THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES

Interhemispheric Subdural Hematoma
Neville A. Russell, Raquel del Carpio-O'Donovan, K.B. Mallya,
Brien G. Benoit and Gary Belanger

ABSTRACT: Although relatively uncommon, interhemispheric subdural hematoma (ISDH) occurs more frequently
than was suspected before the advent of computerized tomographic (CT) scanning. When its mass is sufficiently large
to compress the medial cerebral hemisphere, specific focal neurological abnormalities may occur. These include
weakness of the contralateral leg, or contralateral hemiparesis with the leg being weaker than the arm. On the
unenhanced CT scan ISDH is seen as a crescent shaped, midline hyperdensity. Treatment is dictated by the clinical
course. Evacuation of the hematoma by parasagittal craniotomy is recommended if the symptoms are pronounced.
RESUME: Hematome sous-dural interhemispherique Meme si cette entite est relativement rare, I'hematome sousdural interhemispherique (HSDI) survient plus frequemment qu'on ne le soup§onnait avant l'avenement de la
tomographic axiale assistee par ordinateur. Quand la masse de I'hematome est suffisamment importante pour
comprimer la face interne de l'hemisphere, des anomalies neurologiques focales specifiques apparaissent. Parmi
celles-ci, notons la faiblesse de la jambe contralaterale ou l'hemiparesie contralaterale, la jambe etant plus faible que
le bras. A la tomographic axiale sans perfusion de produit de contraste, l'HSDI apparait comme une zone d'hyperdensite
m£diane en forme de croissant. Le traitement est determine par revolution clinique. Si la symptomatologie est
importante, il est recommande de proceder a l'evacuation de I'hematome par craniotomie parasagittal.
Can. J. Neurol. Sci. 1987; 14:172-174

Interhemispheric subdural hematoma (ISDH) was first
described at autopsy by Airing and Evans' in 1940 and first
recognized during life by Jacobsen2 in 1955. Prior to the advent
of computerized tomographic (CT) scanning this lesion was
very difficult to detect, a fact which accounts for the paucity of
cases reported before 1974,1"6 and for the persistent belief that
it is very rare 8 ". In this paper we report two additional cases
of ISDH and discuss the unique features of this lesion.

brain swelling. A large hematoma was encountered in the subdural
space deep between the hemispheres, extending onto the tentorium.
Approximately 70 cc's of semi-liquid blood were removed with irrigation and suction. He awakened immediately after surgery, but remained
confused and hemiplegic, with the leg being weaker than the arm. He
continued in this state for 12 days, after which pneumonia developed.
He died of this on the 14th postoperative day. Autopsy revealed no
residual clot in the interhemispheric subdural space. No source of
hemorrhage was detected.
Patient 2

CASE REPORTS
Patient 1
An 80-year-old man fractured the neck of his right femur and struck
his head in a fall. He did not lose consciousness. His past history
included chronic obstructive lung disease and a myocardial infarction.
Because of the latter he had been receiving oral anti-coagulant therapy.
Upon admission to hospital he was alert and without neurologic deficit.
Three days later he was noted to be disoriented and at examination was
found to have a right hemiplegia with right facial weakness. Shortly
afterwards he developed focal right sided seizures, which involved his
leg more than his arm. Prothrombin time was 28 seconds (normal range
10-12), and partial thromboplastin time was 48 seconds (normal range
25-30). A nonenhanced CT scan showed a large left ISDH (Figure I).
Craniotomy was performed via a left sided parasagittal bone flap. The
brain was swollen but no other abnormalities noted upon its surface.
One small bridging vein was coagulated and divided. The medial left
cerebral hemisphere was retracted with some difficulty because of

An 81-year-old woman fell and struck her head. She did not lose
consciousness. She had longstanding diabetes mellitus and had been
having oral anti-coagulant therapy for several years, because of a
cerebrovascular thrombosis. Twenty-four hours after injury she complained of headache and seemed drowsy. Over several subsequent
hours she became unconscious. At examination she was comatose,
with spontaneous movements of her right limbs: the left limbs moved
only to deep pain, with the arm moving better than the leg. Prothrombin
time was 14 seconds (normal range 10-12). Partial thromboplastin time
was 54 seconds (normal range 25-30). A nonenhanced CT scan, showed
a large right ISDH which was virtually identical to that in Case I (Figure
1). The blood had also tracked posteriorly to outline the tentorium.
Craniotomy via a large parasagittal bone flap gave easy access to a
subdural hematoma situated deep between the cerebral hemispheres
and extending onto the tentorium. Approximately 55 cc's of semi liquid
blood were removed using irrigation and suction. The bridging veins
were not disturbed. In the immediate postoperative period she remained
stuporous with focal seizures involving the left leg. These were controlled by anti-convulsant therapy and she gradually recovered to be

From the Division of Neurosurgery and the Department of Diagnostic Radiology, Ottawa Civic Hospital and the University of Ottawa, Ottawa, Ontario
Received September 24, 1986. Accepted December 16, 1986
Reprint requests to: Dr. N.A. Russell, Suite 606, 1081 Carting Avenue, Ottawa, Ontario K1Y 4G2

