Should benign enlargement of subarachnoid spaces be followed radiologically?

Benign Enlargement of Subarachnoid Spaces: Radiological Follow-up

Routine radiological follow-up is not necessary for benign enlargement of subarachnoid spaces (BESS) in asymptomatic infants, as this is a self-limiting condition that resolves spontaneously by 18-24 months of age.

Initial Assessment and Diagnosis

When BESS is identified on imaging, the key diagnostic features include:

• Enlarged frontal subarachnoid spaces (>3 mm sinocortical width, >4 mm craniocortical width, or >6 mm interhemispheric width) with normal or minimally enlarged ventricles 1
• Normal neurodevelopmental status is the critical distinguishing feature from pathological conditions 1, 2
• Macrocephaly is common, with head circumference often at or above the 95th percentile, but growth should parallel normal curves 1, 3

The distinction from brain atrophy is crucial: BESS shows normal or minimally enlarged ventricles, whereas brain atrophy presents with both passive subarachnoid space dilatation AND ventriculomegaly 1.

Recommended Follow-up Strategy

For Confirmed BESS (Asymptomatic):

• One follow-up MRI at 12-18 months to demonstrate stability and resolution is reasonable but not mandatory 4, 2
• Clinical follow-up without mandatory imaging is the preferred approach for asymptomatic cases 4
• No long-term imaging surveillance is necessary once the benign nature is confirmed 4
• Head circumference monitoring should continue with measurements plotted on growth charts for 6 months after diagnosis 1

When to Consider Repeat Imaging:

Repeat imaging should only be performed if:

• Clinical deterioration occurs (new neurological symptoms, developmental regression) 4
• Abnormal head growth velocity deviates from the normal curve 1
• New symptoms suggesting complications develop 4

Natural History and Prognosis

• Resolution occurs spontaneously by 18-24 months of age in the vast majority of cases 2, 3
• >80% of cases remain stable in size over time 4
• Normal neurodevelopment is expected when no associated brain anomalies are present 1, 2
• Head circumference typically remains at or above the 95th percentile even after subarachnoid space normalization 3

Important Clinical Pitfalls

Avoid Misdiagnosis:

• Do not confuse BESS with subdural collections: BESS is associated with incidental subdural collections in approximately 5.8% of cases, which are not indicative of abusive head injury when occurring in the context of BESS 5
• Do not diagnose brain atrophy: This requires both enlarged subarachnoid spaces AND ventriculomegaly, carrying a poor neurodevelopmental prognosis unlike BESS 1
• Do not pursue unnecessary neuroimaging: Further imaging procedures are not needed once BESS is confirmed with normal neurodevelopment 1

Family Counseling:

• Reassure families about the benign, self-limiting nature of this condition 4, 3
• Document family history of macrocephaly, which is commonly present 3
• Emphasize normal development expectations when no associated anomalies exist 1, 2