Posterior fossa neurovascular anomalies in essential hypertension

Relationship of neurovascular compression to central sympathetic discharge and essential hypertension

OBJECTIVES

We planned to examine the relationship between neurovascular compression (NVC) of the rostral ventrolateral medulla (RVLM) and the magnitude of central sympathetic hyperactivity in normal subjects and in patients with untreated and uncomplicated essential hypertension (EHT).

BACKGROUND

Previously it has not been possible to establish a definitive relationship between EHT and NVC of the RVLM, a location containing efferent sympathetic vasoconstrictor neurons. Furthermore, the relationship between NVC and magnitude of sympathetic nerve hyperactivity has not been adequately examined, despite the knowledge that hyperactivity varies according to EHT severity.

METHODS

In 83 subjects, we used magnetic resonance imaging to detect NVC and, independently, peroneal microneurography to quantify muscle sympathetic nerve activity (MSNA), expressed as the mean frequency of multi-unit discharge (m-MSNA) and of single units (s-MSNA). Subjects were classified according to arterial pressure values into groups with normal (NT) (n = 24) or high-normal (HN) (n = 14) arterial pressure and mild (EHT-1) (n = 26) or severe (EHT-2/3) (n = 19) EHT.

RESULTS

A significantly greater sympathetic activity was found in 23 subjects with NVC, compared with 60 subjects without NVC. The prevalence of NVC and the magnitude of sympathetic hyperactivity were greater in the EHT-1 group (p < 0.05) than in the other three groups. There was no significant difference in confounding variables between the groups. Although increased sympathetic activity was strongly predictive of NVC, this was not significantly related to baroreceptor sensitivity controlling the pulse interval (cardiac baroreceptor reflex sensitivity).

CONCLUSIONS

Neurovascular compression of the RVLM may cause central sympathetic activation in normal and hypertensive populations and therefore has significant implications regarding the pathogenesis of EHT.

Three-dimensional visualization of neurovascular relationships in the posterior fossa: technique and clinical application

Object. The goal of this study was to describe the authors' technique for three-dimensional (3D) visualization of neurovascular relationships in the posterior fossa at the surface of the brainstem. This technique is based on the processing of high-resolution magnetic resonance (MR) imaging data. The principles and technical details involved in the accurate simultaneous visualization of vessels and cranial nerves as tiny structures are presented using explicit and implicit segmentation as well as volume rendering.

Methods. In this approach 3D MR constructive interference in steady state imaging data served as the source for image processing, which was performed using the Linux-based software tools SegMed for segmentation and Qvis for volume rendering. A sequence of filtering operations (including noise reduction and closing) and other software tools such as volume growing are used for a semiautomatic coarse segmentation. The subsequent 3D visualization in which implicit segmentation is used for the differentiation of cranial nerves, vessels, and brainstem is achieved by allocating opacity and color values and adjusting the related transfer functions. This method was applied to the presurgical evaluation in a consecutive series of 55 patients with neurovascular compression syndromes and the results were correlated to surgical findings. The potential for its use, further developments, and remaining problems are discussed.

Conclusions. This method provides an excellent intraoperative real-time virtual view of difficult anatomical relationships.

Type 2 diabetes mellitus, etiology and possible treatment: preliminary report

BACKGROUND

Insulin resistance has been proposed as the initial step in the cascade toward type 2 diabetes mellitus. The mechanisms underlying the development of insulin resistance are not fully understood. We hypothesize that neurovascular interactions, in particular arterial elongation, causes compression of the right lateral medulla, triggering a state of autonomic dysfunction including hyperactivity of pancreatic endocrine function, and predisposes to insulin resistance and the development of type 2 diabetes.

METHODS

The clinical and operative findings were reviewed retrospectively in 15 patients with primary diagnoses of various right-sided cranial rhizopathies, but with a common diagnosis of type 2 diabetes mellitus. After microvascular decompression was performed for the primary diagnosis, arterial compression was observed of the lateral medulla and cranial nerve X and treated with microvascular decompression. Known duration of the diabetes ranged from "new" (patient was diagnosed as a result of preoperative blood work) to 16 years (mean 7.3 years). Duration of diabetes diagnosis was unknown in 2 patients. Follow-up was from 3 to 113 months (mean 29.9 months).

RESULTS

Ten of the 15 patients (66%) showed improvement in their blood glucose control; 5 of those 10 (50%) did so with no (4 patients) or less (1 patient) diabetes medication.

CONCLUSIONS

We have shown that arterial compression of the right lateral medulla is consistently present in patients with diabetes mellitus and that microvascular decompression can be performed safely. Further studies are necessary and are under way.

Analysis and 3-dimensional visualization of neurovascular compression syndromes

RATIONALE AND OBJECTIVES

Neurovascular compression syndromes are currently examined with 2-dimensional representations of tomographic volumes. To overcome this drawback, coarse segmentation followed by direct volume rendering of magnetic resonance (MR) data is introduced supporting a detailed 3-dimensional analysis of the related structures.

MATERIALS AND METHODS

This approach is based on MR-CISS (constructive interference in steady state) volumes providing the required high resolution to achieve an improved spatial understanding. In relation to the size of the involved nerves and vessels, an explicit segmentation is extremely difficult. Therefore, a semi-automatic preprocessing sequence was developed consisting of noise reduction, morphologic filtering, and volume growing. To delineate the target structures within the segmented and labeled subvolumes, interactive direct volume rendering was applied that allows delineating the target structures in the area of the cerebrospinal fluid with implicit segmentation based on predefined transfer functions assigning opacity and color values to the intensity values of the image data. For a further improved analysis, registration of the MR-CISS volumes with MR angiography is recommended to support differentiating vessels and nerves on the one side and arteries and veins on the other.