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LE JOURNAL CANADIEN DES SCIENCES NEUROLOGIQUES
subdural space.
Therefore, ISDH is usually unilateral. Associated convexity subdural hematomas were present in a number of the cases reported.'" 3,6,8 " 17,26 ' 28 Some authors consider
these to represent an extension of the hematoma from the
interhemispheric fissure,81019 while others believe they originate from separate bleeding sources. 26 " 28
Major trauma was implicated in only a few of the cases
occurring after blunt head injury. 1 ' 6 " 1 2 1 7 ' 2 4 These patients
were unconscious from the time of injury or shortly thereafter.
More frequently the associated injury was minor, with or without a brief period of unconsciousness. Both of our patients had
minor head injuries, but they were also receiving anti-coagulant
therapy. Usually the onset of symptoms and signs is delayed,
with the delay varying from days, 2 ' 7 - 810 ' 19 to weeks, 416 ' 21,22
to months. 10
Focal neurological abnormalities have been reported in association with ISDH, and were observed in both of our patients.
These include weakness of the contralateral leg 2 5 7 - 2 0 or contralateral hemiparesis with the leg being weaker than the
involving the contralatarm>6,7,8,i2,14.16.18.19.23 o r s e j z u r e s
eral i e g. 1 1 4 . 1 9 2 3 Paraparesis has also been described.' 023 These
signs indicate a medial cerebral hemisphere lesion, have also
been described in patients with interhemispheric subdural
empyema 29,30 and with occlusion of the anterior cerebral
artery. 19 This clinical picture has been referred to as the falx
syndrome. 19,30
Prior to CT scanning, carotid angiography was the investigation of choice for ISDH. 2 ' 3 ' 5 ' 6 ' 7 ' 19 In the anterior-posterior
view it shows a midline avascular space, which is produced by
displacement of the callosomarginal arteries without a similar
displacement of the pericallosals. Angiography has been replaced
by CT scanning, and need only be considered if an aneurysm is
suspected.
Figure I — ISDH in Patient I. The midline hyperdensity has aflatmedial CT scanning gives an immediate and precise diagnosis, definmargin -falx- and a convex lateral border where the lesion bulges into the
ing the exact location, extent and pattern of the ISDH. 8 "' 0,12,
ipsilaleral hemisphere.
16,19,23.24-28 Q n the nonenhanced CT scan, its hallmark is a
able to sit in a chair and feed herself. Recovery continued until the sixth
midline, parafalcial, crescent shaped hyperdense mass. Its flat
postoperative week, when she was discovered unconscious in her bed.
medial border is formed by the falx and its convex lateral
Her blood glucose level was 20 mg%. Resuscitation was unsuccessful.
border
by the hematoma mass bulging into the ipsilateral
Permission for autopsy was refused.
hemisphere. It is differentiated from subarachnoid hemorrhage 31
and intracerebral hematoma' 6 by its size and shape, and from
DISCUSSION
interhemispheric empyema 21 by its density.
Zimmerman et al 26,28 suggest that most of these hematomas
A total of 99 cases of ISDH have been reported in the literature.
resolve spontaneously and that surgical treatment is rarely
All but ten of these have appeared since 1974,8"28 coinciding
necessary. We believe this to be true only if the hematoma is
with the widespread use of CT scanning. Two large series deal
very small. If it is large enough to cause mass effect, it should be
primarily with the CT features of the hematoma. 25 ' 28 All other
treated promptly. If the patient's condition is stable, continupapers except one that describes three cases, 23 and three, each
19 20
ous
monitoring of the intracranial pressure and its control by
describing two cases," ' consist of single case reports.
1012 20
conservative
measures may be adequate. 8 However, acute or
' or
ISDH is usually caused by blunt direct head injury,
progressive neurological deterioration requires surgical interby indirect head injury in young children abused by violent
vention. Craniotomy is preferable to simple burr holes for
shaking. 24,25 It has also been described following penetrating
28
5,13,18
adequate
exploration of the interhemispheric space. 9 ' 2 , 2 8 Since
and in associawounds of the falx, aneurysm rupture,
7 6,23
14,17,2
the hematoma does not present upon the surface, the hemition with anti-coagulant therapy, "'
blood dyscrasias
'
sphere must be retracted in order to achieve a satisfactory
and shunted hydrocephalus.' 0
removal. The bone flap must cross the midline and the expoThe hemorrhage occurs when torsion forces rupture the large
sure
must be large enough to allow retraction of the hemisphere,
fixed bridging veins between the parieto-occipital cortex and
without injuring important draining veins.
the superior sagittal sinus. 9,11,13,24 " 28 Thus it is largest in the
posterior superior part of the interhemispheric fissure, above
ACKNOWLEDGEMENTS
and behind the splenium of the corpus callosum.26"28 Firm
arachnoidal attachments separate the two sides of the interThe authors acknowledge the expert secretarial assistance of Miss
hemispheric fissure from each other and from the convexity
Donna Headrick.

Volume 14, No. 2 — May 1987
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