Background: "Unidentified bright objects" (UBOs) have been observed as areas of increased T2-weighted signal intensity on MRI in 43% to 93% of children with neurofibromatosis 1 (NF1). Because of this high frequency and the fact that the NIH diagnostic criteria often do not permit diagnosis of NF1 in early childhood, UBOs have been proposed as an additional diagnostic criterion.

Methods: The authors examined the sensitivity and specificity of UBOs for NF1 in 19 affected children and 19 age-matched controls. Eleven of the control patients had CNS pathology that might be classified as UBOs on MRI scan. The authors measured the agreement in recognition of UBOs between two pediatric neuroradiologists who independently examined the MRI studies of these patients. They also assessed the effect of adding UBOs to the NIH diagnostic criteria on ability to diagnose NF1 in young patients.

Results: Sensitivity and specificity of UBOs for NF1 averaged 97% and 79%, respectively. Agreement between the two radiologists was 84% overall, but varied greatly from one brain region to another. Adding UBOs as a diagnostic criterion permitted the diagnosis of 30% of young patients with NF1 mutations who do not meet the existing NIH diagnostic criteria for NF1. The value of including UBOs is less in older patients because a larger proportion of them meet the existing diagnostic criteria.

Conclusions: UBOs are difficult to identify with certainty and occur in children with suspected CNS disorders who do not have NF1, but they tend to occur in different brain regions. UBOs may be more useful for diagnosis of NF1 in young children if they can be defined precisely and if only the cerebellum, brainstem, and basal ganglia are considered.