Spinal Cord, Meninges, and Vasculature PDF

SPINAL CORD SPINAL MENINGES VASCULATURE OF SPINAL CORD Mariam Tetradze MD  SPINAL CORD The spinal cord is a tubular bundle of nervous tissue and supporting cells that extends from the brainstem to the lumbar vertebrae. Together, the spinal cord and the brain...

SPINAL CORD SPINAL MENINGES VASCULATURE OF SPINAL CORD Mariam Tetradze MD  SPINAL CORD The spinal cord is a tubular bundle of nervous tissue and supporting cells that extends from the brainstem to the lumbar vertebrae. Together, the spinal cord and the brain form the central nervous system.  SPINAL CORD The spinal cord is a cylindrical structure, greyish-white in color. It has a relatively simple anatomical course: The spinal cord arises cranially as a continuation of the medulla oblongata (part of the brainstem). It then travels inferiorly within the vertebral canal, surrounded by the spinal meninges containing cerebrospinal fluid. At the L2 vertebral level the spinal cord tapers off, forming the conus medullaris.  SPINAL CORD As a result of the termination of the spinal cord at L2, it occupies around two thirds of the vertebral canal. The spinal nerves that arise from the end of the spinal cord are bundled together, forming a structure known as the cauda equina.  SPINAL CORD During the course of the spinal cord, there are two points of enlargement. The cervical enlargement extends from the C4 through the T1 segments of the spinal cord, and most of the anterior rami of the spinal nerves arising from it form the brachial plexus of nerves, which innervates the upper limbs.  SPINAL CORD The lumbosacral (lumbar) enlargement extends from the L1 through the S3 segments of the spinal cord, and the anterior rami of the spinal nerves arising from it contribute to the lumbar and sacral plexuses of nerves, which innervate the lower limbs. The spinal nerve roots arising from the lumbosacral enlargement and conus medullaris form the cauda equina, the bundle of spinal nerve roots running inferior to the spinal cord through the lumbar cistern (subarachnoid space).  CAUDA EQUINA SYNDROME The cauda equina is a bundle of spinal nerves that arise from the distal end of the spinal cord. They run in the subarachnoid space, before exiting at their appropriate vertebral level. Compression of these nerves produces a range of signs and symptoms collectively termed cauda equina syndrome. There are many causes of compression, including intervertebral disc prolapse, extrinsic or primary cord tumors, spinal stenosis, trauma and abscess formation.  CAUDA EQUINA SYNDROME Suspected cauda equina patients should be assessed with a full lower limb neurological assessment. The main signs to assess for are: Saddle-area anaesthesia. Incontinence / retention of urine or faeces. Reduced anal tone. Paralysis ± sensory loss. If sufficient clinical evidence exists, an MRI is required immediately for diagnosis. Any confirmed case must be sent for surgery within 36 hours of first presentation of the symptoms for surgical decompression.  SPINAL MENINGES The spinal meninges are three membranes that surround the spinal cord – the dura mater, arachnoid mater, and pia mater. They contain cerebrospinal fluid, acting to support and protect the spinal cord. They are analogous with the cranial meninges. Distally, the meninges form a strand of fibrous tissue, the filum terminale, which attaches to the vertebral bodies of the coccyx. It acts as an anchor for the spinal cord and meninges.  SPINAL MENINGES Dura Mater The spinal dura mater is the most external of the meninges. It is a tough, cylindrical covering of connective tissue forming a dural sac which envelops the entire spinal cord and cauda equina. It extends from the foramen magnum to the filum terminale, separated from the walls of the vertebral canal by the epidural space. This space contains some loose connective tissue, and the internal vertebral venous plexus. The dura mater and dural sac terminate inferiorly at the second sacral vertebra level. As the spinal nerves exit the vertebral canal, they pierce the dura mater, temporarily passing in the epidural space. In doing so, the dura mater surrounds the nerve root, and fuses with the outer connective tissue covering of the  EPIDURAL SPACE The epidural space is located between the inner walls of the vertebral canal and the dura mater. It contains fat and the internal vertebral venous plexus. The venous plexus runs the entire length of the epidural space and continues superiorly through the foramen magnum to connect with dural venous sinuses in the cranial cavity.  SPINAL MENINGES Arachnoid Mater The spinal arachnoid mater is a delicate membrane, located between the dura mater and the pia mater. It is separated from the latter by the subarachnoid space, which contains cerebrospinal fluid. Distal to the conus medullaris, the subarachnoid space expands, forming the lumbar cistern. This space accessed during a lumbar puncture (to obtain CSF fluid) and spinal anaesthesia.  