RESULTS

The presented method was applied in a consecutive series of 47 cases of different neurovascular compression syndromes, supporting the presurgical analysis of the image data. Additionally, the results were compared with the operative findings.

CONCLUSION

Overall, this approach contributes significantly to an optimized 3-dimensional analysis and understanding of neurovascular compression syndromes. Based on the obtained results, it is of high value for the planning of surgery.

Vascular Compression of Rostral Medulla Oblongata: Prospective MR Imaging Study in Hypertensive and Normotensive Subjects

PURPOSE

To prospectively evaluate prevalence of neurovascular contacts (NVCs) at the rostral medulla oblongata in normotensive and hypertensive subjects.

MATERIALS AND METHODS

Forty-three patients with severe essential hypertension and 45 normotensive subjects were matched for age, sex, and body mass index. Magnetic resonance (MR) imaging included transverse and coronal T2-weighted turbo spin-echo (section thickness, 3.0 mm), transverse three-dimensional (3D) time-of-flight MR angiographic (section thickness, 0.8 mm), and 3D constructive interference in steady state (CISS) (section thickness, 1.0 mm) sequences. All MR images were reviewed by two radiologists who were blinded to the hypertensive status of subjects. Presence and degree of NVC at rostral medulla and left/right rostral ventrolateral medulla (RVLM) were evaluated together with conspicuity of anatomic structures on MR images. Differences in prevalence of NVC among normotensive and hypertensive subjects were tested for statistical significance (P <.05) by using nonparametric tests.

RESULTS

Among hypertensive patients, 34 (79%) of 43 showed NVC of rostral medulla at any location, and 14 (33%) of 43 had NVC at the left RVLM. In controls (normotensive subjects), 35 (78%) of 45 showed NVC of rostral medulla, and 17 (38%) of 45 had NVC at left RVLM. Prevalence of NVC was not significantly different between both groups at any location of rostral medulla. Compared with T2-weighted turbo spin-echo and 3D time-of-flight MR imaging sequences, 3D CISS offered better contrast resolution of neural and vascular structures and superior delineation of outer vascular contours.

CONCLUSION

Vascular compression of the rostral medulla oblongata is a frequent finding in both hypertensive and normotensive subjects. Results of this study do not support NVC at left RVLM as an etiologic factor in essential hypertension.

Neurovascular compression associated with trigeminal neuralgia and systemic arterial hypertension: surgical treatment

OBJECTIVE AND IMPORTANCE

To highlight arterial hypertension as an additional factor favoring surgical indication in neurovascular compression syndromes such as trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia.

CLINICAL PRESENTATION

A 52-year-old woman with trigeminal neuralgia concomitant with systemic arterial hypertension, submitted initially to unsatisfactory conservative treatment, presents tortuousness and enlargement of the vertebral artery (VA) topography on magnetic resonance imaging (MRI). A microsurgical neurovascular decompression of the trigeminal nerve and the medulla was performed, revealing that the compression was due to the superior cerebellar artery instead of the VA. Both the neuralgia and the hypertension were controlled with no need of medication during a 1-year follow-up.

CONCLUSION

Surgical indication in neurovascular compression disorders should be reinforced in the presence of concomitant arterial hypertension and a compatible MRI examination.

Mendelian forms of human hypertension and mechanisms of disease

Mendelian forms of hypertension have ushered in a revolution in our knowledge of blood pressure and volume regulation. If we include information on syndromes involving low blood pressure, this knowledge base is doubled. Glucocorticoid remediable aldosteronism, apparent mineralocorticoid excess, and mutations in the mineralocorticoid receptor gene have given us brilliant insights into mineralocorticoid-induced hypertension. The latter discovery has elucidated how mutations may modify the receptor sufficiently to allow erstwhile antagonists to have an agonistic action. The epithelial sodium channel (ENaC) has been elucidated. Gain-of-function mutations in the beta and gamma subunits of ENaC cause Liddle's syndrome. Loss-of-function mutations in all three subunits of ENaC cause hypotension (pseudohypoaldosteronism type I). Thus, all three subunits can be mutated, causing either hyper or hypotension. Three loci have been described for Gordon's syndrome, pseudohypoaldosteronism type II. Two members of the WNK serine-threonine kinase family have recently been found to be responsible. Their function has been largely elucidated. Autosomal dominant hypertension with brachydactyly features normal sodium and renin-angiotensin-aldosterone responses. The gene has been mapped to chromosome 12p. The condition is interesting because it may represent a novel neural form of hypertension. Finally, at least 5 different genes have been described that when mutated can cause pheochromocytoma. Thus, the elucidation of Mendelian blood pressure-regulatory disorders has been a resounding success.

Investigations using magnetic resonance imaging: is neurovascular compression present in patients with essential hypertension?

OBJECT

A possible relationship between neurovascular compression of the rostral ventrolateral medulla oblongata (RVLM) and essential hypertension is investigated using a specifically designed magnetic resonance (MR) imaging method. In conjunction with the ninth and 10th cranial nerves, baroreceptor afferents enter the RVLM, which represents a crucial relay for regulation of autonomic blood pressure. In 1985 Jannetta and coworkers proposed a causal relationship between essential hypertension and intraoperatively observed neurovascular compression of the left RVLM.

METHODS

Currently, MR imaging is the method of choice for the assessment of neurovascular relationships at the brainstem. By obtaining axial images of a thin-slice turbo inversion-recovery sequence and three-dimensional time-of-flight MR angiograms (fast imaging with steady-state precision), the authors documented the occurrence of neurovascular contacts with the RVLM at the level of the root entry zones (REZs) of the ninth and 10th cranial nerves in 25 patients with essential hypertension, 30 normotensive volunteers, and 10 patients with renal hypertension. Neurovascular contacts with the REZ at the left RVLM were found in 32% of patients with essential hypertension, 37% of normotensive volunteers, and 20% of patients with renal hypertension. In total, neurovascular contacts on either side of the RVLM were documented in 68% of patients with essential hypertension, 53% of normotensive volunteers, and 50% of patients with renal hypertension.

