Kazuho Hirahara

Identification of the Cerebral Motor Cortex by Focal Magnetic Stimulation: Clinical Application to Neurosurgical Patients

A figure-8 coil was designed that was capable of generating currents over a relatively limited area. In this study, we used the figure-8 coil to localize human cerebral motor cortex by transcranial magnetic stimulation and assessed its value as a diagnostic tool for neurosurgical disease. The subjects were 10 normal volunteers and 12 neurosurgical patients. The points obtaining a response were plotted and the response area was delineated for each stimulus output. Rectangular coordinates were subsequently determined for the C3-Cz-C4 line with the stimulation sites set 1.0 cm apart. Then amplitude and latency maps were displayed by a computer wave map program. In normal volunteers, the posterior margin of the site where a threshold +5% stimulus obtained a response from the THE or ADM muscles almost coincided with the central sulcus. The optimal areas were relatively narrow on the amplitude and latency maps. In the patient with a left frontal convexity meningioma, the left threshold +5% area for the THE and ADM muscles showed marked anterolateral shift. No threshold map could be obtained on the affected side in patients with metastatic tumor and astrocytoma. Low perfusion areas caused by moyamoya disease and arteriovenous malformations produced narrowing of the optimal zone on the threshold map of the affected side. Hyperexcitability of the motor cortex was recognized in the arteriovenous malformation patients. Transcranial focal magnetic stimulation is a useful noninvasive diagnostic method for identification of the human cerebral motor cortex. It provides important information about changes in the localization and excitability of the motor cortex in neurosurgical patients and should be helpful for treatment planning.

An applicability study on a CT-guided stereotactic technique for functional neurosurgery.

When a CT-guided stereotactic technique for functional neurosurgery is adopted, extremely precise targeting is needed to obtain satisfactory surgical results. In this study the authors have investigated the accuracy of the target points determined by CT-guided techniques and compared with those of conventional roentgenographically controlled stereotactic procedures. Stereotactic surgery, employing the Brown-Roberts-Wells (BRW) system, was performed contemporarily 26 times in 23 patients, that is, 9 times in 8 patients for functional neurosurgery using with the roentgenographic method, and 17 times in 15 patients with the CT-guided method only for intracranial neoplasm biopsy. As a result, there were no problems of accuracy of determining the target points by CT-guided stereotactic surgery with the BRW system. When applying this technique for functional neurosurgery, it should be pointed out that there could be a discrepancy within 2 mm from the conventional target determination.

Subfrontal schwannoma mimicking neuroblastoma: case report.

Computed tomography (CT), performed in a healthy 28-year-old man after minor head injury, detected a frontal base tumor. Neurological examination revealed left hyposmia. On magnetic resonance imaging scans, there was a heterogeneously enhanced tumor located in the left paramedian frontal base with extension into the left ethmoid sinus. Angiography showed a hypervascular mass in the left anterior cranial fossa; it was mainly fed by the left ethmoidal artery. Positron emission tomography scanning showed moderate accumulation of 11-methylmethionine and low accumulation of 18-fluorodeoxyglucose (FDG) at the tumor site. Bone image CT disclosed compressive, nondestructive deformation of the left frontal base. The preoperative diagnosis was olfactory neuroblastoma or meningioma. The tumor was totally resected via bifrontal craniotomy. The tumor was histologically diagnosed as typical schwannoma; it was positive for S-100 protein. We report a rare subfrontal schwannoma with extension into the nasal cavity that mimicked neuroblastoma. Low FDG accumulation and compressive deformation of the anterior skull base may help in the differential diagnosis of these tumors.

Lateral Suboccipital Retrosigmoid Approach with Tentorial Incision for Petroclival Meningiomas: Technical Note

Introduction The resection of petroclival meningiomas presents great neurosurgical challenges. Although multiple surgical approaches have been developed, the retrosigmoid route tends to be used to address tumors that are predominantly located in the posterior fossa. Our modification of the lateral suboccipital retrosigmoid approach with the placement of a tentorial incision yields good visualization of the supratentorial part of the tumor around the midbrain. Methods We treated four patients, one with primary and three with recurrent petroclival meningioma, by our modified approach. After lateral suboccipital craniotomy, the infratentorial part of the tumor was removed after detaching it from the tentorial surface. The cerebellar tentorium was then carefully incised from the supracerebellar angle, taking care not to damage the superior cerebellar artery and trochlear nerve. Results The operative field surrounding the midbrain was widened by this procedure, and safe dissection of the tumor from the brainstem and other neurovascular structures was performed with direct observation of the interface. Conclusions Our approach is a useful modification of the retrosigmoid approach to petroclival meningiomas. It facilitates the safe resection of the supratentorial part of the tumor in the ambient cistern behind the tentorium.

Pituitary adenoma with cholesterol clefts

Histologically, cholesterol clefts are often observed in craniopharyngioma, Rathke’s cleft cyst, and various granulomas. However, pituitary adenomas with cholesterol clefts are rare. A 46-year-old woman developed visual field disturbance. She had no history of severe headache that would suggest pituitary apoplexy. She presented with homonymous bitemporal hemianopsia and galactorrhea. Blood prolactin level was 63.1 ng/mL. Other hypophysial hormone levels were within normal range. Magnetic resonance imaging revealed a pituitary tumor with intratumoral cyst. The cyst showed high intensity on T1- and T2-weighted images. The tumor was demonstrated with iso intensity on T1-weighted image and with high intensity on T2-weighted image.She underwent trans-sphenoidal surgery. The tumor was soft, with yellowish, oily fluid, probably the cyst content. By light microscopy with hematoxylin and eosin staining, a typical chromophobic adenoma of the pituitary was identified. Immunostaining revealed immunoreactivity for ACTH in several cells. Many cholesterol clefts and several hemosiderin pigment containing macrophages were observed. Electron microscopy demonstrated a pituitary adenoma with sparse and small secretory granules and numerous lysosomes. The cyst was most likely caused by focal hemorrhagic infarction, followed by the formation of cholesterol crystals, the appearance of hemosiderin containing macrophages, foreign body product cells, and accumulation of lysosomes.

Intrasellar Epidermoid Cyst

A rare case of an intrasellar epidermoid cyst with ophthalmologic and endocrinological disorders is reported. A 54-year-old male complained of decreased visual acuity and visual field defects. On admission, bitemporal hemianopsia and panhypopituitarism were revealed. Computed tomography (CT) demonstrated a homogeneous low density area in the sellar region. The margin of the low density area was slightly enhanced. The low density area was clearly distinguished from the cerebrospinal fluid space in the metrizamide CT cisternography. The mass lesion was totally removed by the transsphenoidal approach. Histological examination of the surgical specimen showed that the cyst wall consisted of stratified squamous epithelium with keratinization and confirmed the diagnosis of epidermoid cyst.

An effective technique for preventing the subcutaneous migration of the abdominal lumboperitoneal shunts catheters.

Migration of the lumboperitoneal shunt catheter into the abdominal subcutaneous space is not uncommon. We devised a new simple method (Transrectus Gap method we call) for installment of peritoneal tube aiming to prevent the migration.