When a patient has spinal cord disease, identifying where in the cord the lesion sits is the central localizing question. A C5 lesion produces a profoundly different picture from a T10 lesion or a conus medullaris lesion, and the imaging, urgency, and surgical considerations differ accordingly. Cord level localization rests on a few well-defined principles: the sensory level marks the upper extent of the lesion; the motor level reflects the segments at and below; the reflex changes and the presence of pyramidal signs distinguish above-versus-at-level damage; and the bowel/bladder findings narrow conus from cauda equina. This page covers cord level localization from a practical bedside standpoint.

What Defines a Cord Level?

A spinal cord level is the rostral-caudal vertical position of a lesion within the cord. The localization is determined by:

• The sensory level: an abrupt change in sensation at a horizontal line on the trunk identifies the dermatomal level of cord injury.
• The motor level: muscles innervated at and below the lesion are weak; muscles innervated above are spared.
• The reflexes: at-level lower motor neuron lesions produce decreased reflexes at that level; below-level upper motor neuron lesions produce hyperreflexia.
• The bladder and bowel: any cord lesion above S2 produces upper motor neuron bladder (spastic, small-capacity); a conus or cauda equina lesion produces a lower motor neuron picture (areflexic, distended).

The Sensory Level

The single most useful localization sign for a cord lesion. Examination:

1. Use a sharp object (broken cotton swab, safety pin) to test pinprick from feet upward toward the trunk.
2. Watch for the patient to say “now it feels normal” — that is the sensory level.
3. Confirm by testing temperature with a cold tuning fork or similar.
4. Confirm vibration: run a tuning fork up the spinous processes from sacrum upward; the patient should perceive normal vibration above the lesion.

Key landmarks for sensory levels on the trunk:

Pitfall: pain-temperature sensory levels often appear one to two segments below the actual cord lesion (because the spinothalamic tract decussates one to two segments above where the fibers enter the cord). Vibration levels are more accurate. Image one to two segments above the apparent pain-temperature level if uncertain.

The Motor Level

The motor level is the lowest myotome with normal strength. Beneath, weakness develops. Key motor levels for cord localization:

Reflex Changes

At the level of the lesion: if the lesion damages the anterior horn motor neurons (lower motor neuron component), reflexes at that level are decreased or absent.

Below the level of the lesion: corticospinal tracts are interrupted — upper motor neuron syndrome with hyperreflexia, spasticity, and extensor plantar response (Babinski sign).

The combination is a useful localization marker. In a C5-C6 cord lesion, biceps and brachioradialis reflexes may be decreased (at level), while triceps, finger flexion, and lower extremity reflexes are hyperactive (below level). This is a “mixed UMN/LMN” picture at the cervical level — sometimes seen in cervical spondylotic myelopathy.

The Bladder and Bowel

Cord lesions affect bladder/bowel function in a characteristic way:

• Above S2 (cord lesions in cervical, thoracic, or upper lumbar cord): spastic bladder — small capacity, urgency, urge incontinence. UMN-type. Reflex emptying eventually develops.
• Conus (S2-S4 segments at L1-L2 vertebral level): combination of UMN and LMN; severe bladder dysfunction with retention; saddle anesthesia early; symmetric distal leg weakness.
• Cauda equina (below the conus, lumbosacral roots): flaccid bladder with retention and overflow incontinence; loss of anal tone; loss of bulbocavernosus reflex; LMN-type. Often asymmetric, with severe radicular pain.

The bulbocavernosus reflex and anal wink are critical: their absence in conjunction with leg weakness and saddle anesthesia identifies cauda equina syndrome — a surgical emergency.

