otherwise healthy young person, the loss of
brain function eventually results in failure of the
systemic circulation within a few days or, rarely,
after several weeks. That the brain has been
dead for some time prior to the cessation of the
heartbeat is attested to by the fact that the or-
gan in such cases is usually autolyzed (respirator
brain) when examined postmortem.
15
Because
function of the cerebral hemispheres depends
on the brainstem (see ascending arousal system
section below), and because cerebral hemi-
sphere function is extremely difficult to assess
when the brainstem is nonfunctioning, physi-
cians in the United Kingdom have developed
the concept of brainstem death,
16
defined as
‘‘irreversible loss of the capacity for conscious-
ness, combined with irreversible loss of the
capacity to breathe.’’ The criteria for the diag-
nosis of brain death and brainstem death are al-
most identical. They are detailed in Chapter 8.
Acute alterations of consciousness are dis-
cussed in Chapters 2 through 5. Subacute and
chronic alterations of consciousness are discus-
sed in Chapter 9.
APPROACH TO THE DIAGNOSIS
OF THE COMATOSE PATIENT
Determining the cause of an acutely depressed
level of consciousness is a difficult clinical
challenge. The clinician must determine rapidly
whether the cause of the impairment is struc-
tural or metabolic, and what treatments must
be instituted to save the life of the patient. Since
the last edition of this monograph in 1980,
there has been a revolution in brain imaging.
Computed tomography (CT) scans and some-
times magnetic resonance imaging (MRI) are
immediately available in the emergency room
to evaluate acutely ill patients. In appropriate
clinical circumstances, if the initial examina-
tion suggests structural brain damage, a scan
may identify the cause of the alteration of con-
sciousness and dictate the therapy. However,
when the scan does not give the cause, there is
no simple solution; usually no single laboratory
test or screening procedure will sift out the
critical initial diagnostic categories as effectively
as a careful clinical evaluation.
If the cause of coma is structural, it generally
is due to a focal injury along the course of the
neural pathways that generate and maintain a
normal waking brain. Therefore, the clinical
diagnosis of structural coma depends on the
recognition of the signs of injury to structures
that accompany the arousal pathways through
the brain. Structural processes that impair the
function of the arousal system fall into two ca-
tegories: (1) supratentorial mass lesions, which
may compress deep diencephalic structures and
hence impair the function of both hemispheres,
and (2) infratentorial mass or destructive le-
sions, which directly damage the arousal system
at its source in the upper brainstem. The re-
mainder of Chapter 1 will systematically exam-
ine the major arousal systems in the brain and
the physiology and pathophysiology of consci-
ousness. Chapter 2 addresses examination of the
patient with a disturbance of consciousness, par-
ticularly those components of the examination
that assay the function of the arousal systems
and the major sensory, motor, and autonomic
systems that accompany them. Once the exam-
ination is completed, the examiner should be
able to determine whether the source of the
impairment of consciousness is caused by a
structural lesion (Chapters 3 and 4) or a diffuse
and therefore presumably metabolic process
(Chapter 5).
Although it is important to question family
members or attendants who may have details of
the history, including emergency medical per-
sonnel who bring the patient into the emergency
department, the history for comatose patients
is often scant or absent. The neurologic exam-
ination of a patient with impaired conscious-
ness, fortunately, is brief, because the patient
cannot detect sensory stimuli or provide vol-
untary motor responses. The key components
of the examination, which can be completed by
a skillful physician in just a few minutes, in-
clude (1) the level of consciousness of the pa-
tient, (2) the pattern of breathing, (3) the size
and reactivity of the pupils, (4) the eye move-
ments and oculovestibular responses, and (5)
the skeletal motor responses. From this infor-
mation, the examiner must be able to recon-
struct the type of the lesion and move swiftly
to lifesaving measures. Before reviewing the
components of the coma examination in detail,
however, it is necessary to understand the ba-
sic pathways in the brain that sustain wakeful,
conscious behavior. Only from this perspective
is it possible to understand how the compo-
nents of the coma examination test pathways
that are intertwined with those that maintain
consciousness.
Pathophysiology of Signs and Symptoms of Coma
9
Box 1–1 Constantin von Economo and the Discovery of
Intrinsic Wake and Sleep Systems in the Brain
Baron Constantin von Economo von San Serff was born in 1876, the son of Greek
parentage. He was brought up in Austrian Trieste, studied medicine in Vienna,
and in 1906 took a post in the Psychiatric Clinic under Professor Julius von
Wagner-Jauregg. In 1916 during World War I, he began seeing cases of a new and
previously unrecorded type of encephalitis and published his first report of this
illness in 1917. Although subsequent accounts have often confused this illness
with the epidemic of influenza that swept through Europe and then the rest of the
world during World War I, von Economo was quite clear that encephalitis le-
thargica was not associated with respiratory symptoms, and that its appearance
preceded the onset of the latter epidemic. Von Economo continued to write and
lecture about this experience for the remainder of his life, until his premature
death in 1931 from heart disease.
Based on his clinical observations, von Economo proposed a dual center the-
ory for regulation of sleep and wakefulness: a waking influence arising from the
upper brainstem and passing through the gray matter surrounding the cerebral
aqueduct and the posterior third ventricle; and a rostral hypothalamic sleep-
promoting area. These observations became the basis for lesion studies done by
Ranson in 1939,
20
by Nauta in 1946,
21
and by Swett and Hobson in 1968,
22
in
which they showed that the posterior lateral hypothalamic lesions in monkeys,
rats, and cats could reproduce the prolonged sleepiness that von Economo had
observed. The rostral hypothalamic sleep-promoting area was confirmed exper-
imentally in rats by Nauta in 1946
21
and in cats by Sterman and Clemente in the
1960s.
23
Interestingly, von Economo also identified a third clinical syndrome, which
appeared some months after the acute encephalitis in some patients who had
Figure B1–1A. A photograph of Baron Constantin von Economo, and excerpts from the title
page of his lecture on the localization of sleep and wake promoting systems in the brain. (From von
Economo,
19
with permission.)
(continued)
10