Susac syndrome: serial diffusion-weighted MR imaging

Diagnostic Criteria and Treatment Algorithm for Susac Syndrome

BACKGROUND

Susac syndrome (SS) classically presents with the clinical triad of retinal artery occlusion, sensorineural hearing loss, and encephalopathy and the neuroimaging triad of white matter lesions, deep gray matter lesions, and leptomeningeal disease. However, patients can present with an incomplete clinical or neuroimaging triads making diagnosis difficult in certain situations. A standard treatment paradigm also is lacking in this illness. It is important for neuro-ophthalmologists to recognize clinical and radiographic findings that are pathognomonic for this syndrome and have a basic understanding of the available treatment options.

EVIDENCE ACQUISITION

Review of medical literature.

RESULTS

A definite diagnosis of SS is made when the clinical triad or the neuroimaging triad is present. There are numerous reports of 2 other imaging findings in this condition: arteriolar wall hyperfluorescence (AWH) on fluorescein angiography in retinal arterioles remote from retinal ischemia and central callosal lesions on MRI. Both of these imaging findings are diagnostic of SS. Gass plaques in retinal arterioles are almost always seen in the acute phase of the illness but are not pathognomonic for SS. The most common medications used in this syndrome are corticosteroids and intravenous immunoglobulin. A number of other medications have been used including mycopheolate, rituximab, azathioprine, and cyclophosphamide.

CONCLUSIONS

In the absence of the clinical triad or magnetic resonance imaging triad for SS, AWH remote from retinal vascular injury and central callosal lesions are confirmatory of the diagnosis because they have never been described in any other condition. The presence of Gass plaques in retinal arterioles should strongly suggest the diagnosis. Despite the lack of clinical trial data, patients with SS must be treated promptly and aggressively. In more fulminant cases, addition of mycophenolate mofetil or rituximab is required, followed by cyclophosphamide when disease is refractory to other medications.

The splenium of the corpus callosum: embryology, anatomy, function and imaging with pathophysiological hypothesis

BACKGROUND AND PURPOSE

The splenium of the corpus callosum is the most posterior part of the corpus callosum. Its embryological development, anatomy, vascularization, function, imaging of pathology, possible pathophysiological mechanisms by which pathology may develop and the clinical consequences are discussed.

METHODS

A literature-based description is provided on development, anatomy and function. MR and CT images are used to demonstrate pathology. The majority of pathology, known to affect the splenium, and the clinical effects are described in three subsections: (A) limited to the splenium, with elaboration on pathophysiology of reversible splenial lesions, (B) pathology in the cerebral white matter extending into or deriving from the splenium, with special emphasis on tumors, and (C) splenial involvement in generalized conditions affecting the entire brain, with a hypothesis for pathophysiological mechanisms for the different diseases.

RESULTS

The development of the splenium is preceded by the formation of the hippocampal commissure. It is bordered by the falx and the tentorium and is perfused by the anterior and posterior circulation. It contains different caliber axonal fibers and the most compact area of callosal glial cells. These findings may explain the affinity of specific forms of pathology for this region. The fibers interconnect the temporal and occipital regions of both hemispheres reciprocally and are important in language, visuospatial information transfer and behavior. Acquired pathology may lead to changes in consciousness.

CONCLUSION

The development, location, fiber composition and vascularization of the splenium make it vulnerable to specific pathological processes. It appears to play an important role in consciousness.

Diagnosis and classification of Susac syndrome

Susac syndrome (SS) is an autoimmune disease characterized by the clinical triad of encephalopathy, branch retinal artery occlusions and neuro-sensorial hearing loss; it is due to a microangiopathy affecting the precapillary arterioles of the brain, retina and inner ear. SS is characterized by typical radiological features on magnetic resonance imaging (MRI) which, together with clinical symptoms, may permit a diagnosis. Branch retinal artery occlusions (BRAOs) are best evaluated using fluorescein angiography (FA) which may show the typical multifocal fluorescence. SS is an autoimmune endotheliopathy that requires treatment with immunosuppressive agents: steroids, azathioprine, mycophenolate mofetil, methotrexate, cyclophosphamide and intravenous immunoglobulin, usually in combination. Plasma exchange is also useful. In addition, antiplatelet agents may be a useful adjunct. Correct immunosuppressive therapy results in significant clinical and radiological improvement. An early diagnosis and treatment are important to delay the disease progression and prevent permanent disability.

Susac syndrome: an organ-specific autoimmune endotheliopathy syndrome associated with anti-endothelial cell antibodies

Susac syndrome (SS) is the triad of encephalopathy, branch retinal artery occlusions (BRAOs), and hearing loss. Migraines may herald and accompany encephalopathy. Little is known about pathogenesis. Based on light microscopic findings in brain biopsy material analogous to anti-endothelial cell antibody (AECA)-mediated microvascular injury, we postulated that SS microangiopathy was attributable to AECAs. We examined serum samples from 11 patients with SS for AECAs; 9 were positive by indirect immunofluorescence and Western blot studies. A highly distinctive band on Western blots corresponding to a 50-kDa protein was observed in 8 positive SS samples; the other positive case exhibited specific reactivity with a protein band at 40 kDa. Of the 2 negative cases, 1 had been inactive since 1988; the other was an abortive variant characterized solely by BRAOs. There was enhanced surface binding of SS serum using live endothelial cell substrates compared with samples from healthy subjects. Additional serum samples from apparently healthy patients, 2 with atypical migraines, and patients with other forms of autoinflammatory disease did not show the distinctive band of immunoreactivity. SS is a distinct autoimmune endotheliopathy syndrome associated with AECAs; the antibody target seems specific in many cases and may be a disease biomarker. The exact role of AECAs in disease propagation remains unanswered.