Localization by Region

Cervical Cord

• High cervical (C1-C4): quadriparesis (UMN), respiratory failure if phrenic nerve nucleus involved (C3-C5), sensory level high on the body. Diaphragmatic paralysis from C3-C4 lesions can be lethal. Sleep apnea, Ondine curse from medullary involvement.
• Mid-cervical (C5-C6): arms affected with LMN at level (decreased biceps/brachioradialis, weak shoulder/elbow flexion), hyperreflexia in legs.
• Low cervical (C7-C8/T1): hand affected with LMN intrinsic weakness, hyperreflexia in legs.
• Cervical spondylotic myelopathy: chronic, often with hand clumsiness (“dropping objects”), gait imbalance, urinary urgency, hyperreflexia in legs, Hoffmann sign, Lhermitte sign (electrical sensation down spine with neck flexion).

Thoracic Cord

• Spares the arms (above lesion).
• Symmetric leg weakness (paraplegia) with hyperreflexia.
• Sensory level on the trunk.
• Bladder and bowel dysfunction.
• Most common causes: transverse myelitis (demyelinating, autoimmune, infectious), epidural metastasis, epidural abscess, thoracic disc, dural AV fistula, anterior spinal artery infarct.

Lumbar Cord (Conus)

• Cord ends at L1-L2 vertebral level (in adults).
• Conus lesions produce a combination of UMN and LMN with predominant saddle anesthesia, severe bladder/bowel dysfunction, often symmetric.
• Leg weakness less prominent than cauda equina; pain less severe.
• Causes: tumor, MS plaque, vascular.

Cauda Equina

• Below the conus, the lumbar/sacral roots form the cauda equina.
• Compression produces multi-root LMN syndrome: asymmetric leg weakness, dermatomal sensory loss, severe radicular pain, saddle anesthesia, bladder retention with overflow, absent anal tone and bulbocavernosus reflex.
• Surgical emergency.
• Causes: large central disc herniation, epidural metastasis, abscess, hematoma.

Vertebral-Cord Relationship

An important practical point: the cord is shorter than the vertebral column. Approximate relationship:

• Cervical cord segments lie within cervical vertebrae 1 above their vertebra.
• Upper thoracic cord segments lie within vertebrae 2 above their vertebra.
• Lower thoracic cord segments lie within vertebrae 2-3 above their vertebra.
• Lumbar cord segments lie within T11-T12 vertebrae.
• Sacral cord segments lie within T12-L1 vertebrae.
• Cord ends at L1-L2 vertebral level in adults; below this, lumbosacral roots form the cauda equina within the vertebral canal.

This matters for imaging. A T10 cord level corresponds to a lesion around T8 vertebral body level. A patient with leg weakness and a T10 sensory level needs imaging that covers vertebrae T6-T10 to capture the actual cord lesion (and a few segments above just to be safe).

Differential Patterns by Lesion Geometry

The shape of the cord lesion shapes the syndrome:

Transverse (Complete)

Affects the entire cross-section. Below the level: complete motor, sensory, reflex, and autonomic loss. Common in spinal shock acutely, then evolving to spastic paraplegia with bladder dysfunction over weeks.

Partial / Incomplete

• Brown-Séquard (hemisection): ipsilateral motor loss (corticospinal — UMN below level), ipsilateral dorsal column loss (vibration, proprioception), contralateral spinothalamic loss (pain, temperature) below level. Often from penetrating trauma, MS plaque, tumor, or disc.
• Anterior cord (anterior spinal artery): motor (corticospinal), pain-temperature (spinothalamic) loss; vibration and proprioception preserved (dorsal columns spared). Often from aortic disease, vascular event, severe hypotension.
• Posterior cord: dorsal column loss (vibration, proprioception). Rare in pure form. Often from B12 deficiency (combined with corticospinal involvement → subacute combined degeneration), copper deficiency, NO2 abuse.
• Central cord: motor loss worse in upper than lower extremities (cervical somatotopy with arms more central in the corticospinal tract), with cape-like pain-temperature loss from decussating fibers at the anterior white commissure. Classic in cervical hyperextension injury in older patients with cervical stenosis, syringomyelia, intramedullary tumor.
• Conus medullaris: mixed UMN/LMN with predominant saddle, bladder/bowel involvement.
• Cauda equina: multi-root LMN syndrome with saddle, severe pain.

