= CNS TRAUMA

Incidence: 0.2–0.3% significant CNS trauma annually in USA; 550÷100,000 persons with peak age of 15–24 years; second peak >50 years of age

Cause: motor vehicle accidents (51%), fall (21%), assault and violence (12%), sports and recreation (10%)

Classification:

1. Primary traumatic lesion
   1. primary neuronal injury
      1. Cortical contusion
      2. Diffuse axonal injury
      3. Subcortical gray matter injury
         = injury to thalamus ± basal ganglia
      4. Primary brainstem injury
   2. primary hemorrhages (from injury to a cerebral artery / vein / capillary)
      1. Subdural hematoma
      2. Epidural hematoma
      3. Intracerebral hematoma
      4. Diffuse hemorrhage (intraventricular, subarachnoid)
   3. primary vascular injuries
      1. Carotid-cavernous fistula
      2. Arterial pseudoaneurysm
         Location: branches of ACA + MCA, intracavernous portion of ICA, pCom
      3. Arterial dissection / laceration / occlusion
      4. Dural sinus laceration / occlusion
   4. traumatic pia-arachnoid injury
      1. Posttraumatic arachnoid cyst
      2. Subdural hygroma
   5. cranial nerve injury
2. Secondary traumatic lesion
   • deterioration of consciousness / new neurologic signs some time after initial injury
   1. Major territorial arterial infarction
      Cause: prolonged transtentorial / subfalcine herniation pinching the artery against a rigid dural margin
      Location: PCA, ACA territory
   2. Boundary + terminal zone infarction
   3. Diffuse hypoxic injury
   4. Diffuse brain swelling / edema
   5. Pressure necrosis from brain herniation
      Cause: increased intracranial pressure
      Location: cingulate, uncal, parahippocampal gyri, cerebellar tonsils
   6. Secondary “delayed” hemorrhage
   7. Secondary brainstem injury (mechanical compression, secondary (Duret) hemorrhage in tegmentum of rostral pons + midbrain, infarction of median / paramedian perforating arteries, necrosis)
   8. Other (eg, fatty embolism, infection)
   • Duret hemorrhage
     = delayed 2^ndary hemorrhage in ventral + paramedian aspects of upper brainstem (mesencephalon + pons) due to massive temporal lobe herniation causing stretching + laceration of pontine perforating branches of basilar artery
   • Kernohan phenomenon
     = contusion of contralateral brainstem caused by pressure of free edge of tentorium
     Pathophysiology:
     • expanding supratentorial mass forces medial aspect of temporal lobe downward over tentorium compressing the neighboring oculomotor nerve (III); lateral pressure on midbrain compresses opposite crus cerebri against free edge of tentorium forming indentation in crus (Kernohan notch)
       • ipsilateral pupillary dilatation
       • ipsilateral oculomotor nerve palsy
       • ipsilateral hemiparesis (false localizing sign)

Pathomechanism:

1. Direct impact on brain ← fracture / skull distortion
   • scalp / skull abnormal
   • superficial neural damage localized to immediate vicinity of calvarial injury
   1. Cortical laceration ← depressed fracture fragment
   2. Epidural hematoma
2. Indirect injury irrespective of skull deformation
   • scalp / skull normal
   1. compression-rarefaction strain = change in cell volume without change in shape (rare)
   2. shear strain = change in shape without change in volume
      • rotational acceleration forces (more common)
        • bilateral multiple superficial / deep lesions possibly remote from the site of impact
        1. Cortical contusion (brain surface)
        2. Diffuse axonal injury (white matter)
        3. Brainstem + deep gray matter nuclei
      • linear acceleration forces (less common)
        1. Subdural hematoma
        2. Small superficial contusion

Prognosis: 10% fatal, 5–10% with residual deficits

Centripetal approach in search of injury:

1. Scalp
   1. Scalp abrasion: not visible
   2. Scalp laceration: air inclusion
   3. Scalp contusion: salt-and-pepper densities
2. Subgaleal hematoma
   Location: between periosteum of outer table and galea (= underneath scalp fat)
3. Skull fracture:
   linear ~, stellate ~, depressed ~, basilar ~, eggshell fracture
4. Epidural hematoma
5. Subdural hematoma
6. Subarachnoid hemorrhage
7. Brain injury
   1. Contusion/ edema
   2. Brain hematoma
8. Ventricular hemorrhage

Indications for radiographic skull series:

Only in conjunction with positive CT scan findings!

1. Evaluation of difficult depressed skull fracture / fracture of base of skull

Indications for CT:

1. Loss of consciousness (more than transient)
2. Altered mental status during observation
3. Focal neurologic signs
4. Clinically suspected basilar fracture
5. Depressed skull fracture (= outer table of fragment below level of inner table of calvarium)
6. Penetrating wound (eg, bullet)
7. Suspected acute subarachnoid hemorrhage, epidural / subdural / parenchymal hematoma

CT report in CNS trauma must address:

• midline shift
• localized mass effect
• distortion / effacement of basal, perimesencephalic, suprasellar, quadrigeminal cisterns
• pressure on brainstem, brainstem abnormality
• hemorrhage / contusion: extraaxial, intraaxial, subarachnoid, intraventricular
• edema: generalized / localized
• hydrocephalus
• presence of foreign bodies, bullet, bone fragments, air
• base of skull, face, orbit
• scalp swelling

Indications for MR:

1. Postconcussive symptomatology
2. Diagnosis of small sub- / epidural hematoma
3. Suspected diffuse axonal (shearing) injury, cortical contusion, primary brainstem injury
4. Vascular damage (eg, pseudoaneurysm formation due to basilar skull fracture)

Sequelae of head injury:

1. Posttraumatic hydrocephalus (⅓)
   = obstruction of CSF pathways ← intracranial hemorrhage; develops within 3 months
2. Generalized cerebral atrophy (⅓)
   = result of ischemia + hypoxia
3. Encephalomalacia
   • focal areas of decreased density, but usually higher density than CSF
4. Pseudoporencephaly
   = CSF-filled space communicating with ventricle / subarachnoid space from cystic degeneration
5. Subdural hygroma
6. Leptomeningeal cyst
   = progressive protrusion of leptomeninges through traumatic calvarial defect
7. Cerebrospinal fluid leak
   • rhinorrhea, otorrhea (indicating basilar fracture with meningeal tear)
8. Posttraumatic abscess
   due to (a) penetrating injury, (b) basilar skull fracture, (c) infection of traumatic hematoma
9. Parenchymal injury
   brain atrophy, residual hemoglobin degradation products, wallerian-type axonal degeneration, demyelination, cavitation, microglial scarring

Prognosis: up to 10% fatal; 5–10% with some degree of neurologic deficit

Mortality: 25÷100,000 per year (traffic-related in 20–50%, gunshot 20–40%; falls)