Neuroradiological changes in neurocutaneous diseases: I. neurofibromatosis

Abstract

In current neurological evaluation of numerous neurocutaneous syndromes (facomatosis) there is routine utilization of computerized tomopgraphy (CT) and magnetic resonance imaging (MRI). From neoplastic lesions in neurofibromatosis type I (NF1) the most common are optic nerve gliomas, other gliomas of the brain and medula oblongata, plexiform neurofibromas and neurofibrosarcomas. Non-neoplastic lesions are hyperplastic or dysplastic glial proliferation – hamartomas, heterotopias and areas of dysmyelinization. CT signs of optic gliomas are hyperdense spindle-shaped masses attached to the optic nerve, from which they cannot be distinguished, with slight imbibition of contrast and without compression signs. When there is involvement of the hiasma, hypotalamus, thalamus or basal ganglia, the compressive effect can be evident, giving us the impression of real tumors and imbibition can be also accentuated. On native imaging these tumors are hyperdense. MRI reveals a high signal of nodosal appearance in the above mentioned localizations in T2 and FLAIR imaging and hypo or isointensive signal on T1. Hamartomas can be seen as higher signals on T2, slightly higher signals on T1 without signs of compression. In about 43%-93% of patients with NF1 there are so called UBO (Unidentified Bright Objects) lesions on MRI- hyperintensive signals on FLAIR and T2 weighted pictures, exclusively in the white matter without imbibition after contract. Acustic neurinomas in neurofibromatosis type 2 (NF2) show the same features on CT as neurinomas in any other localization. Vestibular neurinomas on MRI are hypo or isointensive on T1 and hyperintensive on T2-weighted pictures. Heterogenous imbibition is present because of cystic and degenerative changes inside the tumor and they can be easily distinguished from meningeomas showing homogenous imbibition. Meningeomas can have calcifications or prominent blood vessels and dura thickening, as common signs of meningeomas. They are isointensive with the grey matter of the brain on T2 and slightly hypointensive on T1-weighted brain MRI.