KEY POINT: Ⅲ A notch in the SPINAL CORD ANATOMY, inferior aspect of the pedicle will LOCALIZATION, AND contribute to the boundary of the intervertebral OVERVIEW OF SPINAL foramen when adjacent CORD SYNDROMES vertebrae are articulated and Gregory Gruener, Jose´ Biller through which the spinal nerve and intervertebral ABSTRACT vessels will pass. Spinal cord syndromes are “unique” clinical presentations that localize lesions to the spinal cord by their pattern of anatomic dysfunction while implying their underlying etiology. Recognizing these patterns and their significance is best accomplished by relearning and appreciating the relevant anatomy and relationships, which are the major focus of this review. This clinical-anatomic background will provide the frame- work for the clinical topics that follow in this issue. ANATOMY OF THE SPINAL A notch in the inferior aspect of the CORD pedicle will contribute to the boundary of the intervertebral foramen when ad- Relationship to the Vertebral jacent vertebrae are articulated and Levels and Spine through which the spinal nerve and in- The typical vertebra consists of a co- tervertebral vessels will pass. lumnar body with a larger transverse An intervertebral disc is interposed than anterior-posterior diameter and between each vertebral body and con- serving as the primary support for the sists of alternating, crisscrossing bands spine. The vertebral arch extends from of fibrous connective tissue, the annu- the body, forming a protective enclo- lus fibrosus, which surround a gelati- sure, and consists of a pedicle on ei- nouslike core, nucleus pulposus. The ther side that unites posteriorly vertebral discs will contribute 25% of the through the two laminae. Three pro- height of the vertebral column. Several 11 cesses arise from the vertebral arch, ligaments and fibrous attachments of laterally the transverse and posteriorly muscles help to bind together and en- the spinous, serving as the attachment close the vertebral column. The most site for muscles (Figure 1-1). Four prominent are the anterior longitudinal separate articular processes, a superior (along the anterior aspect of the bodies), pair extending cranially and an infe- the posterior longitudinal (along their rior pair extending caudally, serve to posterior aspect), the ligamentum fla- direct or limit movement to specific vum (posterior wall of spinal canal), and directions by articulating with the ver- the interspinous ligament. tebra above and below (Figure 1-2). The fused periosteum of the cra- Relationship Disclosure: Dr Gruener has received personal compensation for speaking engagements with Medical Education Resources, Inc. Dr Biller has nothing to disclose. Unlabeled Use of Products/Investigational Use Disclosure: Drs Gruener and Biller have nothing to disclose. Copyright © 2008, American Academy of Neurology. All rights reserved. ‹ SPINAL CORD ANATOMY, LOCALIZATION, SYNDROMES FIGURE 1-1 Functions of the constituent parts of a vertebra. Reprinted with permission from Grant JCB. An atlas of anatomy. 6th ed. Baltimore: Williams & Wilkins, 1972. nium and meningeal layer of the dura space, epidural space, which extends matter will separate caudal to the fo- the length of the spinal column (Fig- ramen magnum, forming an anatomic ure 1-3). Within this space reside fatty 12 FIGURE 1-2 Lateral view of a lumbar (second) vertebra. Sup ϭ superior; Inf ϭ inferior. Modified with permission from Grant JCB. An atlas of anatomy. 6th ed. Baltimore: Williams & Wilkins, 1972. Continuum: Lifelong Learning Neurol 2008;14(3) KEY POINT: tissue and the vertebral venous plexus. tively numbered vertebrae (C2 Ⅲ At birth the The separation of these fused layers of through C7), but C8 above the T1 ver- spinal cord connective tissue allows the vertebral tebrae. The remaining spinal nerves typically extends column to move separately relative to will exit below the vertebrae of the to the lower the dural sac that surrounds the spinal corresponding number. The spinal border of L3. By cord and roots. The dorsal and ventral nerves will have a dorsal root ganglion adulthood its tip roots will enter a dural sleeve at the usually located within the interverte- is usually at the level of their intervertebral foramina, bral foramen. C1 lacks a cutaneous L1-2 vertebral lateral to the dorsal spinal ganglia, fus- sensory dermatome. Below the L1 ver- disk level but ing to form the spinal nerves. A layer tebra, lumbar and sacral spinal nerve can end at T12 of pia mater surrounds the surface of roots need to descend in order to or descend to the spinal cord, and between it and the reach their point of exit; this collection the lower border of the L2 inner layer of the arachnoid tissue is of spinal roots is called the cauda vertebrae. the subarachnoid space. Between suc- equina. The cord will terminate in a cessive nerve roots, a bandlike exten- thin-walled sac covered by pia mater, sion of the pia mater will arise from the filum terminale, which fuses with the surface of the spinal cord, dentic- the