Spontaneous disappearance of temporo-frontal arachnoid cyst in a child.

We report a child with a large temporo-frontal arachnoid cyst which resolved spontaneously. There was no history of a head injury. The patient was a boy aged 1.6 years. Though a large head was pointed out (+2SD), no therapeutic intervention was made because the relationship of the head circumference and the cyst was not established. No change in cyst size was visualized on the follow-up CTs at the age of 2.5 years and 6 years. At the age of 7 years, the arachnoid cyst had completely disappeared on CT. In order not to overlook a minute change in cyst size, the volumetry of the cyst and the intracranial cavity was performed, using the Photoshop, Macintosh. Both the cyst volume and the volume ratio of the cyst to the intracranial cavity slightly decreased and then increased. It is speculated that the cyst spontaneously ruptured by factors such as extreme breath holding and crying on the presence of the higher intracystic tension which might become a factor to accelerate spontaneous rupture of the cyst. Since a number of paediatric cases of symptomatic arachnoid cysts in need of surgical intervention has been larger than that of adult cases, we can speculate that a large arachnoid cyst might spontaneously resolve more frequently than we had expected. This case demonstrates that the surgical treatment of asymptomatic arachnoid cyst in the middle cranial fossa is not necessarily indicated in children.