Peduncular Hallucinosis:
Magnetic Resonance
Imaging Confirmation
of Mesencephalrc
Infarction During Life
Thomas J. Geller, MD,” and Srinath N. Bellur, MDt

We describe a patient with peduncular hallucinosis and
a mesencephalic infarct; the infarct was diagnosed during life by magnetic resonance imaging.
Geller TJ, Bellur SN: Peduncular hallucinosis:
magnetic resonance imaging confirmation
of mesencephalic infarction during life.
Ann Neurol 21602-604, 1987

The occurrence of acute visual hallucinosis does not
generally aid in localizing the site of central nervous
system dysfunction except in the instance of peduncular hallucinosis. Peduncular hallucinosis is characterized by vivid, nonstereotypical, colorful imagery that is
nonthreatening to the patient. The hallucinations occur
in the presence of mesencephahc dysfunction. Welldocumented cases are few, and most of these have
included autopsy findings. We report a case of peduncular hallucinosis in which the anatomical diagnosis was
confirmed during life by magnetic resonance imaging

(MW.
Case Report
A 61-year-old man with insulin-dependent diabetes mellitus
and atherosclerotic cardiovascular disease was admitted to
the West Side Veterans’ Hospital, Chicago, with a 1-day
history of inability to open his right eye and clumsiness and
weakness of the left side of his body. During this time his
family noticed that he was drowsy and his speech was
slurred. They also noted that the patient spoke of visual
images that were clearly hallucinatory.
When questioned, the patient described seeing images of
cats running about the floor, flowery outdoor scenes in
bright purple colors, and the faces of neighbors and friends.
These images appeared continuously in all areas of the visual
fields and lasted for minutes to hours. The patient was aware
that the visual images were not real and was not apprehensive about them.

From the “Department ef Neurology, University of Illinois at
Chicago, and the ?Neurology Service, West Side Veterans’ Administration Hospital, Chicago, IL.
Received July 28, 1986, and in revised form Oct 7. Accepted for
publication Oct 10, 1986.
Address correspondence to Dr Geller, Department of Neurology,
Universiry of Illinois at Chicago, 912 S Wood St, Chicago, IL 60612.

602

H e had had diabetes for the past 21 years, and diabetic
retinopathy in the right eye had been treated by laser therapy. The patient had had two previous “silent” myocardial
infarctions and had had his left great toe amputated because
of severe peripheral vascular disease. The patient had no
prior history of stroke.
General physical findings were unremarkable except for
the healing amputation site on his left foot. On neurological
examination, the patient ‘was found to be mildly somnolent
and time-disoriented, but his language functions were intact.
His visual acuity was 20140 in the left eye and he could see
only hand movements in the right. His visual acuity was
unchanged from a previous examination 18 months before.
The patient had bilateral ptosis, but it was much more evident on the right. Also noted were a complete right thirdnerve paralysis with absent pupillary light response, a left
central seventh-nerve palsy, and a left hemiparesis. Occasional opsoclonic eye movements were seen, along with as.terixis in the upper extremities, which was more pronounced
on the left.
Computed tomographic (CT) brain scan failed to demonstrate clearly any brainstem abnormalities. An MRI scan using a 0.3-Tesla source demonstrated an area of hyperdense
signal intensity on the T2-weighted phase in the right midbrain tegmentum and cerebral peduncle, most consistent
with a bland infarction in the distribution of one of the small
mesencephalic branches of the posterior cerebral or superior
cerebellar arteries (Figure).
The patient’s somnolence and hallucinations slowly resolved over an approximate 10-day period, and he was left
with mild right ptosis and left hemiparesis.

Discussion
Peduncular hallucinosis is an unusual but welldescribed phenomenon that has been noted in vascular
lesions involving the cerebral peduncles or adjacent
midbrain structures. The earliest postmortem studies
of this disorder were published by Lhermitte and associates {lo} and van Bogacrrt 112). The hallucinations
usually appear as isolated vivid visual images, often in
bright colors, which do not invoke fear in the patient.
In fact, the patient is usually amused by the imagery
and is aware of the “unreality” of the phenomenon
{ 11). Our patient’s hallucinacions were consistent with
this pattern.
A number of explanations have been proposed for
the origin of visual hallucinations in vascular lesions
that are so distant from the visual system. None to date
seems entirely satisfactory. Cogan’s theory of visual
hallucinations posits two separate mechanisms of hallucinogenesis: “irritation” and “release” [43. In the irritative type, stereotypical paroxysmal disturbances in
cortical function occur, som.etimes associated with
other dysfunction in the motor or sensory realms. It is
believed that, when the irritative focus is occipital,
brief stereotypical flashes of light or color are described by the subject. When the focus is in the temporal lobe, the subject reports complex stereotypical
formed images.

