Seiichi Furuya

Neurovascular Compression of the Rostral Ventrolateral Medulla Related to Essential Hypertension

The rostral ventrolateral medulla (RVLM) is thought to serve as a final common pathway for the integration of central cardiovascular information and to be important for the mediation of central pressor responses. An association between essential hypertension and neurovascular compression of the RVLM has been reported. To confirm this relationship and to quantitatively measure the distances between the RVLM and the neighboring arteries, we performed magnetic resonance imaging using a high-resolution 512x512 matrix and magnetic resonance angiography in 49 subjects (21 patients with essential hypertension, 10 patients with secondary hypertension, and 18 normotensive subjects). One patient with essential hypertension was excluded from the evaluations because of inadequate assessment due to poor images. Neurovascular compression of the RVLM was observed in 15 of 20 (75%) patients with essential hypertension. In contrast, neurovascular compression was observed in only 1 of 10 (10%) patients with secondary hypertension and only 2 of 18 (11%) normotensive subjects. The rate of observed neurovascular compression in the essential hypertension group was significantly higher than that in the secondary hypertension group and the normotensive group (P<.01 for both). The distances between the RVLM and the nearest arteries in the essential hypertension group were significantly shorter than those in the other groups (P<.05 for all). On the other hand, the distances between the surface of the medulla oblongata and the nearest arteries did not differ among these three groups. These results suggest that neurovascular compression of the RVLM, but not of the other regions of the medulla oblongata, is particularly related to essential hypertension.

Decreases in Blood Pressure and Sympathetic Nerve Activity by Microvascular Decompression of the Rostral Ventrolateral Medulla in Essential Hypertension

BACKGROUND Neurovascular compression of the rostral ventrolateral medulla, a major center regulating sympathetic nerve activity, may be causally related to essential hypertension. Microvascular decompression of the rostral ventrolateral medulla decreases elevated blood pressure. CASE DESCRIPTION A 47-year-old male essential hypertension patient with hemifacial nerve spasms exhibited neurovascular compression of the rostral ventrolateral medulla and facial nerve. Microvascular decompression of the rostral ventrolateral medulla successfully reduced blood pressure and plasma and urine norepinephrine levels, low-frequency to high-frequency ratio obtained by power spectral analysis, and muscle sympathetic nerve activity. CONCLUSIONS This case suggests not only that reduction in blood pressure by microvascular decompression of the rostral ventrolateral medulla may be mediated by a decrease in sympathetic nerve activity but also that neurovascular compression of this area may be a cause of blood pressure elevation via increased sympathetic nerve activity.

Sympathetic activation and contribution of genetic factors in hypertension with neurovascular compression of the rostral ventrolateral medulla.

OBJECTIVE The rostral ventrolateral medulla is an important center for the regulation of sympathetic and cardiovascular activities. Reportedly, neurovascular compression of the rostral ventrolateral medulla may be causally related to essential hypertension. We aimed to determine the mechanism behind elevated blood pressure in hypertensive patients with compression of the rostral ventrolateral medulla and to investigate whether genetic factors contribute to the etiology of hypertension with compression. DESIGN AND METHODS The study included 56 patients with essential hypertension and 25 normotensive individuals. With the use of magnetic resonance imaging, the essential hypertension group was subdivided into hypertension with compression and without compression groups. We compared plasma levels of hormones that raise blood pressure and family histories of hypertension between the two hypertension groups and the normotension group. RESULTS Plasma norepinephrine levels, but not plasma renin activity, aldosterone, epinephrine, or vasopressin levels, were significantly higher in the hypertension with compression group (389+/-53 pg/ml) than in the hypertension without compression group (217+/-38, P<0.05) or in the normotension group (225+/-30, P<0.05). The percentage of individuals who had two hypertensive parents was significantly higher in the hypertension with compression group (39.4%) than in the hypertension without compression group (13.0%, P<0.05) or in the normotension group (8.0%, P<0.01). CONCLUSIONS These results indicate that neurovascular compression of the rostral ventrolateral medulla might be, at least in part, causally related to essential hypertension by increasing sympathetic nerve activity. They also suggest that genetic factors might contribute to the etiology of hypertension with neurovascular compression.

APPLICATION OF PROTON CHEMICAL SHIFT IMAGING IN MONITORING OF GAMMA KNIFE RADIOSURGERY ON BRAIN TUMORS

Our objective was to assess proton chemical shift imaging for potential clinical application in monitoring response to gamma knife radiosurgery. Twenty-five proton chemical shift imaging studies and conventional magnetic resonance images were performed on six patients with intracranial tumors. The peak areas of N-acetylaspartate, choline-containing compounds (Cho), creatine, and lipids were calculated and normalized to N-acetylaspartate in the contralateral hemisphere. The spectra from the lesion before treatment showed a relatively high Cho peak, reported as a characteristic spectrum of tumors. Tumor size and Cho level after radiosurgery did not increase except in two cases. In these cases, radiation necrosis was observed with elevated Cho and a mobile lipid peak. Stable or decreased Cho seems to suggest a loss of tumor viability, and changes in Cho indicate the effectiveness of radiosurgery. Increasing Cho and the appearance of the mobile lipid peak may distinguish radiation necrosis from recurrent tumors, which cannot be distinguished by magnetic resonance imaging.

