Below is a patient who presented with complaints of binocular horizontal diplopia. The patient’s MRI scan shows a large tumor in the left hemisphere creating a mass effect. On exam, a left sixth nerve palsy was noted. A sixth nerve palsy in a patient without a history of hypertension or diabetes is concerning for a brain etiology. The sixth nerve is the cranial nerve most likely to be involved in brain disease, such as brain edema, because it has the longest length and course.