E/x/epki, 40(4):516-519, 1999
Lippincott Williams & Wilkins, Inc., Philadelphia

0 Internalional League Against Epilepsy

Brief Communication

Unidirectional Olfactory Hallucination Associated with
Ipsilateral Unruptured Intracranial Aneurysm
Masahiro Mizobuchi, Naoki Ito, Chiharu Tanaka, Kazuya Sako, *Yoshihiro Sumi, and
“Takehiko Sasaki
Depurtments of Neurology and *Neurosurgery, Nukamum Memorial Hospital, Sapporo, Japan

Summary: Purpose: We describe a patient with complex partial seizure with unidirectional olfactory aura associated with

artery and compression of the right orbitofrontal cortex. Small
spikes were recorded from the right orbitofrontal and superior
temporal gyri and from the uncus by the cortical electrodes
during clipping of the aneurysm.
Conclusions: The orbitofrontal cortex may have a function
related to the ipsilateral directional olfactory sensation. Key
Words: Complex partial seizure-Unilateral olfactory auraUnmptured aneurysm-Orbitofrontal cortex.

ipsilateral unruptured aneurysm.
Methods and Results: The patient felt a sweet pleasant smell
coming from behind her right side every time before the attack.
Cranial magnetic resonance imaging ( M R I ) and threedimensional computed tomography (CT) angiography revealed
a large aneurysm at the bifurcation of the right middle cerebral

Unruptured intracranial aneurysm is one of rare causes
of epilepsy. Daly ( 1 ) reported one in 55 patients with
epilepsy with uncinate fits, and Currie et al. (2) had only
one in 666 patients with temporal lobe epilepsy. Several
other patients (3-7) associated with intracranial aneurysm were reported. Seizure types of most of the patients
consisted of complex partial seizures and a few patients
noticed a sensory aura.
Olfactory aura was produced by Penfield and Jasper
(8) on stimulation of the uncus and amygdala. Although
functions of the secondary olfactory center are not”ful1y
understood, olfactory aura may result from epileptic discharges in the secondary olfactory center.
We report a patient with unilateral olfactory aura associated with unruptured cerebral aneurysm located in
the ipsilateral orbitofrontal lobe.

the smell, which always came from behind her right side,
and never the left side or front, and never spread to
left side or front. After a few seconds, she became
confused. During the attack, she could respond verbally
but could not remember recent events. After the attack,
she could not recall what she had done. The longest
attack lasted -20 min without generalized seizures.
Automatism, visual or gustatory hallucinations, and d6ja
vu were not present. There was no neurologic abnormality including olfaction. Interictal EEG showed
paroxysmal discharges over the right temporal region.
Cranial magnetic resonance imaging (MRI) showed a
round flow-void lesion -I cm in diameter between the tip
of the right temporal lobe and the orbitofrontal gyrus
(Fig. 1). Three-dimensional computed tomography (CT)
angiography revealed a large aneurysm at the bifurcation
of the right middle cerebral artery (Fig. 2). Before the
operation, carbamazepine (CBZ) was started but stopped
because of an allergic reaction, and zonisamide (ZNS)
was started, 300 mg per day, and the seizures were well
controlled. Clipping of the aneurysm was done. Operative findings showed the aneurysm was located in the
anterior part of the insula without focal hemorrhage, hemosiderin pigmentation, or cortical gliosis. EEG was recorded from the cortices around the aneurysm and
showed electrical activities from the orbitofrontal and
superior temporal gyri and uncus (Fig. 3). Two years
after the operation, she stopped taking ZNS and had no
seizures.

CASE REPORT
A 49-year-old woman complaining of attacks of impaired consciousness was admitted to our hospital. In the
past 6 months, she felt a sweet pleasant smell like flowers or sweet fruits as an aura, which she had not previously experienced. She clearly identified the direction of
Accepted October I?, 1998.
Address correspondence and reprint requests to Dr. M. Mizobuchi at
Department of Neurology, Nakamura Memorial Hospital, Minami I ,
Nishi 14, Chuo-ku, Sapporo 060-8570, Japan.

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UNILATERAL OLFACTORY AURA AND ANEURYSM

517

FIG. 1. Sagittal, coronal, and axial
views (T,WI) and sagittal view (T,WI)
on magnetic resonance imaging
(MRI). It shows a round flow-void lesion between the tip of the right temporal lobe and the orbitofrontal gyrus.

