may fix at midposition, and neither eye elevates,
depresses, or turns medially with oculocephalic
or caloric vestibular testing. Either decorticate
or decerebrate posturing may be seen.
Clinical Findings in Central
Herniation Syndrome
DIENCEPHALIC STAGE
The first evidence that a supratentorial mass is
beginning to impair the diencephalon is usually
a change in alertness and behavior. Initially,
subjects might find it difficult to concentrate
and may be unable to retain the orderly details
of recent events. As the compression of the di-
encephalon progresses, the patient lapses into
torpid drowsiness, and finally stupor and coma.
Respiration in the early diencephalic stage
of central herniation is commonly interrupted
by sighs, yawns, and occasional pauses (Figure
3–11). As the sleepiness deepens, many pa-
tients lapse into the periodic breathing of
Cheyne-Stokes respiration. The pupils are typ-
ically small (1 to 3 mm), and it may be difficult
to identify their reaction to light without a
bright light source or a magnifying glass. How-
ever, the pupils typically dilate briskly in re-
sponse to a pinch of the skin over the neck
(ciliospinal reflex).
58
The eyes are typically con-
jugate or slightly divergent if the patient is not
awake, and there may be roving eye move-
ments, with slow to-and-fro rolling conjugate
displacement. Oculocephalic testing typically
demonstrates brisk, normal responses. There is
typically a diffuse, waxy increase in motor tone
(paratonia or gegenhalten), and the toe signs may
become bilaterally extensor.
The appearance of a patient in the early di-
encephalic stage of central herniation is quite
similar to that in metabolic encephalopathy.
This is a key problem, because one would like to
identify patients in the earliest phase of central
herniation to institute specific therapy, and yet
these patients look most like patients who have
no structural cause of coma. For this reason,
every patient with the clinical appearance of
metabolic encephalopathy requires careful serial
examinations until a structural lesion can be
ruled out with an imaging study and a metabolic
cause of coma can be identified and corrected.
During the late diencephalic stage (Figure
3–12), the clinical appearance of the patient
becomes more distinctive. The patient becomes
gradually more difficult to arouse, and eventu-
ally localizing motor responses to pain may dis-
appear entirely or decorticate responses may
appear. Initially, the upper extremity flexor and
lower extremity extensor posturing tends to ap-
pear on the side contralateral to the lesion, and
only in response to noxious stimuli. Later, the
response may become bilateral, and eventually
the contralateral and then ipsilateral side may
progress to full extensor (decerebrate) posturing.
The mechanism for brain impairment during
the diencephalic stage of central herniation is
not clear. Careful quantitative studies show that
the depressed level of consciousness correlates
with either lateral or vertical displacement of
the pineal gland, which lies along the midline at
the rostral extreme of the dorsal midbrain.
59,60
The diencephalic impairment may be due to the
stretching of small penetrating vessels tethered
to the posterior cerebral and communicating
arteries that supply the caudal thalamus and
hypothalamus. There is little evidence that ei-
ther increases in ICP or changes in cerebral
blood flow can account for these findings. On
the other hand, if patients with diencephalic
signs of the central herniation syndrome worsen,
they tend to pass rapidly to the stage of mid-
brain damage, suggesting that the same patho-
logic process has merely extended to the next
more caudal level.
The clinical importance, therefore, of the di-
encephalic stage of central herniation is that it
warns of a potentially reversible lesion that is
about to encroach on the brainstem and create
irreversible damage. If the supratentorial process
can be alleviated before the signs of midbrain
injury emerge, chances for a complete neuro-
logic recovery are good. Once signs of lower di-
encephalic and midbrain dysfunction appear, it
becomes increasingly likely that they will reflect
infarction rather than compression and revers-
ible ischemia, and the outlook for neurologic re-
covery rapidly becomes much poorer.
As herniation progresses to the midbrain stage
(Figure 3–13), signs of oculomotor failure ap-
pear. The pupils become irregular, then fixed at
midposition. Oculocephalic movements become
more difficult to elicit, and it may be necessary to
examine cold water caloric responses to deter-
mine their full extent. Typically, there is limited
and slower, and finally no medial movement of
the eye contralateral to the cold water stimu-
lus, and bilateral warm or cold water irrigation
Structural Causes of Stupor and Coma
107
confirms lack of vertical eye movements. Motor
responses are difficult to obtain or result in ex-
tensor posturing. In some cases, extensor pos-
turing appears spontaneously, or in response to
internal stimuli. Motor tone and tendon reflexes
may be heightened, and plantar responses are
extensor.
After the midbrain stage becomes complete,
it is rare for patients to recover fully. Most
patients in whom the herniation can be re-
versed suffer chronic neurologic disability.
61,62
Hence, it is critical, if intervention is antici-
pated, that it begin as early as possible and that
it be as vigorous as possible, as the patient’s life
hangs in the balance.
As the patient enters the pontine stage (Fig-
ure 3–14) of herniation, breathing becomes
more shallow and irregular, as the upper pon-
tine structures that modulate breathing are lost.
As the damage approaches the lower pons, the
lateral eye movements produced by cold water
caloric stimulation are also lost. Motor tone be-
Eupneic, with deep sighs
or yawns
Cheyne-Stokes
Small range of contraction
DOLL’S HEAD MANEUVER
ICE WATER CALORICS
Small pupils
Full conjugate lateral,
ipsilateral to ear injected
Appropriate motor
response to noxious
orbital roof
pressure
Bilateral
Babinski’s
Paratonic
resistance
Respiratory
pattern
a.
Pupillary
size and
reactions
b.
Oculocephalic
and
oculovestibular
responses
c.
Motor
responses
at rest
and to
stimulation
d.
Full conjugate lateral,
opposite
to direction
of turning
Figure 3–11. Signs of central transtentorial herniation or lateral displacement of the diencephalon, early diencephalic stage.
108
Plum and Posner’s Diagnosis of Stupor and Coma