Lumbar veins

The lumbar veins are paired systemic veins located within the lumbar region. They typically accompany the lumbar arteries and are responsible for draining the dorsal body wall, including muscles and vertebrae of the lumbar region, into the caudal vena cava and azygos system.

Origin and Tributaries

Lumbar veins usually arise from the dorsal body wall structures:

• Epaxial muscles

• Lumbar vertebrae and ligaments

• Spinal cord and meninges (via intervertebral veins)

Each lumbar vein may receive:

• Muscular branches (from multifidus, longissimus, and iliocostalis groups)

• Vertebral branches

• Spinal branches through the intervertebral foramina (venous drainage from spinal cord and meninges)

They travel medially, accompanying lumbar arteries and segmental nerves, toward larger collecting veins.

Drainage Patterns

Dog and Cat

• Generally, 5–7 pairs of lumbar veins are present.

• The cranial lumbar veins (1st–3rd) commonly drain into the azygos vein (right azygos only in dogs and cats).

• The caudal lumbar veins (4th–7th) drain directly into the caudal vena cava.

• A spinal venous plexus communicates with these veins inside the vertebral canal.

Horse

• Usually has 6–7 pairs of lumbar veins.

• Drainage pattern similar to carnivores: cranial into the right azygos vein (horses lack a left azygos), caudal into the caudal vena cava.

• Due to large muscle mass, lumbar veins in horses are well developed.

• Communicating veins from internal vertebral venous plexus are prominent.

Ruminants (Ox, Goat, Sheep)

• Typically possess 6 lumbar veins.

• Drainage is more variable: most veins drain directly into the caudal vena cava.

• Unlike horses, left azygos vein persists and may receive some lumbar veins.

• There may be anastomoses with intercostal veins.

Pig

• Commonly has 6–7 lumbar veins.

• Drainage into both caudal vena cava and the left azygos vein, which is well developed in pigs (in contrast to horses and carnivores).

• Venous drainage patterns may be highly segmental and anastomotic.

Communications and Anastomoses

• Internal vertebral venous plexus: Within the vertebral canal; communicates with lumbar veins via intervertebral veins. Provides a potential route for metastasis of infections or neoplasms.

• Intersegmental anastomoses: Between adjacent lumbar veins, and with intercostal veins cranially.

• Vertebrocostal and vertebro-pelvic anastomoses may exist in some species.