Introduction: MRI of the brain in children with NF1 may show areas of increased T2 – weighted signal intensity called UBOs present in 43% up to 92% of the cases. As UBOs are almost constantly observed at an age in which all signs of the disease are not present, they are of great interest for the diagnosis.

Objetives: To investigate the frequency and location of UBOs in patients with NF1.

Materials and methods: Observational retrospective study. Brain MRIs of 83 patients aged 0 to 21 years were included. 43 suffered from NF1 and 40 had a MRI performed at the hospital for any other condition unrelated to NF1.

Results: UBOs were identified in 53% of patients with NF1and in 67% of the children between 4-12 years old. No patient aged 0-3 years nor controls presented UBOs. Cerebellum and globus pallidum were the predominant affected areas (35% and 33% respectively) The sensitivity of the presence of UBOs was 53% with a false negative rate of 47%,a specificity of 100% and a false positive rate of 0%.

Conclutions: When diagnostic criteria for NF1 are not fully present -especially in children aged 4 to 12 years- high frequency and specificity of UBOS identified by MRI can be used as a complementary diagnostic tool.