## Morphology and Boundaries **Key Point:** The shape and distribution of intracranial blood collections are determined by the anatomical barriers they encounter. ### Epidural Hematoma - **Shape:** Lens-shaped or biconvex (convex on both sides) - **Boundary:** Confined by the dura mater, which is firmly adherent to the inner table of the skull - **Midline crossing:** Does NOT cross the midline because the falx cerebri (dural fold) acts as a barrier - **Typical location:** Temporal region (middle meningeal artery injury) ### Subdural Hematoma - **Shape:** Crescent-shaped (concave toward brain) - **Boundary:** Follows the brain contour because it lies between dura and brain surface - **Midline crossing:** CAN cross the midline because it is not confined by dural folds - **Distribution:** Follows gravity and brain surface anatomy **High-Yield:** The lens shape (epidural) vs. crescent shape (subdural) is the single most tested morphological distinction on imaging exams. | Feature | Epidural | Subdural | |---------|----------|----------| | Shape | Lens-shaped (biconvex) | Crescent-shaped (concave) | | Crosses midline | No | Yes | | Follows brain contour | No | Yes | | Crosses suture lines | No | Yes (may) | | Location | Between skull & dura | Between dura & brain | **Clinical Pearl:** A lens-shaped hematoma that respects the midline and suture lines is epidural until proven otherwise — this morphology is pathognomonic. 
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