A 68-year-old man on warfarin for atrial fibrillation presents to the emergency department after a fall from standing height. CT head shows a crescentic hyperdense collection marked **A** in the diagram, with 8 mm midline shift and sulcal effacement. Which of the following best describes the pathophysiology of the structure marked **A**?
A. Blood accumulation between skull and dura mater from tearing of middle meningeal artery
B. Blood accumulation within the brain parenchyma from rupture of cortical vessels
C. Blood accumulation between dura mater and arachnoid mater from tearing of bridging veins during deceleration injury
D. Blood accumulation in the subarachnoid space from rupture of major cerebral arteries
Explanation
Why "Blood accumulation between dura mater and arachnoid mater from tearing of bridging veins during deceleration injury" is right
The crescentic hyperdense subdural collection marked A represents an acute subdural hematoma (SDH). By definition, SDH is blood accumulation in the subdural space—between the dura mater and arachnoid mater—caused by tearing of bridging veins during deceleration head injury. The crescent shape (concave, not lens-shaped) and the fact that it does not cross the midline (limited by the falx) are pathognomonic for SDH. This patient's age, anticoagulation, and mechanism (fall) are classic risk factors for bridging vein rupture. (Harrison's 21e Ch 443; Brain Trauma Foundation Guidelines)
Why each distractor is wrong
Blood accumulation between skull and dura mater from tearing of middle meningeal artery: This describes an epidural hematoma, which is lens-shaped (biconvex), crosses suture lines, and is limited by dural attachments at the sutures—not the crescent shape seen in A.
Blood accumulation within the brain parenchyma from rupture of cortical vessels: This describes a traumatic intracerebral hemorrhage or contusion, which would appear as a focal hyperdense area within brain tissue, not a crescentic collection between membranes.
Blood accumulation in the subarachnoid space from rupture of major cerebral arteries: This describes a subarachnoid hemorrhage, which appears as hyperdensity in the basal cisterns and sulci, not as a crescentic extraaxial collection.
High-YieldNEET PG
Acute SDH = crescent (concave), does NOT cross midline (falx barrier), crosses sutures; Epidural = lens (biconvex), crosses midline, does NOT cross sutures.
Harrison's 21e Ch 443; Brain Trauma Foundation Guidelines
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