General
- PBI vs TBI
- PBI is less prevalent
- PBI has worse prognosis
- Gunshot wounds to the head (GSWH),
- Which are the typically lethal, as more than 90% of GSWH have a fatal outcome
Mechanism
- Projectile breaches cranium and dura mater
- Perforating brain injury: When a projectile also induces an exit wound
- The projectile can cause the following
- Crushes soft brain tissue in its path
- Generates bone fragments at impact, which can require surgical debridement.
- Degree of tissue damage depends on
- Shape of projectile
- Kinetic energy of projectile E = 1/ 2mv2
- A high velocity projectile generates waves of compression and reexpansion (cavitation wave) and inflicts focal shearing damage, parenchymal contusions, and haematomas.
- In through and through missile wounds to the skull, the entrance wound is typically smaller.
- Characteristics of a projectile:
- Kinetic energy
- High-velocity wounds
- Create a more complex pattern of injury based on cranial vault penetration and kinetic energy.
- After KE depletion, cavity collapses under negative pressure, may suck in surrounding debris.
- Permanent cavity can be tenfold larger than projectile diameter, especially in inelastic tissue like brain.
- For low-velocity
- Projectiles, permanent and temporary cavities are nearly the same diameter.
- Yaw:
- Angle between the line of flight and the bullet’s long axis;
- Causes tumbling in tissue.
- Precession:
- Rotation of the bullet long axis around the centre of mass.
- Yaw and precession decrease with distance from the barrel; precession and nutation contribute more to stability than tissue damage.
- Nutation:
- Small circular movement at the bullet tip.
- Drag:
- Force resisting a bullet’s forward velocity;
- Determines effective range.
- Caliber
- Shape
- Other factors:
- Fragmentation
- Explosive potential
- Ricochet
- Jacketed vs. unjacketed rounds,
- Hollow-nosed or soft-pointed cartridges.
- Bullets produce tissue damage via
- Laceration/crushing:
- Along the projectile's track, maximum width is the long axis of the bullet/fragment.
- Shock waves:
- Compressive force, travel ahead and to the sides of the bullet.
- Cavitation:
- Brief, compressive force expanding tangentially from the primary injury tract.
Presentation
- CSF leak
- Common vascular complications following PBI include
- Traumatic intracranial aneurysms,
- Arteriovenous fistulas (AVFs),
- SAH,
- Vasospasm
Investigations
- CT
- Provides clear characterization of in- driven bone fragments, missile trajectory, extent of tissue damage, haematomas, and mass effects.
- Cerebral angiography may not show small aneurysms;
- Indications:
- Penetrating injury through pterion, orbit, or posterior fossa
- Penetrating fragment with intracranial hematoma
- Known cerebral artery sacrifice or pseudoaneurysm at the time of initial exploration
- Blast-induced penetrating injury with Glasgow Coma Scale score <8
- Delayed Transcranial Doppler or computed tomography angiographic evidence of severe vasospasm, venous sinus occlusion, or de novo pseudoaneurysm formation in previously occluded branches
- DSA more effective.
- Recommended due to the high risk of vascular injury.
- In particular when the projectile trajectory is near the
- Sylvian fissure,
- Supraclinoid carotid artery
- Vertebrobasilar vessels,
- Cavernous sinus region,
- Major dural venous sinuses,
- A delayed hematoma or SAH develops
- High risk factors
- Penetrating track crossing the ventricle, involving both hemispheres,
- Crossing the geographical centre of the brain or associated vascular injury.
Management
- Aim
- Prevent secondary brain injury (raised ICP, hypotension/ischemia, delayed infection).
- Surgery
- Indicated
- CSF leak
- Significant mass effect, necrotic brain tissue and bone fragments
- Routine bone or projectile removal in the eloquent areas is not recommended
- Any significant intracerebral haemorrhages with significant mass effect should be evacuated
- Foreign body
- Indications:
- Fragment movement
- Abscess formation
- Vascular compression
- Ventricular obstruction (hydrocephalus)
- Heavy metals identified in cerebrospinal fluid
- Do not unscrew the Foreign body out as it can cause more damage.
- Instead retract it out without twisting
- Do a large craniotomy so you can visualize the brain and soft tissues
- Seizure control following PBI is a key part of clinical management.
- Prophylactic antibiotics
- PBI high risk of CNS infection since contaminated foreign bodies are driven into the brain tissue along the projectile track,
- Should be started as soon as possible
- Neurosurgical principles:
- Brainstem decompression,
- ICP reduction,
- Anatomical continuity restoration,
- Haemostasis
- Focal injuries (e.g., open depressed skull fracture):
- Debridement of entry wound, fracture elevation may suffice.
- Hemispheric or bilateral injury:
- Evacuate accessible mass lesions (hematoma) with large decompressive craniectomy.
- Caution with deep embedded fragments due to potential associated injury;
- Primary debridement for superficial fragments.
- Penetrating wounds without exit:
- Consider ricochet, potential to penetrate another intracranial compartment.
- Injuries crossing two dural compartments: may require staged decompressive procedures.
- Depressed bone fragment compromising venous sinus:
- Carefully elevate with bone flap, allowing direct sinus repair if needed.
- Delayed venous infarction:
- May cause supratentorial ICP elevations;
- Posterior fossa decompression first if necessary.
- Surgical intervention
- Less clear in diffuse injury cases (e.g., global hypoxic brain damage) indicated by early obliteration of basal cisterns, loss of sulcal and gyral pattern, unexplained midline shift, or hemispheric oedema.
Made with Bullet