Focal areas of signal intensity (brain)

Focal areas of signal intensity (FASI), alternatively called focal abnormal signal intensity or unidentified bright objects, are bright areas on T2-weighted images commonly identified in the basal ganglia (often the globus pallidus), thalamus, brainstem (pons), cerebellum, and subcortical white matter. 

FASI areas are the most common neuroimaging feature in neurofibromatosis type 1 (NF1) patients 1. A study showed a significant frequency (86%) of one or more FASI areas in children with NF1 2

There is considerable debate about its real role within the NF1 spectrum and its potential relationship with cognitive dysfunction 3.  The association between these focal areas of high signal and cognitive deficits remains controversial, wherein recent studies have found a favorable relationship with the presence, number and location of FASI areas 3-6. However, only the thalamic lesions seem to be strongly associated with cognitive impairment 3-5

DiPaolo et al published the findings of FASI areas on pathology study as characterized by spongiform myelinopathy or vacuolar change of myelin with no inflammatory reaction in the around tissue and no frank demyelination. The high T2 signal was explained by the vacuoles being filled with water. It remained unclear why FASI areas sometimes regress 7. Further studies are needed to establish the real origin of FASI areas 1


FASI lesions demonstrate bright signal on T2 and FLAIR weighted images. They are usually isointense to hyperintense on T1, without contrast enhancement 9

There is no mass effect, and they most commonly occur in the basal ganglia, brainstem, thalamus, optic tracts and cerebellum.

MRS is usually normal, helping in distinguish them from tumours 9

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Article Information

rID: 31085
Sections: Approach, Pathology
Synonyms or Alternate Spellings:
  • FASI
  • Unidentified bright objects (brain)
  • Focal areas of signal intensity (FASI)
  • UBO`s
  • neurofibromatosis bright objects

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Cases and Figures

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    Case 1: coronal T2
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    Case 2
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    Cor T2
    Case 3
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    Case 4
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    Case 5: right thalamus
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