Anatomy Atlas

Spinal cord

Medulla spinalis
Also: Conus medullaris · Anterior spinal artery · Artery of Adamkiewicz
OrganHigh-yielddraftNeuro

Continuation of the medulla within the vertebral canal, ending at the conus medullaris at about L1–L2 in adults. Its blood supply and level of termination explain spinal cord injury syndromes and safe lumbar puncture sites.

Core anatomy

Location

Vertebral canal, from the foramen magnum to the conus medullaris at about the L1–L2 disc in adults (lower, about L3, in newborns). verify

Parts
  • Cervical enlargement (about C4–T1, for the brachial plexus) and lumbosacral enlargement (about L1–S3 segments, for the lumbosacral plexus)
  • Conus medullaris: tapered lower end; filum terminale continues to the coccyx
  • 31 pairs of spinal nerves (8 C, 12 T, 5 L, 5 S, 1 Co) from dorsal (sensory) and ventral (motor) rootlets
  • Internal organization: central gray matter (dorsal, lateral T1–L2 sympathetic, and ventral horns) surrounded by white matter tracts (dorsal columns, spinothalamic, corticospinal)
Relations

Surrounded by the spinal meninges and spaces; roots below the conus form the cauda equina. Because the cord is shorter than the column, lower cord segments lie higher than their vertebrae (e.g. the lumbar segments lie at about T10–T12).

Arterial supply

One anterior spinal artery (from the vertebral arteries) supplies the anterior two-thirds of the cord. Two posterior spinal arteries supply the posterior third (dorsal columns). They are reinforced by segmental medullary arteries, the largest being the great anterior segmental medullary artery (of Adamkiewicz), usually on the left between about T9 and T12, supplying the lower cord. verify

Venous drainage

Spinal veins → internal vertebral venous plexus (vertebral venous plexus).

Mentioned in

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Lumbar puncture anatomy (sagittal view)The spinal cord ends at the conus medullaris at about L1–L2; the cauda equina continues in the dural sac, which ends at about S2. A needle entering between the L3 and L4 spinous processes passes the ligaments and epidural space into the subarachnoid space below the cord. The intercristal line crosses L4.T12L1L2L3L4L5SacrumSpinal cordConus medullaris (L1–L2)← Cauda equinaDural sac ends ≈ S2Supraspinous / interspinous lig.Ligamentum flavumEpidural space → dura → CSFLP needle (L3–L4)Intercristal (Tuffier) line ≈ L4AnteriorPosterior

Swipe sideways to see the whole diagram →

Lumbar puncture anatomy. Sagittal schematic (not to scale): the cord ends at about L1–L2, the dural sac at about S2. The needle enters at L3–L4, just above the intercristal line (≈ L4), well below the conus.
Original schematic, created for this atlas.
Spinal cord with the dura opened showing anterior and posterior nerve roots, the denticulate ligament and spinal nerves in their sheaths
Spinal cord with the dura opened: anterior and posterior roots and the denticulate ligament.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 796. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Segment of spinal cord with anterior and posterior roots, the spinal ganglion on the posterior root and their union into a spinal nerve
Formation of a spinal nerve from anterior and posterior roots; the spinal ganglion lies on the posterior root.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 675. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Anterior spinal artery (anterior cord) syndrome PANCE

Mechanism / lesion

Infarction of the anterior two-thirds of the cord, e.g. after aortic surgery or dissection (loss of the artery of Adamkiewicz), hypotension, or flexion injury.

Classic presentation

Paraplegia or quadriplegia and loss of pain and temperature below the lesion, with preserved proprioception and vibration (dorsal columns). Bladder dysfunction.

Incomplete cord injury syndromes PANCE

Mechanism / lesion

Central cord: hyperextension in an older patient with cervical spondylosis. Brown-Séquard: hemisection (penetrating trauma). See also the anterior cord syndrome above.

Classic presentation

Central cord: weakness greater in the arms than the legs, variable sensory loss. Brown-Séquard: ipsilateral weakness and loss of proprioception/vibration, contralateral loss of pain and temperature below the lesion.

