Magnetic resonance imaging in acute optic neuritis in Singapore

<p><b>INTRODUCTION</b>The Optic Neuritis Treatment Trial (ONTT) has established that the magnetic resonance imaging (MRI) findings at the time of presentation of optic neuritis (ON) is the strongest indicator of the development of multiple sclerosis (MS). Reports from Singapore as well as other Asian countries have indicated that these abnormalities are less frequently encountered compared to that reported by the ONTT. This paper aims to describe systematically the brain MRI as well as the optic nerve abnormalities in patients after an episode of acute optic neuritis.</p><p><b>MATERIALS AND METHODS</b>Patients who presented with acute optic neuritis were retrieved from our prospective optic neuritis study and their MRI scans were reviewed and graded in accordance with the standardised classification employed in the ONTT.</p><p><b>RESULTS</b>Fifteen of 24 patients had MRI brain and optic nerves performed during the acute episode. In the evaluation of brain abnormalities, 40% were classified as grade 0, 20% grade I, 20% grade II, 6.7% grade III and 13.3% grade IV. Optic nerve abnormalities were observed in 80% of cases. At study entry, 10 patients had idiopathic (monosymptomatic) ON, 3 had multiple sclerosis (MS), one each with infective and autoimmune optic neuritis, respectively. The single patient who developed MS at study completion presented with grade II brain abnormalities at the initial MRI. For those with idiopathic ON, our study revealed a higher percentage of grade 0-I brain changes as well as a lower lesion load compared to the ONTT.Lesion Load and grade was also lower in anterior optic neuritis compared with retrobulbar disease.</p><p><b>CONCLUSION</b>Our study revealed a lower percentage of grade II-IV brain MRI abnormalities as well as less lesion load in idiopathic ON compared to the ONTT. This may be related to the lower prevalence of MS in our predominantly Asian population. As diagnostic tests and understanding of neuromyelitis optica or Devic's disease improves, we may see more patients being diagnosed with this condition, which may also explain our findings. Our data also showed that MRI grade and lesion load in cases of anterior ON was lower than for retrobulbar disease. MRI in ON has an essential role in characterising the disease, evaluating for associated brain lesions, and assessing prognosis in retrobulbar disease but may be less useful in anterior disease.</p>

Superior sagittal sinus thrombosis: subtle signs on neuroimaging

<p><b>INTRODUCTION</b>The aim of this study was to review the clinical, computed tomography (CT) and magnetic resonance imaging (MRI) diagnosis and the frequency of positive neuroimaging findings in patients with cerebral venous thrombosis (CVT) involving the superior sagittal sinus.</p><p><b>MATERIALS AND METHODS</b>A clinical and radiological database of patients with final diagnosis of CVT was compiled from the inpatient hospital information service of a tertiary neurological hospital over 5 years. CT and MRI studies in 22 patients were retrospectively examined for direct signs of venous sinus thrombosis and for complications of CVT. The diagnosis of CVT before and after CT and MRI was reviewed.</p><p><b>RESULTS</b>Clinical diagnosis of possible CVT was suspected in only 1 patient. When the diagnosis was not suspected, CT diagnosis was difficult and there was a high false negative rate of 52.6%. MRI fared better, but the false negative rate was still 11%. Directs signs of venous sinus thrombosis such as the triangle sign, empty delta sign on CT and loss of the normal flow voids on MRI, could be retrospectively detected in 57.9%, 100% and 100% of patients respectively. Although 4 patients presented with subarachnoid haemorrhage, these direct signs were present in 3 patients.</p><p><b>CONCLUSION</b>Clinical diagnosis of CVT is rarely suspected before CT and MRI, and although subtle positive signs are often present, these may not be appreciated unless there is a high index of suspicion or image review at multidisciplinary team meetings.</p>