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Transverse - Caudal L7

(Jones et al., 1995)

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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. Internal vertebral venous plexus

4. 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).

5. S1 nerve roots: lead to the cranial gluteal, caudal gluteal, sciatic, and pudendal peripheral nerves. The cranial gluteal peripheral nerve innervates the middle gluteal, deep gluteal, and tensor fascia lata muscles. The caudal gluteal peripheral nerve innervates the superficial gluteal, and middle gluteal muscles.

6. Lateral recess: Paired grooves in the caudolateral margins of the lumbar vertebral foramina. These grooves contain the exiting nerve roots and spinal ganglia. In dogs with degenerative lumbosacral stenosis, nerve tissues within these recesses can be compressed due to endplate bone spurs and enlarged articular processes.

7. Spinal ganglion: Synonym dorsal root ganglion. Aggregation of nerve cell bodies for the spinal nerve. Contains both sensory (afferent) and motor (efferent) nerve cell bodies. In dogs with degenerative lumbosacral stenosis, these ganglia can be compressed within the lateral recesses or intervertebral foramina.

8. 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.

9. Multifidus muscles: one of the largest epaxial muscle groups in the lumbar region. Divided into 11 individual portions that orginiate from the articular processes of the sacrum and mammillary processes of T12-L7. Can appear atrophied in dogs with chronic degenerative spinal disease or degenerative myelopathy.

10. Sacrocaudalis dorsalis medialis

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