Benign enlargement of the subarachnoid spaces in infancy

Findings

The head CT shows there is prominence of bilateral frontal extra-axial CSF spaces without evidence of mass effect on the adjacent cerebral parenchyma. The lateral ventricles are also mildly prominent.

Differential diagnosis:
- Benign enlargement of the subarachnoid spaces in infancy (BESSI)
- Cerebral atrophy
- Non-accidental trauma
- Acquired external obstructive hydrocephalus


Diagnosis: Benign enlargement of the subarachnoid spaces in infancy (presumed)


Key points

BESSI – enlarged extra-axial CSF spaces with little to no ventricular dilation in an infant with an enlarging head
Previously used terms for this condition – external hydrocephalus, extraventricular obstructive hydrocephalus, benign subdural collections of infancy
Key to diagnosis is enlarged head circumference and resolution without treatment
Resolves by 2 years; normal outcome
Etiology unclear but may be related to immature CSF drainage pathways
Familial cases have been reported


Radiology

Widening of the bifrontal and anterior interhemispheric CSF spaces (>5mm). No flattening of adjacent gyri. Usually normal sulci posteriorly (unlike in atrophy)
Enlarged basal cisterns
Mild ventriculomegaly in the majority of cases
Symmetric
Cortical veins traverse the fluid when visualized with CT, MR or US (displaced to the cortical surface with subdural collections)
No blood products on MRI
Normal intraventricular CSF flow with phase contrast MRI