Anatomy Atlas

Cranial meninges and intracranial hemorrhage

Meninges encephali
Also: Dura mater · Arachnoid mater · Pia mater · Epidural hematoma · Subdural hematoma · Subarachnoid hemorrhage · Meningitis · Falx cerebri · Tentorium cerebelli
Space / regionHigh-yielddraftNeuroID

Three membranes — dura, arachnoid and pia — that cover the brain and define the epidural, subdural and subarachnoid spaces. Each space has its own classic bleed and CT appearance.

Core anatomy

Location

Between the skull and the brain; continuous through the foramen magnum with the spinal meninges and spaces.

Boundaries
dura mater
Tough outer layer with a periosteal layer (fused to the skull) and a meningeal layer; they separate to enclose the dural venous sinuses and fold inward as the falx cerebri (between the hemispheres), tentorium cerebelli (over the cerebellum), falx cerebelli and diaphragma sellae
arachnoid mater
Thin avascular layer under the dura; arachnoid granulations project into the sinuses
pia mater
Delicate layer adherent to the brain surface, following every gyrus
Contents
  • Epidural space (potential): between skull and dura — contains the middle meningeal artery and meningeal veins
  • Subdural space (potential): between dura and arachnoid — crossed by bridging veins from the cortex to the sinuses
  • Subarachnoid space: between arachnoid and pia — CSF, the cerebral arteries of the circle of Willis, and enlargements called cisterns
Communications

The subarachnoid space is continuous with the ventricles via the fourth ventricle apertures and with the spinal subarachnoid space (see ventricular system and CSF).

Notes

The dura is pain-sensitive: supratentorial dura is supplied by the trigeminal nerve and infratentorial dura by C2–C3 (and CN X) — which is why posterior fossa lesions cause occipital/neck pain. The brain parenchyma itself has no pain fibers.

Mentioned in

Generated automatically from links in other entries.

Flow of cerebrospinal fluid and the causes of hydrocephalusCerebrospinal fluid is made mainly by the choroid plexus, about 500 mL a day. It flows from the lateral ventricles through the interventricular foramina of Monro into the third ventricle, through the cerebral aqueduct into the fourth ventricle, and out through the median aperture of Magendie and the lateral apertures of Luschka into the subarachnoid space and cisterns. It is absorbed through the arachnoid granulations into the superior sagittal sinus and drains via the transverse and sigmoid sinuses to the internal jugular vein. A block within the ventricular system causes noncommunicating hydrocephalus: a colloid cyst at the foramen of Monro, aqueductal stenosis, or a posterior fossa tumor, Chiari II or Dandy–Walker malformation at the fourth ventricle. Failed absorption at the arachnoid granulations, after subarachnoid hemorrhage or meningitis or in normal pressure hydrocephalus, causes communicating hydrocephalus.Choroid plexusmakes about 500 mL a dayLateral ventriclesThird ventricleFourth ventricleSubarachnoid spaceand cisterns (and central canal)Superior sagittal sinusInternal jugular veinvia the transverse and sigmoid sinusessecretes intoInterventricular foramina (Monro)Cerebral aqueduct (Sylvius)Median (Magendie) and lateral (Luschka) aperturesArachnoid granulationsdrains toColloid cyst of the third ventricle(positional headache, drop attacks)Aqueductal stenosis: lateral and thirdventricles dilated, fourth normalPosterior fossa tumor, Chiari II,Dandy–WalkerAfter subarachnoid hemorrhage ormeningitis; normal pressure hydrocephalusNoncommunicating (obstructive)block inside the ventriclesCommunicatingabsorption fails✕ = where hydrocephalus starts

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Flow of cerebrospinal fluid. Lateral ventricles → foramina of Monro → third ventricle → cerebral aqueduct → fourth ventricle → Magendie and Luschka → subarachnoid space → arachnoid granulations → superior sagittal sinus. A block anywhere inside the ventricles causes noncommunicating (obstructive) hydrocephalus, with the ventricles dilated upstream of the block; failed absorption at the granulations causes communicating hydrocephalus.
Original schematic, created for this atlas.
Dura mater exposed by removing half of the skull and brain: the falx cerebri, tentorium cerebelli, great cerebral vein, and the cranial nerves (optic to accessory) passing through the dura
Dura mater: the falx cerebri and tentorium cerebelli, with cranial nerves piercing the dura.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 567. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Coronal section through the vertex: skin, subcutaneous tissue, galea aponeurotica, loose areolar tissue, pericranium, skull, dura, arachnoid, pia and the superior sagittal sinus
Layers of the scalp, skull and meninges.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 1196. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Lateral skull outline with the course of the middle meningeal artery branches (red) and the brain outline (blue) projected onto the surface
Surface course of the middle meningeal artery (epidural hematoma).
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 1198. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Epidural hematoma PANCE

Mechanism / lesion

Arterial bleeding, classically the middle meningeal artery torn by a temporal bone (pterion) fracture.

Classic presentation

Head injury with brief loss of consciousness, a lucid interval, then rapid deterioration (headache, vomiting, ipsilateral blown pupil, contralateral hemiparesis — uncal herniation). CT: biconvex (lens-shaped) hyperdensity that does not cross suture lines. Emergency craniotomy.

