Teaching neuroimages: MRI "target sign" and neurofibromatosis type 1.

A 9-year-old girl presented with a firm occipital swelling. She had multiple café-au-lait lesions without other clinical features or family history of neurofibromatosis type 1 (NF1). MRI showed subcutaneous soft tissue mass in the left occipitotemporal region with “target sign” suggestive of plexiform neurofibroma (figure 1). There were supra and infratentorial T2-weighted hyperintense lesions, so-called unidentified bright objects characteristic of NF1 (figure 2). MRI target sign helped to confirm plexiform neurofibroma which is one of the clinical criteria for the diagnosis of NF1.1 Target sign in plexiform neurofibroma is due to central fibrocollagenous core (T2-hypointense) surrounded by myxomatous tissue (T2-hyperintense).2