CONCLUSIONS

The results do not support the theory of neurovascular compression in cases of essential hypertension. Findings of neurovascular contacts on MR images are not indications for decompression surgery. For further clarification, however, prospective MR imaging studies should be considered in young patients with essential hypertension in whom the history of high blood pressure is short.

Practice-based randomized controlled-comparison clinical trial of chiropractic adjustments and brief massage treatment at sites of subluxation in subjects with essential hypertension: pilot study

OBJECTIVE

To determine the feasibility of conducting a randomized clinical trial in the private practice setting examining short- and long-term effects of chiropractic adjustments for subjects with essential hypertension compared with a brief soft tissue massage, as well as a nontreatment control group.

DESIGN

Randomized controlled-comparison trial with 3 parallel groups.

SETTING

Private practice outpatient chiropractic clinic.

PATIENTS

Twenty-three subjects, aged 24 to 50 years with systolic or diastolic essential hypertension.

INTERVENTIONS

Two months of full-spine chiropractic care (ie, Gonstead) consisting primarily of specific-contact, short-lever-arm adjustments delivered at motion segments exhibiting signs of subluxation. The massage group had a brief effleurage procedure delivered at localized regions of the spine believed to be exhibiting signs of subluxation. The nontreatment control group rested alone for a period of approximately 5 minutes in an adjustment room.

MAIN OUTCOME MEASURES

Cost per enrolled subject, as well as systolic and diastolic blood pressure (BP) measured with a random-0 sphygmomanometer and patient reported health status (SF-36). Pilot study outcome measures also included an assessment of cooperation of subjects to randomization procedures and drop-out rates, recruitment effectiveness, analysis of temporal stability of BPs at the beginning of care, and the effects of inclusion/exclusion criteria on the subject pool.

RESULTS

Thirty subjects enrolled, yielding a cost of $161 per enrolled subject. One subject was later determined to be ineligible, and 6 others dropped out. In both the chiropractic and massage therapy groups, all subjects were classified as either overweight or obese; in the control group there were only 2 classified as such. SF-36 profiles for the groups were similar to that of a normal population. The mean change in diastolic BP was -4 (95% confidence interval [CI]: -8.6, 0.5) in the chiropractic care group, 0.5 (95% CI: -3.5, 4.5) in the brief massage treatment group, and -4.9 (95% CI: -9.7, -0.1) in the no treatment control group. At the end of the study period, this change was -6.3 (95% CI: 13.1, 0.4), -1.0 (95% CI: -7.5, 15.6), -7.2 (95% CI: -13.3, -1.1) in the 3 study groups. The mean improvements in the chiropractic care and no treatment control groups remained consistent over the follow-up period.

CONCLUSIONS

This pilot study elucidated several procedural issues that should be addressed before undertaking a full-scale clinical trial on the effects of chiropractic adjustments in patients with essential hypertension. A multidisciplinary approach to recruitment may need to be used in any future efforts because of the limited subject pool of patients who have hypertensive disease but are not taking medications for its control. Measures need to be used to assure comparable groups regarding prognostic variables such as weight. Studies such as these demonstrate the feasibility of conducting a full-scale 3-group randomized clinical trial in the private practice setting.

Neurovascular contact and blood pressure response in young, healthy, normotensive men

BACKGROUND

Neurovascular contact (NVC) of the left rostral ventrolateral medulla has been implicated in the pathogenesis of "essential" hypertension, and recent studies suggest that this anomaly may be genetically determined. We therefore assessed the prevalence of this vascular anomaly in young normotensive volunteers. We also studied blood pressure, heart rate reactivity, and changes in baroreflex sensitivity in response to mental and physical stress in a subset of subjects with positive and negative brainstem findings.

METHODS

Magnetic resonance imaging of the brainstem was performed in 113 young (aged 25 +/- 8 years), normotensive male volunteers. Baroreflex sensitivity was then assessed in 13 subjects with positive brainstem findings and 20 subjects with negative findings.

RESULTS

Left-sided NVC was found in 19 subjects. Blood pressure levels, heart rate, and baroreflex sensitivity were similar in all groups. However, modulation of baroreflex sensitivity was reduced under mental and physical stress in subjects with a positive finding for NVC. Subjects with a positive finding also had a significantly lower body mass index than those with a negative finding.

CONCLUSIONS

Left-sided NVC is present in approximately one-fifth of young normotensive men, and may modulate the baroreceptor reflex under stress in these individuals.

Hypertension in patients with neurovascular compression is associated with increased central sympathetic outflow

Recent data suggest a causal relationship between essential hypertension and neurovascular compression (NVC) at the rostral ventrolateral medulla. An increase of central sympathetic outflow might be an underlying pathomechanism. The sympathetic nerve activity to muscle was recorded in 21 patients with hypertension with NVC (NVC+ group) and in 12 patients with hypertension without NVC (NVC- group). Heart rate variability, respiratory activity, BP, and central venous pressure at rest and during unloading of cardiopulmonary baroreceptors with lower-body negative pressure and during a cold pressor test were also measured. Resting sympathetic nerve activity to muscle was twice as high in the NVC+ group compared with the NVC- group (34 +/- 22 versus 18 +/- 6 bursts/min; P < 0.05). Resting heart rate (P = 0.06) and low- to high-frequency power ratio values (P = NS) (as indicators of cardiac sympathovagal balance) tended to be augmented as well in the NVC+ group. The sympathetic nerve activity to muscle response to the cold pressor test was increased in the NVC+ group versus the NVC- group (+15 +/- 11 versus 6 +/- 12 bursts/min; P = 0.05), but hemodynamic and sympathetic nerve responses to lower-body negative pressure did not differ between the two groups. It is concluded that NVC of the rostral ventrolateral medulla in patients with essential hypertension is accompanied by increased central sympathetic outflow. Therefore, these data support the hypothesis described in the literature: in a subgroup of patients, essential hypertension might be causally related to NVC of the rostral ventrolateral medulla, at least in part, via an increase in central sympathetic outflow.

