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Neurofibromatosis Type 1 (NF1)

Last Updated: October 1, 2018

Open Table of Contents: Neurofibromatosis Type 1 (NF1)

Figure 1: Though associated with many tumors, these NF lesions are merely tumor mimics. Notice the FLAIR-hyperintense (left) nonenhancing (right) abnormalities within the globus pallidi and to a lesser extent the dorsal thalami - compatible with focal areas of signal intensity (FASI). These regions can be seen in the basal ganglia, thalami, brainstem, cerebellum, or subcortical white matter.

Figure 1: Though associated with many tumors, these NF lesions are merely tumor mimics. Notice the FLAIR-hyperintense (left) nonenhancing (right) abnormalities within the globus pallidi and to a lesser extent the dorsal thalami - compatible with focal areas of signal intensity (FASI). These regions can be seen in the basal ganglia, thalami, brainstem, cerebellum, or subcortical white matter.

Figure 2: Axial FLAIR images through the basal ganglia (top row left) and pons (top row right) demonstrate expansile hyperintense lesions most compatible with NF dysplasias, a tumor mimic. Low grade tumors may also be present in NF 1, including optic nerve glioma seen as right greater than left optic nerve enlargement on coronal T2FS (bottom row left) and sagittal T1 post-contrast (bottom row right) images.

Figure 2: Axial FLAIR images through the basal ganglia (top row left) and pons (top row right) demonstrate expansile hyperintense lesions most compatible with NF dysplasias, a tumor mimic. Low grade tumors may also be present in NF 1, including optic nerve glioma seen as right greater than left optic nerve enlargement on coronal T2FS (bottom row left) and sagittal T1 post-contrast (bottom row right) images.

Description

  • Multisystem neurocutaneous disorder with variable expression but 100% penetrance
  • Most common phakomatosis, occurring in 1 out of 2,000 live births
  • 50% are inherited as an autosomal dominant condition, while the other 50% are a result of a new mutation

Pathology

  • NF1 gene locus on chromosome 17q11.2
  • Gene product is neurofibromin 1, which normally functions as a tumor suppressor

Clinical Features

  • Symptoms
    • Highly variable
    • Diagnosis requires 2 or more of the following
      • > 6 café au lait spots
      • 2 or more neurofibromas
      • 1 plexiform neurofibroma
      • Optic nerve glioma​
      • Sphenoid wing dysplasia
      • Lisch nodules
      • Axillary or inguinal freckles
      • Primary relative with NF1​
    • Often have associated learning disabilities
  • Age
    • 50% meet the criteria by 1 year of age
    • 95% meet the criteria by 8 year of age
  • Gender
    • No gender predilection

Imaging

  • Findings highly variable with multisystem involvement
  • CNS findings
    • Optic Nerve Glioma
      • CT
        • Fusiform or exophytic enlargement and enhancement with associated kinking or buckling
      • MR
        • T1WI
          • Hypo- to isointense enlargement
        • T2WI
          • Hyperintense centrally, hypointense along the periphery
        • Contrast
          • Variable enhancement
    • Focal areas of signal intensity (FASI)
      • Identified in the basal ganglia, thalamus, brainstem, cerebellum and subcortical white matter. No associated mass effect
      • Usually resolve or decrease with age
      • CT
        • Normal
      • MR
        • T1WI
          • Iso- to slightly hyperintense
        • T2WI
          • Hyperintense
        • Enhancement
          • None
      • MR Spectroscopy
        • Usually normal
    • Sphenoid wing dysplasia
      • Can be isolated or associated with underlying plexiform neurofibroma
      • CT is the most effective imaging modality
    • Moyamoya
      • A rare finding in NF1
      • CT
        • Atrophy most notable anteriorly
        • May have associated hemorrhage
      • CT Angiogram
        • Attenuated, abnormal circle of willis with net-like collaterals
      • MR
        • T1WI
          • Multiple dot-like flow voids in the basal ganglia
        • T2WI
          • Hyperintense lacunar infarcts
        • T2*/SWI/GRE
          • Hypointense signal if prior hemorrhage
        • DWI
          • Reduced diffusivity in regions of acute infarction
        • Contrast
          • Enhancing dots in basal ganglia with associated leptomeningeal enhancement
  • Imaging Recommendations
    • MR brain and orbits with contrast
  • Mimic
    • Many tumor types are present in NF1 (optic gliomas, neurofibromas). FASI are not true neoplasms and are usually easily distinguished from neoplasms by their typical locations, signal intensities and tendency to involute over time.

For more information, please see the corresponding chapter in Radiopaedia.

Contributor: Sean Dodson, MD; Jacob A. Eitel, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.02.20

References

Aoki S, et al. Neurofibromatosis types 1 and 2: cranial MR findings. Radiology. 1989; 172(2):527-34.

Fortman BJ, et al. Neurofibromatosis Type 1: A Diagnostic Mimicker at CT. Radiographics. 2001; 21:601-12.

Van Es S, et al. MRI Findings in Children with Neurofibromatosis Type 1: A Prospective Study. Pediatr Radiol. 1996; 26:478-87.

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