No abstract

Aim: To report a case of arachnoid cyst incidentally detected in a child who initially presented with concomitant intermittent right exotropia that progressed to incomitancy. Methods: This is a case report of a 3-year-old boy with concomitant intermittent right exotropia who was initially listed for strabismus surgery. However, 2 months later, prior to the operation, he was found to have developed constant V-pattern right exotropia and bilateral inferior oblique overactions. Results: Urgent CT and MRI revealed the incidental finding of a temporal arachnoid cyst measuring 2.8 cm  3.8 cm  3.2 cm displacing the temporal lobe posteriorly. Urgent marsupialisation of the cyst was done with subsequent improvement to the strabismus. Conclusion: Arachnoid cysts are developmental anomalies that occasionally cause sudden neurological deficit due to cyst expansion or bleeding. Although concomitant exotropia is generally benign in a child, intracranial lesions need to be investigated if the child shows progressive worsening of strabismus, especially with the recent onset of incomitance.