Long-term outcome in Susac syndrome

Susac syndrome is characterized by the clinical triad of encephalopathy, hearing loss, and retinal artery branch occlusions, mostly in young women. To our knowledge, long-term outcome and impact of pregnancy have not been specifically addressed. We report a series of 9 patients (7 female, 2 male) followed at the same institution, with special emphasis on clinical outcome including pregnancy and long-term sequelae. Clinical, brain magnetic resonance imaging (MRI), funduscopy, retinal angiography, and audiogram data were recorded every 3-12 months. We also analyzed the 92 previously reported cases of Susac syndrome. Mean follow-up was 6.4 years. Age at onset was 30.4 years. The first symptom occurred between April and September in 7 of 9 patients in the current study, and in 68% of all patients. The complete triad at onset was clinically obvious in only 1 of 9 patients. Brain involvement was heralded by headache and symptoms of encephalopathy. Cerebrospinal fluid was abnormal in 5 patients showing pleocytosis (mean, 24.6; range, 6-85 cells/mL) and elevated protein level (mean, 210; range, 113-365 mg/dL). Over time, quantitative brain MRI analysis showed that the number of lesions diminished and did not parallel clinical flares, and MRI never normalized. At the end of follow-up, no patient had severe impairment, and all but 1 returned to work. Inner ear involvement was present at onset in 2 patients and occurred in others with a mean delay of 11 months. Initially unilateral in 3, it became bilateral in all. Mean hearing loss was 34 dB (range, 15-70 dB). Hearing loss never improved, either spontaneously or under treatment. The eye was involved at onset in 8 patients, and after 3 years in 1. All had multiple bilateral retinal artery branch occlusions and/or dye leakage with hyperfluorescence of the arterial wall on fluorescein angiography. Over time, angiography normalized in 3 patients. In others, it was still abnormal at the end of follow-up (range, 1.5-10 yr). On late findings, fluorescein leakage was more frequent than true arterial occlusion. Eye involvement was mostly asymptomatic, unilateral, peripheral, and resumed spontaneously to remit in other sites over time. Corticosteroids were efficient to treat encephalopathy, with relapses occurring when the dosage was tapered. Steroid treatment did not improve hearing loss or prevent new retinal arteriolar occlusions. Anticoagulation had a role in treating encephalopathy and retinal arteriolar occlusions. Three patients had 4 pregnancies. Two pregnancies needed induced abortion. One pregnancy was uneventful. One pregnancy was complicated with Susac disease flare in the early postpartum period. In conclusion, at the end of follow-up, most patients had returned to work and none had severe impairment. Pregnancy may affect the course of Susac syndrome, with relapse of encephalopathy postpartum. Our main finding was that the course of Susac syndrome is not self-limited as previously thought, since isolated retinal arteriolar involvement may occur as a very late manifestation.

Cerebral small vessel diseases: manifestations in young women

PURPOSE OF REVIEW

Cerebral small vessel diseases are responsible for 20-30% of ischemic strokes as well as for a considerable proportion of cerebral hemorrhages and encephalopathies. Less known than the manifestations in old age are those in young women comprising posterior encephalopathy and Susac's syndrome.

RECENT FINDINGS

Magnetic resonance imaging has allowed us to identify posterior encephalopathy, characterized by headache, seizures, visual disturbances and hypertension, as a frequent complication of preeclampsia/eclampsia syndrome in the perinatal and postpartum period. Magnetic resonance findings are pathognomonic with bilateral cortical-subcortical lesions in the posterior hemispheres typically sparing the calcarine fissure. Conversely, white matter lesions on magnetic resonance imaging particularly involving the corpus callosum, and a (subclinical) sensorineural hearing loss are diagnostic of the retinocochleocerebral vasculopathy called Susac's syndrome.

SUMMARY

Posterior encephalopathy can also follow from a broad spectrum of endotheliotoxic conditions like chemotherapy, immunosuppression and sepsis. Early recognition of the disorder is decisive for a benign outcome since therapy consists of removal of precipitating factors, lowering of blood pressure and treatment with magnesium sulfate. The retinocochleocerebral vasculopathy appears to be underdiagnosed. An autoimmune-mediated arteriolopathy is presumed and the disease is nearly always monophasic. A variety of therapeutic approaches have been recommended, none of which, however, is based on anything other than anecdotal evidence.

Update on Susac's syndrome

PURPOSE OF VIEW: We review recent developments in the clinical course and imaging modalities for Susac's syndrome, a clinical triad consisting of encephalopathy, branch retinal artery occlusions and sensorineural hearing loss.

RECENT FINDINGS

Susac's syndrome has variable clinical presentations; recently described presentations include epileptic seizures and transient inverted vision. Advances in neuroradiology suggest that magnetic resonance imaging demonstrates distinctive patterns in the white and grey matter and in the leptomeninges. Reports have verified that Susac's syndrome is under-diagnosed because of its multisystem involvement and confusion with other imitating disorders (such as multiple sclerosis), and because of the fact that neuroradiologists are not acquainted with this syndrome.

SUMMARY

The precise aetiology of Susac's syndrome is still unknown and many areas have not yet been explored. Magnetic resonance imaging is the neuroimaging study of choice. Findings include multiple small hyperintense foci on T2-weighted images and contrast enhancement in white and grey matter of both supratentorial and infratentorial structures, corpus callosum and, occasionally, leptomeninges. Callosal lesions typically involve the central fibres and are probably pathognomonic for Susac's syndrome. When assessing patients with unexplained encephalopathy involving white and grey matter, leptomeninges and corpus callosum, the findings of sensorinueral hearing loss or visual disturbances may yield important clues regarding the possibility of Susac's syndrome.