Focal areas of signal intensity (brain)
Updates to Article Attributes
Focal areas of signal intensity (FASI), also known as focal abnormal signal intensity or or unidentified bright objects (UBO), 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 in children with neurofibromatosis type 1(NF1) and probably also in Noonan syndrome.
Epidemiology
FASI areas are the most common neuroimaging feature in NF1 patients 1. A A study showed a significant frequency (86%) of one or more FASI in children with NF1 2. Patients Patients younger than 10 commonly have an increase in either size or number lesions, but such an increase beyond 10 years of age raises concern for a neoplasm 10. Recent evidence suggests FASI areas may occur in Noonan syndrome in addition to NF1.14
Clinical presentation
There is considerable debate about its real role within the NF1 spectrum and its potential relationship with cognitive dysfunction 3. The The association between these focal areas of high signal and cognitive deficits remains controversial, wherein recent studies have found a favourable relationship with the presence, number and location of FASI areas 3-6. However, only only the thalamic lesions seem to be strongly associated with cognitive impairment 3-5.
Pathology
Di Paolo et al. published published the findings of FASI areas on pathology study as characterised by spongiform myelinopathy or vacuolar change of myelin with no inflammatory reaction in the surrounding 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 Further studies are needed to establish the real origin of FASI areas 1.
Radiographic features
MRI
T1: isointense to hyperintense
T2/FLAIR: hyperintense
T1 C+ (Gd): usually no enhancement, although enhancing FASI (including potential of regression over time) have been reported 13
MR spectroscopy: normal (useful to distinguish from tumours 9)
FASI areas do not demonstrate mass effect, and most commonly occur in the basal ganglia, brainstem, thalamus, optic tracts, cerebellum, and infrequently cerebral hemispheres 11,12.
-<p><strong>Focal areas of signal intensity (FASI)</strong>, also known as <strong>focal abnormal signal intensity</strong> or <strong>unidentified bright objects (UBO)</strong>, are bright areas on T2-weighted images commonly identified in the <a href="/articles/basal-ganglia">basal ganglia</a> (often the <a href="/articles/globus-pallidus">globus pallidus</a>), <a href="/articles/thalamus">thalamus</a>, <a href="/articles/brainstem">brainstem</a> (<a href="/articles/pons">pons</a>), <a href="/articles/cerebellum">cerebellum</a>, and subcortical white matter in children with <a href="/articles/neurofibromatosis-type-1">neurofibromatosis type 1</a> (NF1) and probably also in Noonan syndrome.</p><h4>Epidemiology</h4><p>FASI areas are the most common neuroimaging feature in NF1 patients <sup>1</sup>. A study showed a significant frequency (86%) of one or more FASI in children with NF1 <sup>2</sup>. Patients younger than 10 commonly have an increase in either size or number lesions, but such an increase beyond 10 years of age raises concern for a neoplasm <sup>10</sup>. Recent evidence suggests FASI areas may occur in Noonan syndrome in addition to NF1.<sup>14</sup></p><h4>Clinical presentation</h4><p>There is considerable debate about its real role within the NF1 spectrum and its potential relationship with cognitive dysfunction <sup>3</sup>. The association between these focal areas of high signal and cognitive deficits remains controversial, wherein recent studies have found a favourable relationship with the presence, number and location of FASI areas <sup>3-6</sup>. However, only the thalamic lesions seem to be strongly associated with cognitive impairment <sup>3-5</sup>. </p><h4>Pathology </h4><p>Di Paolo et al. published the findings of FASI areas on pathology study as characterised by spongiform myelinopathy or vacuolar change of myelin with no inflammatory reaction in the surrounding 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 <sup>7</sup>. Further studies are needed to establish the real origin of FASI areas <sup>1</sup>. </p><h4>Radiographic features</h4><h5>MRI</h5><ul>-<li><p><strong>T1:</strong> isointense to hyperintense</p></li>-<li><p><strong>T2/FLAIR:</strong> hyperintense</p></li>-<li><p><strong>T1 C+ (Gd):</strong> usually no enhancement, although enhancing FASI (including potential of regression over time) have been reported <sup>13</sup></p></li>-<li><p><strong>MR spectroscopy: </strong>normal (useful to distinguish from tumours <sup>9</sup>)</p></li>- +<p><strong>Focal areas of signal intensity (FASI)</strong>, also known as <strong>focal abnormal signal intensity</strong> or <strong>unidentified bright objects (UBO)</strong>, are bright areas on T2-weighted images commonly identified in the <a href="/articles/basal-ganglia">basal ganglia</a> (often the <a href="/articles/globus-pallidus">globus pallidus</a>), <a href="/articles/thalamus">thalamus</a>, <a href="/articles/brainstem">brainstem</a> (<a href="/articles/pons">pons</a>), <a href="/articles/cerebellum">cerebellum</a>, and subcortical white matter in children with <a href="/articles/neurofibromatosis-type-1">neurofibromatosis type 1</a> (NF1) and probably also in Noonan syndrome.</p><h4>Epidemiology</h4><p>FASI areas are the most common neuroimaging feature in NF1 patients <sup>1</sup>. A study showed a significant frequency (86%) of one or more FASI in children with NF1 <sup>2</sup>. Patients younger than 10 commonly have an increase in either size or number lesions, but such an increase beyond 10 years of age raises concern for a neoplasm <sup>10</sup>. Recent evidence suggests FASI areas may occur in Noonan syndrome in addition to NF1.<sup>14</sup></p><h4>Clinical presentation</h4><p>There is considerable debate about its real role within the NF1 spectrum and its potential relationship with cognitive dysfunction <sup>3</sup>. The association between these focal areas of high signal and cognitive deficits remains controversial, wherein recent studies have found a favourable relationship with the presence, number and location of FASI areas <sup>3-6</sup>. However, only the thalamic lesions seem to be strongly associated with cognitive impairment <sup>3-5</sup>. </p><h4>Pathology </h4><p>Di Paolo et al. published the findings of FASI areas on pathology study as characterised by spongiform myelinopathy or vacuolar change of myelin with no inflammatory reaction in the surrounding 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 <sup>7</sup>. Further studies are needed to establish the real origin of FASI areas <sup>1</sup>. </p><h4>Radiographic features</h4><h5>MRI</h5><ul>
- +<li><p><strong>T1:</strong> isointense to hyperintense</p></li>
- +<li><p><strong>T2/FLAIR:</strong> hyperintense</p></li>
- +<li><p><strong>T1 C+ (Gd):</strong> usually no enhancement, although enhancing FASI (including potential of regression over time) have been reported <sup>13</sup></p></li>
- +<li><p><strong>MR spectroscopy: </strong>normal (useful to distinguish from tumours <sup>9</sup>)</p></li>
Image 9 MRI (FLAIR) ( create )
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