difference between sub dural and epidural hemorrhagic strokes according to harrison

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Epidural vs. Subdural Hematoma - Harrison's Principles of Internal Medicine (22nd Ed., 2025)

Source: Chapter 454, "Epidural and Subdural Hematomas"

Overview

Both are hemorrhages that produce mass effect and raised intracranial pressure (ICP), and may be life threatening. The key anatomical distinction: epidural bleeds occur between the dura and the skull, while subdural bleeds occur beneath the dura (between dura and arachnoid). They can coexist with underlying brain contusions, making it difficult to isolate the contribution of each to the clinical state.

Epidural Hematoma (Fig. 454-1)

Anatomy: Dura-skull interface

Source of bleeding: Arterial - usually tearing of the middle meningeal artery from an overlying skull fracture (typically temporal bone fracture).

Classic presentation:

"Lucid interval" - a period of several minutes to hours of apparent normalcy before rapid neurologic deterioration. This is a hallmark feature.
Occurs in up to 10% of severe head injury cases.

Underlying cortical damage: Less frequently associated with underlying cortical damage compared to subdural hematomas.

CT appearance: Characteristic lenticular (lens/biconvex) shape - the tightly adherent dura is stripped from the inner table of the skull.

Treatment: Rapid surgical evacuation with ligation or cautery of the damaged vessel.

Prognosis: If recognized and treated rapidly, patients often have a favorable outcome.

Figure 454-1: Acute epidural hematoma - lenticular-shaped hyperdense clot on noncontrast CT

Fig. 454-1: Acute epidural hematoma. Lenticular-shaped hemorrhage on noncontrast CT from tearing of the middle meningeal artery.

Subdural Hematoma

Acute Subdural Hematoma (Fig. 454-2)

Anatomy: Beneath the dura

Source of bleeding: Primarily venous in origin (bridging veins), though arterial bleeding is sometimes found at operation; a few large hematomas have a purely arterial origin.

Trauma required: Direct cranial trauma may be minor or absent - especially in the elderly and those on anticoagulants. Acceleration forces alone (e.g., whiplash) can be sufficient.

Classic presentation:

Up to one-third have a lucid interval (minutes to hours), but most are drowsy or comatose from the moment of injury.
Unilateral headache and slightly enlarged pupil ipsilateral to the hematoma (not invariably present).
Small hematomas may be asymptomatic and often do not require evacuation if they don't enlarge.
Larger hematomas: stupor/coma, hemiparesis, unilateral pupillary enlargement.

CT appearance: Hyperdense clot with an irregular border with the brain; causes disproportionate horizontal displacement (mass effect) relative to its thickness, due to large rostral-caudal extent.

Prognosis: In contrast to epidural hematomas, there is significant morbidity and mortality associated with acute subdural hematomas requiring surgery.

Subacute/Chronic Subdural Hematoma

Evolves over days to weeks after injury.
Common in the elderly (cerebral atrophy creates more subdural space) and those on anticoagulants.
Presents with drowsiness, headache, confusion, or mild hemiparesis.
The injury that caused it is often trivial and frequently forgotten.
The hematoma gradually increases in size via osmotic shifts and repeated small bleeds.
Surgical drainage is often required, and recurrence is not uncommon.

Figure 454-2: Acute subdural hematoma - irregular-bordered hyperdense clot on noncontrast CT

Fig. 454-2: Acute subdural hematoma. Irregular-bordered clot with disproportionate mass effect. Compare to Fig. 454-1.

Side-by-Side Comparison Table

Feature	Epidural Hematoma	Subdural Hematoma
Location	Between dura and skull	Beneath dura
Bleeding source	Arterial (middle meningeal a.)	Primarily venous (bridging veins)
Trauma required	Yes - usually skull fracture	May be minor/absent
Lucid interval	Classic - minutes to hours	Up to 1/3; most comatose from onset
CT shape	Lenticular/biconvex	Irregular/crescent, large extent
Cortical damage	Less common	More commonly associated
Prognosis	Favorable if treated rapidly	Significant morbidity/mortality
Subacute form	Not typical	Common (days to weeks, elderly)
Surgery	Evacuation + vessel ligation	Craniotomy (acute); drainage (chronic)

Harrison's Principles of Internal Medicine, 22nd Ed. (2025), Chapter 454 - Head Injury, pp. 2071-2094

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Epidural vs Subdural Clinical Decision Guide
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Here's what's inside the document (9 sections, color-coded red for EDH, blue for SDH throughout):

Section	Contents
1. Anatomy & Pathophysiology	Side-by-side anatomy boxes - where each hematoma sits, bleeding source, why dura constrains EDH at sutures
2. Risk Factors & Typical Patients	Young + high-energy trauma (EDH) vs. elderly / anticoagulated / alcoholic (SDH)
3. Clinical Presentation	Lucid interval breakdown, acute vs. subacute vs. chronic SDH presentations
4. Decision Algorithm	Step-by-step flowchart table - ABCs → CT → interpret shape → pathway
5. Imaging Guide	CT feature table with the isodense SDH pitfall highlighted
6. Step-by-Step Workup	7-row parallel workup table covering history, exam, imaging, labs, neurosurgery, ICP, anticoagulation reversal
7. Management Overview	Surgical indications, observation criteria, ICP and seizure management per type
8. Master Comparison Table	13-row full feature comparison
9. Memory Aids	"Talk and Die" mnemonic, CT shapes mnemonic (E = Ellipse, S = Sickle), prognosis pearl

All content is sourced from Harrison's Principles of Internal Medicine, 22nd Ed. (2025), Chapter 454.

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