The open-ring sign.

A 12-year-old boy presented to us with subacute onset of progressive quadriparesis and blurring of vision in the right eye. His sensorium was normal. There was hyper-reflexia and spasticity in all four limbs and the plantar reflex was bilaterally extensor. Vision in the right eye was 6/18. The fundus examination was normal. Cerebrospinal fluid revealed normal sugar, normal cells with raised proteins (80 mg%) and raised IgG levels. His visual evoked potential study showed a delayed P100 peak of 130 ms in the right eye. The computer tomography (CT) scans showed bifrontoparietal ring-enhancing lesions with central hypodensity [Figure 1]. On magnetic resonance imaging (MRI), the lesions were hypointense on the T1WI [Figure 2], hyperintense on the T2WI [Figure 3] and showed incomplete ring enhancement on the postcontrast study [Figure 4]. The ring was complete towards the white matter and broken towards the cortex. This gave the appearance of an open ring – the ‘open-ring sign.’ The patient was started on intravenous methyl-prednisone and showed rapid recovery. To the best of our knowledge, only two such reports have described this sign so far.