Long-term results after microvascular decompression in essential hypertension

BACKGROUND AND PURPOSE

In 1998, 8 patients with severe, intractable arterial hypertension and MR tomography-demonstrated neurovascular contact of a looping artery at the root entry zone of cranial nerves IX and X, causing neurovascular compression, underwent neurosurgical decompression. The short-term results showed a normalization of blood pressure with a markedly reduced antihypertensive drug regimen in 7 patients. To determine the longer-term outcome concerning blood pressure and secondary organ damage after neurovascular decompression, we studied these 8 operated patients prospectively for a mean follow-up of 3.5 years after surgical intervention.

METHODS

Eight hypertensive patients who had undergone microsurgical decompression were monitored every 6 months after surgery to assess blood pressure (by 24-hour ambulatory pressure readings) and the need for antihypertensive medication. To evaluate secondary organ damage, echocardiographic assessment of left ventricular hypertrophy, fundoscopic assessment of hypertensive lesions, and analysis of renal function and proteinuria were done.

RESULTS

Three of the 8 operated patients remained normotensive in the long-term period with decreased antihypertensive medication. Two patients required gradual increases of antihypertensive medication after the first postoperative year, after which arterial blood pressure levels were 10% to 15% lower than preoperative levels. Three patients suffered serious cardiovascular and renal complications, with the incidence of lethal intracerebral hemorrhage in 1 patient and end-stage renal disease in 2 patients, of whom 1 experienced sudden cardiac death.

CONCLUSIONS

The long-term results verify that microsurgical decompression is a successful alternative therapy in a certain subgroup of patients with arterial hypertension due to neurovascular compression. However, the relevance of the looping artery in the other cases, who did not improve, is not clear. Prospective studies to elucidate the pathophysiological role of neurovascular abnormalities and arterial hypertension are needed.

Microvascular decompression in the treatment of hypertension: review and update

BACKGROUND

Neurogenic hypertension in association with vascular compression of the left rostral ventrolateral medulla has been documented. A recent group of these clinical reports has raised great interest in decompression of this area of the brainstem as a definitive therapy for essential hypertension.

METHODS

To further clarify the mechanism by which decompression of the left rostral ventrolateral medulla relieves neurogenic hypertension, we describe in detail the basic science, animal models, human studies, and most recent clinical trials regarding surgical decompression of this area.

CONCLUSION

Multi-disciplinary evidence supports the hypothesis that a sub-population of hypertensive patients achieve significant relief of their hypertension after microvascular decompression. A multi-institutional, prospective, randomized study is necessary to determine the efficacy of microvascular decompression for neurogenic hypertension.

Neurovascular Contact of Cranial Nerve IX and X Root-Entry Zone in Hypertensive Patients

-Neurovascular contact of the left rostral ventrolateral medulla has been implicated in the pathogenesis of "essential" hypertension, and recent intervention studies suggest that surgical decompression of the ventrolateral medulla lowers blood pressure in these patients. We assessed the prevalence of this vascular anomaly in patients with essential hypertension by using an advanced MRI technique. We performed MRI of the brain stem in 125 hypertensive patients and in 105 age-matched, sex-matched, and body mass index-matched normotensive control subjects. Imaging of the root-entry zone of cranial nerves IX and X was performed by combining a high-resolution 3D constructive interference in steady-state sequence with a flow-sensitive time-of-flight technique, and images were independently assessed by 4 readers using predefined criteria. Left-sided neurovascular contact was found in 23% of the hypertensive patients and in 16% of the normotensive individuals (P:=0.12). Blood pressure level, heart rate, and number of antihypertensive medications in treated hypertensive patients were similar among patients with positive, borderline, and negative brain stem findings. Our findings cast doubt on the importance of left-sided neurovascular contact as a frequent cause of essential hypertension or as a major factor determining the severity of hypertension in patients with this anomaly.

Vascular compression of the rostral ventrolateral medulla in sympathetic mediated essential hypertension

The pathophysiological factors of neurogenic or sympathetically mediated essential hypertension are unknown. Neurons close to the surface of the ventrolateral medulla (specifically, in the retro-olivary sulcus [ROS]) are integrally involved in the control of blood pressure by means of efferent connections to presympathetic neurons in the spinal cord. It is hypothesized that vascular contact with the ROS is pathogenically involved in neurogenically mediated hypertension. We evaluated that theory in 20 subjects with uncomplicated stage 1 to stage 2 essential hypertension (EHTN) (18 of whom completed the study). The baseline supine plasma norepinephrine level served as an index of central sympathetic outflow. The response of blood pressure to clonidine was used as a surrogate marker for neurogenically mediated hypertension. We also examined the relationship between those markers and evidence of anatomic abnormalities in the area of the ROS that was provided by magnetic resonance imaging. A vessel contacted the left ROS in 5 of the 18 subjects. Those 5 subjects had higher plasma norepinephrine concentrations than did the 13 subjects without this vascular contact (358+/-46 versus 76+/-43 pg/mL, P<0.001). These 5 subjects also exhibited a significant depressor response to clonidine that tended to be greater than that seen in the 13 subjects without vascular contact (-20.6+/-3.2 versus -13.6+/-9 mm Hg). Both race and baseline mean blood pressure had only an independent effect on the depressor response to clonidine. The findings are consistent with the theory that vascular contact with the left ROS may contribute to neurogenically mediated "essential" hypertension in some patients.

