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Transverse - Caudal L6

(Jones et al., 1995)

1. Thecal sac: Synonym dural sac. Soft tissue opacity CT structure that is enclosed by the dura mater. Tissues inside the thecal sac include the arachnoid membrane, fluid-filled subarachnoid space, nerve roots, and spinal cord. Individual soft tissues inside of the thecal sac are silhouetted in plain CT images and cannot be discriminated.

2. Epidural fat: fat deposits are normally present in the epidural space and appear darker than surrounding nerve tissues on CT images. These fat deposits help provide cushioning and protection of the nerve tissues. In dogs with degenerative lumbosacral disease, loss of visualization of the epidural fat is a sign of nerve tissue compression.

3. Anastomosis: General term that means “communication”. In the lumbosacral spine, the paired branches of the ventral internal vertebral venous plexus have an anastomosis along the dorsal margins of each of the intervertebral discs.

4. L6 nerve roots lead to the femoral, obturator, cranial gluteal, and sciatic peripheral nerves-- innervating the iliopsoas, quadriceps, and sartorius muscles, the external obturator, pectineus, gracilis, and adductor muscles, the middle gluteal, deep gluteal, and tensor fascia lata muscles, and the biceps femoris, semimembranosus muscles.

5. L7 nerve roots lead to the cranial gluteal, caudal gluteal, and sciatic peripheral nerves. The cranial and caudal gluteal peripheral nerves innervate the middle gluteal, deep gluteal, and tensor fascia lata muscles, and the superficial gluteal muscles. The sciatic peripheral nerve innervates the biceps femoris, semimembranosus, and semitendinosus muscles, as well as the common peroneal nerve (which innervates the peroneus longus, lateral digital extensor, long digital extensor, and cranial tibial muscles), and the tibial nerve (which innervates the gastrocnemius, popliteus, superficial digital flexor, and deep digital flexor muscles).

6. Spinous process: dorsally projecting bony prominence arising from the center of each vertebral lamina. Serves as an attachment site for epaxial muscles and the interspinous ligament. The lamina of L7 and the L7 spinous process are often removed for lumbosacral decompressive surgeries.

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