Residency · Residency · Neurology

Spinal Cord Syndromes and Localization

Overview

Spinal cord lesions produce predictable patterns of motor, sensory, and autonomic dysfunction based on the anatomy of the ascending and descending tracts. Localizing a lesion to a specific spinal cord level requires careful identification of the sensory level, pattern of weakness, and reflex changes. Distinguishing intramedullary from extramedullary lesions is essential because it fundamentally changes the differential diagnosis and management approach.

Spinal Cord Anatomy

Cross-Sectional Organization

The spinal cord is organized with gray matter at its center in an H-shaped configuration and white matter tracts surrounding it. The dorsal horn processes sensory information including pain, temperature, and touch. The ventral horn contains the lower motor neurons (alpha motor neurons) that directly innervate skeletal muscle. The intermediolateral cell column, present from T1 to L2, houses sympathetic preganglionic neurons. The sacral parasympathetic nuclei at S2-S4 control bladder, bowel, and sexual function.

The surrounding white matter carries several critical tracts. The dorsal columns transmit ipsilateral proprioception, vibration, and fine touch, with the fasciculus gracilis (lower extremity fibers, positioned medially) and the fasciculus cuneatus (upper extremity fibers, positioned laterally); these fibers decussate in the medulla. The lateral corticospinal tract carries ipsilateral voluntary motor fibers that have already crossed in the medullary pyramids, organized somatotopically with cervical fibers medial and sacral fibers lateral. The lateral spinothalamic tract transmits contralateral pain and temperature sensation, with fibers crossing one to two levels above their entry point in the anterior white commissure. The anterior spinothalamic tract conveys contralateral crude touch. The spinocerebellar tracts carry ipsilateral proprioceptive information to the cerebellum.

Vascular Supply

The anterior spinal artery is a single vessel supplying the anterior two-thirds of the cord, encompassing the corticospinal tracts, spinothalamic tracts, and ventral horns. The paired posterior spinal arteries supply the posterior one-third, primarily the dorsal columns. Segmental radicular arteries provide reinforcement along the cord's length; the most important of these is the artery of Adamkiewicz, which typically arises at T9-T12 on the left side and serves as the major radicular contributor to the lower thoracic and lumbar cord. The mid-thoracic cord represents a watershed zone and is therefore the most vulnerable region to ischemia.

Key Spinal Cord Levels

Several spinal levels have particular clinical importance. C3-C5 supplies the diaphragm via the phrenic nerve -- the mnemonic "C3, 4, 5 keeps the diaphragm alive" is clinically essential. C5 through T1 provides motor and sensory innervation to the upper extremities. A T1 lesion may produce Horner syndrome if sympathetic fibers are disrupted. The intermediolateral cell column extends from T1 to L2, carrying sympathetic outflow. The conus medullaris lies at the L1-L2 vertebral level. Below L2, the neural elements are the cauda equina, consisting of peripheral nerve roots rather than spinal cord.

Classic Spinal Cord Syndromes

Complete Transverse Myelopathy

A complete transverse myelopathy produces total loss of all motor, sensory, and autonomic function below the level of the lesion. There is bilateral weakness in an upper motor neuron pattern below the lesion with lower motor neuron signs at the level of the lesion itself. All sensory modalities are lost below the level, and bladder and bowel dysfunction are present. Causes include trauma, transverse myelitis, epidural compression, and vascular events such as aortic dissection. In the acute phase, spinal shock produces initial flaccidity and areflexia below the lesion lasting hours to weeks, followed by the emergence of spasticity and hyperreflexia.

Brown-Sequard Syndrome (Hemisection)

The Brown-Sequard syndrome results from hemisection of the cord, though it is rarely seen in pure form and usually presents as a partial pattern. Ipsilateral to the lesion, there is upper motor neuron weakness (because the corticospinal tract has already crossed), loss of proprioception and vibration (because the dorsal columns are uncrossed at this level), and lower motor neuron signs at the level of the lesion from ventral horn damage. Contralateral to the lesion, there is loss of pain and temperature beginning one to two levels below the lesion (because the spinothalamic tract has already crossed). Common causes include penetrating trauma (stab wounds), multiple sclerosis, tumor, and radiation myelopathy. Among incomplete cord syndromes, Brown-Sequard has the best prognosis for recovery of ambulation.

Central Cord Syndrome

Central cord syndrome is the most common incomplete spinal cord injury pattern. It characteristically produces disproportionate upper extremity weakness relative to the lower extremities in a "cape-like" distribution. This occurs because of the somatotopic organization of the corticospinal tract: cervical fibers are positioned medially, closer to the central canal, and are preferentially damaged by a central lesion, while sacral fibers, located most laterally, are relatively spared. Sensory loss is variable, often producing a "suspended" pattern of pain and temperature loss in a cape distribution with sacral sparing. Bladder dysfunction is common. Typical causes include hyperextension injuries in elderly patients with pre-existing cervical spondylosis, syringomyelia, and intramedullary tumors.

