Meningeal Layers (Outer to Inner)

The Three Meninges

• Dura mater: Tough, fibrous outer layer; consists of periosteal layer (adherent to inner skull table) and meningeal layer (inner dura)
• Arachnoid mater: Thin, avascular membrane closely adherent to inner surface of dura
• Pia mater: Delicate membrane intimately adherent to brain surface; follows all sulci and gyri

Epidural Space

• Potential space between inner skull table and periosteal dura — does not normally exist
• Dura firmly adherent to skull, especially at suture lines → epidural collections do NOT cross sutures
• Dura most loosely attached at temporal region → most common site for epidural hematoma
• Middle meningeal artery runs in groove on inner table of temporal bone — temporal bone fracture → arterial rupture → EDH
• Posterior fossa EDH: venous (transverse or sigmoid sinus tear) rather than arterial

Subdural Space

• Potential space between the dural border cell layer (innermost dura) and arachnoid membrane
• Bridging veins traverse this space from cortical surface to dural venous sinuses — vulnerable to shearing injury
• No suture-line adhesions → subdural collections spread freely over the convexity, crossing suture lines
• Limited by dural reflections (falx cerebri, tentorium cerebelli) — SDH does not cross midline or cross the tentorium

Subarachnoid Space

• Between arachnoid and pia — contains CSF, cerebral arteries, and veins
• SAH from aneurysmal rupture or trauma fills this space — distinct entity from SDH/EDH

Epidemiology & Risk Factors

• Incidence: 1–4% of traumatic brain injuries; 5–15% of fatal head injuries
• Age: Predominantly young adults (20–40 years) — rare in elderly (dura firmly adherent to skull) and rare in children <2 years (skull deformable)
• Mechanism: Head trauma with temporal bone fracture in ~85–95% of cases
• Location: Temporal (70–80%), frontal (10%), posterior fossa (5–10%), vertex/parasagittal (rare)
• Male:female ratio: ~4:1

Pathophysiology

• Temporal EDH (most common): Temporal bone fracture → rupture of middle meningeal artery (branch of internal maxillary artery from ECA) → arterial bleeding strips dura from inner skull table
• Middle meningeal artery enters skull through foramen spinosum → runs in groove on inner table of temporal squamous bone
• Posterior fossa EDH: Occipital bone fracture → tear of transverse or sigmoid sinus (venous) or meningeal arteries
• Vertex EDH: Tear of superior sagittal sinus (venous)
• Arterial pressure rapidly dissects dura from skull → rapidly expanding mass lesion
• EDH volume expands quickly due to arterial pressure → rapid rise in ICP → herniation

Clinical Presentation

The “Lucid Interval” (Classic “Talk and Die” Pattern)

• Phase 1: Initial loss of consciousness at time of impact (concussion)
• Phase 2: “Lucid interval” — transient neurological improvement lasting minutes to hours (patient appears well, talks, follows commands)
• Phase 3: Rapid deterioration as hematoma expands → rising ICP → ipsilateral pupil dilation (uncal herniation) → contralateral hemiparesis → coma → death if untreated
• Lucid interval present in only ~20–50% of EDH cases — absence does NOT exclude the diagnosis
• Some patients never lose consciousness initially; others never regain consciousness

Herniation Progression Sequence

• Expanding temporal EDH → medial temporal lobe (uncus) herniates over tentorial edge
• Step 1: Ipsilateral CN III compression → ipsilateral fixed, dilated pupil (parasympathetic fibers on outside of CN III compressed first)
• Step 2: Ipsilateral cerebral peduncle compression → contralateral hemiparesis
• Step 3: Contralateral cerebral peduncle against opposite tentorial edge (Kernohan notch) → ipsilateral hemiparesis (false localizing sign)
• Step 4: Bilateral pupil dilation, bilateral posturing, brainstem compression → respiratory arrest

Imaging

CT Characteristics

• Shape: Biconvex (lens-shaped / lenticular) — blood collects between skull and dura, creating a convex inner margin
• Does NOT cross suture lines — dura is firmly adherent at sutures (pathognomonic distinguishing feature from SDH)
• CAN cross midline if it extends across the vertex (unlike SDH which is limited by falx)
• Density: Hyperdense (60–80 HU) when acute; “swirl sign” (mixed density with hypodense areas) = active bleeding (surgical emergency)
• Location: Most commonly temporal/temporoparietal; adjacent temporal bone fracture in ~85%
• Usually unilateral; bilateral EDH very rare (<5%)

MRI

• Not the primary imaging modality for EDH (CT is faster and more practical in trauma)
• Useful for posterior fossa EDH (better than CT for brainstem assessment)
• Signal follows blood product evolution: acute = isointense T1, hypointense T2; subacute = hyperintense T1

Surgical Indications & Management

Indications for Surgical Evacuation

• Hematoma thickness >15 mm
• Midline shift >5 mm
• Any neurological deterioration (decreasing GCS, new pupillary asymmetry, new focal deficit)
• GCS ≤8 with anisocoria (herniation) — requires emergent craniotomy
• Posterior fossa EDH: Lower threshold for surgery due to limited space and risk of brainstem compression → rapid decompression indicated even for smaller collections

Surgical Technique

• Craniotomy (standard of care): Temporal craniotomy with ligation/cauterization of middle meningeal artery
• Emergent burr hole can be performed as temporizing measure if craniotomy not immediately available
• Hematoma evacuation + hemostasis + dural tacking sutures to prevent recurrence

Conservative Management

• Small EDH (<15 mm thickness, <5 mm midline shift) in neurologically intact patient (GCS 15)
• Requires close neurological monitoring and serial imaging
• Any deterioration → immediate surgery

Prognosis

• Excellent prognosis with timely surgical evacuation — mortality <5% when operated before herniation
• Mortality increases dramatically with delayed surgery or herniation at time of operation
• Functional outcome heavily dependent on pre-operative GCS and pupillary status