Axial view of midbrain structures using mgnetic resonance imaging. Arrow indicates area of byperdense signal intensity in the
rigbt midbrain tegmentam and cerebral peduncle. (R = right.)

The release type of visual hallucinosis is characterized by more continuous visual images that change
from one episode to the next, but it is not characterized by an association with any other motor or sensory
disturbance. The hallucinations are attributed to a loss
of normal visual input occurring as a consequence of a
lesion anywhere in the visual system or as a consequence of sensory deprivation. Generally, release hallucinations are therefore less valuable in localizing central nervous system lesions. One exception, however,
is the phenomenon of peduncular hallucinosis. When
peduncular hallucinosis occurs, it is associated with
other signs of midbrain dysfunction, as in our patient.
Although midbrain infarction is common, peduncular hallucinosis is rare. It is tempting to speculate that
visual system dysfunction, coexisting with midbrain reticular formation dysfunction, precipitates peduncular
hallucinations. Our patient had a preexisting visual dysfunction (functional blindness, left eye; visual acuity,
20140, right eye) prior to his midbrain infarction. A
review of 10 previously published confirmed cases of
peduncular hallucinosis reveals that there was definite

visual system dysfunction in only 3 (2, 7, 8f. In 4 cases
there was no comment or uncertain evidence of visual
impairment (1, 9, 123, and in 3 cases visual acuity and
visual fields were entirely normal [ 5 , 6, 11). The exact
mechanism involved in the occurrence of peduncular
hallucinosis is therefore unclear, but the continuous
and nonstereotypical nature of the phenomenon suggests a release mechanism.
Peduncular hallucinations are described in association with hemorrhagic or thrombotic midbrain stroke
(3, 4, 7, 91. A report of peduncular hallucinosis with
angiographically diagnosed hypoplasia of the vetebral
artery was published in the Italian literature 13). Similarly, the phenomenon was described as a complication
of vertebral angiography by Rozanski in 1952 [ll). A
single report of an extraaxial compressive lesion of the
midbrain with surgically reversible peduncular hallucinosis appears in an article by Dunn and colleagues
(71. However, to our knowledge, this is the first
clinicoradiological documentation (using MRI) of a
mesencephalic infarct during life in a case of peduncular hallucinosis.
Even though formed visual hallucinations do not
generally have a strong localizing value, any overt or
subtle signs of a brainstem disorder should be carefully
sought in patients with acute formed visual hallucinations. Radiological confirmation of the brainstem disorder in peduncular hallucinations can be better accomplished by MRI than by CT studies.

We would like to thank Nona C . Flores, PhD, for her editorial
assistance in the preparation of this article.

References
1. Alajouanine T: Usion prorrub6rantielle base d’origine vasculaire et hallucinose. Rev Neurol (Paris) 7690-91, 1944
2. Alajouanine T, Copcevitch M: Hallucinose, prehypnique, automatisme ambulatoire et verbal nocturne, eclipses confusionelles
paroxystiques chez une malade atteinte d’un syndrome parkinsonien postencephalitique, avec syndrome de Parinaud respectant les mouvements automatico-reflexes, et crisis toniques des
membres I? type de crampes vesperales. Rev Neurol (Paris)
501714-718, 1928
3. Bossi L, Nobili M, Benedetto P [Peduncular hallucinosis in a
young woman with vertebrobasilar insufficiency.] Arch Sci Med
(Torino) 137:347-350, 1980
4. Cogan DG: Visual hallucinations as release phenomena. Albrecht Von Graefes Arch Klin Exp Ophthalmol 188:139-150,
1973
5. DeMorsier G: Pathogenie de I’hallucinose pedonculaire. Rev
Neurol 64:606, 1935
6. DeMorsier G Pathogenie de I’hallucinose pedonculaire: ?I propos d‘un nouveau cas. Schweit Med Wochenschr 66:645, 1936
7. Dunn DW, Weisberg LA, Nadell J: Peduncular hallucinations
caused by brainstem compression. Neurology 33: 1360-1 36 1,
1983
8. Lhermitte J: Les fondements anatomo-physiologiques de certaines hallucinations visuelles. Confin Neurol 9:43-57, 1949

