Itchy or irritated eyes are easy to pin on seasonal allergies, which is what one 30-year-old woman in London suspected when she stopped in at an ophthalmologist’s office last month.

But Gurcharan Kaur, who at that point was having trouble blinking and noticed swelling in her eye, would soon learn that her symptoms were more troubling than a simple pollen irritation, and were actually due to a tumor in the middle of her brain.

A colloid cyst is a slow-growing tumor typically found near the center of the brain, according to UCLA Health. Patients typically complain of headaches, but may present with other symptoms. For Kaur, the diagnosis required a two-hour operation to remove the cyst, and two months of anti-epilepsy medication.