Pressor response to pulsatile compression of the rostral ventrolateral medulla mediated by nitric oxide and c-fos expression

It has been reported that neurovascular compression of the rostral ventrolateral medulla might be causally related to essential hypertension. Recently, we found that pulsatile compression of the rostral ventrolateral medulla increases sympathetic nerve activity and elevates arterial pressure via activation of glutamate receptors in rats. We also found that increases in sympathetic and cardiovascular activities by microinjection of L-glutamate into the rostral ventrolateral medulla are mediated by c-fos expression-related substance(s) following activation of the nitric oxide-cyclic GMP pathway. Herein, we investigated whether responses to pulsatile compression are mediated by local activation of the nitric oxide-cyclic GMP pathway and/or c-fos expression-related substance(s) in rats. Increases in arterial pressure (15+/-1 mmHg), heart rate (9+/-1 b.p.m.), and sympathetic nerve activity (% change: 8.5+/-1.1%) induced by pulsatile compression were partially but significantly inhibited after local microinjection of a nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (8+/-2 mmHg, 1+/-1 b.p.m., 4.0+/-1.3%; P<0.05 vs compression without pretreatment) or 7-nitroindazole (7+/-2 mmHg, 2+/-1 b.p.m., 4.0+/-1. 5%; P<0.05), or a soluble guanylate cyclase inhibitor, methylene blue (9+/-1 mmHg, 4+/-1 b.p.m., 4.1+/-1.4%; P<0.05). In addition, increases in arterial pressure, heart rate, and sympathetic nerve activity by pulsatile compression were significantly reduced 6 h after microinjection of antisense oligodeoxynucleotide to c-fos mRNA (2+/-2 mmHg, 2+/-1 b.p.m., 1.0+/-1.0%; P<0.05 vs sense oligodeoxynucleotide). These results suggest that increases in sympathetic and cardiovascular activities induced by pulsatile compression of the rostral ventrolateral medulla are mediated, at least in part, by local activation of the nitric oxide-cyclic GMP pathway and c-fos expression-related substance(s) in rats.

Neurogenic hypertension. A new MRI protocol for the evaluation of neurovascular compression of the cranial nerves IX and X root-entry zone

OBJECTIVE

Neurovascular compression of the rostral ventrolateral medulla (RVLM) has been implicated in the pathogenesis of essential hypertension. Although MRI has been widely used to evaluate the morphologic relation of structures in this region, spatial resolution of the previously used techniques was limited. This article describes the use of a new MRI protocol that combines two sequences with improved spatial resolution and complementary image information as well as a set of defined criteria for image analysis.

METHODS

MRI of the brain stem was performed in 60 hypertensive and 50 normotensive subjects using a 3D-CISS and a 3D-FISP-MRA sequence. Neurovascular contact in the RVLM was independently assessed by four readers using predefined criteria and compared with a consensus finding. Agreement was expressed by kappa statistics on a 0 to 1 scale.

RESULTS

Left-sided neurovascular contact within the RVLM was found in 13 (22%) hypertensive and 6 (12%) control subjects. The inter-reader agreement for positive and negative findings ranged from 0.47 to 0.79; agreement to the consensus finding ranged from 0.65 to 0.90.

CONCLUSIONS

The combination of 3D-CISS and arterial flow-sensitive 3D-FISP, together with the evaluation criteria defined in this study, can be used for describing the finer anatomic features of the brain stem, and in particular for investigation of neurovascular contact of the IX/X cranial nerve root-entry zone. The high quality of images and the substantial or almost perfect reader-consensus agreement should make this protocol useful for future investigations of the neurovascular compression syndrome in patients with essential hypertension and possibly in other neurovascular compression syndromes, such as trigeminal neuralgia and hemifacial spasm.

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.

Hemifacial spasm and arterial hypertension

BACKGROUND

Hemifacial spasm (HFS) is a form of segmental myoclonus often associated with vascular compression of the seventh nerve at its exit in the brain stem. Although a few uncontrolled studies describe the association of arterial hypertension (AH) with HFS, their relationship remains to be elucidated.

OBJECTIVES

To compare the clinical and radiologic features of patients with HFS and subjects with blepharospasm (BLS) with special emphasis on the presence of AH.

MATERIAL AND METHODS

Chart review of all patients with HFS and BLS seen at a hospital-based movement disorders clinic from July 1993 through March 1998, analyzing the following parameters: gender, age at onset, frequency of AH, and abnormalities on computerized tomography (CT) or magnetic resonance imaging (MRI) studies. Neuroimaging studies (52 CT and 14 MRI) were performed in 45 subjects with HFS and in 21 with BFS. All patients were examined by one of the authors (FC).

RESULTS

HFS and BLS were diagnosed in 48 (31 women, 17 men) and 34 (28 women, 6 men) patients, respectively. The age at onset was 50.1 +/- 12.6 years in HFS and 50.3 +/- 16.5 years in BLS. AH was diagnosed in 32 (66.7%) subjects with HFS and in 13 (38.2%) patients with BLS (chi-square p = 0.01). Neuroimaging evidence of vascular tortuosity in the cerebello-pontine angle was identified in 16 (25.4%) patients, all of whom had HFS (38.1%). Thirteen of 37 patients with AH who had imaging studies displayed vascular tortuosity in the cerebello-pontine angle (chi-square p = 0.01).

CONCLUSIONS

AH is significantly more common in HFS than in BLS. AH is related to vascular tortuosity in the cerebello-pontine angle. Our findings suggest that AH may be an important risk factor for HFS.

Autonomic function in hypertensive patients with neurovascular compression of the ventrolateral medulla oblongata

OBJECTIVE

To study whether abnormalities of autonomic function exist in patients with essential hypertension and neurovascular compression (NVC) of the medulla oblongata.

