PULSATILE COMPRESSION OF THE ROSTRAL VENTROLATERAL MEDULLA AS A CAUSE OF 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.

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.