Post on 03-Jun-2020
transcript
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