Arteriovenous glomeruli of the human spinal cord and their possible functional implications

Abstract

A previous investigation of the radiculomedullary vascular distribution of the human spinal cord showed an immediate filling of the peripheral spinal veins during arterial injections. Because the perfused medium, a mixture of latex and India ink, had a sufficient viscosity to preclude capillary passage, an extensive system of arteriovenous anastomoses (AVA) was indicated. The injection of five additional anatomic cadaver spinal cords was undertaken to specifically determine the intraparenchymal position and structure of these AVA. It was found that only cleared and transilluminated longitudinal parasagittal sections adequately showed that the AVA were formed by an extensive array of intricately coiled arteriovenous glomeruli (AVG) that could pass substantial amounts of blood from third order arterial branches to equivalently sized veins, bypassing the capillary bed. The epithelioid structure of these AVG channel walls, coupled with their highly innervated adventitial tissue indicated a possible functional relationship to similar structures found in the ends (digital pads) of mammalian extremities. Stained serial sections of injected cords showed the vascular relations with nerve fibers derived from the intraspinal parenchyma as well as a possible extraparenchymal autonomic fiber source. The numbers and extent of these AVG complexes suggested they might be involved in the remarkable autoregulation of spinal cord blood flow (SCBF) that is impervious to middle range changes in systemic blood pressure. Future research may more accurately determine the functional role of these previously unreported human spinal AVG, particularly in their possible relation to SCBF autoregulation in normal and injured spines.

Effect of norepinephrine on spinal cord blood flow and parenchymal hemorrhage size in acute-phase experimental spinal cord injury

“…A key hypothesis for explaining the absence of an SCBF response to epinephrine alone involves the intrinsic autoregulatory capabilities of the spinal cord. Some arteriovenous glomeruli located in the gray matter can open, shunting blood from the arteries to the veins and therefore bypassing the capillary bed and regulating the parenchymal blood flow [16,27]. These glomeruli may be devoid of receptors for catecholamines, thereby explaining the absence of effect of NE and epinephrine on SCBF.…”

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

“…Carlson and associates addressed the question of reperfusion after injury in dogs and found that duration of spinal cord compression (30,60 and 180 minutes) and reperfusion after decompression was inversely related (Carlson, Minato et al, 1997, pp. 951-962).…”

“…Carlson and associates 9 addressed the question of reperfusion after injury in dogs and found that duration of spinal cord compression (30,60, and 180 minutes) and reperfusion after decompression were inversely related. Five minutes after compression, SCBF increased from baseline (21.4 ± 2.2 ml/100 g/min) in both the 30-minute group (49.1 ± 3.1 ml/100 g/min) and 60-minute group (~ 44 ml/100 g/min) but fell slightly in the 180-minute group (19.8 ± 6.2 ml/100 g/min).…”

“…Glomeruli found in capillary beds within the spinal cord may act as sensors within the spinal cord. 60 One reason for this supposition is that these glomeruli resemble arteriovenous glomerular clumps, which are found in fingers, toes, the penis, and other parts of the body, and act as components of nerve root circulation capable of shunting blood from arteries to veins and bypassing the capillaries. Such shunting can also occur in the spinal cord.…”

Evaluating perfusion of thoracic spinal cord blood using CEUS during thoracic spinal stenosis decompression surgery

“…10 The latest research shows that a baroreceptor may exist around the capillary bed of the anterior and dorsal spinal horns. 11 The baroreceptor can detect tension due to muscle crush of the anterior spinal artery walls and thus directly regulate local blood flow of the spinal cord. In this study, the second contrast-enhanced ultrasound scan was performed after spinal circular decompression to evaluate the blood flow perfusion of the compressed spinal cord after complete circular decompression.…”