AJR 2005; 184:1688-1690
© American Roentgen Ray Society
MRI of Susac's Syndrome
Rocky Saenz1,
Albert W. Quan1,
Alvaro Magalhaes2 and
Karl Kish2
1 Department of Radiology, Botsford General Hospital, Michigan State University,
28050 Grand River Ave., Farmington Hills, MI 48336.
2 Department of Radiology, Harper University Hospital, Wayne State University
School of Medicine, Detroit, MI 48202.
Received May 29, 2004;
accepted after revision August 12, 2004.
Address correspondence to A. W. Quan
(aquan{at}botsford.org).
Introduction
Susac's syndrome is an uncommon neurologic disorder of unknown cause. It
has been described as a clinical triad of encephalopathy, hearing loss, and
branch retinal artery occlusions
[1]. Clinically, the diagnosis
is difficult when the patient presents with only a portion of the triad. In
this circumstance, MRI may be crucial in aiding the neurologist to make the
diagnosis. Neuroradiologists and general radiologists frequently attribute the
MRI findings seen in patients with Susac's syndrome to multiple sclerosis or
acute disseminated encephalomyelitis. In this case report, we review the MRI
findings of Susac's syndrome.
Case Report
A 27-year-old woman presented with frontal headaches, bilateral hearing
loss, and visual changes. She complained of difficulty speaking and walking.
Her family reported a recent change in her behavior. They noted mood changes
and inappropriate gestures. She described several bouts of urinary
incontinence in the prior month. There was no medical or surgical history. On
physical examination, mild unsteadiness of gait was observed. The visual
acuity of her left eye was 20/70, and funduscopic examination revealed a
retinal hemorrhage. The right visual acuity was 20/40, and the fundus was
normal. No other neurologic deficits or abnormalities were present.
Laboratory studies were negative for antinuclear antibodies, hepatitis
panel, Epstein-Barr polymerase chain reaction, cardiolipin antibodies, and
herpes infection. CSF analysis was negative for oligoclonal bands and
nonreactive for the Venereal Disease Research Laboratory (VDRL) test.
Electroencephalography revealed moderate slowing with no epileptiform
activity. A gallium scan was negative for adenopathy and for acute
inflammation.
Gadolinium-enhanced MRI was performed next. Multiple foci of increased T2
signal intensity in the periventricular white matter, left middle cerebellar
peduncle, corpus callosum, and right internal capsule were shown (Figs.
1A,
1B,
1C). None of the foci enhanced
after the administration of gadolinium. Diffusion-weighted images showed
increased signal in the right internal capsule. Because the apparent diffusion
coefficient (ADC) map was normal, this finding was attributed to T2
"shine-through." Sagittal and coronal FLAIR images also showed
areas of increased signal that corresponded to areas of T2 signal change. In
the corpus callosum, multiple lesions of mixed signal intensity on FLAIR
sequences were identified (Fig.
1D).
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Fig. 1A. —27-year-old woman with Susac's syndrome. Sagittal T1-weighted
image (TR/TE, 500/14; flip angle, 90°) shows multiple round hypointense
lesions centrally located in corpus callosum. These lesions are characteristic
of Susac's syndrome.
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These findings were interpreted as representative of Marburg's variant of
multiple sclerosis or CNS vasculitis. One month later, our patient underwent
MRI-guided stereotactic brain biopsy. Six separate specimens were obtained
from the white matter of the right frontal lobe. The pathologist's
interpretation was white matter reactive glial changes with evidence of
degeneration. The white matter was well myelinated on Luxol fast blue stain
and periodic acid–Schiff stain. The axon density was normal with the
Bodian method. No definitive evidence of demyelination or neoplasm was found.
Electron microscopy showed no viral particles.
The patient's symptoms improved after plasma exchange but did not improve
with steroids. A second MRI examination with gadolinium enhancement was
performed 4 months after the initial study. Again shown were multiple
periventricular white matter lesions of high signal intensity on T2-weighted
and FLAIR sequences (Figs. 1G,
1H,
1I,
1J). The right internal
capsule lesion had resolved. The posterior fossa lesions were diminished.
Multiple lesions in the body and splenium of the corpus callosum were of
increased signal intensity on T2-weighted images and decreased signal on
T1-weighted images. None of the lesions enhanced with gadolinium, and they
were essentially unchanged. These well-demarcated callosal changes had a
"punched-out" appearance (Figs.
1A and
1G). They were centrally
located within the corpus callosum fiber tracts and were similar in appearance
compared with their appearance on the initial examination.
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Fig. 1G. —27-year-old woman with Susac's syndrome. Images of follow-up
studies obtained 4 months after A–F. Sagittal T1-weighted
(G) (500/14), sagittal T2-weighted (H) (4,020/98), and sagittal
FLAIR image (I) (9,000/76; inversion time, 2,500 msec; flip angle,
130°) images again show the characteristic "punched out"
callosal lesions of Susac's syndrome.
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Fig. 1H. —27-year-old woman with Susac's syndrome. Images of follow-up
studies obtained 4 months after A–F. Sagittal T1-weighted
(G) (500/14), sagittal T2-weighted (H) (4,020/98), and sagittal
FLAIR image (I) (9,000/76; inversion time, 2,500 msec; flip angle,
130°) images again show the characteristic "punched out"
callosal lesions of Susac's syndrome.
