Physiology: Most cases of neurosurgical emergencies are related to the volume-occupying relationship between the brain matter, cerebral blood volume, and cerebrospinal fluid volume sharing space in the fixed-volume compartment of the skull (See Figure 39-1)
Changes in the relative volume of one of these components require compensatory change in the volume occupied by one or more of the other components
In the event that a change in the volume of one component overwhelms compensatory mechanisms, brain matter may move along the path of least resistance as it is pushed by pathologically elevated pressure within the calvarium
Cerebellar herniation via the foramen magnum
Transtentorial herniation across the falx cerebri
Transcalvarial herniation via a surgical or traumatic defect in the skull
Clinical presentation:
Cerebellar herniation (brainstem compression and hydrocephalus)
Somnolence/coma
Pupillary dilatation
Unilateral or bilateral
Nonreactive or sluggishly reactive
Due to compression of third cranial nerve
Respiratory pattern
Hyperventilation
Cheyne-Stokes
Decorticate or decerebrate posturing
Transtentorial herniation
Cushing’s triad: Clinical presentation of acute intracranial hypertension
Hypertension
Reflex bradycardia
Hypopnea
May not be apparent in setting of intubated and mechanically ventilated patient
May present as change in respiratory pattern
Diagnostic approach: Aimed at determining underlying cause and developing definitive treatment plan
Computerized tomography (CT) brain
Advantages
Rapid study
Readily available at most institutions
Can identify:
Blood collection
Extraaxial
Intraparenchymal
Intraventricular
Hydrocephalus
Cerebral edema
Some masses
Skull defects
Contrast enhances ability to identify:
Vascular abnormalities (thromboses and anatomic variants)
Infectious processes (abscess)
CT angiography
Disadvantages
Limited ability to image posterior fossa for mass (though this is often overcome with sagittal reconstructions)
Large ionizing radiation exposure
Magnetic resonance imaging (MRI) brain
Advantages
Can reliably identify mass lesions in all parts of the central nervous system (CNS)
Can reliably identify acute ischemia, cerebral edema, and inflammatory parenchymal lesions
No ionizing radiation
Disadvantages
Not readily available in all centers
Long duration study (the use of the fast-brain MRI has improved this greatly)
Material restrictions for magnet exposure
Cerebral edema: Wide variety of conditions
Trauma
Diabetic ketoacidosis
Hepatic encephalopathy
Ischemic brain injury
Stroke
Hypoxic ischemic encephalopathy
Encephalitis
Treatment
Hyperosmolar therapy
Hypertonic saline
3 to 5 mEq/kg bolus
1 mEq/kg can predictably increase serum sodium by 1
Mannitol
0.25 to 1 g/kg
Results in diuresis, which can cause hypotension and should be treated immediately
Decompressive surgery
Lesion
Skull
Brain mass: Tumors
Discussion of specific tumor types is beyond the scope of this chapter
Surgical decompression as necessary
Surrounding edema may be treated with dexamethasone acutely or subacutely