Subdural hematoma PANCE

Mechanism / lesion

Tearing of bridging veins — elderly (brain atrophy), alcohol use disorder, anticoagulation, falls; infants (abusive head trauma).

Classic presentation

Acute (after major trauma) or chronic (weeks after minor trauma — gradual headache, confusion, fluctuating consciousness, mild hemiparesis). CT: crescent-shaped collection that crosses sutures but not the falx; hyperdense acute, isodense subacute, hypodense chronic. Shaken infants: subdural hematomas + retinal hemorrhages.

Subarachnoid hemorrhage PANCE

Mechanism / lesion

Rupture of a saccular (berry) aneurysm of the circle of Willis (most nontraumatic cases); also trauma and AVMs. Risks — hypertension, smoking, ADPKD, connective tissue disorders, family history.

Classic presentation

Sudden "thunderclap" headache ("worst of my life"), vomiting, neck stiffness, photophobia, decreased consciousness. Noncontrast CT (very sensitive within 6 hours) → if negative, lumbar puncture (xanthochromia, RBCs that do not clear) → CTA to find the aneurysm. Complications: rebleeding, vasospasm (days 3–14 — nimodipine), hydrocephalus, hyponatremia. Secure the aneurysm (coiling or clipping).

Bacterial meningitis PANCE

Mechanism / lesion

Infection of the leptomeninges and subarachnoid space — S. pneumoniae, N. meningitidis, Listeria (age > 50, immunocompromised, neonates), GBS and E. coli in neonates.

Classic presentation

Fever, headache, neck stiffness, altered mental status, petechial rash (meningococcus). CSF: high opening pressure, neutrophils, low glucose, high protein. Give dexamethasone and empiric antibiotics (ceftriaxone + vancomycin ± ampicillin) immediately — do not delay for CT or LP.

High-yield PANCE pearls

  • Lucid interval + lens-shaped bleed not crossing sutures → epidural (middle meningeal artery).
  • Crescent crossing sutures in an elderly/alcoholic/anticoagulated patient → subdural (bridging veins).
  • Thunderclap headache → noncontrast CT → if negative, LP for xanthochromia → SAH (berry aneurysm).
  • SAH → nimodipine to prevent vasospasm.
  • Meningitis: neutrophils + low glucose + high protein → bacterial → antibiotics + dexamethasone without delay.

Imaging anatomy

CT

Noncontrast CT head — first test for trauma and suspected hemorrhage (epidural = biconvex; subdural = crescent; SAH = blood in the basal cisterns and sulci).

MRI

MRI for subacute/chronic subdural collections, small SAH (FLAIR), meningeal enhancement in meningitis.

Key views & landmarks
  • CT angiography for aneurysm after SAH
  • Lumbar puncture: opening pressure, cells, glucose, protein, Gram stain, xanthochromia

Physical exam

Surface landmarks

The pterion (junction of frontal, parietal, temporal and sphenoid bones, about 3 cm above the zygomatic arch midpoint) overlies the anterior branch of the middle meningeal artery.

Strength / function testing

Glasgow Coma Scale, pupils, focal deficits; meningeal signs — neck stiffness, Kernig (pain on extending the knee with the hip flexed) and Brudzinski (neck flexion causes hip flexion) signs, which are specific but insensitive.

Self-quiz

Q1.

A 19-year-old is hit in the temple by a baseball, is briefly unconscious, then talks normally for 2 hours before becoming drowsy with a dilated right pupil. CT shows a lens-shaped hyperdensity. Which vessel is most likely injured?

Show answer

B

A lucid interval and a biconvex (lens-shaped) collection after a temporal blow indicate an epidural hematoma from the middle meningeal artery — a neurosurgical emergency.

Q2.

A 45-year-old has a sudden severe headache during exercise. Noncontrast CT 10 hours later is normal. What is the next step?

Show answer

B

A thunderclap headache needs subarachnoid hemorrhage excluded. If CT is negative (especially after 6 hours), perform an LP looking for xanthochromia and persistent RBCs (or CTA per local protocol).

Q3.

An 82-year-old on warfarin has had increasing confusion for 3 weeks after a minor fall. CT shows a crescent-shaped hypodense collection over the left hemisphere that crosses suture lines. What is the diagnosis?

Show answer

B

A crescent collection crossing sutures is subdural; hypodensity after weeks means it is chronic. Elderly anticoagulated patients are at high risk from bridging vein tears.

Q4.

Which drug is given after aneurysmal subarachnoid hemorrhage to reduce the risk of ischemia from vasospasm?

Show answer

A

Nimodipine is given after SAH to reduce ischemic complications of vasospasm, which peaks at days 3–14.

Q5.

Which nerve carries pain from the supratentorial dura?

Show answer

D

The supratentorial dura is supplied by the trigeminal nerve; the infratentorial dura by C2–C3 (and CN X), which is why posterior fossa lesions cause occipital and neck pain. The brain itself has no pain fibers.

Flashcards

See also