The posterior intercostal vein: A thermoregulatory gateway to the internal vertebral venous plexus

Abstract

The internal vertebral venous plexus (IVVP) plays a putative role in thermoregulation of the spinal cord. Cold cutaneous venous blood may cool, while warm venous blood from muscles and brown fat areas may warm the spinal cord. The regulating mechanisms for both cooling and warming are still unknown. Warm venous blood mainly enters the IVVP via the intervertebral veins. In the thoracic area these veins are connected to the posterior intercostal veins. In this study, anatomical structures were investigated that might support the mechanisms by which warmed venous blood from the intercostal muscles and the recently described paravertebral patches of brown adipose tissue are able to drain into the vertebral venous plexus. Therefore, tissue samples from human cadavers (n = 21) containing the posterior intercostal vein and its connections to the IVVP and the azygos veins were removed and processed for histology. Serial sections revealed that the proximal parts of the posterior intercostal veins contained abundant smooth muscle fibers at their opening into the azygos vein. Furthermore, the walls of the proximal parts of the posterior intercostal veins contain plicae that allow the vessel to dilate, thereby allowing it to serve as a pressure chamber. It is suggested that a cold induced closure of the intercostal/azygos opening can result in retrograde blood flow from the proximal posterior intercostal vein towards the IVVP. This blood flow would be composed of warm blood from the paravertebral brown adipose tissue and blood containing metabolic heat from the muscles draining into the intercostal veins.

Neural-Dural Transition at the Thoracic and Lumbar Spinal Nerve Roots: A Histological Study of Human Late-Stage Fetuses

“…Thus, the present specimens appeared to show a stage later than the “developmental delay” in the posterior part of the fetal internal plexus [ 13 ]. We found valves in the external veins, but smooth muscles in the internal veins were not identified although these structures were recently discussed in relation to thermoregulation of the adult spinal cord [ 14 , 15 ].…”

INTERVERTEBRAL VEINS DIRECTLY CONNECTING THE VERTEBRAL VENOUS SYSTEM TO THE AZYGOS VENOUS SYSTEM RATHER THAN THE PROXIMAL END OF THE POSTERIOR INTERCOSTAL VEINS. Venas intervertebrales conectando directamente el sistema venoso vertebral al sistema venoso

“…The present observations do not appear to have been reported previously in the literature. According to Hoogland et al (2013), the vertebral venous system connects with the proximal part of the posterior intercostal veins via IVVs: they are considered to play an important role in heat transportation from the posterior intercostal veins to the vertebral venous system. Hoogland et al concluded that PIVs are essential anastomoses between the internal vertebral venous plexus and the AV.…”

“…The intervertebral veins (IVVs) connect the vertebral venous system with the azygos venous system indirectly via the PIVs. A complete valve is located at the proximal end of each PIV (Maros, 1981), which allows venous blood to drain into the vertebral venous system via the IVV (Hoogland et al, 2013). The main aims of this study were to examine the anatomical variations of the azygos venous system and compare the observations with existing classification systems, applying modifications as appropriate.…”

Paraspinal structures of thermoregulation

“…P.V. Hoogland et al [13] указывают, что проксимальные части задних межреберных вен при их впадении в непарные вены имеют клапаны и гладкомышечные сфинктеры. Последние позволяют задним межреберным венам расширяться, превращая их в своеобразные камеры давления, и в тех сегментах, где в них впадают межпозвоночные вены, обусловливают ретроградный кровоток во внутренние позвоночные венозные сплетения.…”

“…Так, в работе P.V. Hoogland et al [13] представлены фото гистологических препаратов, на которых в местах впадения межреберных вен в непарную вену демонстрируются клапаны в сочетании с гладкими мышечными сфинктерами, образующими утолщения стенок.…”