Acute vs Chronic Cord Disease

Bedside Workflow for Cord Lesion

1. Define motor pattern: paraparesis vs quadriparesis vs hemiparesis. Symmetric or asymmetric.
2. Find the sensory level. Test pinprick from feet up the trunk. Confirm with vibration on spinous processes.
3. Test reflexes: at level (may be decreased), below level (hyperactive). Plantar response (Babinski).
4. Examine for Lhermitte sign, neck pain, focal back tenderness.
5. Test anal tone, bulbocavernosus reflex, saddle sensation.
6. Identify red flags: progressive deficit, retention/incontinence, fever, IV drug use, cancer history, immunocompromise, anticoagulation.
7. Image with MRI of the suspected level (image one to two levels above and below the apparent sensory level). Add gadolinium if inflammation, infection, or tumor suspected.

🔍 Did You Know?

The classical “cape distribution” sensory loss of a high cervical central cord lesion — a band of pain and temperature loss over the shoulders, neck, and upper arms with preserved sensation above and below — reflects the precise anatomy of the anterior white commissure. The spinothalamic tract is formed by axons that decussate within one to two segments of their entry into the cord. The crossing happens through the anterior white commissure, just anterior to the central canal. A central cord lesion at the cervical level (syringomyelia, intramedullary tumor, even hyperextension injury with cord edema) damages these crossing fibers but spares the longitudinal long tracts. The result: a band of dissociated sensory loss in the dermatomes whose fibers are crossing at the affected level — typically shoulders and arms (C5-T1) for a high cervical syrinx. Above and below the lesion, fibers cross normally and reach the lateral spinothalamic tract en route to the brain. The pattern is so characteristic that recognizing it at the bedside often points immediately to the diagnosis. Vibration and proprioception, which travel ipsilaterally in the dorsal columns without crossing until the medulla, are preserved.

Pitfalls and Pearls

• Pain-temperature sensory level is one to two segments below the actual cord lesion. Vibration level is more accurate. Image above.
• Cord is shorter than vertebral column: a cord lesion at T10 segment is around T8 vertebral level.
• Cord ends at L1-L2. Below that, cauda equina.
• Brown-Séquard: ipsilateral motor and vibration loss, contralateral pain-temperature loss below the level.
• Anterior cord syndrome: motor + pain-temp loss; vibration spared. Aortic, vascular.
• Central cord syndrome: arms > legs (cervical somatotopy), cape sensory loss. Hyperextension in cervical stenosis.
• Conus vs cauda equina: conus is symmetric, sudden, less painful; cauda equina is asymmetric, gradual, painful, with severe radicular features.
• Cauda equina is a surgical emergency. Bladder retention + saddle anesthesia + bilateral leg weakness → MRI immediately.
• Spinal shock: acute cord injury can show flaccid paralysis and areflexia initially; UMN signs develop over days to weeks.
• Hyperreflexia + Babinski + sensory level: cord lesion above that level.
• Lhermitte sign: electrical sensation down the spine on neck flexion — suggests cervical cord disease (MS, B12, cervical spondylotic myelopathy).
• Cervical spondylotic myelopathy: hand clumsiness + gait imbalance + hyperreflexia + Hoffmann sign in an older patient.
• Image one to two segments above and below the apparent level. The lesion may be higher than expected.

References

1. Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 7th ed. Wolters Kluwer; 2017.
2. Maynard FM Jr, Bracken MB, Creasey G, et al. International Standards for Neurological and Functional Classification of Spinal Cord Injury. Spinal Cord. 1997;35(5):266-274.
3. Kim DH, Vaccaro AR, Berta SC, et al. Acute spinal cord injury: pathophysiology, neuropathologic findings, and current concepts of pharmacologic therapy. J Am Acad Orthop Surg. 2003;11(6):347-358.
4. Greenberg JO. Neuroimaging: A Companion to Adams and Victor’s Principles of Neurology. 2nd ed. McGraw-Hill; 1999.
5. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor’s Principles of Neurology. 11th ed. McGraw-Hill; 2019.