SUBARACHNOID SPACE The subarachnoid space is a pressurized space located between the arachnoid and pia mater layers. It contains cerebrospinal fluid (CSF), which bathes the spinal cord and spinal nerve roots within the dural sac, and terminates at the second sacral vertebral level. There are 2 important vertebral levels. The Ll or L2 vertebrae is the inferior limit of the spinal cord in adults ( conus medullaris). S2 vertebra is the inferior limit of the dural sac and the subarachnoid space (cerebrospinal fluid).  SPINAL MENINGES Pia Mater The spinal pia mater is the innermost of the meninges. It is a thin membrane that covers the spinal cord, nerve roots and their blood vessels. Inferiorly, the spinal pia mater fuses with the filum terminale. Between the nerve roots, the pia mater thickens to form the denticulate ligaments. These ligaments attach to the dura mater – suspending the spinal cord in the vertebral canal.  SPINAL NERVES A total of 31 pairs of spinal nerves are attached to the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal The spinal nerves are mixed nerves that originate from the spinal cord, forming the peripheral nervous system. Each spinal nerve begins as an anterior (motor) and a posterior (sensory) nerve root. These roots arise from the spinal cord, and unite at the intervertebral foramina, forming a single spinal nerve.  SPINAL NERVES The anterior (Ventral) roots of spinal nerves contain efferent (motor) fibers to skeletal muscle and many contain presynaptic autonomic fibers. The cell bodies of somatic axons contributing to the anterior roots are in the anterior horns of gray matter  SPINAL NERVES the cell bodies of axons making up the posterior (Dorsal) roots are outside the spinal cord in the spinal ganglia (posterior root ganglia) at the distal ends of the posterior roots.  SPINAL NERVES Spinal nerve is formed by the union of the ventral and dorsal roots; it exits the vertebral column by passing through the intervertebral foramen Dorsal rami innervate the skin of the dorsal surface of the back, neck, zygapophyseal joints, and intrinsic skeletal muscles of the deep back Ventral rami innervate the skin of the anterolateral trunk and limbs, and the skeletal muscles of the anterolateral trunk and limbs (ventral rami form the brachia! and lumbosacral plexuses)  LUMBAR PUNCTURE A lumbar puncture is used to inject anesthetic material in the epidural space or to withdraw CSF from the subarachnoid space. A spinal tap is typically performed at the L4-L5 interspace. A horizontal line drawn at the top of the iliac crest marks the level of the L4 vertebra.  LUMBAR PUNCTURE During a lumbar puncture, a needle is passed through the interlaminar space while the vertebral column is flexed. The needle passes through the following layers: Skin Superficial fascia Deep fascia Supraspinous ligament lnterspinous ligament lnterlaminar space Epidural space Dura Arachnoid Subarachnoid space  EPIDURAL ANESTHESIA An anesthetic agent can be injected into the extradural (epidural) space using the position described for lumbar spinal puncture. The anesthetic has a direct effect on the spinal nerve roots of the cauda equina after they exit from the dural sac.  EPIDURAL ANESTHESIA The patient loses sensation inferior to the level of the block. An anesthetic agent can also be injected into the extradural space in the sacral canal through the sacral hiatus (caudal epidural anesthesia) or through the posterior sacral foramina (trans-sacral epidural anesthesia). The distance the agent ascends (and hence the number of nerves affected) depends on the amount injected and on the position assumed by the patient.  VASCULATURE OF SPINAL CORD The arterial supply to the spinal cord is via three longitudinal arteries – the anterior spinal artery and the paired posterior spinal arteries. Anterior spinal artery – formed from branches of the vertebral arteries. They travel in the anterior median fissure. Posterior spinal arteries – originate from the vertebral artery or the posteroinferior cerebellar artery. They anastomose with one another in the pia mater.  VASCULATURE OF SPINAL CORD Additional arterial supply is via the anterior and posterior segmental medullary arteries – small vessels which enter via the nerve roots. The largest anterior segmental medullary artery is the artery of Adamkiewicz. It arises from the inferior intercostal or upper lumbar arteries, and supplies the inferior 2/3 of the spinal cord.  VASCULATURE OF SPINAL CORD Venous drainage is via three anterior and three posterior spinal veins. These veins are valveless, and form an anastomosing network along the surface of the spinal cord. They also receive venous blood from the radicular veins. The spinal veins drain into the internal and external vertebral plexuses, which in turn empty into the systemic segmental veins. The internal vertebral plexus also empties into the dural venous sinuses superiorly.