A 25-year old patient who had a Road traffic accident was initially conscious but later became unconscious and subsequently died. On postmortem examination, multiple petechial Others hemorrhages are seen in the corpus callosum, what is the probable diagnosis?

Correct Answer: C. Diffuse axonal injury

Diffuse axonal injury (DAI) is the hallmark pathological finding in severe traumatic brain injury from high-velocity head trauma, particularly in road traffic accidents. The key discriminator here is petechial hemorrhages in the corpus callosum — this is pathognomonic for DAI. These microhemorrhages occur at the gray-white matter junctions and in white matter tracts (corpus callosum, brainstem, cerebellum) due to shearing forces during acceleration-deceleration injury. The patient's clinical course — initial consciousness followed by deterioration and death — reflects the progressive nature of DAI, where primary axonal injury is followed by secondary inflammatory cascades and axonal degeneration. Unlike focal hematomas (SDH, EDH), DAI is diffuse and microscopic, making it difficult to detect on early imaging but evident on postmortem examination. The corpus callosum is particularly vulnerable because it is a major white matter tract at the junction of different tissue densities. In Indian trauma centers, DAI accounts for significant morbidity and mortality in RTA victims, especially in high-speed collisions on highways. The absence of a focal mass lesion on imaging in a deteriorating patient should raise suspicion for DAI.

Why the other options are wrong

A. SDH — Subdural hematoma (SDH) presents as a focal collection of blood between dura and arachnoid, typically visible on CT/MRI as a crescent-shaped lesion. While SDH can cause deterioration and death, it does NOT characteristically produce petechial hemorrhages in the corpus callosum. SDH is a mass lesion that causes mass effect and herniation, not diffuse axonal injury. The postmortem finding of corpus callosum petechiae points to DAI, not SDH. B. Subdural hematoma — This is a duplicate of option A (SDH). Epidural hematoma (EDH) is a focal arterial bleed between skull and dura, presenting as a lens-shaped lesion on imaging. EDH typically causes rapid deterioration due to mass effect and increased ICP, but does not produce the characteristic petechial hemorrhages in white matter tracts like the corpus callosum. The corpus callosum finding is specific to DAI from shearing injury. D. EDH — Epidural hematoma (EDH) is a focal arterial hemorrhage between skull and dura, classically presenting with a 'talk and die' syndrome. While EDH can cause rapid deterioration, it produces a localized mass lesion visible on imaging, not diffuse petechial hemorrhages in the corpus callosum. EDH is associated with middle meningeal artery injury, not the diffuse shearing injury characteristic of DAI. The corpus callosum petechiae are pathognomonic for DAI.

High-Yield Facts

Mnemonics

DAI Triad Diffuse (not focal), Axonal (white matter), Injury (shearing). Remember: petechiae in corpus callosum = DAI until proven otherwise. RTA Deterioration Pattern Talk → Deteriorate → Die = Think DAI (not EDH which is 'Talk → Die' rapidly). DAI has a slower, progressive course.

NBE Trap

NBE may pair 'unconscious after RTA' with SDH/EDH to test whether students reflexively choose focal hematomas. The corpus callosum petechiae are the discriminator — this finding is exclusive to DAI and rules out focal mass lesions.

Clinical Pearl

In Indian trauma centers, DAI is often missed on initial CT because microhemorrhages are not visible on conventional imaging; MRI with gradient echo sequences or postmortem examination reveals the pathology. A patient who is initially conscious but deteriorates without a focal lesion on imaging should raise suspicion for DAI — this is the classic presentation in highway RTAs.

_Reference: Bailey & Love Ch. 58 (Head Injury); Robbins Ch. 28 (CNS Trauma)_