Anterior Cord Syndrome

Anterior cord syndrome produces bilateral loss of motor function (from corticospinal tract involvement) and bilateral loss of pain and temperature sensation (from spinothalamic tract involvement) below the lesion, while dorsal column function -- proprioception, vibration, and fine touch -- is preserved. The most common cause is anterior spinal artery occlusion, which can occur during aortic surgery, from aortic dissection, atherosclerosis, or vasculitis. Disc herniation compressing the anterior cord can produce a similar picture. Among incomplete cord syndromes, anterior cord syndrome carries the worst prognosis for motor recovery.

Posterior Cord Syndrome

Posterior cord syndrome is rare in isolation. It produces loss of proprioception, vibration, and fine touch from dorsal column involvement, resulting in sensory ataxia with a positive Romberg sign. Motor function and pain and temperature sensation are preserved. Causes include vitamin B12 deficiency (subacute combined degeneration), tabes dorsalis from neurosyphilis, copper deficiency, multiple sclerosis, and compressive lesions.

Conus Medullaris Syndrome

The conus medullaris sits at the L1-L2 vertebral level and contains the sacral cord segments S2-S5. A conus lesion produces early bladder, bowel, and sexual dysfunction -- often the presenting symptom. Bilateral saddle anesthesia in the perianal and perineal area is characteristic. Lower extremity weakness may be mild or absent. Ankle jerks may be preserved because the S1 reflex arc lies above the conus, but the bulbocavernosus reflex is absent. The presentation is typically symmetric. Causes include trauma, tumors (especially ependymoma), and vascular malformations.

Cauda Equina Syndrome

Cauda equina syndrome results from compression of the lumbosacral nerve roots below the conus (below L2). Because these are peripheral nerves rather than spinal cord, this is a lower motor neuron pattern. The presentation is typically asymmetric with radicular pain, weakness, and sensory loss in the lower extremities. Saddle anesthesia is present. Urinary retention from an areflexic bladder is a critical finding, though it tends to appear late. Ankle jerks are diminished or absent, and the bulbocavernosus reflex is absent. Common causes include large disc herniation (L4-5 or L5-S1), tumors, and epidural abscess. Cauda equina syndrome is a surgical emergency, and urgent decompression within 48 hours improves outcomes.

Conus vs. Cauda Equina Comparison

Intramedullary vs. Extramedullary Lesions

Intramedullary (Within the Cord)

Intramedullary lesions produce a central cord syndrome pattern with sacral sparing. Sacral sparing occurs because the spinothalamic fibers from sacral segments are positioned most laterally and are therefore farthest from a centrally expanding lesion. There is typically dissociated sensory loss, with pain and temperature affected while proprioception is initially spared. Sphincter dysfunction tends to appear early. Lower motor neuron signs develop at the level of the lesion. Common causes include syringomyelia, ependymoma, astrocytoma, multiple sclerosis, and neuromyelitis optica.

Extramedullary (Outside the Cord)

Intradural-Extramedullary

These lesions produce early radicular pain and progressive cord compression from outside. Sacral segments are affected first (no sacral sparing), which is the opposite of the intramedullary pattern, because the outer layers of the cord are compressed first. Upper motor neuron signs develop below the level of compression. Common causes include meningioma, schwannoma and neurofibroma, and leptomeningeal metastases.

Extradural

Extradural lesions present with prominent back pain and can progress rapidly. Common causes include disc herniation, metastatic epidural compression, epidural abscess, epidural hematoma, and spondylosis.

Diagnostic Workup

MRI of the spine with and without gadolinium is the imaging modality of choice. Sagittal and axial T2-weighted sequences reveal edema, cord signal abnormality, and compression, while T1 post-contrast sequences show enhancement in inflammatory, neoplastic, or vascular lesions. Whole-spine MRI should be considered when the etiology of myelopathy is unclear. CT myelography is an alternative when MRI is contraindicated or inconclusive. CSF analysis is obtained when inflammatory, infectious, or neoplastic myelopathy is suspected. Electrophysiology, including somatosensory evoked potentials for dorsal column function and EMG/nerve conduction studies to distinguish from peripheral neuropathy or motor neuron disease, can be helpful. Laboratory workup includes B12, methylmalonic acid, copper, zinc, RPR/FTA-ABS, AQP4-IgG, MOG-IgG, and HIV testing.

