A dark spot can appear on an X-ray or scan for any number of reasons. Brain lesions usually are discovered accidentally when you're being diagnosed for an unrelated symptom, according to MayoClinic.com. Dark spots that indicate brain lesions usually are discovered after undergoing a magnetic resonance imaging test, or MRI, or a CT scan, otherwise called a computerized tomography scan.
A dark spot on the brain can be a leftover stain from an old injury or resolved medical condition and pose no threat. On the other hand, a lesion that appears on a test as a dark stain can indicate a number of serious conditions varying from a tumor to an aneurysm or congenital brain abnormality. Further tests and examinations may be required to diagnose the spot, or your doctor may choose to monitor the lesion to watch for changes.
A brain tumor that originates in the brain is called a primary brain tumor. Cancer that has spread to the brain from another part of the body is called metastatic brain tumors, according to the National Cancer Institute. Other neurological symptoms such as headaches or vision loss may prompt further tests to look for dark spots. A dye may be injected in the bloodstream to highlight the potential brain tumor.
An MRI is the most commonly used technique when diagnosing brain lesions. Advances in MRI technology allow doctors to see with greater detail how much damage is associated with the dark spot and what the underlying disease may be that's causing the abnormality. An MRI is performed in a large tube-shaped machine that you enter while resting on a movable table. Loud banging noises occur throughout the procedure that can last up to an hour while the scans are taken.
While symptoms of a tumor or lesion on the brain may prompt your doctor to order scans of your brain, the only definitive way to identify a tumor is through a biopsy, according to the American Brain Tumor Association. X-rays and scans can indicate the presence of a dark spot and help to determine the general skull condition surrounding the tumor, guiding surgeons in their probes. Images can help to provide preliminary diagnoses and direct further tests.
To concretely identify the dark spot as a malignant brain tumor, other tests usually are provided, notes the National Cancer Institute. A biopsy is performed by making a small incision in the skull and taking out a piece of the spot to test it under a microscope and in the laboratory. A spinal tap that removes fluid from the top of the spine that leads to the brain also may help identify if cancer is present in the tumor.