AUTHOR(S): Bartels, Ronald H.M.A., M.D.;
Verhagen, Wim I.M., M.D., Ph.D.; Prick, Mathé J.J.,
M.D., Ph.D.; Dalman, Johanna E., M.D.
Department of Neurology, Canisius Wilhelmina
Hospital, Nijmegen, The Netherlands
Neurosurgery 36; 1210-1214, 1995
ABSTRACT: THE INTERHEMISPHERIC
SUBDURAL hematoma is a relatively uncommon
type of subdural hematoma, especially seen in
patients with blood clotting disturbances. When its
mass becomes sufficiently large, specific
neurological abnormalities such as hemiparesis and
signs of the falx syndrome are seen. Treatment can
consist of conservative observation or craniotomy
and is dictated by the clinical course. Conservative
management is the treatment of choice for patients
without disturbances of consciousness and for
patients with stable clinical conditions. Surgical
treatment is necessary in patients with progressive
deterioration. Three case reports are presented, as
well as a review of 64 cases described in the
literature. The salient aspects of this clinical entity
are discussed.
KEY WORDS: Blood coagulation; Computerassisted tomography; Interhemispheric;
Subdural hematoma
The interhemispheric subdural hematoma (ISH) in
adults is a rare type of subdural hematoma. Since the
first description by Aring and Evans in 1940 (1), only
64 cases have been described in detail (1-4,6-8,10-16,18-23,
25-46,48-50)
. Zimmerman et al. (52) described the brain
computed tomography (CT) findings, but not the
clinical features, of 25 adult patients. Particularly
because of its location, the ISH is considered to be a
distinct entity. Recent experience with three patients
prompted us to carefully review the literature.
CASE REPORTS
Patient 1
Four days before admission, a 78-year-old woman
struck her head during a fall. One day later, she
noticed difficulties with walking. Over the next 3
days, these complaints gradually progressed. Twelve
hours before admission, she also noticed problems
with talking and speech. These symptoms also
worsened. She was using an oral anticoagulant agent
and 0.125 mg of Lanoxin (Burroughs Wellcome,
Research Triangle Park, NC) daily because of atrial
fibrillation.
At admission, her consciousness was undisturbed.
She had symptoms of nuchal rigidity and was
suffering from dysphasia. Except for right central
facial paresis, no other signs of cranial nerve

involvement were present. Her right arm and leg were
equally paretic (motor strength = 1/5, Medical
Research Council scale). Stretch reflexes were
exaggerated on both sides with a right extensor
plantar reflex.
Laboratory examinations were within normal
values except for an International Normalized Ratio
of 3.9. Electrocardiography showed atrial fibrillation.
CT revealed a left ISH extending over the falx
toward the tentorium (Fig. 1). Two weeks after
admission, this had completely resolved.
It was decided to conservatively manage the
patient. Immediately after admission, she received
medication to counteract the anticoagulant agent. No
changes were observed for 2 weeks. After this period,
gradual improvement was noticed in her speech and
in her right arm strength. Three days later, there was
also improvement in her right leg. Six weeks after
admission, she was able to walk without any
assistance. She was discharged to her own home and
regained the ability to perform almost all of her
normal activities.
Patient 2
A 70-year-old woman was recovering from an
intracerebral hemorrhage in the right internal capsule
112 days before admission. Ten hours before
admission, she fell out of bed and hit her head. She
had amnesia regarding this event, but it was uncertain
whether she had lost consciousness. Afterwards, she
complained of right-sided headaches. She vomited
several times and noticed progressive gait
disturbance, which deteriorated so that she was no
longer able to walk, even with assistance. Her
medications were 100 mg of acetylsalicylic acid daily
and 20 mg of isosorbide dinitrate thrice daily. At
admission, she was fully alert. The cranial nerves
were intact, except for a left central facial paresis and
a slight deviation of the tongue to the left. She had
left hemiparesis involving the leg (3/5) more than the
arm (4/5), which was more pronounced than it was
before the fall (arm and leg, 4/5). On both sides, brisk
stretch reflexes and positive Hoffmann's, Trömner's,
and extensor plantar reflexes were seen. There was no
sensory loss.
The results of laboratory investigations were
within normal limits. CT was compatible with a dense
interhemispheric collection of fresh blood on the
right side. A minimal amount of blood was also seen
in the subarachnoid space (right sylvian fissure).
We decided to conservatively manage the patient.
Three weeks after admission, the ISH had almost
completely resolved; 2 weeks later, the results of the
CT were unremarkable. In the meantime, the patient's
muscle strength had gradually increased. After 3
months, she was able to walk with the assistance of
two persons, and after 6 months, she was able to walk
alone.
Patient 3
A 75-year-old man had been complaining of
headaches for 2 weeks and was admitted because of a
decreasing level of consciousness that had started the
day before. On that day he had fallen twice. He had