Evaluation of metabolic heterogeneity in brain tumors using 1H‐chemical shift imaging method

Seventeen brain tumors were measured by 1H‐CSI (chemical shift imaging) in a 1.5 T clinical magnetic resonance scanner. The metabolic peaks obtained were evaluated by two methods. One method was to obtain the percentage of each metabolite relative to the combined choline, creatine and NAA peak areas, and the other method was to obtain a ratio of the tumor to contralateral brain. The percentage of choline (%Cho) and choline ratio increased, and the %NAA and NAA ratio decreased in the gliomas and malignant tumors. In relation to grading, %Cho increased but the choline ratio did not. We believed the reason for this was that there were many foci of microscopic necrosis in the glioma grade IV. Free lipids were observed in most of the high grade gliomas and in a malignant tumor. Lactate increased in higher grade tumors. Meningiomas showed the highest %Cho. Statistical differences between the grades of glioma were not detected because many tumors had heterogeneous tissue. One resolution to this problem was metabolite mapping. Mapping of the percentage of metabolites was suitable because it described the regional metabolic changes and the resulting signal to noise ratio was better than that achieved by other methods of evaluation.

Clinical application of magnetoencephalography in a patient with corticobasal degeneration.

Previous neuroimaging studies in corticobasal degeneration (CBD), such as MRI and positron emission tomography, showed lateralized cortical atrophy and a decrease in cortical oxygen metabolism, respectively. The advantage of magnetoencephalography in the research of the auditory system is that activity of both hemispheres can be detected separately. Auditory‐evoked magnetic fields (AEFs) were then applied to a patient with corticobasal degeneration. The strength of N1 OOm equivalent current dipoles (ECD) in left hemisphere was extremely smaller (20 nAm) than that in right hemisphere (48 nAm). This results implies that CBD patient might have a decrease in the number of neurons in the primary auditory cortex. This study suggests that AEF measurement is one of the most powerful tools for detecting latent impairment of auditory function in patients with corticobasal degeneration.

Diagnostic Imaging of Brain Function and Metabolism by Magnetic Resonance Methods

Brain metabolism and function were examined by using multimodality magnetic resonance methods. In magnetic resonance spectroscopy (MRS) and chemical shift imaging (CSI), various intrinsic metabolites in the brain were detected and their distribution was visualized. Energy metabolism and phospholipid metabolism can be examined by using the 31P nucleus. Increased phosphomonoesters in brain tumors and infant brain indicate the changes of phospholipid metabolism. Decreased phosphocreatine and increased lactate in acute cerebral infarction indicate the impairment of aerobic metabolism. Amino acids, choline, creatine, and lactate can be detected by using the nucleus. Decrease of N-acetyl aspartate (NAA) in brain tumors, degenerative diseases, and cerebral infarction indicated the loss of neurons. Increased lactate was observed in hypoxic cell fractions such as malignant tumors and infarction. In diffusion weighted imaging (DWI), anisotropy of water diffusion was detected in the white matter. The apparent diffusion coefficient (ADC) was different among three types of brain edema, between benign astrocytoma and cerebral infarction, and between arachnoid and epidermoid cysts. In functional magnetic resonance imaging (fMRI) using the gradient echo method on conventional MRI scanners, a rapid increase of signal intensity was observed in the primary cortical area corresponding to each activation task such as finger movements, photic stimulation, and hearing of words. The fMRI was also obtained during complex tasks such as imagination of hand grasping. The multimodality MR methods using various analytical techniques, such as MRS, CSI, DWI, and fMRI, are unique and useful methods to examine brain metabolism and function noninvasively; consequently, these are promising methods for examining the pathophysiology of various cerebral disorders.

Neuroimaging of Cerebral Metabolism in Severe Diffuse Brain Injury in Chronic Stage: Part 2. MR Spectroscopy and Spectroscopic Imaging

We have developed the 31P- and 1H-magnetic resonance spectroscopic imaging (MRSI) and applied them to severe diffuse brain injury(SDBI) in the chronic stage. The three patients are all young male and had the so called diffuse axonal injury (DAI) by the traffic accident. The DAI was judged by neurological symptoms, computed tomography (CT) and magnetic resonance imaging (MRI). 31P- and 1H-MRSI were performed 2 to 16 months after injury. The decrease of phosphocreatine (PCr) was observed by 31P-MRSI and the decrease of NAA by 1H-MRSI in the wide area of the brain. The decrease of NAA reflects the neuronal damage and consequently indicates the functional deterioration. Therefore, it is suggested that the amount of NAA could be the indicator of neuronal function and 1H-MRSI is useful for the examination of the neurological condition in SDBI.