What does a brain tumor look like?

The MRI image. Shows a mass, commonly surrounded by edema. Pathology shows abnormal blood vessel proliferation (and they leak), necrosis (dead cell areas), and abnormal mitoses.
It varies. This varies depending on the kind of tumor. Some tumors, like meningioma, are solid and look like a mass. Others, like astrocytoma, or glioblastoma multiforme may be hollowed out with necrotic of dead centers. Many brain tumors present with different looks. For example, CNS lymphomas present as one mass in immunocompetent patients or as multiple lesions in the immunocompromised patient.
Different appearance. Different tumors have different appearances. Melanomas are purple, meningiomas are reddish pink, glioblastoma is grayish to dark red. There are too many to name but these are a few.

Related Questions

I went to eye doctor because I had photopsia. He found nothing wrong but I worry about having a brain tumor. What does photopsia caused by brain tumor look like?

Don't panic. May be something as simple as a migraine or indeed something more serious. If you are worried about a brain tumor, speak with your regular doctor. Read more...
An eye doctor is you. Eye doctor is your best source to answer this question. Unless you have headaches or any neurological symptoms, it is unlikely that your eye problem is due to a brain tumor. If the eye problem persists or gets worse you need to go see your doctor again and ask him this question. Read more...