periosteum of the dorsal surface of ulate ligament, attaching to the dura the coccyx. and serving to anchor the spinal cord The gray matter of the spinal cord (Figure 1-4). The ventral nerve roots can be divided into a posterior column lie anterior and the dorsal nerve roots posterior to this ligament. The spinal cord is cylindrical in shape, but flattened dorsoventrally. It is widest at the cervical enlargement, and a second enlargement occurs in the lumbosacral level of the cord, both reflecting the innervation levels of the limbs. At birth the spinal cord typically extends to the lower border of L3. By adulthood its tip is usually at the L1-2 vertebral disk level but can end at T12 or descend to the lower border of the L2 vertebrae. Each segment of the spinal cord usually has a set of dorsal (sensory) 13 and ventral (motor) rootlets that emerge and join together to form their corresponding root; dorsal roots have their corresponding ganglia (dorsal root ganglia). The dorsal and ventral roots will fuse to form the spinal nerve as it exits from the spinal canal. The spinal nerves then divide into individ- ual branches. There are usually 31 pairs of spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral, and usually one coccygeal (Figure FIGURE 1-3 Spaces associated with the spinal meninges. 1-5). The first pair of spinal nerves will Modified with permission from Fitzgerald MJ, Gruener G, Mtui E. Clinical neuroanatomy and neuroscience. 5th ed. exit between the skull and the atlas London: Saunders, 2007:49. Copyright © 2007, Elsevier. (C1), the next six above their respec- Continuum: Lifelong Learning Neurol 2008;14(3) ‹ SPINAL CORD ANATOMY, LOCALIZATION, SYNDROMES KEY POINT: Ⅲ The first pair of spinal nerve roots will exit between the skull and the atlas (C1), the next six above their respectively numbered vertebrae (C2 through C7), but C8 above the T1 vertebrae. The remaining spinal nerves will exit Relationships of the sixth cervical spinal nerve. below the FIGURE 1-4 vertebrae of the Reprinted with permission from Fitzgerald MJ, Gruener G, Mtui E. Clinical neuroanatomy and neuroscience. 5th ed. London: Saunders, 2007:171. Copyright © 2007, Elsevier. corresponding number. (or horn), a lateral column, and an laminae I through V, more clearly anterior column (or horn) that respec- demonstrate a laminated appearance. tively “divide” the adjacent white mat- ter into a posterior, lateral, and ante- Major Ascending Tracts rior funiculus. At the junction The diagrammatic representation of between white and gray matter are both ascending and descending tracts short ascending and descending axons within the spinal cord reflects a level that arise from small neurons within of certainty that, while useful for com- the spinal cord gray matter and com- prehension, oversimplifies a more prise the intrinsic or intersegmental re- complex anatomic distribution and an- flex pathways, proprius bundles (or atomic variations that likely exist system)orfasciculi proprii and are (Nathan et al, 1990; Nathan et al, 1996; named by their location. While the Nathan et al, 2001). Indeed, the con- posterior funiculi primarily consist of cept of a tract as a homogenous group ascending sensory fibers, they also of fibers is also an oversimplification. 14 contain their descending collateral fi- Despite their shortcomings, however, bers, which serve to further integrate such generalizations have proven to intrinsic spinal reflexes and form their be clinically useful. own distinct, but small, fasciculi. The sensory pathways and tracts Within the gray matter of the spi- we will first review are responsible for nal cord cell groups can be identified transmitting sensory information that (right portion of Figure 1-6), with is perceived (conscious) as well as those in the posterior horn participat- nonconscious sensation. The dorsal ing in sensory pathways and those in root ganglia contribute nerve fibers the intermediate and anterior horns that at the dorsal root entry zone will serving motor functions. In addition, further segregate into a medial group layers of synaptic inputs within the of large-diameter fibers, which will en- spinal cord have also been identified. ter the posterior funiculi of the spinal These are called Rexed laminae and cord, and a lateral group of small-di- are labeled I to X (left side of Figure ameter myelinated and unmyelinated 1-6). Those within the posterior horn, fibers. This segregation is modality Continuum: Lifelong Learning Neurol 2008;14(3) specific and will give rise to the major ascending tracts within the spinal cord (Figure 1-7). This lateral group of fi- bers will divide into short ascending and descending branches within the tract of Lissauer and predominantly synapse on neurons within laminae I and II of the posterior horn. The posterior column–medial lem- niscal pathway receives its input from the largest group of sensory receptors (neuromuscular spindles and Golgi tendon organs) entering through the medial portion of the dorsal root entry zone.