--- module: 081-01 language: en chapter: 81 title: "Structural Neuroanatomy and Lesion Localisation" module_title: "Spinal cord organisation, ascending pathways, descending tracts, and lesion patterns" source_sha256: 678d2fa8549f0afee81ad72a69ef734bef0edd626bda599cee6c3d6b63be736b --- # Spinal cord organisation and lesion patterns ## Segments and orientation ### Deficit set by level, side, tract, crossing, somatotopy ### Medulla to conus near L1 or L2 #### Column outgrows cord, roots descend as cauda equina ### Dorsal-root ganglion: pseudounipolar sensory bodies ### Ventral root: somatic and preganglionic motor axons ### Level by proportions #### Cervical: abundant white matter #### Lumbar: broad grey horns #### Thoracic: lateral horn ## Grey-matter circuits ### Dorsal horn receives afferents #### Superficial: nociception and temperature #### Deeper: touch and proprioception ### Ventral horn lower motor neurons #### Medial axial and proximal, lateral distal #### Alpha extrafusal, gamma spindle sensitivity ### Intermediate zone #### Sympathetic intermediolateral column T1 to L2 #### Sacral parasympathetic S2 to S4 #### Clarke nucleus relays proprioception to cerebellum ### Reflexes #### Stretch reflex monosynaptic core, modulated #### Intensity reflects central and peripheral excitability ## Dorsal column-medial lemniscus ### Touch, vibration, conscious proprioception ### First-order axons ascend ipsilaterally #### Gracilis lower body medial, cuneatus upper lateral ### Synapse in gracile and cuneate nuclei ### Internal arcuate fibres cross, medial lemniscus #### Ventral posterolateral thalamus to sensory cortex ### Cord lesion: ipsilateral loss below ### Sensory ataxia worse with eyes closed ## Anterolateral system ### Pain, temperature, itch, crude touch ### Lissauer tract, then dorsal horn synapse ### Cross in anterior white commissure #### Contralateral loss begins slightly below lesion ### Spinothalamic: localisation and discrimination ### Spinoreticular, spinomesencephalic: arousal, modulation ### Syrinx damages crossing fibres #### Bilateral segmental loss, dorsal columns spared ## Spinocerebellar pathways ### Posterior tract from Clarke nucleus, inferior peduncle ### Anterior tract crosses twice, ends ipsilateral ### Cerebellum compares intended and actual movement ### Lesion: ipsilateral ataxia, no conscious loss ## Motor pathways ### Corticospinal via internal capsule and pyramids #### Most cross at pyramidal decussation #### Cord lesion ipsilateral, above medulla contralateral ### Lateral tract: fractionated distal movement ### Anterior tract: axial muscles ### Brainstem motor tracts #### Reticulospinal: posture, tone, locomotion #### Vestibulospinal: stability, antigravity #### Tectospinal orients, rubrospinal upper limb ### Upper motor neuron: hyperreflexia, clonus, plantar ### Lower motor neuron: atrophy, fasciculation, hyporeflexia ### Cord level gives mixed pattern ## Autonomic pathways ### Hypothalamospinal fibres in dorsolateral cord #### Cervical lesion can cause Horner syndrome ### Bladder needs pontine and cortical coordination #### Suprasacral: detrusor-sphincter dyssynergia #### Conus, cauda, peripheral: areflexic ### High injury: neurogenic shock ### Above about T6: autonomic dysreflexia ## Arterial territories ### Anterior spinal artery: anterior two-thirds #### Infarct: bilateral motor and pain-temperature loss ### Posterior spinal arteries: dorsal columns and horns ### Lower cord depends on artery of Adamkiewicz ### Border zones vulnerable in aortic surgery ## Canonical spinal syndromes ### Brown-Séquard hemicord #### Ipsilateral weakness and dorsal-column loss #### Contralateral pain-temperature loss below ### Central cord: upper limbs worst ### Anterior cord: dorsal columns spared ### Posterior cord: sensory ataxia ### Conus: early symmetric saddle and sphincter loss ### Cauda: asymmetric radicular, lower motor signs ## Localisation strategy ### Start from highest abnormal level ### One pattern should explain every finding ### Sacral sparing suggests incomplete central lesion ### Interpret imaging against anatomy