemisphere were studied. The AF tractography was accomplished by placing initiation and termination sites (seed and target points) in the frontal and temporal regions, which were functionally identified by using functional magnetic resonance (fMR) imaging in conjunction with a verb generation task and magnetoencephalography (MEG) in conjunction with a reading task. The combination of fMR imaging and MEG data clearly demonstrated the hemispheric dominance of language functions, which was confirmed by an intracranial amobarbital test (Wada procedure). In all 22 patients, the authors were able to consistently visualize the AF by DT imaging–based tractography, using the functionally identified seed and target points and a fractional anisotropy value of 0.16. In two of 22 cases investigated, the functional information, including the results of AF tractography, fMR imaging, and MEG, was imported to a neuronavigation system and was validated by bipolar electric stimulation of the cortical and subcortical areas during awake surgery. The cortical stimulation to the gyrus that included the area of activation identified in fMR imaging with the language task evoked speech arrest, while the subcortical stimulation close to the AF reproducibly caused paranomia without speech arrest. Postoperative AF tractography showed that the distances between the stimulus points and the AF were within 6 mm.
The combination of these techniques facilitated accurate identification of the location of the AF and verification of the language fibers.
Kyousuke Kamada, Tomoki Todo, Takahiro Ota, Kenji Ino, Yoshitaka Masutani, Shigeki Aoki, Fumiya Takeuchi, Kensuke Kawai and Nobuhito Saito
To validate the corticospinal tract (CST) illustrated by diffusion tensor imaging, the authors used tractography-integrated neuronavigation and direct fiber stimulation with monopolar electric currents.
Forty patients with brain lesions adjacent to the CST were studied. During the operation, the motor responses (motor evoked potential [MEP]) elicited at the hand by the cortical stimulation to the hand motor area were continuously monitored, maintaining the consistent stimulus intensity (mean 15.1 ± 2.21 mA). During lesion resection, direct fiber stimulation was applied to elicit MEP (referred to as fiber MEP) to identify the CST functionally. The threshold intensity for the fiber MEP was determined by searching for the best stimulus point and changing the stimulus intensity. The minimum distance between the resection border and illustrated CST was measured on postoperative isotropic images.
Direct fiber stimulation demonstrated that tractography accurately reflected anatomical CST functioning. There were strong correlations between stimulus intensity for the fiber MEP and the distance between the CST and the stimulus points. The results indicate that the minimum stimulus intensity of 20, 15, 10, and 5 mA had stimulus points ~ 16, 13.2, 9.6, and 4.8 mm from the CST, respectively. The convergent calculation formulated 1.8 mA as the electrical threshold of the CST for the fiber MEP, which was much smaller than that of the hand motor area.
The investigators found that diffusion tensor imaging–based tractography is a reliable way to map the white matter connections in the entire brain in clinical and basic neuroscience applications. By combining these techniques, investigating the cortical-subcortical connections in the human CNS could contribute to elucidating the neural networks of the human brain and shed light on higher brain functions.
Taichi Kin, Hirofumi Nakatomi, Masaaki Shojima, Minoru Tanaka, Kenji Ino, Harushi Mori, Akira Kunimatsu, Hiroshi Oyama and Nobuhito Saito
In this study, the authors used preoperative simulation employing 3D computer graphics (interactive computer graphics) to fuse all imaging data for brainstem cavernous malformations. The authors evaluated whether interactive computer graphics or 2D imaging correlated better with the actual operative field, particularly in identifying a developmental venous anomaly (DVA).
The study population consisted of 10 patients scheduled for surgical treatment of brainstem cavernous malformations. Data from preoperative imaging (MRI, CT, and 3D rotational angiography) were automatically fused using a normalized mutual information method, and then reconstructed by a hybrid method combining surface rendering and volume rendering methods. With surface rendering, multimodality and multithreshold techniques for 1 tissue were applied. The completed interactive computer graphics were used for simulation of surgical approaches and assumed surgical fields. Preoperative diagnostic rates for a DVA associated with brainstem cavernous malformation were compared between conventional 2D imaging and interactive computer graphics employing receiver operating characteristic (ROC) analysis.
The time required for reconstruction of 3D images was 3–6 hours for interactive computer graphics. Observation in interactive mode required approximately 15 minutes. Detailed anatomical information for operative procedures, from the craniotomy to microsurgical operations, could be visualized and simulated three-dimensionally as 1 computer graphic using interactive computer graphics. Virtual surgical views were consistent with actual operative views. This technique was very useful for examining various surgical approaches. Mean (± SEM) area under the ROC curve for rate of DVA diagnosis was significantly better for interactive computer graphics (1.000 ± 0.000) than for 2D imaging (0.766 ± 0.091; p < 0.001, Mann-Whitney U-test).
