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Differential Diagnosis of Nervous System Disorders

  1. INFECTION (<1%)
    1. Bone flap infection (44% of all infections)
      At risk: postoperative CSF leakage, breach of paranasal sinuses, septic surgery performed for active infection, source of intracerebral contamination (compound skull fracture / penetrating injury)
    2. Meningitis
    3. Extradural abscess (0.43% of all craniotomies)
    4. Subdural empyema (0.11% of all craniotomies)
    5. Brain abscess
  2. PERTAINING TO CRANIOTOMY / CRANIECTOMY
    1. Extracranial herniation after decompressive craniectomy
      Cause: created craniectomy defect too small
      Cx: compression of cortical veins → venous infarction; contusion of brain at craniectomy margins
    2. Subdural / subgaleal hygroma (21–50%)
      Cause: disturbance of CSF circulation after craniectomy
      Location: fluid collection ipsilateral to craniectomy / contralateral / interhemispheric space
      Timing: appearance within days of surgery, resorption over weeks to months
    3. External brain tamponade
      Cause: subgaleal fluid accumulates under pressure and pushes on the brain across craniectomy defect
      • bulging skin flap + subgaleal fluid collection
    4. Trephine syndrome (13%)
      = sinking skin flap syndrome = syndrome of the trephined
      Cause: atmospheric pressure + gravity overwhelm intracranial pressures → brain appears sunken
      Time after surgery: 28–188 days
      • headaches, seizures, dizziness, undue fatigability
      • depressed skin flap at craniectomy site
      • concave deformity of adjacent brain
    5. Postsurgical brain herniation (see below)
  3. HEMORRHAGE
    1. “Plunging” = inadvertent breach of dura during drilling
      Cx: intracerebral hematoma (71%), cortical laceration (16%), extradural hematoma (5%), subdural hematoma (5%), intraventricular hemorrhage (3%)
    2. Postoperative hemorrhage (6–7%)
      Location: intraparenchymal (43%), extradural (33%), subdural (5%), mixed (8%)
    3. Extradural hematoma
      Location: regional (63%) = beneath bone flap; adjacent (31%) = at craniotomy margins: remote (6%) = distant to craniotomy site
    4. Intraparenchymal hemorrhage (11%)
    5. Remote cerebellar hemorrhage
      = CSF volume depletion → sagging of cerebellum → occlusion of superior bridging veins → hemorrhagic infarction
      • “zebra” sign = streaky curvilinear areas of increased attenuation in cerebellar sulci + folia

Postsurgical Brain Herniation

Fungus Cerebri

= EXTRACRANIAL HERNIATION

= herniation of brain tissue through skull defect after trauma / therapeutic craniectomy

Cx: brain infarction

Paradoxical Brain Herniation

= SYNDROME OF THE TREPHINED

  • Neurosurgical emergency!
  • mesodiencephalic herniation syndrome: depressed level of consciousness, autonomic instability, signs of brainstem release, focal neurologic deficits

At risk: large craniectomy defect followed by CSF drainage procedure (lumbar puncture, external ventricular drainage, ventriculoperitoneal shunting)

Pathophysiology:

  • decrease in CSF pressure → reduction in intracranial pressure to below atmospheric pressure
  • sunken skin flap
  • subfalcine / transtentorial herniation of brain away from craniectomy defect:
    • midline shift
    • compression of midbrain
    • effacement of basal cisterns

Rx: Trendelenburg position, clamping of ventricular shunt / drain, intravenous fluid, lumbar epidural blood patch, performing early cranioplasty to restore continuity of calvaria

Tension Pneumocephalus

◊Rare life-threatening neurosurgical emergency!

= commonly following neurosurgical decompression of subdural hematoma / posterior fossa craniotomy

Cause: air enters via subdural defect → check-valve mechanism prevents escape of air → increasing intracranial pressure

  • falling Glasgow coma scale
  • “peaking” sign = subdural air collections compress both frontal lobes
  • “Mount Fuji” sign = compression and separation of frontal lobes by air → widening of interhemispheric space
  • transtentorial ± tonsillar herniation