Specific Myelopathies

Compressive Myelopathy

Cervical spondylotic myelopathy is the most common cause of myelopathy in adults over 55. It presents with gradual onset of hand clumsiness, gait imbalance, and Lhermitte sign (an electric shock-like sensation radiating down the spine with neck flexion). Examination findings include Hoffman sign, hyperreflexia, and the myelopathic hand (finger escape sign).

Transverse Myelitis

Transverse myelitis is an acute inflammatory myelopathy and a diagnosis of exclusion after compressive and other causes are ruled out. In multiple sclerosis, the lesion is typically partial, asymmetric, and short-segment (less than 3 vertebral segments). In neuromyelitis optica spectrum disorder (NMOSD), the lesion is longitudinally extensive (3 or more segments) with a central cord predominant pattern. MOG antibody-associated disease may mimic NMOSD but tends to affect the conus and carries a better prognosis.

Subacute Combined Degeneration (Vitamin B12 Deficiency)

This condition involves both the posterior and lateral columns. It produces a distinctive combination of proprioceptive loss (dorsal columns), upper motor neuron signs including spasticity and Babinski signs (lateral corticospinal tract), and peripheral neuropathy. Macrocytic anemia may be absent. Methylmalonic acid and homocysteine are more sensitive markers than serum B12 alone.

<image>A series of cross-sectional spinal cord diagrams illustrating the five classic cord syndromes. Each cross-section shows the damaged area shaded in red: (1) complete transverse myelopathy with the entire cord shaded, (2) Brown-Sequard with the right half shaded, (3) central cord syndrome with a central zone shaded, (4) anterior cord syndrome with the anterior two-thirds shaded, and (5) posterior cord syndrome with the dorsal columns shaded. Below each cross-section, a human figure shows the distribution of motor loss (red) and sensory loss (blue for dorsal column, green for spinothalamic) on the body.</image>

<image>An anatomical illustration of the spinal cord vascular supply showing the anterior spinal artery and paired posterior spinal arteries in a longitudinal view. The artery of Adamkiewicz is highlighted entering at T9-T12 on the left side. A cross-sectional inset shows the territories supplied by the anterior spinal artery (anterior two-thirds, shaded red) and the posterior spinal arteries (posterior one-third, shaded blue). The watershed zone in the mid-thoracic region is labeled with a warning indicator. A separate inset shows the pattern of anterior spinal artery occlusion with preserved dorsal columns.</image>

<image>A comparative diagram of intramedullary versus extramedullary spinal cord lesions. The left panel shows an intramedullary lesion (e.g., syringomyelia) on sagittal and axial MRI schematic with expansion of the cord and central cavitation. The lamination pattern of the spinothalamic tract is shown with sacral fibers lateral and cervical fibers medial, explaining sacral sparing. The right panel shows an extramedullary intradural lesion (e.g., meningioma) compressing the cord from outside, with sacral fibers affected first (no sacral sparing). Clinical features are listed below each panel.</image>

Clinical Pearls

A sensory level on the trunk is pathognomonic for a spinal cord lesion and should always prompt a careful sensory examination in any patient presenting with bilateral symptoms. Sacral sparing -- preserved perianal sensation, rectal tone, and great toe flexion -- suggests an intramedullary lesion due to the lamination of the spinothalamic tract, with sacral fibers positioned most laterally. Brown-Sequard syndrome carries the best prognosis for functional recovery among incomplete spinal cord injuries. Central cord syndrome is the most common incomplete cord injury pattern and typically occurs from hyperextension in elderly patients with pre-existing cervical spondylosis. Cauda equina syndrome is a surgical emergency; urinary retention is a late finding, and imaging should not be delayed waiting for it. In any patient with new bilateral leg weakness or bladder dysfunction, it is essential to check for a sensory level, reflexes including Babinski, and rectal tone. Anterior spinal artery syndrome preserves proprioception and vibration (dorsal columns), producing a "dissociated sensory loss" pattern that is characteristic. Subacute combined degeneration from B12 deficiency can create a confusing combination of upper motor neuron signs (from lateral corticospinal tract involvement) and peripheral neuropathy with sensory ataxia (from dorsal column and peripheral nerve damage).

References

• Blumenfeld H. Neuroanatomy Through Clinical Cases. 3rd ed. Sinauer Associates; 2021.
• Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology. 12th ed. McGraw-Hill; 2023.
• Aminoff MJ, Josephson SA. Aminoff's Neurology and General Medicine. 6th ed. Academic Press; 2021.
• Transverse Myelitis Consortium Working Group. Proposed diagnostic criteria and nosology of acute transverse myelitis. Neurology. 2002;59(4):499-505.

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