Spine & Spinal Cord Injuries: Neuroanatomy, connections and pathwaysLou Graham MD PM&R and Pain Medicine

SPINAL CORD INJURY

• Intro & Overview• Neuroanatomy, Connections, pathways• Physiology, chemistry, neurotransmitters

LANDMARKS

• C2: 1st palpable midline spinous process (2 finger breaths from occiput). Angle of mandible anteriorly

• C7 (prominens): Largest spinous process/first non bifid

• T3: spine of scapula• T7/8: Inferior angle of scapula• T12: Lowest rib• L4: iliac crests• S2: PSIS

SPINE SURFACE LANDMARKS

• 33 vertebrae: C-7, T-12, L-5, S-5, C-4• Spinal canal formed by vertebrae, pedicles, lamina• Facet joints: synovial joint formed by superior and

inferior articular process with capsule/articularcartilage/meniscus

• Dual innervation from the medial branches of the dorsal ramusof nerve root

• Spinal Cord in upper 2/3 of vertebral column• Conus Medullaris is the terminal portion of the cord

and becomes the cauda equina at L1-L2

SPINE ANATOMY REVIEW-BONY

INTERVERTEBRAL DISC

• Nucleus Pulposus: viscous muco-protein gel mixture of water and proteoglycan in a network of Type II collagen

• Annulus Fibrosis: Type I collagen arranged in obliquely running lamellae

• Encase nucleus pulposus and attached to endplate• Withstands bending/distraction forces well but weaker

for torsional forces• Thinner posteriorly

• Vertebral Endplate: cartilaginous covering of vertebral body apophysis forming top/bottom of disc

INTERVERTEBRAL DISC

• Essentially avascular by adulthood receives some nutrition by passive diffusion

• Outer 1/3 of disc (annulus fibrosis) receives dual innervations from ventral rami

• Anterolateral: ventral rami/grey rami communicans• Posterior: Sinuvertebral nerves (recurrent branch off

ventral rami)• Nucleus pulposus lacks innervation

• SC receives blood supply from 1 anterior and 2 posterior arteries

• also anterior/posterior radicular arteries• Anterior spinal artery supplies anterior 2/3rds of SC• Posterior Spinal arteries arise directly and indirectly

from vertebral arteries (25%) or PICA (75%)• supply posterior 1/3 of SC

• Radicular arteries are branches of local arteries (vertebral, cervical, intercostal, lumbar, sacral)

• Enter vertebral canal thru foramina and reinforce the anterior/posterior spinal arteries.

BLOOD SUPPLY

ANTERIOR CORD BLOOD SUPPLY

• Artery of Adamkiewicz: major radiculomedullaryartery that supplies the LS blood supply of the SC.

• Usually arises from the left intercostal or lumbar artery at T6-L3 and provides the major blood supply to the lower 2/3rds of cord

• Lower thoracic region is “watershed area” bc fewer radicular arteries supply this area. T4-T6 is most affected by low blood flow (ex. Clamping of aorta)

BLOOD SUPPLY

POSTERIOR SPINAL ARTERIES

SPINAL CORD ANATOMY

• White matter surrounds gray matter• White: neuronal cell bodies, neuroglia, blood vessels

• Nerve fibers form spinal tracts (ascending/descending/ intersegmental)

• Gray: few myelinated fibers• Anterior horn: cell bodies of interneurons & motor neurons • Posterior (dorsal) horn: cell bodies of sensory neurons

SPINAL CORD SEGMENTS

•Spinal cord ends L1-2 (T12-L3 variants)•Spinal cord segments do not line up with bony levels, esp in thoracolumbar spine

•L1-L5 SC aligns w T11-12 vertebrae•S1-S5 SC aligns w L1 vertebrae

*occurs to smaller extent in cervical/thoracic spinal cord

LAYERS OF MENINGES

• Pia: thin membrane attached to SC permiable to water/nutrients• Arachnoid: contains villi producing csf in subarachnoid space (aka

intrathecal space)• Dura: thicker membrane protecting SC

• Csf pushes arachnoid directly against dura

• Fasciculus gracilis (medial dorsal columns)• proprioception of LEG/light touch/vibration (T7-S5)

• Fasciculus cuneatus (lateral dorsal columns)• proprioception of ARM/light touch/vibration (T6 & above)

