who suffer from brain trauma.
104
These cases
usually do not present a diagnostic dilemma, as
there is usually history or external evidence of
trauma to suggest the cause of the impaired con-
sciousness.
DIENCEPHALIC INJURY
The relay nuclei of the thalamus provide the
largest ascending source of input to the cere-
bral cortex. As a result, it is no exaggeration to
say that virtually any deficit due to injury of a
discrete cortical area can be mimicked by in-
jury to its thalamic relay nucleus. Hence, tha-
lamic lesions that are sufficiently extensive can
produce the same result as bilateral cortical
injury. The most common cause of such lesions
is the ‘‘tip of the basilar’’ syndrome, in which
vascular occlusion of the perforating arteries
that arise from the basilar apex or the first
segment of the posterior cerebral arteries
can produce bilateral thalamic infarction.
105
Figure 1–11. A series of drawings
illustrating levels through the brain-
stem at which lesions caused im-
pairment of consciousness. For each
case, the extent of the injury at each
level was plotted, and the colors
indicate the number of cases that
involved injury to that area. The
overlay illustrates the importance
of damage to the dorsolateral pon-
tine tegmentum or the paramedian
midbrain in causing coma. (From
Parvizi and Damasio,
110
with
permission.)
32
Plum and Posner’s Diagnosis of Stupor and Coma
However, careful examination of the MRI scans
of such patients, or their brains postmortem,
usually shows some damage as well to the para-
median midbrain reticular formation and often
in the posterior hypothalamus. Other causes of
primarily thalamic damage include thalamic
hemorrhage, local infiltrating tumors, and rare
cases of diencephalic inflammatory lesions (e.g.,
Behc¸et’s syndrome).
106,107
Another example of severe thalamic injury
causing coma was reported by Kinney and col-
leagues
108
in the brain of Karen Anne Quinlan,
a famous medicolegal case of a woman who
remained in a persistent vegetative state (Chap-
ter 9) for many years after a hypoxic brain in-
jury. Examination of her brain at the time of
death disclosed unexpectedly widespread tha-
lamic neuronal loss. However, there was also
extensive damage to other brain areas, includ-
ing the cerebral cortex, so that the thalamic
damage alone may not have caused the clinical
loss of consciousness. On the other hand, tha-
lamic injury is frequently found in patients with
brain injuries who eventually enter a persistent
vegetative state (Chapter 9).
104
Ischemic lesions of the hypothalamus are
rare, because the hypothalamus is literally en-
circled by the main vessels of the circle of Willis
and is fed by local penetrating vessels from all
the major arteries. However, the location of the
hypothalamus above the pituitary gland results
in localized hypothalamic damage in cases of
pituitary tumors.
109
The hypothalamus also may
harbor primary lymphomas of brain, gliomas, or
sarcoid granulomas. Patients with hypothalamic
lesions often appear to be hypersomnolent ra-
ther than comatose. They may yawn, stretch, or
sigh, features that are usually lacking in patients
with coma due to brainstem lesions.
UPPER BRAINSTEM INJURY
Evidence from clinicopathologic analyses firmly
establishes that the midbrain and pontine area
critical to consciousness in humans includes the
paramedian tegmental zone immediately ven-
tral to the periaqueductal gray matter, from the
caudal diencephalon through the rostral pons.
110
Numerous cases are on record of small lesions
involving this territory bilaterally in which there
was profound loss of consciousness (see Figure
1–11). On the other hand, we have not seen loss
of consciousness with lesions confined to the
medulla or the caudal pons. This principle is
illustrated by the historical vignettes on pages
30 and below.
HISTORICAL VIGNETTES
Patient 1–2
A 62-year-old woman was examined through the
courtesy of Dr. Walter Camp. Twenty-five years
earlier she had developed weakness and severely
impaired position and vibration sense of the right
arm and leg. Two years before we saw her, she
developed paralysis of the right vocal cord and
wasting of the right side of the tongue, followed by
insidiously progressing disability with an unsteady
gait and more weakness of the right limbs. Four
days before coming to the hospital, she became
much weaker on the right side, and 2 days later she
lost the ability to swallow.
When she entered the hospital she was alert and
in full possession of her faculties. She had no diffi-
culty breathing and her blood pressure was 162/
110 mm Hg. She had upbeat nystagmus on upward
gaze and decreased appreciation of pinprick on the
left side of the face. The right sides of the pharynx,
palate, and tongue were paralyzed. The right arm
and leg were weak and atrophic, consistent with dis-
use. Stretch reflexes below the neck were bilaterally
brisk, and the right plantar response was extensor.
Position and vibratory sensations were reduced on
the right side of the body and the appreciation of
pinprick was reduced on the left.
The next day she was still alert and responsive,
but she developed difficulty in coughing and speak-
ing and finally she ceased breathing. An endotra-
cheal tube was placed and mechanical ventilation
was begun. Later, on that third hospital day, she
was still bright and alert and quickly and accu-
rately answered questions by nodding or shaking
her head. The opening pressure of cerebrospinal
fluid (CSF) at lumbar puncture was 180 mm of
water, and the xanthochromic fluid contained
8,500 red blood cells/mm
3
and 14 white blood
cells/mm
3
.
She lived for 23 more days. During that time she
developed complete somatic motor paralysis below
the face. Several hypotensive crises were treated
promptly with infusions of pressor agents, but no
pressor drugs were needed during the last 2 weeks
of life. Intermittently during those final days, she had
brief periods of unresponsiveness, but then awakened
and signaled quickly and appropriately to questions
Pathophysiology of Signs and Symptoms of Coma
33