Brief Communication: Geller and Bellur: Peduncular Hallucinosis 603

9. Lhermitte J, Bineau R. Les hallucinations visuelles consecutives
a m lesions pedonculaires en foyer. Rev Neurol (Paris) 68327,
1937
10. Lhermitte J, Levy G, TrellesJ: L'hallucinose pedonculaire (etude
anatomique d'un cas). Rev Neurol (Paris) 1:382, 1932
11. Rozanski J: Peduncular hallucinosis following vertebral angiography. Neurology 2:341-349, 1952
12. van Bogaert L L'hallucinose pedonculaire. Rev Neurol (Paris)
47:608-617, 1927

No Sex-Related
Differences in Human
comus callosum
Basid on Magnetic
Resonance Imagery
Jeffrey S. Oppenheim, AB, Benjamin C. P. Lee, MD,
Ruth Nass, MD, and Michael S. Gazzaniga, PhD

Recent studies have reported sex-related differences in
the morphology of the human corpus callosum in
cadaver brains. To further investigate these reports,
sagittal magnetic resonance image scans from 40 male
and 40 female subjects were used to compare callosal
morphology. Relative callosal measurements were calculated by morphometric analysis. Significant sexrelated differences were not found for callosal areas,
maximal callosal width, or callosal curvature. These results indicate the need for further study before claims of
sex-related differences can be accepted.
Oppenheim JS, Lee BCP, Nass R, Gazzaniga MS:
No sex-related differences in human corpus
callosum based on magnetic resonance imagery.
Ann Neurol21:604-606, 1987

spheres have also been reported. Wada and associates
181 found that the left planum temporale-a brain region closely associated .with language skills 1 2 1 4 s
likely to be larger in adult men than in adult women.
Recent interest has focused on morphological sexrelated differences of the corpus callosum. delacosteUtamsing and Holloway [b} reported greater splenial
width and area (the posterior fifth of the callosum), but
not greater callosal length, in 5 female versus 9 male
cadaver brains. In addition, the total cross-sectional
area, although indistinguishable as an absolute value,
was larger in the females when calculated relative to
brain weight.
Witelson {9},who examined 12 male and 2 1 female
cadaver brains, found no sex-related difference in callosal or splenial areas. Consistent with the previous
finding {b],however, fernales had a larger callosal area
only when calculated relative to brain weight. Witelson
also reported that ambid.extrous subjects had a slightly
larger callosal area than those who were right-handed
(0.75 cm2), but this difference was unrelated to sex.
delacoste-Utamsing and Holloway I61 defined the
splenium by dividing the maximal callosal length into
fifths and calculating the area of the most posterior
fifth. They argued that the female splenium is more
bulbous, but offer no quantitative evidence. Alterna
tively, a larger spleniuni might be observed if the callosum had a greater curvature. Since the area subtended by an arc increases with the curvature of the
arc, a callosum with a greater curvature should be subtended by a larger area
The poor replication and uncertain interpretation of
these earlier studies iridicated the need for a larger
study. Magnetic resonance imagery (MRI) offers the
advantage of an in vivo analysis on a larger number of
subjects. In this study, MRI was used to examine callosal morphology for several sex-related differences.

Method
The sagittal images evaluated were produced by a 0.5-T Tes-

Neuropsychological studies suggest that males show
greater cerebral lateralization of language and spatial
skills, whereas females evidence greater bilateralization
of function, particularly for language [ 11. Sex-related
anatomical differences between the cerebral hemi-

From the Division of Cognitive Neuroscience, Department of Neurology, CornelJ University Medical College, New York, NY.

Address correspondence to Dr Gazzaniga, Division of Cognitive
Neuroscience, Cornell University Medical College, 525 E 68th St,
New York, N Y 10021.
Received Aug 29, 1986, and in revised form Oct 27. Accepted for
publication Oct 28, 1986.

Go4

lacon MRI system at the Cornell University Medical Center
(see { 5 ] ) . The subjects, 4 0 men and 40 women, were patients
at the New York Hospital-Cornell Medical Center, and
were suffering from diseases that did not involve either the
cerebral hemispheres or the corpus callosum. The MR images had a nominal in-phase resolution of 1.0 x 1.3 mm,
enabling detailed observation of callosal morphology.
Tracings of the MR images were enlarged, and morphometric area measurements were made using a Zeiss
MOP-3 X,Y image digitizer. The methods of measurement
previously employed [d, 91 were not accurately descrihed;
however, a similar method was estimated. Measured areas
were determined as follows (Figure). A straight line (line A)
was drawn through the most inferior borders of the splenium
and rostrum. From this Line, perpendicular lines were drawn