• Spinocerebellar tracts• muscular position, tone, unconscious proprioception

• Lateral Spinothalamic• pain and thermal sensation

• Ventral Spinothalamic• tactile sensation of crude touch and pressure

LONG TRACTS OF THE CORD

• Lateral Corticospinal (pyramidal): Motor • theorized to have fibers running medial (cervical) to

lateral (sacral)• Anterior Corticospinal: motor w neck and trunk

movements

LONG TRACTS OF THE CORD

• Lateral Corticospinal Tracts: origin is precentral gyrus. Axons descend through internal capsule to the medulla oblongata

• -80-90% of axons decussate to the contralateral side at medullary pyramids

• Remaining 10-20% of axons travel w ventral CS tract• decussate at the corresponding level of muscles they innervate

• At each level of spinal cord, axons from LCS tract enter gray matter of the ventral horn to synapse w secondary neurons

• They are UMN until they synapse w “secondary” neurons and become LMN

• Cerebral lesions result in contralateral deficits typically

DESCENDING PATHWAYS

LATERAL CORTICOSPINAL TRACT

• Lateral Spinothalamic: transmit pain/temperature from contralateral side of the body.

• Enter the SC and synapse in the dorsal horn of the gray matter.

• Decussate within 1-3 vertebral segments• Ascend in the Lat ST tracts to the thalamus on the

opposite side and ascend in the internal capsule to the postcentral gyrus of the cortex.

• Lesion results in loss of sensation contralaterally below lesion

ASCENDING PATHWAYS

LATERAL SPINOTHALAMIC TRACT

• Dorsal Columns: transmit proprioception, fine touch & vibration from the Ipsilateral side of the body

• Fibers synapse at DRG and immediately ascend in ipsilateral dorsal white columns

• Ascend and decussate at medulla where they form a bundle termed “medial lemniscus” which ascends to the postcentral gyrus.

• Lesion causes loss ipsilaterally below the level of lesion.

ASCENDING PATHWAYS

ASCENDING PATHWAYS

• Spinocerebellar Tracts: unconscious proprioceptionon ipsilateral side of the body.

• Ventral spinocerebellar tract: “dirty” double crosser• Dorsal spinocerebellar tract: no decussation

• Most common incomplete syndrome (9% of total sci)

• Results in sacral sparing• UE weakness > LE weakness- possibly due to

cervical LCS tracts being more medial. • Variable loss of sensation, bowel/bladder function• Originally described with intramedullary

hemorrhage but actually uncommon• Probably due to central cord edema associate w trauma

• Common in older pts w cervical spondylosis who sustain hyperextension injury from fall

CENTRAL CORD SYNDROME

• 2-4% of all traumatic SCI • Lesion causing hemisection of cord• Classic Case is stabbing but many other causes• Deficits include

• Ipsilateral flaccid paralysis at level• Ipsilateral vibration/position sense loss below lesion• Contralateral loss of pain/temp below lesion

BROWN-SEQUARD SYNDROME

• Anterior 2/3 of spinal cord and preserves posterior columns

• Occurs w flexion injuries, retropulsed disc or bone fragments, direct injury to the anterior spinal cord, anterior spinal artery lesions

• Variable loss of motor function (corticospinal tract) and sensitivity to pain/temp (spinothalamic tract), pinprick sensation

• Preservation of proprioception, light touch, and deep pressure sensation

• Spinocerebellar tract involved

ANTERIOR CORD SYNDROME

ANTERIOR CORD SYNDROME

• Least frequent syndrome and has been omitted from recent version of the International Standards

• Injury to the posterior columns results in proprioceptive loss (dorsal columns) with muscle strength, pain, and temperature modalities spared

• Prognosis for ambulation is poor, secondary to the proprioceptive deficits.

POSTERIOR CORD SYNDROME

• The terminal segment of the adult spinal cord lies at the inferior aspect of the L1-L2 vertebrae

• Injury to the sacral cord (conus) and lumbar nerve roots within the spinal canal

• Usually results in areflexic bladder and bowel and LE areflexia

• High conus lesions preserve bulbocavernous reflex and micturition reflexes

CONUS MEDULLARIS SYNDROME

• Injuries below the L1-L2 vertebral levels usually affect the cauda equina (nerve rootlets), which innervate Lumbar and sacral segments

• Lower motor neuron injury• Motor weakness and atrophy of the lower

extremities (L2-S2) with bowel and bladder involvement (S2-S4), impotence, areflexia of DTRs

• Absent bulbocavernous reflex• Better prognosis relative to UMN injuries for

recovery. Nerve Roots more resilient to injury and can regenerate bc peripheral nerves

CAUDA EQUINA SYNDROME