Neurofibromatosis, Type 1 (NF1)

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Diagnosis Definition

NF1 is the most common neurocutaneous disorder (phakomatosis)
It is an autosomal dominant mutation of the neurofibromin gene, which is a tumor suppressor gene of the RAS/MAPK pathway, referred to as a rasopathy
The diagnosis of NF1 is clinical and criterion-based

Imaging Findings

On MRI, NF1 presents as areas of high signal on T2/FLAIR sequences in the deep white matter and basal ganglia; these areas represent myelin vacuolation that don’t enhance and often resolve during the second decade
Optic pathway gliomas are associated with NF1 and are best seen on thin-section fluid sensitive sequences (such as CISS or SPACE); they typically present as fusiform enlargement of parts of the optic pathways; they may enhance and be accompanied by tortuosity of the nerve and dilatation of the optic nerve sheath
Buphthalmos (enlargement of the globe) can result from increased intraocular pressure
Greater sphenoid wing dysplasia may be seen, best on CT, but also on MRI as dark signal cortical enlargement; this feature can result from neurofibromas or CSF pulsation
Plexiform neurofibromas are STIR/T2 FS hyperintense fusiform and nodular masses along the course of nerves, often seen coalescing along the brachial, lumbar plexi and various cranial nerves
Dural ectasia, a result of cerebrospinal fluid (CSF) pulsation, is seen on T2 sequences as outpouching of high signal CSF into the neural foramina and scalloping of the vertebral bodies

Pearls

Another manifestation of NF1 in the brain is moyamoya disease, which is caused by blocked arteries at the base of the brain; the name moyamoya means “puff of smoke” in Japanese and describes the appearance of tiny vessels that form to compensate for the blockage
Plexiform neurofibromas may undergo malignant degeneration and surveillance imaging is performed to monitor for new enhancement or growth

References

Ferner RE, Huson SM, Thomas N, et al. Guidelines for the diagnosis and management of individuals with neurofibromatosis 1. Journal of Medical Genetics 2007; 44(2):81-88
Van Meerbeeck S, Verstraete K, Janssens S, Mortier G. Whole body MR imaging in neurofibromatosis type 1. European Journal of Radiology 2009; 69(2):236-242

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