Introduction:
Anisocoria is a condition characterized by unequal pupils. There are two described types: physiologic and pathologic. Pathologic anisocoria is caused by interruption in reflex arc. Reason of anisocoria can be difficult to define due to variety of possible diseases that may be causing it.

Aim:
Case presentation of anisocoria caused by congenital cystic lesions of the brain.

Case Study:
12-year-old girl after head trauma was admitted to the Emergency Department due to anisocoria noticed by family doctor. Patient had headache, sleepiness, dizziness and lacrimation. After looking at patients’ childhood photo it was stated, that anisocoria was present before the injury. In physical examination decreased mobility of left eyeball, left-sided ptosis and left-sided decreased reaction to the light (both, direct and consensual) were noted. Head CT scan was performed, which revealed bilateral cystic lesions in basal ganglia, thalamus and in mesencephalon. The biggest lesions were located in left thalamus – 29x15mm. Biopsy of the biggest cyst was performed. No neoplastic tissue was found. Final diagnosis was stated: diencephalic and mesencephalic polycyclic lesions of unknown origin. Surgical approach was departed and conservative treatment was applied (regular head MRI scans)

Results and discussion:
Described case report was an example of diagnostic difficulties which can be caused by anisocoria. In this case pathologic anisocoria was caused by congenital cystic lesions of the brain that were detected in the age of 12.

Conclusions:
Anisocoria can be a sign of many different pathologies, but also can be physiologic. If pathologic anisocoria is suspected, imaging diagnostics should always be performed.