19.1 Case Presentation

19.2 Imaging Analysis

19.2.1 Imaging Findings and Impression

Brain MRI axial T2-weighted (T2w; ▶ Fig. 19.1a,b), axial T2*GRE (gradient recalled echo; ▶ Fig. 19.1c,d), and coronal T1-weighted (T1w) with gadolinium (▶ Fig. 19.1e) images show prominence of the subarachnoid spaces overlying the anterior cerebral convexities (asterisks) consistent with benign enlargement of subarachnoid spaces (BESS) of infancy, which is a normal variant. Note the presence of small bridging veins crossing the subarachnoid spaces (white arrow in ▶ Fig. 19.1e). Lack of susceptibility signal from blood degradation products on T2*GRE images (▶ Fig. 19.1c,d) further supports diagnosis of BESS.

19.3 Differential Diagnosis

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  BESS:

  
  
  
  
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    Normal transient enlargement of the subarachnoid spaces associated with macrocephaly.

  
  
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  Chronic subdural hematoma:

  
  
  
  
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    It should be suspected if the collection thickness is wider than 6 mm, shows higher T2 fluid-attenuated inversion recovery (FLAIR) signal as compared to cerebrospinal fluid (CSF), and displays hemorrhagic staining on T2*GRE. ¹

    
    
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    The collection is usually asymmetric, displaces the bridging veins toward the brain surface, and has mass effect.

  
  
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  Cerebral volume loss/brain atrophy:

  
  
  
  
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    When present, it is usually accompanied by small head circumference, and “pointed” forehead due to early metopic suture fusion.

    
    
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    Benign enlargement of subarachnoid spaces causes an increase of the head circumference and a flat forehead due to frontal bossing.

  
  
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  Acquired communicating hydrocephalus:

  
  
  
  
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    It usually is caused by a hemorrhagic, inflammatory, or neoplastic process.

    
    
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    Some congenital causes include achondroplasia due to narrow foramen magnum and jugular foramina.

    
    
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    Density or signal intensity of extra-axial collection does not follow the CSF.

19.4 Diagnostic Pearls

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  Widening of the vertical distance between calvarium and brain frontal parenchyma ≥ 5 mm.

  
  
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  It is usually accompanied by enlarged cisterns (suprasellar and suprachiasmatic) and mildly enlarged ventricles (66%).

  
  
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  Normal veins are traversing subarachnoid space, the fluid in subarachnoid space follow the CSF signal on all sequences, and there is no abnormal meningeal enhancement. ^{2 , 3 , 4 , 5 , 6}