Observation of the the progression of tension in intracranial arachnoid cyst: A case report and review of literature

Arachnoid cysts (ACs) are common benign intracranial space-occupying lesions in children can be categorized into tensional and non-tensional cysts based on imaging features. The majority of ACs are clinically silent and remain static in size; however, some intracranial ACs may gradually increase in size. However, the relationship between tension in cyst and cyst enlargement is currently unclear. Due to the rarity of observed progression of tension in intracranial ACs, controversies persist regarding when and how to perform surgery. We present a rare case of a progressive increase in head circumference over one year in a 15-month-old child caused by growing tensional AC at the left cerebellopontine angle. Brain magnetic resonance imaging (MRI) at 6 days after birth revealed a small non-tension AC at the left cerebellopontine angle with no apparent compression of adjacent brain tissue and clear sulci and gyri. At 15 months, the MRI revealed a significant enlargement of AC, brain stem was displaced, sulci of the adjacent brain tissue disappeared, and the cyst-brain tissue interface displayed a tensional arc-type change, accompanied by obstructive hydrocephalus. Through fenestration, the AC was reduced, exhibiting non-tension changes, significantly alleviating pressure on adjacent brain tissue, and hydrocephalus significantly improved. Subsequent follow-ups showed no obvious abnormalities. In conclusion, the degree of tension seen in AC imaging is the result of cyst enlargement, guiding surgical intervention and postoperative efficacy evaluation.