Now before you panic and think that the cause of your one dilated pupil is an acoustic neuroma, this is highly unlikely.įirst off, this rare brain tumor will cause other symptoms long before it encroaches upon the brainstem. This is when an acoustic neuroma becomes life-threatening. It may also interfere with the brainstem’s commands to make the heart beat. Howver, this slow growing brain tumor can indirectly lead to third nerve damage by pressing against the brainstem, leading to one pupil becoming dilated. One type of brain tumor that can press up against (though not invade) the brainstem is called acoustic neuroma, though the location of this growth would not directly involve the third cranial nerve - and hence, would not dilate a pupil via that route. “There are many causes of third nerve damage, but the most worrisome is compression from a brain tumor, aneurysm or swelling in the brain.” “A dilated pupil on one side could be a sign of third nerve damage,” continues Dr. Kulkarni, MD, board certified ophthalmologist and neuro-ophthalmologist in private practice in New York. “The third cranial nerve is a nerve that comes out of the brainstem (midbrain) and travels to the eye to constrict the pupil,” says Kaushal M. Not just Brain Tumor, but Aneurysm Can Make Pupils Unequal
A brain tumor can cause one pupil to be bigger or more dilated than the other.īut so can less serious conditions including totally benign.