SUBJECTS AND METHODS

We studied 25 untreated patients with essential hypertension (13 men and 12 women, 27-74 years old). High-resolution magnetic resonance imaging and magnetic resonance angiography were used to detect NVC. Twenty-four-hour ambulatory monitoring of blood pressure and electrocardiogram were performed, and the power spectrum of heart rate variability was analyzed. On a separate day, various autonomic activity tests, including mental stress, hand grip, cold pressor, and Valsalva maneuver were performed. Baroreflex sensitivity was calculated from changes of blood pressure and R-R interval during phenylephrine infusion. A clonidine suppression test was also performed, with measurement of plasma catecholamine levels.

RESULTS

Fourteen of 25 patients (56%) had NVC (C group), and 11 patients did not have NVC (NC group). There were no significant differences in age, sex, family history, or duration of hypertension between the C and NC groups. Average 24-h systolic blood pressure was similar between the two groups, although 24-h diastolic blood pressure was higher in the C group than the NC group. Daytime, night-time, and 24-h heart rate was significantly higher in the C group than in the NC group. Night-time low frequency/high frequency ratio was slightly higher in the C group. Plasma norepinephrine levels were significantly higher (467 +/- 217 versus 299 +/- 122 pg/ml), and baroflex sensitivity was slightly lower in the C group than in the NC group. Responses of blood pressure and heart rate to mental stress, cold pressor, hand grip, Valsalva maneuver, phenylephrine infusion, and clonidine tests were not significantly different between the two groups.

CONCLUSIONS

NVC of the medulla oblongata was frequently found in patients with essential hypertension. Patients with NVC appeared to have enhanced sympathetic nervous activity compared with those without the compression.

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.

Brainstem compression as a cause of neurogenic hypertension

Primary or essential hypertension affects more than 50 million Americans, more than 6 million of whom cannot achieve adequate control of their condition with medication. The current neurophysiologic literature indicates that some forms of primary hypertension may be secondary to compression of the left rostral ventrolateral medulla near the root entry zones of cranial nerves 9 and 10 by arteries or veins. Surgical brainstem decompression may alleviate this hypertension or make it medically controllable. This paper reviews the experimental, anatomic, and clinical literature that supports the neurogenic theory of hypertension.

Pressor response to compression of the ventrolateral medulla mediated by glutamate receptors

The rostral ventrolateral medulla (RVLM) is considered a major center for the regulation of sympathetic and cardiovascular activities. Several clinical studies have indicated a possible causal relationship between neurovascular contact of the left RVLM and essential hypertension, and some investigators have suggested that the left RVLM is more sensitive to pulsatile compression than the right RVLM. Previously, we reported that pulsatile compression of the RVLM elevates arterial pressure by enhancing sympathetic outflow in rats; however, we have not investigated the laterality of the responses to the compression. In addition, it remains to be elucidated whether RVLM neurons are activated by compression and, if so, how they are activated. Therefore, we performed compression experiments in rats to investigate these issues. Pulsatile compression was performed on the unilateral RVLM with a pulsating probe in anesthetized and artificially ventilated rats. Pulsatile compression of the unilateral RVLM increased arterial pressure, heart rate, and sympathetic nerve activity. The pressor response to compression was inhibited significantly after local microinjection of glutamate receptor antagonists. Pulsatile compression of the RVLM increased Fos immunoreactivitiy, a marker of neuronal activation, within the nuclei of postsynaptic RVLM neurons. All results were observed symmetrically. The data indicate that the responses to pulsatile compression of the unilateral RVLM are similar on both sides. They also suggest that pulsatile compression of the RVLM increases sympathetic and cardiovascular activities by activating postsynaptic RVLM neurons through the stimulation of the local glutamate receptors in rats.

Volhard Lecture. Brain, blood pressure and stroke

BRAIN AND BLOOD PRESSURE IN EXPERIMENTAL ANIMALS: Our experiments in models of experimental hypertension in the rabbit in the early 1970s demonstrated that increased activity of bulbospinal pressor neurons containing noradrenaline or serotonin mediated the elevated arterial blood pressure. Other workers had demonstrated decreased activity of noradrenergic neurons in the medulla. Accordingly, I proposed the hypothesis that the hypertension in these models arose from 'disinhibition', due to unrestrained activity of descending pressor pathways, released from the inhibitory influences present in normal animals. Over the next 15-20 years, experiments from our group and from other laboratories demonstrated that there were two distinct bulbospinal pressor pathways descending from the rostral ventral medulla, one containing adrenaline, neuropeptide Y and glutamate, and the other containing serotonin, substance P and glutamate. It has also been established that the key depressor area is in the caudal ventrolateral medulla and that the main inhibitory input, restraining the activity of the bulbospinal pressor pathways, is a short gamma-aminobutyric acid (GABA) projection ascending from the caudal ventrolateral medulla to the rostral ventral medulla. More recent experiments in the spontaneously hypertensive rat (SHR) using the immediate-early gene c-fos as a marker of neuronal activity, have demonstrated that impaired activity of this short inhibitory GABA pathway in the SHR disinhibits the bulbospinal pressor pathway, thus contributing to the hypertension in this model. BLOOD PRESSURE AND STROKE IN HUMANS: The risks of primary stroke and of secondary or recurrent stroke are both directly related to the level of blood pressure and clinical trials have clearly demonstrated that lowering blood pressure markedly reduces the incidence of primary stroke. The Perindopril Protection Against Recurrent Stroke Study (PROGRESS) was launched to test the hypothesis that lowering the blood pressure in subjects who have already had a stroke or a transient ischaemic attack will also reduce the risk of stroke. A major unresolved issue for practising clinicians is how to manage the raised blood pressure that is so common in the acute phase of stroke. Accordingly, the PROGRESS investigators are planning another major multinational trial to assess the benefits and risks of lowering blood pressure in the first 3 days after the onset of a stroke.

