Neuroanatomy: Cranial Meninges

Introduction

• The brain and spinal cord are protected by three layers of meninges: dura mater, arachnoid mater, and pia mater.
• Meninges protect the brain and spinal cord and create spaces: epidural, subdural, and subarachnoid.

Structure and Function

Epidural Space

• Lies between skull and dura mater, generally non-existent unless pathologically developed.

Dura Mater

• Outermost meningeal layer with two layers: periosteal and meningeal.
• Forms venous sinuses and dural reflections (falx cerebri, tentorium cerebelli).

Subdural Space

• Exists between dura and arachnoid mater, usually visible only pathologically.

Arachnoid Mater

• Avascular membrane involved in CSF metabolism.
• Has arachnoid villi that communicate with the venous system.

Subarachnoid Space

• Contains CSF and major brain arteries.
• CSF cushions the brain and spinal cord, supplies nutrients, and removes waste.

Pia Mater

• Innermost layer, follows brain contours.
• Forms sheaths around blood vessels, creating the perivascular space.

Embryology

• Dura mater (pachymeninx) originates from mesoderm.
• Arachnoid and pia mater (leptomeninges) come from ectoderm.

Blood Supply and Lymphatics

Epidural Space and Dura Mater

• Supplied by major arteries like middle meningeal artery (MMA).
• Venous drainage through dural venous sinuses.

Subdural Space

• Bridging veins drain into dural venous sinuses.

Arachnoid Mater and Subarachnoid Space

• Cisternae in the subarachnoid space contain major arteries.

Pia Mater

• Highly vascularized, nourishing the brain.

Meningeal Lymphatic Vessels

• Discovered in 2015, connect with cervical lymph nodes and absorb CSF.

Nerves

• Innervated mainly by vagus and trigeminal nerves.
• Different cranial fossa have specific nerve supply routes.

Surgical Considerations

• Meningiomas - common cranial tumors, often benign.
• Surgical removal is complex; strategy depends on tumor location and characteristics.

Clinical Significance

• Bacterial Meningitis: Inflammation caused by bacteria like Streptococcus pneumoniae.
• Intracranial Hemorrhages: Conditions like epidural hematoma can result from trauma, leading to brain compression.
• Subarachnoid Hemorrhages: Often spontaneous, resulting from aneurysms and causing severe headaches.

Review Questions

• Diagrammatic section of the skull showing meningeal layers and associated veins and sinuses.

References

• A set of scholarly references supporting the lecture's content.