the characteristic pattern of sudden onset of
unconsciousness with tiny but reactive pupils
(although it may require a magnifying glass or
the plus 20 lens of the ophthalmoscope to vi-
sualize the light response). Most patients have
impairment of oculocephalic responses, and
eyes may show skew deviation, ocular bobbing,
or one of its variants. Patients may have decer-
ebrate rigidity, or they may demonstrate flac-
cid quadriplegia. We have seen one patient in
whom a hematoma that dissected along the
medial longitudinal fasciculus, and caused ini-
tial vertical and adduction ophthalmoparesis,
was followed about an hour later by loss of con-
sciousness (see Patient 2–1). However, in most
patients, the onset of coma is so sudden that
there is not even a history of a complaint of
headache.
180
SUPRATENTORIAL DESTRUCTIVE
LESIONS CAUSING COMA
The most common supratentorial destructive
lesions causing coma result from either anoxia
or ischemia, although the damage may occur
due to trauma, infection, or the associated im-
mune response. To cause coma, a supraten-
torial lesion must either involve bilateral cor-
tical or subcortical structures multifocally or
diffusely or affect the thalamus bilaterally.
Following recovery from the initial insult, the
Figure 4–9. A pair of scans without contrast from two patients with pontine strokes. (A) A noncontrast computed to-
mography scan demonstrating a small hemorrhage into the right pontine base and tegmentum in a 55-year-old man with
hypertension, who presented with left hemiparesis and dysarthria. He was treated by blood pressure control and improved
markedly. (B) A diffusion-weighted magnetic resonance imaging (MRI) scan of a medial pontine infarct in a 77-year-old
man with hypertension, hyperlipidemia, and prior history of coronary artery disease. He presented with left hemiparesis,
dysarthria, and diplopia. On examination, there was right lateral gaze paresis and inability to adduct either eye on lateral
gaze (one-and-a-half syndrome). There was extensive irregularity of the vertebrobasilar vessels on MR angiogram. He was
treated with anticoagulants and improved slowly, although with significant residual diplopia and left hemiparesis at discharge.
Specific Causes of Structural Coma
151
coma is usually short lived, the patient either
awakening, entering a persistent vegetative
state within a few days or weeks, or dying (see
Chapter 9).
VASCULAR CAUSES
OF SUPRATENTORIAL
DESTRUCTIVE LESIONS
Diffuse anoxia and ischemia, including carbon
monoxide poisoning and multiple cerebral em-
boli from fat embolism
181
or cardiac surgery,
182
are discussed in detail in Chapter 5. We will
concentrate here on focal ischemic lesions that
can cause coma.
Carotid Ischemic Lesions
Unilateral hemispheric infarcts due to carotid
or middle cerebral occlusion may cause a quiet,
apathetic, or even confused appearance, as the
remaining cognitive systems in the patient’s
functional hemisphere attempt to deal with the
sudden change in cognitive perspective on the
world. This appearance is also seen in patients
during a Wada test, when a barbiturate is in-
jected into one carotid artery to determine the
lateralization of language function prior to sur-
gery. The appearance of the patient may be
deceptive to the uninitiated examiner; acute
loss of language with a dominant hemisphere
lesion may make the patient unresponsive to
verbal command, and acute lesions of the non-
dominant hemisphere often cause an ‘‘eye-
opening apraxia,’’ in which the patient keeps his
or her eyes closed, even though awake. How-
ever, a careful neurologic examination demon-
strates that despite the appearance of reduced
responsiveness, true coma rarely occurs in such
cases.
183
In the rare cases where unilateral carotid oc-
clusion does cause loss of consciousness, there
is nearly always an underlying vascular abnor-
mality that explains the observation.
184,185
For
example, there may be pre-existing vascular
anomaly or occlusion of the contralateral ca-
rotid artery, so that both cerebral hemispheres
may be supplied, across the anterior commu-
nicating artery, by one carotid. In the absence
of such a situation, unilateral carotid occlusion
does not cause acute loss of consciousness.
Patients with large hemispheric infarcts are
nearly always hemiplegic at onset, and if in
the dominant hemisphere, aphasic as well. The
lesion can be differentiated from a cerebral
hemorrhage by CT scan that, in the case of in-
farct, may initially appear normal or show only
slight edema with loss of gray-white matter
distinction (Figure 4–10). MRI scans, however,
show marked hyperintensity on the diffusion-
weighted image, indicating ischemia. Symptoms
may be relieved by early use of thrombolytic
agents,
186
but only if the stroke is identified and
treated within a few hours of onset. There are
currently no neuroprotective agents that have
demonstrated effectiveness. Patients with mas-
sive infarcts should be given good support-
ive care to ensure adequate blood flow, oxygen,
and nutrients to the brain, but hyperglyce-
mia should be avoided as it worsens the out-
come.
187,188
These patients are best treated in
a stroke unit
189
; they should be watched care-
fully for the development of brain edema and
increased ICP.
Although impairment of consciousness is
rare as an immediate result of carotid occlusion,
it may occur 2 to 4 days after acute infarction in
the carotid territory, as edema of the infarcted
hemisphere causes compression of the other
hemisphere and the diencephalon, and may
even result in uncal or central herniation.
186,190
This problem is presaged by increasing leth-
argy and pupillary changes suggesting either
central or uncal herniation. Many patients who
survive the initial infarct succumb during this
period. The swelling does not respond to cor-
ticosteroids as it is cytotoxic in origin. It may
be diminished transiently with mannitol or hy-
pertonic saline,
191
but these agents soon equil-
ibrate across the blood-brain barrier and cease
to draw fluid out of the brain, if they ever
did
192,193
(see Chapter 7). Surgical resection of
the infarcted tissue may improve survival,
194,195
but this approach often results in a severely
impaired outcome. Decompressive craniotomy
(removing bone overlying the damaged hemi-
sphere) may increase survival, but many of the
patients have a poor neurologic outcome.
196
Distal Basilar Occlusion
Distal basilar occlusion typically presents with
a characteristic set of findings (the ‘‘top of the
basilar syndrome’’) that can include impairment
152
Plum and Posner’s Diagnosis of Stupor and Coma