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Cranial Meninges

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TERMINOLOGY

Definitions

• “Pachymeninges” (thick meninges): Dura
• Leptomeninges (thin meninges): Arachnoid, pia
• Extradural space (EDS)

Potential space between dura, skull; seen only in pathologic conditions (infection, hematoma, etc.)
• Subdural space (SDS)

Potential space between inner dura, arachnoid; seen only in pathologic conditions
• Subarachnoid space (SAS)

Normal cerebrospinal fluid (CSF)-filled space between arachnoid, pial-covered brain
• Subpial space (SPS)

Potential space between pia, glia limitans of cortex
• Perivascular space (PVS)

Pial-lined, interstitial fluid (ISF)-filled invagination along penetrating arteries

Key part of brain “glymphatic” system

GROSS ANATOMY

Overview

• Brain encased by 3 meninges

Dura

– Dense fibrocollagenous sheet

– 2 layers: Outer (periosteal) and inner (meningeal)

– Closely adherent except where separate to enclose venous sinus; also tightly adherent to skull at sutural attachments

– Outer layer forms periosteum of inner calvarium

– Inner layer folds inward

Forms falx cerebri, tentorium cerebelli, etc.

Continues extracranially (into orbit, through foramen magnum into spinal canal)

– At other foramina, meningeal dura fuses with epineurium of cranial/peripheral nerves, adventitia of carotid/vertebral arteries

– Blood supply from numerous dural vessels, many with extensive extra/intracranial anastomoses

Middle, accessory meningeal arteries

Cavernous/tentorial branches of internal carotid artery (ICA)

Posterior meningeal branches of vertebral artery

Transosseous meningeal branches of external carotid artery (ECA), etc.

– Brain interstitial fluid is collected in perivenous spaces, enters dural meningeal lymphatics

Dural lymphatics are part of brain’s “glymphatic” system

Provides macroscopic clearance of interstitial solutes from brain parenchyma

Drainage from dura, paravascular spaces into cervical lymphatics

Arachnoid

– Thin, nearly transparent

– Outer surface loosely adherent to dura, easily separated

– Arachnoid follows dura; does not invaginate into sulci

– SAS lies between arachnoid, pia and is traversed by sheet-like bridging trabeculae

– Arachnoid villi/granulations = endothelial-lined extensions of arachnoid + SAS into dural sinus

Pia

– Innermost layer of leptomeninges

– Covers brain, invaginates into sulci

– Follows penetrating cortical arteries into brain, forming PVSs (Virchow-Robin spaces)

– CSF in PVSs, ISF continuously interchange, facilitated by AQP4 water channels

IMAGING ANATOMY

Overview

• Dura

Capillaries lack endothelial tight junctions so macromolecules (e.g., contrast agents) easily leak into dura

Dura enhances normally on CECT, T1 C+ scans

– Should be smooth, 1-2 mm thick

– Most prominent near vertex, least prominent under temporal lobes

– Enhancing segments appear discontinuous on 1.5T but typically well seen on 3T as continuous curvilinear enhancement that hugs inner calvarium

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Tags: Imaging Anatomy Brain and Spine

Mar 13, 2021 | Posted by admin in NUCLEAR MEDICINE | Comments Off

Main Text

TERMINOLOGY

Definitions

GROSS ANATOMY

Overview

IMAGING ANATOMY

Overview

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