Neurogenic shock PANCE

Mechanism / lesion

Loss of sympathetic outflow after cervical or high thoracic (above about T6) cord injury.

Classic presentation

Hypotension with bradycardia and warm, dry skin (unlike hemorrhagic shock with tachycardia). Treat with fluids and vasopressors.

Neural tube defects PANCE

Mechanism / lesion

Failure of neural tube closure. Risk reduced by periconceptional folic acid; elevated maternal AFP.

Classic presentation

Spina bifida occulta: bony defect with a tuft of hair or dimple, usually asymptomatic. Meningocele: meninges protrude. Myelomeningocele: cord and meninges protrude, with leg paralysis, bladder dysfunction, and Chiari II malformation/hydrocephalus. Tethered cord: low-lying conus causing back pain, gait and bladder problems.

High-yield PANCE pearls

  • Cord ends at L1–L2 in adults → LP at L3–L4 or L4–L5.
  • Anterior spinal artery syndrome: motor + pain/temperature loss, preserved vibration/proprioception; after aortic surgery (Adamkiewicz).
  • Central cord: arms > legs, older patient, hyperextension. Brown-Séquard: ipsilateral motor/dorsal columns, contralateral pain/temperature.
  • Neurogenic shock: hypotension + bradycardia after high cord injury.
  • Folic acid prevents neural tube defects; hair tuft over the spine → spina bifida occulta.

Imaging anatomy

X-ray

Plain films show bony injury and alignment only.

CT

Bony injury in trauma; CT myelography when MRI is contraindicated.

MRI

MRI is the test of choice for the cord: compression, contusion/edema, infarction (diffusion changes), demyelination, syrinx, tumor, tethered cord.

Ultrasound

In infants (before posterior element ossification), spinal ultrasound evaluates a low-lying conus and tethered cord (e.g. a sacral dimple).

Key views & landmarks
  • MRI spine (sagittal T2 and STIR, axial T2)

Physical exam

Surface landmarks

The conus lies at about the L1–L2 vertebral level; the intercristal line (L4) is safely below it.

Strength / function testing

Localize by sensory level, myotomes and reflexes; UMN signs below the lesion (spasticity, hyperreflexia, Babinski) and LMN signs at the level. Assess rectal tone and perianal sensation (sacral sparing indicates an incomplete injury). The ASIA/ISNCSCI exam grades injury severity.

Self-quiz

Q1.

After repair of a thoracoabdominal aortic aneurysm, a patient cannot move his legs and cannot feel pinprick below the umbilicus, but vibration and position sense are preserved. Which vessel was compromised?

Show answer

B

Anterior spinal artery syndrome spares the dorsal columns (vibration, proprioception). The lower cord's anterior supply depends on the artery of Adamkiewicz, which can be lost during aortic surgery.

Q2.

A 70-year-old man falls forward and hits his chin, hyperextending his neck. He has marked weakness of both hands with much milder leg weakness. What is the most likely syndrome?

Show answer

B

Central cord syndrome (arms weaker than legs) typically follows hyperextension in an older patient with cervical spondylosis.

Q3.

A patient with a C5 spinal cord injury is hypotensive (80/40) with a heart rate of 48 and warm extremities. What is the cause?

Show answer

B

Loss of sympathetic tone after high cord injury causes hypotension with bradycardia and warm skin: neurogenic shock.

Q4.

At what vertebral level does the spinal cord typically end in adults?

Show answer

C

The conus medullaris ends at about L1–L2 in adults, so lumbar puncture is performed at L3–L4 or L4–L5.

Q5.

After a stab wound to the right side of the thoracic spine, which pattern of deficits is expected below the lesion?

Show answer

D

Brown-Séquard (hemisection) causes ipsilateral weakness (corticospinal) and loss of vibration/proprioception (dorsal columns), with contralateral loss of pain and temperature because the spinothalamic fibers have already crossed.

Flashcards

See also