Volume change of cranial arachnoid cysts after successful endoscopic fenestration in symptomatic children

Endoscopic fenestration remains a first-line treatment option for symptomatic arachnoid cysts. After fenestration, the cyst does not collapse but reaches an equilibrium state. The aim of this study was to evaluate the change in cyst volume following successful fenestration and symptomatic improvement.

Cyst volume was measured on serial MR scans of 4 children (1 female, 3 males) with symptomatic arachnoid cysts (middle fossa n = 2, choroidal fissure n = 1 and posterior fossa n = 1), who experienced symptom resolution after endoscopic fenestration. Average follow-up was 20.5 months (range 3-48).

Significant cyst volume reduction was seen in all four patients. In patient 1, preoperative cyst volume was 336 cm³ and decreased to 194 cm³ at 7 months (42% reduction). In patient 2, preoperative volume was 12.64 cm³ and reduced to 1.51 cm³ at 3 months (88% reduction). In patient 3, preoperative volume was 105 cm³ and reduced to 72 cm³ in 2 months (30% reduction). In patient 4, preoperative volume was 125 cm³ and reduced to 54 cm³ at 7 months (56% reduction). All remained stable after 7 months and there has been no late increase in volume.

Significant reduction in arachnoid cyst volume at the order of 30-40% is seen after successful endoscopic fenestration. The cyst volume appears to decrease gradually in the first 3-7 months and reaches a plateau after that. Complete resolution of symptoms in the presence of residual volume may indicate that cyst volume below a threshold may not correlate directly with clinical status.