Case of the Month: December 2013, Page 3

E. Benign external hydrocephalus. CT images reveal and enlarged extra axial space with fluid density that of CSF and a bulging anterior fontanelle.

Discussion Points

  • Benign external hydrocephalus or Benign enlargement of the subarachnoid spaces (BESS) is typically characterized clinically by macrocrania and frontal bossing.
  • BESS is more common in males and there is often a family history of macrocrania.
  • It is theorized to be due to a delay in development of arachnoid villi in the saggital sinus leading to faulty CSF resorption.
  • Imaging features include:
    • Widening of bifrontal CSF spaces > 5mm
    • No flattening of adjacent gyri
    • Enlarged anterior fontanelle
    • Normal ventricle size and no atrophy
    • No blood products
    • No cortical vein displacement
  • The enlarged subarachnoid fluid collection usually resolves by age 2, however, the macrocrania may persist.
  • While BESS is typically benign, there have been reported associations with increased risk of subdural hemorrhage, communicating hydrocephalus, and psychomotor delay.


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