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Neurosurgery 1992-98
June 1995, Volume 36, Number 6
1210 Interhemispheric Subdural Hematoma in
Adults: Case Reports and a Review of the Literature
Case Report

DISCUSSION
Incidence
The exact incidence of ISHs is unknown. Only 67
adult patients, including our patients, have been
described in detail (1-4,6-8,10-16,18-23,25-46,48-50). The maleto-female ratio in adult patients was 1.87:1. In both
sexes, ISHs occurred most often in the 6th, 7th, and
8th decades (Fig. 3). The incidence in children might
be much higher than in adults because of child abuse
by shaking; Zimmerman et al. (51) found ISHs in 17 of
28 children.
Pathogenesis
Preceding head trauma was mentioned in 61 ISH
cases (91.0%). In two cases, the ISH occurred
spontaneously; in two cases, it was caused by a
ruptured intracranial aneurysm, and in the remaining
two cases, no underlying mechanism was mentioned.
The site of impact of the head trauma in 7 cases was
frontal, in 18, occipital, in 3, vertex, and in 2, parietal,
and it was not mentioned in the remaining cases.
In Table 1, accompanying factors or diseases are
shown. One of the patients in whom the ISH
spontaneously appeared had hemophilia B (40); the
other had been using an oral anticoagulant agent for
arteritis (23), whereas another patient had been using
an anticoagulant agent for cardiological reasons (22).
The generally accepted causative mechanism for
the development of ISHs is tearing of the fixed
bridging veins between the medial cerebral cortex
and the superior sagittal sinus. Torsion forces are
known to be important, which is in accordance with
the high incidence of frontal and occipital sites of
impact. Tight connection of the arachnoid trabeculae
between the brain and the parasagittal dura prevents
further extension of a fresh clot to the ipsilateral
subdural space over the convexity (6,11,19,21,23,48,52). If a
solid clot liquefies, it may migrate into the space over
the convexity and behave like a chronic subdural
hematoma, as has been demonstrated by Ogsbury et
al. (34).
Signs and symptoms
The symptoms of the patients with ISHs included

disturbances of consciousness (38.8%), hemiparesis
(55.2%), monoparesis of the contralateral leg
(10.5%), epileptic manifestations (generalized,
11.9%, and focal seizures, 3.0%), gait ataxia (3.0%),
dementia (6.0%), language disorders (4.5%), and
oculomotor nerve dysfunction (3.0%). The
characteristic falx syndrome, consisting of
contralateral hemiparesis affecting the leg much more
than the arm, was present in 62.2% of the patients
with hemiparesis. None of the patients were symptom
free.
Many patients (23 of 60) were admitted within 24
hours after the trauma or onset of symptoms; 53
patients were admitted within 1 week, and for 7
patients, the time interval was not reported.
Neuroradiology
Plain cranial radiographs were taken in 18 patients;
a cranial fracture was detected in only 5 patients
(27.8%). The frequency of cranial fractures in
patients with subdural hematomas reported in the
literature varies from 38 to 77% (5,9,17).
For many years, cerebral angiography was the
diagnostic tool of choice. Characteristic features on
the anterior-posterior view are an avascular space
between the falx and the medial surface of the brain
and a separation of the right and left callosal marginal
branches above the free edge of the falx, if both
anterior cerebral arteries are opacified (3,41). Cerebral
arteriography was performed in 28 patients and
suggested a space-occupying lesion in the
interhemispheric subdural space.
CT has now replaced cerebral angiography.
Angiography is mandatory only in nontraumatic ISHs
(35)
. CT was performed on 55 patients (82.1%). In
accordance with the series of Zimmerman et al. (52),
hyperdensity in the interhemispheric fissure was seen
in most patients (87.3%). Several conditions may
cause hyperdensity in the interhemispheric fissure,
including a normal falx, dural calcification, a
subarachnoid hemorrhage, a subdural hematoma, and,
in children, diffuse cerebral edema (52). Hypodensity
and isodensity were each described once (23,36).
Pseudomembranes in an ISH, such as those observed
in Patient 3, were described once (23). In three
patients, the CT findings were not reported in detail.
The right and left interhemispheric subdural spaces
were affected equally. Bilateral ISHs were rare. Only
three cases have been described in detail (6,28,48),
although Zimmerman et al. (52) described the CT
scans of another three cases.
Treatment and outcome
Surgical treatment, including craniotomies (30 of
46 patients) and burr holes (13 of 46 patients), was
performed on 46 patients, and in 3 patients, the
surgical treatment was not specified. The remaining
21 cases were conservatively managed (Table 2).
Conservative management and surgical
intervention have been equally advocated. If the
neurological condition of the patient is stable or if
any accompanying diseases contraindicate surgery,
conservative therapy is generally preferred. For the
whole group of patients, the mortality rate after