DISCUSSION
The central olfactory pathway and its function in humans, especially the secondary olfactory center, are still
unknown. The olfactory tracts from the olfactory bulb
reach five areas of the primary olfactory cortices. Piriform cortex, one of the primary olfactory cortices, is

thought to function in the perception of smell. The fibers
from the piriform cortex project to the orbitofrontal
cortex, known as the secondary olfactory cortex. The
orbitofrontal cortex is thought to function in the discrimination of smell. By using electrical stimulation,
Penfield and Jasper (8) proved that the uncus and

FIG. 2. Three-dimensional computed
tomography (CT) angiography from the
frontal and top view. A large aneurysm at
the bifurcation of the right middle cerebral artery is present.

Epilrpsia, Vol. 40, No. 4, 19YY

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M . MIZOBUCHI ET AL.

FIG. 3. Cortical electrical activities from the right orbitofrontal and superior temporal gyri and from the uncus. About 300 pV spike
activities are recorded.

amygdala were related to the olfactory sensation. But
other locations, including the secondary olfactory center,
were not examined. Recently Tonoike et al. (9) described
an ipsilateral dominance of the lateral orbitofrontal
cortex concerning smell. This may suggest that a unilateral epileptogenic lesion of the orbitofrontal cortex
produces ipsilateral smell sensation. In our patient,
the aneurysm compressed the right orbitofrontal cortex,
and her olfactory aura came from behind her right
side. Because she vividly experienced the aura, not
only on one side but also the direction of the aura,
the orbitofrontal cortex may have a function related
to the discrimination of direction and laterality of
smell.
Most olfactory auras were reported as unpleasant
smells like a rotten odor (l), but some were pleasant
like flowers, perfumes, and fried meat (1,lO). Although
most of the patients of epilepsy associated with cerebral aneurysms had complex partial seizures, only two
patients had olfactory auras. One of the Whittle’s two
patients (6) smelled a fragrance like roses and had
secondarily generalized seizures. The aneurysm compressed the uncus and medial temporal gyrus, but it
was too large to be determined as a pathogenetic lesion,
and there was an infarction in the superior temporal gyms. The other patient had olfactory hallucinations after
the operation, so it was not purely associated with the
aneurysm. Concerning these cases and our patient, it remains unclear whether medial temporal structures or secondary olfactory centers or both are associated with the
type of smell.
Unruptured cerebral aneurysm is one of rare causes of
complex partial seizures. The incidence of epilepsy associated with aneurysm is not known. Cume et al. (2)

reported only one in 666 patients with temporal lobe
epilepsy. Morley and Barr (3) reported three in 28 patients with unruptured aneurysm had epilepsy, and Jomin
et al. (1 1) reported four in 50 patients. Most of the aneurysms of these patients (3-7) were located in the
middle cerebral artery region, the size was large to giant,
and the types of epileptic seizures were complex partial
and secondarily generalized.
Three mechanisms of seizures associated with aneurysm were postulated (4). First, the aneurysm directly
compress the cortex. Second, local hemorrhage from
the ruptured aneurysm produces an epileptic focus;
and third, focal ischemia due to embolism from the
aneurysm leads to seizures. In our patient, focal compression of the cortex between the frontal part of the
insula and orbitofrontal gyrus was observed, but hemosiderin, cortical atrophy, or gliosis was not present at
operation, and infarction was not present on MRT. Focal
compression of the cortex around the aneurysm was suspected to be associated with seizures. Whittle et al. (6)
reported the seizures in operated patients. Two patients
were well controlled by clipping the aneurysm, but others were not well controlled by wrapping. This may indicate that focal compression can cause epilepsy. Partial
bleeding around the aneurysm and gliosis of the surrounding cortex tend to cause intractable seizures (7). In
our patient, simple compression of the cortex without
focal hemorrhage or cortical gliosis resulted in good control.
There has been no report of unilateral olfactory aura
except one patient with a smell in the left nostril (1). Our
patient may show that the orbitofrontal cortex has a function related to the ipsilateral directional olfactory sensation.

UNILATERAL OLFACTORY AURA AND ANEURYSM

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Epilepsia, Vol. 40,No. 4, 1999