Specific Imaging Findings

Unidentified bright objects (UBOs) are the most common intracranial lesions in patients with neurofibromatosis type 1 (NF1), occurring in about two-thirds of the patients. They typically appear as hyperintense foci on long repetition time (T2-weighted, FLAIR, PD) MR images and iso- to mildly hypointense on T1-weighted images; sometimes they show slight T1 shortening, which has been related to myelin clumping or microcalcification. Mass effect, vasogenic edema, and contrast enhancement are characteristically absent. These lesions typically appear at around 3 years of age, increase in number and size until 10–12 years, and then tend to spontaneously decrease in size and number, or even completely disappear. They are typically multiple and most commonly involve the white matter and basal ganglia (especially the globi pallidi), usually in a bilateral asymmetric fashion. Other common locations include the middle cerebellar peduncles, cerebellar hemispheres, brainstem, internal capsule, splenium of the corpus callosum, and hippocampi. MRS performed within these lesions may be normal or show slightly decreased NAA and increased choline levels.

Pertinent Clinical Information

The correlation between the presence and extent of UBOs and the cognitive deficit or learning disability is still controversial. It has been suggested that the anatomic location of neurofibromatosis bright objects (NBOs) is more important than their presence or number. It seems that thalamic NBOs are in particular significantly associated with neuropsychological impairment. A patient with NF1 may present other CNS lesions (optic pathway tumors and other brain and/or spine low-grade gliomas), skin lesions (café-au-lait spotzs, axillary and inguinal freckling and cutaneous neurofibromas), ocular Lisch nodules and skeletal and skull manifestations (kyphoscoliosis, overgrowth or undergrowth of bone, erosive defects due to neurofibromas, pseudoarthrosis of the tibia and dysplasia of the greater sphenoidal wing).