Decrease of blood pressure by ventrolateral medullary decompression in essential hypertension

BACKGROUND

About 20% of adults worldwide will develop hypertension. Studies and clinical observations suggest an association between hypertension and pulsatile compression of the ventrolateral medulla oblongata by a looping artery. We investigated whether neurosurgical microvascular decompression substantially decreases blood pressure long-term in patients with severe essential hypertension.

METHODS

We included eight patients who had received three or more antihypertensive drugs without adequate control of blood pressure, intolerable side-effects, or both. All patients underwent microvascular decompression at the root-entry zone of cranial nerves IX and X after neurovascular compression of the ventrolateral medulla oblongata was seen on magnetic-resonance angiography.

FINDINGS

3 months after surgery, blood pressure and antihypertensive regimens had decreased substantially in three patients. Four patients who were followed up for more than 1 year became normotensive, but their antihypertensive regimens remained the same as those at 3 months. One patient did not improve. No complications associated with decompression occurred. One patient experienced a transient vocal-cord paresis after the laryngeal part of the vagus nerve was manoeuvered during surgery.

INTERPRETATION

We showed a direct causal relation between raised blood pressure and irritation of cranial nerves IX and X. A subgroup of patients with essential hypertension may exist who have secondary forms of hypertension related to neurovascular compression at the ventrolateral medulla and who may be successfully treated with decompression.

Microvascular decompression of the left lateral medulla oblongata for severe refractory neurogenic hypertension

OBJECTIVE

To demonstrate that microvascular decompression of the left medulla oblongata is a safe and effective modality for treating elevated blood pressure in patients with severe medically refractory "essential" hypertension (HTN).

METHODS

Twelve patients with medically intractable HTN with or without autonomic dysreflexia underwent microvascular decompression of the left rostral ventrolateral medulla oblongata. Causes such as pheochromocytoma, carcinoid syndrome, and renal disease were ruled out before surgery. Indications for surgery included systolic blood pressures greater than 180 mm Hg refractory to three or more medications, severe blood pressure lability, or medically resistant HTN at systolic pressures greater than 160 mm Hg associated with autonomic dysreflexia and/or magnetic resonance images demonstrating left medullary compression. The median age and follow-up duration were 51 years and 4.1 years, respectively.

RESULTS

Ten of 12 patients experienced reductions in systolic blood pressure greater than 20 mm Hg. Of these 10 patients, pressure reductions were temporary (6 mo) in two. Seven of eight patients experienced improvement in blood pressure lability and/or autonomic dysreflexia, with five patients showing sustained improvements.

CONCLUSION

Microvascular decompression of the left rostral ventrolateral medulla oblongata may be an effective treatment modality for patients suffering from severe HTN and/or autonomic dysreflexia refractory to medical management.

Magnetic resonance evaluation of ventrolateral medullary compression in essential hypertension

OBJECT

The authors designed a blinded prospective study comparing patients with essential hypertension to patients without hypertension in which magnetic resonance (MR) imaging was used to evaluate the role of lateral medullary compression by adjacent vascular structures as a cause of neurogenic hypertension.

METHODS

Patients with documented essential hypertension were recruited to undergo thin-slice axial brainstem MR imaging evaluation. Nonhypertensive (control) patients scheduled to undergo MR imaging for other reasons also underwent thin-slice MR imaging to form a basis for comparison. Magnetic resonance images obtained in patients from the hypertensive (30 patients) and the control (45 patients) groups were then compared by four independent reviewers (two neuroradiologists and two neurosurgeons) who were blinded to the patients' diagnosis and hypertensive status. Images were reviewed with regard to left versus right vertebral artery (VA) dominance, compression of the medulla on the left and/or right side, and brainstem rotation. Medullary compression was graded as either vessel contact without associated brainstem deformity or vessel contact with associated brainstem deformity.

CONCLUSIONS

There was a tendency toward left VA dominance in the hypertensive group compared with the control group, although a significant difference was shown by only one of the four reviewers. There were no differences in brainstem compression or rotation between the hypertensive and nonhypertensive groups. These results are contrary to those of recently published studies in which MR imaging and/or MR angiography revealed lateral brainstem vascular compression in hypertensive patients but not in nonhypertensive (control) patients. Reasons for this discrepancy are discussed. On the basis of their own experience and that of others, the authors believe that neurogenic hypertension does exist. However, thin-slice MR imaging may not be a reliable method for detecting neurovascularly induced essential hypertension and the prevalence of neurovascular compression as the source of hypertension may be overestimated when using current imaging techniques.

Brachydactyly-short stature-hypertension (Bilginturan) syndrome: report on two families

We report on two families with autosomal dominant brachydactyly of hands and feet and hypertension. All affected members of the first family had proportionate short stature. However, the propositus and the affected relatives in the second family were only short compared to unaffected relatives. The hypertension was medically responsive in all cases. The propositus in the second family had poor compliance and a striking generalized vasculopathy. All patients were of normal intelligence and had a normal facial appearance. The brachydactyly-short stature-hypertension syndrome was first reported by Bilginturan et al. [1973] in a Turkish family and the families reported by us are Caucasian and Hispanic. The gene causing this condition in the original Turkish family was recently mapped to 12p. Our report expands our existing knowledge and the ethnic diversity of this syndrome.

Neurovascular compression at the ventrolateral medulla in autosomal dominant hypertension and brachydactyly

BACKGROUND AND PURPOSE

Autosomal dominant hypertension with brachydactyly features severe hypertension that causes stroke usually before the age of 50 years. We recently characterized the hypertension as featuring normal renin, aldosterone, and catecholamine responses and mapped the gene responsible to chromosome 12p. Since angiography in an affected subject had earlier shown tortuous vessels, we performed magnetic resonance tomography (MRT) angiography to look for possible neurovascular anomalies (NVA), which have been previously associated with hypertension. NVA can be caused by a looping posterior inferior cerebellar or vertebral artery. Experimental and clinical evidence suggests that NVA may cause hypertension by a compression of the ventrolateral medulla.

