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NEUROSURGICAL EMERGENCIES

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MONRO KELLIE DOCTRINE

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  • 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

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FIGURE 39-1

The Monro Kellie doctrine states that the skull is a fixed-volume container and that an increase in the proportion of intracranial volume occupied by any of these tissues requires a compensatory decrease in the relative volume of the other tissues.

Graphic Jump Location
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DISORDERS RESULTING IN INCREASE IN PARENCHYMAL VOLUME OF INTRACRANIAL COMPARTMENT

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  • 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 ...

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