Benign enlargement of subarachnoid spaces

Case contributed by Dr Blake Kightlinger


7 month old boy with history of prematurity and complex medical history who was noted to have a bulging anterior fontanelle. Vitals: Temp: 97.4 °F (36.3 °C) BP: 100/70 mmHg Heart Rate: 112 Respiratory Rate: 44 SpO2: 93 % Exam: Awake PERRL Fontanelle full but soft Moving all extremities HC-37cm Imaging: A head ultrasound was ordered for further work up.

Patient Data

Age: 7 months
Gender: Male

There is an enlarged extra axial space overlying the frontal convexities with complex fluid and a bulging fontanelle.

Benign enlargement of subarachnoid space. CT images reveal and enlarged extra-axial space with fluid density that of CSF and a bulging anterior fontanelle.

Case Discussion

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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Case information

rID: 25801
Case created: 8th Nov 2013
Last edited: 11th Sep 2015
Tag: crop
Inclusion in quiz mode: Included

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