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been using an oral anticoagulant agent because of a
myocardial infarction 6 weeks before. At admission,
he was also suffering from nausea and vomiting and
was stuporous. Cranial nerve functions were
undisturbed. He had mild (4/5) hemiparesis on the
right side. The arm stretch reflexes were symmetrical
and normal, whereas the right patellar reflex was
exaggerated. He had a flexor plantar response on the
left side and an equivocal response on the right.
The results of laboratory examinations were within
normal limits except for an International Normalized
Ratio of 5.0. CT was compatible with an acute ISH on
the left side within a more chronic subdural
hematoma, because "pseudomembranes" were present
(Fig. 2). The oral anticoagulant was stopped and
antagonized immediately. His clinical condition very
rapidly deteriorated. However, his relatives refused
surgical treatment, and 22 hours after admission, he
died. Autopsy was not permitted.

Received, June 3, 1994.
Accepted, November 11, 1994.
Reprint requests: W.I.M. Verhagen, M.D., Ph.D.,
Department of Neurology, Canisius Wilhelmina
Hospital, Weg door Jonkerbos 100, 6532 SZ
Nijmegen, The Netherlands.

3.
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conservative management was lower than that after
surgical treatment (10.5% and 31.7%, respectively).
The difference in outcome did not reach statistical
significance (χ2 = 5.8572; P = 0.1188). However, the
clinical conditions of the patients who were
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mentioned). When only acute and subacute ISHs
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21.

Jack E. Wilberger
Pittsburgh, Pennsylvania
The authors have reported 3 cases of their own and
have reviewed the reports to date on 64 other cases of
interhemispheric subdural hematomas in adults. The
article provides much useful information, including
the high incidence of this condition in patients with
bleeding disorders and in patients taking oral
anticoagulants. The data show that many of these
patients can be conservatively managed, although
patients with clouding of consciousness or
deteriorating neurological deficits require surgical
treatment.
Charles H. Tator
Toronto, Ontario, Canada

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COMMENTS
The authors have provided three case reports of
patients with interhemispheric subdural hematomas,
as well as a comprehensive review of the current
literature. The uniqueness of interhemispheric
subdural hematomas in the general context of acute
subdural hematomas is emphasized. Interhemispheric
subdural hematomas primarily are a disease of the
elderly. They primarily occur as a result of low
velocity impacts, and in two-thirds of the reported
cases, their occurrence has been associated with
various bleeding disturbances (i.e., anticoagulation).
Although a mortality rate of 25% as quoted by the
authors would seem to be generally low for acute
subdural hematomas, those patients with
interhemispheric subdural hematomas and altered
levels of consciousness actually had a 42% mortality
rate. The authors' cogent review of the incidence,
pathogenesis, signs and symptoms, neuroradiological
features, treatments, and outcomes from
interhemispheric subdural hematomas in adults
should be of interest to all who treat head trauma.

Figure 2. A and B, CT without contrast at admission
disclosing a left-sided ISH with compartments of
various densities and "pseudomembranes" compatible
with a recent hemorrhage in a more chronic ISH.

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Figure 1. CT without contrast at admission showing
an ISH on the left side.

Table 1. Accompanying Diseases or Factors in 67
Patients with Interhemispheric Subdural Hematoma

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Figure 3. Distribution of age related to sex.

Table 3. Outcome in Relation to Long-term Clouding
of the Consciousness and Therapya

Table 4. Correlation between Loss of Consciousness
at the Event Responsible for the Development of
Interhemispheric Subdural Hematoma (Initial Loss of
Consciousness) and the Outcome of Therapya

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Table 2. Treatment versus Outcomea