Benign enlargement of the subarachnoid space in infancy

Epidemiology

• more commonly in boys than in girls.
• in the majority of cases, there is a family history of macrocephaly.

Clinical presentation

Often discovered incidentally or when patients undergo neuroimaging in the workup of macrocephaly. These patients are usually neurologically normal and have no history of trauma.

Pathophysiology

The aetiology is not clear. It has been described as a variation of normal development of the brain, whereby there is a transient accumulation of cerebrospinal fluid in the frontal region. It is also thought to be due to the delayed development or delayed function of the arachnoid villi at the sagittal sinus.

Radiographic features

Ultrasound, CT and MRI imaging of the brain may demonstrate findings seen in BESS:

• widening of the bifrontal and anterior interhemispheric CSF spaces (>5mm).
• no flattening of adjacent gyri.
• usually normal sulci posteriorly.
• the anterior fontanelle is frequently enlarged with the enlargement of the subarachnoid space in the frontoparietal regions.
• it is associated with normal ventricular size. There are no pressure effects on the surrounding brain tissue or cerebral atrophy.
• no blood products on MRI study.
• another key distinction between benign enlargement of the subarachnoid spaces and a subarachnoid fluid collection is that in the former the cortical veins will be adjacent to the inner table of the calvarium on MR and ultrasound; whereas in the latter the veins are displaced away from the inner table, as the arachnoid membrane and subarachnoid space are displaced.

Complications

While these findings are benign in many cases, there is an increased risk of subdural haemorrhage, either spontaneously or following minor trauma. A low percentage of patients may develop communicating hydrocephalus, which may warrant treatment.

Treatment and prognosis

The condition resolves spontaneously by the age of 2 years. Although the macrocephaly may persist, the subarachnoid space fluid collection will resolve or become minimal as the child grows older.

A study shows thatr infants with macrocephaly or rapid head-growth, CT-scan findings of enlarged subarachnoid spaces and normal to minimally increased ventricular size, and who have a parent with macrocephaly, have a good developmental prognosis and a characteristic pattern of neuromotor development in the first year.