Anatomy Atlas

Spinal meninges and spaces

Meninges spinales; spatium epidurale; spatium subarachnoideum
Also: Epidural space · Subarachnoid space · Lumbar cistern · Lumbar puncture · Dura mater
Space / regionHigh-yielddraftNeuro

Three membranes (dura, arachnoid, pia) and the spaces between them surrounding the spinal cord. The epidural space is the target of epidural anesthesia, and the lumbar cistern is sampled by lumbar puncture.

Core anatomy

Location

Within the vertebral canal, surrounding the spinal cord and cauda equina.

Boundaries
epidural space
Between the dura and the walls of the canal (bone, ligamentum flavum). Contains fat and the internal vertebral venous plexus. Unlike the cranial epidural space, it is a real space
dura mater
Tough outer membrane; the dural sac ends at about S2
subdural space
Potential space between dura and arachnoid
subarachnoid space
Between arachnoid and pia; contains CSF. Below the conus it enlarges as the lumbar cistern (about L2–S2), holding the cauda equina
pia mater
Adheres to the cord; forms the denticulate ligaments (lateral anchors) and the filum terminale
Contents
  • CSF, cauda equina nerve roots, spinal vessels
Communications

The subarachnoid space is continuous with the cranial subarachnoid space and ventricular system through the foramen magnum.

Notes

Lumbar puncture is performed at L3–L4 or L4–L5 (identified by the intercristal line at L4), below the conus, where the needle pushes cauda equina roots aside rather than piercing the cord. Epidural anesthesia stops in the epidural space (loss of resistance after the ligamentum flavum); spinal anesthesia goes into the subarachnoid space.

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
Dura opened to show the denticulate ligament and nerve roots in their meningeal sheaths.
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))
Sagittal section of the lumbosacral vertebral canal showing the spinal cord ending near L1, the dural sac ending at the second sacral vertebra and the filum terminale
Sagittal section: the spinal cord ends near L1 while the dural sac continues to the level of S2.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 661. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Lumbar puncture indications, contraindications and CSF PANCE

Mechanism / lesion

Sampling CSF from the lumbar cistern (meningitis, subarachnoid hemorrhage with a negative CT, demyelinating disease, pressure measurement).

Classic presentation

Before LP, obtain head CT if there are signs of raised intracranial pressure or a mass (papilledema, focal deficits, altered consciousness, new seizure, immunocompromise). Other contraindications: coagulopathy or thrombocytopenia, skin infection at the site. In suspected bacterial meningitis, don't delay antibiotics for imaging or LP.

Post-dural puncture headache PANCE

Mechanism / lesion

CSF leak through the dural hole lowers intracranial pressure.

Classic presentation

Positional headache, worse sitting or standing and relieved lying flat, within days of LP or accidental dural puncture during epidural placement. Smaller, atraumatic (pencil-point) needles reduce the risk. Treatment: conservative care, caffeine, and an epidural blood patch if persistent.

Spinal epidural abscess PANCE

Mechanism / lesion

Infection (usually Staphylococcus aureus) in the epidural space, via hematogenous spread (IV drug use, bacteremia) or procedures; risk factors include diabetes.

Classic presentation

Classic triad of back pain, fever and neurologic deficit (often incomplete early). Emergent MRI with gadolinium, blood cultures, IV antibiotics and surgical decompression.

Spinal epidural hematoma

Mechanism / lesion

Bleeding into the epidural space, especially with anticoagulation and neuraxial procedures (epidural catheter placement or removal).

Classic presentation

Sudden back pain with rapidly progressive weakness or numbness and bladder dysfunction; emergency MRI and decompression.

High-yield PANCE pearls

  • LP at L3–L4 or L4–L5 (intercristal line = L4).
  • Get a head CT before LP if there are signs of raised ICP or focal deficits.
  • Post-dural puncture headache: worse upright, better lying flat → epidural blood patch if persistent.
  • Epidural abscess: fever + back pain + neurologic deficit, S. aureus, IV drug use → MRI with contrast.
  • Epidural anesthesia stops in the epidural space; spinal anesthesia enters the subarachnoid space.

Imaging anatomy

CT

Head CT before LP when indicated. CT myelography instills contrast into the subarachnoid space.

MRI

MRI with gadolinium is the test of choice for epidural abscess, hematoma, and leptomeningeal disease; it also shows CSF leaks (with dedicated protocols).

Ultrasound

Ultrasound-assisted LP identifies the midline and interspaces in obese patients or difficult anatomy.

Key views & landmarks
  • MRI spine with and without contrast

Physical exam

Surface landmarks

Intercristal (Tuffier) line crossing L4 or the L4–L5 interspace; midline spinous processes.

Palpation

For LP, position the patient in the lateral decubitus (fetal) position or sitting and flexed to open the interspaces; measure opening pressure only in the lateral position.

Strength / function testing

Before LP, fundoscopy for papilledema and a focal neurologic exam. Afterward, monitor for headache and neurologic change.

Self-quiz

Q1.

A 25-year-old woman develops a severe headache 2 days after a lumbar puncture. It is much worse when she sits up and improves when she lies down. What is the definitive treatment if conservative measures fail?

Show answer

B

A positional post-dural puncture headache comes from a CSF leak. If conservative treatment fails, an epidural blood patch seals the dural hole.

Q2.

A 40-year-old man who injects drugs has fever, severe thoracic back pain and new leg weakness. What is the most appropriate next step?

Show answer

B

The triad of fever, back pain and neurologic deficit suggests a spinal epidural abscess. Obtain an emergent MRI with contrast, blood cultures, IV antibiotics, and surgical consultation.

Q3.

Where does the needle tip lie in a correctly placed lumbar epidural (not spinal) anesthetic?

Show answer

C

The epidural needle stops in the epidural space after the loss of resistance past the ligamentum flavum; puncturing the dura gives a "wet tap".

Q4.

The subarachnoid space (lumbar cistern) extends inferiorly to about which level?

Show answer

D

The dural sac and subarachnoid space extend to about S2, well below the end of the cord (L1–L2).

Q5.

Before a lumbar puncture, which finding means a head CT should be done first?

Show answer

B

Obtain a head CT before LP when there are signs of raised intracranial pressure or a mass: papilledema, focal deficits, altered consciousness, new seizure or immunocompromise. Don't delay antibiotics for imaging when bacterial meningitis is suspected.

Flashcards

See also