The authors report a new method for automatic registration of preoperative imaging data from CT, MRI, and 3D rotational angiography for reconstruction into 1 computer graphic. The diagnostic rate of DVA associated with brainstem cavernous malformation was significantly better using interactive computer graphics than with 2D images. Interactive computer graphics was also useful in helping to plan the surgical access corridor.
Masanori Yoshino, Taichi Kin, Akihiro Ito, Toki Saito, Daichi Nakagawa, Kenji Ino, Kyousuke Kamada, Harushi Mori, Akira Kunimatsu, Hirofumi Nakatomi, Hiroshi Oyama and Nobuhito Saito
The authors assessed whether the combined use of diffusion tensor tractography (DTT) and contrast-enhanced (CE) fast imaging employing steady-state acquisition (FIESTA) could improve the accuracy of predicting the courses of the facial and cochlear nerves before surgery.
The population was composed of 22 patients with vestibular schwannoma in whom both the facial and cochlear nerves could be identified during surgery. According to DTT, depicted fibers running from the internal auditory canal to the brainstem were judged to represent the facial or vestibulocochlear nerve. With regard to imaging, the authors investigated multifused CE-FIESTA scans, in which all 3D vessel models were shown simultaneously, from various angles. The low-intensity areas running along the tumor from brainstem to the internal auditory canal were judged to represent the facial or vestibulocochlear nerve.
For all 22 patients, the rate of fibers depicted by DTT coinciding with the facial nerve was 13.6% (3/22), and that of fibers depicted by DTT coinciding with the cochlear nerve was 63.6% (14/22). The rate of candidates for nerves predicted by multifused CE-FIESTA coinciding with the facial nerve was 59.1% (13/22), and that of candidates for nerves predicted by multifused CE-FIESTA coinciding with the cochlear nerve was 4.5% (1/22). The rate of candidates for nerves predicted by combined DTT and multifused CE-FIESTA coinciding with the facial nerve was 63.6% (14/22), and that of candidates for nerves predicted by combined DTT and multifused CE-FIESTA coinciding with the cochlear nerve was 63.6% (14/22). The rate of candidates predicted by DTT coinciding with both facial and cochlear nerves was 0.0% (0/22), that of candidates predicted by multifused CE-FIESTA coinciding with both facial and cochlear nerves was 4.5% (1/22), and that of candidates predicted by combined DTT and multifused CE-FIESTA coinciding with both the facial and cochlear nerves was 45.5% (10/22).
By using a combination of DTT and multifused CE-FIESTA, the authors were able to increase the number of vestibular schwannoma patients for whom predicted results corresponded with the courses of both the facial and cochlear nerves, a result that has been considered difficult to achieve by use of a single modality only. Although the 3D image including these prediction results helped with comprehension of the 3D operative anatomy, the reliability of prediction remains to be established.
Keisuke Maruyama, Tomoyuki Koga, Kyousuke Kamada, Takahiro Ota, Daisuke Itoh, Kenji Ino, Hiroshi Igaki, Shigeki Aoki, Yoshitaka Masutani, Masahiro Shin and Nobuhito Saito
To prevent speech disturbances after Gamma Knife surgery (GKS), the authors integrated arcuate fasciculus (AF) tractography based on diffusion tensor (DT) MR imaging into treatment planning for GKS.
Arcuate fasciculus tractography was retrospectively integrated into planning that had been previously performed by neurosurgeons and radiation oncologists. This technique was retrospectively applied to 12 patients with arteriovenous malformations adjacent to the AF. Diffusion tensor images were acquired before the frame was affixed to the patient's head and DT tractography images of the AF were created using the authors' original software. The data from DT tractography and stereotactic 3D imaging studies obtained after frame fixation were transported to a treatment planning workstation for GKS and coregistered so that the delivered doses and incidence of posttreatment aphasia could be assessed.
The AF could not be depicted in 2 patients who initially presented with motor aphasia caused by hemorrhaging from arteriovenous malformations. During the median follow-up period of 29 months after GKS, aphasia developed in 2 patients: 30 Gy delivered to the frontal portion of the AF caused conduction aphasia in 1 patient, and 9.6 Gy to the temporal portion led to motor aphasia in the other. Speech dysfunction was not observed after a maximum radiation dose of 10.0–16.8 Gy was delivered to the frontal fibers in 4 patients, and 3.6–5.2 Gy to the temporal fibers in 3.
The authors found that administration of a 10-Gy radiation dose during GKS was tolerated in the frontal but not the temporal fibers of the AF. The authors recommend confirmation of the dose by integration of AF tractography with GKS, especially in lesions located near the temporal language fibers.