Meninges, vascular supply of spinal cord, lumbar puncture

Introduction

The spinal cord is enveloped by protective meninges and nourished by a dedicated vascular network. Together, they maintain the integrity and function of the central nervous system. Understanding their anatomy is essential for clinical procedures such as lumbar puncture and for diagnosing spinal pathologies.

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Meninges of the Spinal Cord

The spinal cord is surrounded by three connective tissue layers, collectively called the meninges:

1. Dura mater:
   • Outermost, tough fibrous layer.
   • Forms a tubular sheath extending from the foramen magnum to S2 vertebral level, where it merges with the filum terminale externa.
   • Separated from vertebral canal by the epidural space (contains fat and venous plexus).
2. Arachnoid mater:
   • Middle, thin avascular membrane lying deep to dura mater.
   • Encloses the subarachnoid space (filled with cerebrospinal fluid, CSF).
3. Pia mater:
   • Innermost layer, closely adherent to the spinal cord.
   • Forms denticulate ligaments (lateral extensions anchoring cord to dura) and filum terminale (anchors cord to coccyx).

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Vascular Supply of the Spinal Cord

Arterial supply:

Longitudinal arteries:

• 1 anterior spinal artery (from vertebral arteries): runs in anterior median fissure; supplies anterior 2/3 of cord.
• 2 posterior spinal arteries (from vertebral/posterior inferior cerebellar arteries): supply posterior 1/3 of cord.

Segmental arteries:

• Radicular and medullary arteries reinforce longitudinal arteries.
• Key vessel: artery of Adamkiewicz (great anterior segmental medullary artery; usually arises left side T9–T12), provides major supply to lower thoracic and lumbar cord.

Venous drainage:

• Internal vertebral venous plexus (in epidural space) → communicates with external vertebral plexus → systemic veins.

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Lumbar Puncture

Lumbar puncture is a diagnostic and therapeutic procedure to access cerebrospinal fluid (CSF) from the subarachnoid space.

Site of puncture:

• Performed at L3-L4 or L4-L5 interspace to avoid spinal cord (ends at L1-L2 in adults).
• Landmark: supracristal line (Tuffier’s line) connecting highest points of iliac crests crosses L4 spinous process.

Layers traversed (superficial to deep):

1. Skin
2. Subcutaneous tissue
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space
7. Dura mater
8. Arachnoid mater → enters subarachnoid space

Indications:

• Diagnose meningitis, subarachnoid hemorrhage
• Measure CSF pressure
• Administer spinal anesthesia, chemotherapy

Contraindications:

• Raised intracranial pressure (risk of brain herniation)
• Coagulopathy

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Clinical Relevance

Knowledge of the meninges and vasculature is essential to prevent complications in spinal procedures. Ischemia of the anterior spinal artery can lead to anterior cord syndrome, characterized by motor and pain/temperature sensory loss below the lesion. Lumbar puncture requires precise anatomical understanding to avoid neurological injury.

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Conclusion

The meninges, vascular supply, and lumbar puncture are intimately related to spinal cord protection, nourishment, and clinical intervention. Comprehensive anatomical knowledge ensures safe procedures and effective diagnosis of central nervous system conditions.

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References

1. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018.
2. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier; 2016.
3. Netter FH. Atlas of Human Anatomy. 7th ed. Elsevier; 2019.