METHODS

We performed MRT in 15 hypertensive affected (aged 14 to 57 years) and 12 normotensive nonaffected (aged 12 to 59 years) family members. We then tested for linkage between the hypertension-brachydactyly phenotypes and the presence of NVA.

RESULTS

All 15 affected persons had MRT evidence for NVA. All had left-sided posterior inferior cerebellar artery or vertebral artery loops, while 6 had bilateral NVA. None of the nonaffected family members had NVA. The phenotypes were linked with an LOD score of 9.2 given a penetrance of 99%.

CONCLUSIONS

Autosomal dominant hypertension and brachydactyly regularly feature NVA, which is frequently bilateral. The early age at which NVA was identified suggests that the condition is primary. We suggest that NVA may be involved in the pathogenesis of this form of hypertension and perhaps essential hypertension as well. Further studies are necessary to address the question of causation.

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.

Pulsatile compression of the rostral ventrolateral medulla in hypertension

The rostral ventrolateral medulla (RVLM) has been known to be a major regulating center of sympathetic and cardiovascular activities. An association between essential hypertension and neurovascular compression of the RVLM has been reported in clinical observations, including magnetic resonance imaging (MRI) studies. To reconfirm this relationship, we performed MRI using a high-resolution 512 x 512 matrix in patients with essential and secondary hypertension and in normotensive subjects. The duration of hypertension and the degree of organ damage by hypertension were not significantly different between the two hypertension groups. Neurovascular compression of the RVLM was observed in 74% of the essential hypertension group, and the incidence of compression was significantly higher than in the secondary hypertension group (11%) or in the normotensive group (13%) (P < .01). These results from the clinical studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. Although blood pressure elevation by pulsatile compression of the RVLM in an experimental baboon model has already been reported, its underlying mechanism is not well known. Accordingly, we performed experiments to investigate whether pulsatile compression of the RVLM would increase arterial pressure and to elucidate the mechanism of the pressor response in rats. Sympathetic nerve activity, arterial pressure, heart rate, and plasma levels of epinephrine and norepinephrine were increased by pulsatile compression of the RVLM. The pressor response was abolished by intravenous treatment with hexamethonium or RVLM injection of kainic acid. In summary, the results from the MRI studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. This was supported by the results from experimental studies using rats indicating that pulsatile compression of the RVLM increases arterial pressure by enhancing sympathetic outflow.

Autosomal dominant hypertension and brachydactyly in a Turkish kindred resembles essential hypertension

We examined a Turkish kindred with a unique form of autosomal dominant hypertension that cosegregates 100% with brachydactyly and maps to chromosome 12p. Affected adults were 10 to 15 cm shorter than unaffected people; however, their body mass index (27 kg/m2) was not different. Blood pressure increased steeply with age in the affected people so that by age 40 years, they had a mean blood pressure of 140 mm Hg, compared with 92 mm Hg in unaffected individuals. Complete clinical, roentgenographic, and laboratory evaluation was performed in 6 subjects, including 24-hour blood pressure measurements and humoral determinations before and after volume expansion with 2 L normal saline over 4 hours followed by volume contraction on the following day with a 20-mmol sodium diet and 40 mg furosemide at 8 AM, noon, and 4 PM. Two affected men aged 46 and 31 years; 3 affected women aged 40, 31, and 30 years; and 1 unaffected man aged 29 years were studied. Systolic pressures ranged from 170 to 250 mm Hg, and diastolic pressures ranged from 100 to 150 mm Hg in affected people; the unaffected man had a blood pressure of 120/70 mm Hg. Thyroid, adrenal, and renal functions were normal; electrolyte and acid-base statuses were normal. Calcium and phosphate homeostasis was normal. Day-night circadian blood pressure rhythm was preserved. The subjects were not salt sensitive; renin, aldosterone, and catecholamine values reacted appropriately to volume expansion and contraction. Affected people had mild cardiac hypertrophy and increased radial artery wall thickness. Fibroblasts from affected people grew more rapidly in culture than from unaffected people. We conclude that this novel form of inherited hypertension resembles essential hypertension.

Cerebrovascular complications of Fabry's disease

Fabry's disease (FD) is a rare, sex-linked disorder resulting from alpha-galactosidase deficiency. Cerebrovascular complications have been reported in the literature but have not been systematically analyzed. We report 2 patients and review 51 previously reported cases (descriptive meta-analysis) to clarify the clinical, radiologic, and pathologic features. The average age at onset of cerebrovascular symptoms was 33.8 years for hemizygous individuals (n = 43) and 40.3 years of heterozygotes (n = 10). The most frequent symptoms and signs were as follows (in descending order of frequency): hemiparesis, vertigo/dizziness, diplopia, dysarthria, nystagmus, nausea/vomiting, head pain, hemiataxia, and ataxia of gait, in the hemizygote group; and memory loss, dizziness, ataxia, hemiparesis, loss of consciousness and hemisensory symptoms, in the heterozygote group. The vertebrobasilar circulation was symptomatic in 67% of the hemizygotes and 60% of the heterozygotes. Intracerebral hemorrhage was found in 4 patients (3 hemizygotes and 1 heterozygote). Elongated, ectatic, tortuous vertebral and basilar arteries were the most common angiographic and pathologic features. For the hemizygotes, the recurrence rate for cerebrovascular disease was 76% and the death rate was 55%; 86% of the heterozygotes had recurrent cerebrovascular event(s) and 40% died. The cerebrovascular manifestations of FD, in both hemizygotes and heterozygotes, are predominantly due to dilative arteriopathy of the vertebrobasilar circulation, frequently recur, and portend a poor prognosis.