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.
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.
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. ...