Chapter 99

Performing an emergent ventriculostomy may be lifesaving when faced with a patient who is deteriorating rapidly from a neurologic perspective and all other therapeutic options have been employed.1 This chapter will discuss some of the situations when this procedure may be considered, other therapeutic options, and an explanation of how to perform an emergent ventriculostomy.

The cranium is a fixed space after infancy that has little capacity for added volume or mass. Pathologic conditions such as tumors, intracranial hemorrhage, infection, massive infarctions, and edema can exert direct pressure on the brain or interrupt flow of the cerebrospinal fluid (CSF). These processes result in fluid accumulation and increased intracranial pressure (ICP).

The patient with increased ICP may display the classic clinical signs of headache, vomiting, and papilledema.1 Vomiting is particularly associated with acute increases in ICP. Other signs include an abducens nerve palsy (cranial nerve VI) that causes diplopia, decreased consciousness, and an elevated blood pressure with bradycardia (Cushing’s phenomenon). An increase in ICP may eventually progress to brain herniation.

Herniation occurs when there exists a force in part of the brain great enough to push other parts of the brain into different compartments. The cranial contents are divided into compartments by invaginations of the dura mater (Figure 99-1).2 The supratentorial space is separated from the infratentorial space by the tentorium cerebelli. The right and left hemispheres are separated by the falx cerebri.

###### Figure 99-1

The falx cerebri and tentorium cerebelli divide the skull into compartments. A. Sagittal view. B. Coronal view. C. Top of the skull removed with a section of tentorium cerebelli also removed.

When a unilateral supratentorial mass exerts enough force, the ipsilateral cerebral hemisphere is pushed medially toward the opposite hemisphere (Figure 99-2A).The medial aspect of the temporal lobe is pushed down towards the brainstem and over the edge of the tentorium cerebelli (Figure 99-2B). This process is known as tentorial herniation. Symptoms of tentorial herniation include a worsening of any headache with vomiting, progressively decreasing consciousness, anisocoria, hemiparesis, and Parinaud’s syndrome (an upward gaze paresis). Compression of the oculomotor nerve results in a sluggish and dilated pupil, usually on the same side as the mass lesion. A progression to a fixed and dilated pupil, with decerebrate rigidity (extensor posturing), is an ominous sign of increased ICP.

###### Figure 99-2

Supratentorial herniation of the brain. A. Tentorial herniation. B. Subfalcial herniation.

Mass effect in the infratentorial compartment of the skull may produce downward pressure of the cerebellum into the foramen magnum (Figure 99-3A) or upward pressure of the midbrain into the supratentorial compartment (Figure 99-3B), the former being more common. ...

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