= WHITE MATTER SHEARING INJURY

Incidence: most common type of primary traumatic injury in patients with severe head trauma (48%)

Cause: high-velocity trauma (MVA) resulting in indirect injury due to rotational / angular (especially coronal) acceleration / deceleration forces (direct impact to head or fracture not required)

Pathogenesis:

• cortex and deep structures move at different speed causing shearing stress of
  1. axons resulting in axonal tears followed by wallerian degeneration
  2. small white-matter vessels resulting in small petechial hemorrhages

Path: much of the injury is microscopic

Histo: multiple axonal retraction balls (HALLMARK), numerous perivascular hemorrhages

• immediate severe impairment of consciousness at time of impact
• persistent vegetative state

Location (according to severity of trauma):

1. lobar white matter at corticomedullary junction (67%): parasagittal region of frontal lobe + periventricular region of temporal lobe; occasionally in parietal + occipital lobes
2. internal + external capsule / basal ganglia, corona radiata, cerebellar peduncles
3. corpus callosum (21%): ¾ of lesions at undersurface of posterior body + splenium
   • often associated with intraventricular hemorrhage
4. brainstem: posterolateral quadrants of midbrain + upper pons; superior cerebellar peduncles especially vulnerable

• sparing of cortex
• 20% of lesions with small central areas of petechial hemorrhage

CT (negative in 30% of positive MR cases):

• foci of decreased density (usually seen when >1.5 cm in size)

MR (most sensitive modality):

• multiple small oval / round foci of decreased signal intensity on T1WI + increased signal on T2WI

Prognosis:

1. Poor due to sequelae (may go on to die without signs of high intracranial pressure)
2. Brain atrophy with enlargement of sulci + ventricles