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Fig. 1I. —27-year-old woman with Susac's syndrome. Images of follow-up
studies obtained 4 months after A–F. Sagittal T1-weighted
(G) (500/14), sagittal T2-weighted (H) (4,020/98), and sagittal
FLAIR image (I) (9,000/76; inversion time, 2,500 msec; flip angle,
130°) images again show the characteristic "punched out"
callosal lesions of Susac's syndrome.
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Fig. 1J. —27-year-old woman with Susac's syndrome. Images of follow-up
studies obtained 4 months after A–F. Sagittal T1-weighted image
(TR/TE, 500/14) left of midline more clearly shows two cerebellar lesions;
these lesions are not significantly changed on this examination compared with
initial MRI examination (C).
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Discussion
Susac's syndrome was first described in 1979
[1,
2]. This syndrome has also been
referred to as "SICRET syndrome" (small infarctions of cochlear,
retinal, and encephalic tissue) or "RED-M" (microangiopathy with
retinopathy, encephalopathy, and deafness)
[1]. It involves a clinical
triad that includes encephalopathy, retinal arterial branch occlusions, and
bilateral hearing loss
[1–6].
The exact cause is unknown, but it is believed to be an immune response with
microembolization [1,
2].
Susac's syndrome is seen most commonly in young women 20–40 years old
[1–6].
Multiple cases have been reported in men
[1,
3]. This entity has also been
described in the Japanese-, Chinese-, French-, German-, Spanish-, and
English-language literature
[1–6].
Therefore, Susac's syndrome occurs in all races.
The encephalopathic changes can manifest as memory impairment, confusion,
behavioral disturbances, ataxia, dysarthria, paranoid psychosis, occasional
mutism, and headaches
[1–6].
The optic changes include scotomata and vision distortion that are due to
branch retinal artery occlusions
[1–6].
Retinal irregularities may be seen on ophthalmoscopy examination or
fluorescein angiography [2].
Cochleovestibular symptoms involve hearing loss at low and medium frequencies
[1,
2,
4]. Of all these symptoms,
headaches with encephalopathy are the most common presentation
[2]. The classic triad is
pathognomonic for Susac's syndrome, but the three elements are not always
present at the same time
[1].
Most case reports and articles concerning Susac's syndrome have been
published in the neurology, otorhinolaryngology, and ophthalmology literature
[2–6].
In 2003, Susac et al. [1]
reported the largest series of cases, and the 27 MRI studies reviewed showed
characteristic changes within the corpus callosum. These changes consisted of
small well-demarcated, spherical, high-signal-intensity lesions located in the
body and splenium of the corpus callosum on FLAIR and T2 sequences
[1]. The lesions had a
punched-out appearance and were located centrally within the fiber tracts of
the corpus callosum. Susac et al.
[1] attributed these lesions to
microinfarctions. They, along with other researchers, have reported that the
MRI findings are commonly confused with demyelinating processes, typically
multiple sclerosis or acute disseminated encephalomyelitis
[1,
3,
4]. However, in multiple
sclerosis the ependymal undersurface of the corpus callosum is usually
involved and callosal atrophy is usually seen
[1,
7].
Callosal lesions located centrally within the fiber tracts without callosal
atrophy, therefore, are highly suggestive of Susac's syndrome. In addition,
high-signal-intensity changes are usually seen in the periventricular white
matter and the deep gray matter
[1]. Contrast enhancement of
the white matter, gray matter, and leptomeninges may be seen, of which the
latter is the least common
[1].
During the preparation of this article, two other articles regarding
Susac's syndrome were published. In the first article, Do et al.
[8] reported another four
cases, but lesions in the corpus callosum were not seen in those cases. In the
second article, White et al.
[9] retrospectively reviewed
the diffusion-weighted images and ADC findings of serial MRI studies. Their
conclusion was that Susac's syndrome may show increased signal intensity on
diffusion-weighted imaging, depending on the time of patient presentation. In
our patient, no diffusion-weighted images or ADC abnormalities were present
with regard to the corpus or other white matter structures (Figs.
1E and
1F).
Although Susac's syndrome is usually selflimited and may stabilize, it can
also lead to complete deafness and blindness
[1–3].
If multiple sclerosis is suspected and only corticosteroids are administered,
the disease may progress. If Susac's syndrome is suspected, immunosuppressive
or antithrombotic agents (or both) should be considered as part of the
treatment regimen [2].
In conclusion, in patients who present without the classic triad of Susac's
syndrome, MRI may aid the clinician in establishing the correct diagnosis.
Because treatment plans differ from those for demyelinating diseases, it is
important for the radiologist to be aware of this entity. Thus, radiologists
should include Susac's syndrome in the differential diagnosis when punched-out
high-signal-intensity lesions are present within the central fibers of the
corpus callosum on T2-weighted images.
Acknowledgments
We thank the following physicians for contributing to this article: Robert
P. Lisak, Richard Lewis, Gregory Van Stavern, and Ramesh Madhavan from the
department of neurology; and William Kupsky from the department of pathology,
Wayne State University School of Medicine.
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- Ayache D, Plouin-Gaudon I, Bakouche P, Elbaz P, Gout O.
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Introduction
Case Report
