Physicians grade brain tumors according to their degree of malignancy. One aspect of a tumor's appearance that affects its grade is whether it is diffuse--with no clear edge or margin--or focal--with a clear margin defining where it begins and ends. Tumors, whether diffuse or focal, can produce focal symptoms that affect specific body functions or locations. Focal symptoms can help physicians learn about a tumor's location. According to the "Handbook of Community Cancer Care," over 50 percent of patients who present with brain tumors have focal neurological deficit symptoms.
Cerebellum
The cerebellum is part of the hindbrain and it plays a role in controlling body movement and cognitive functions that require precise timing. When a tumor develops in the cerebellum, focal symptoms may include tremors and series of muscle control problems called ataxia. This involves unusual muscular movements and loss of coordination. A tumor in the cerebellum may also cause a series of unusual eye movements known as nystagmus, according to the Merck Manual for Healthcare Professionals. This brain tumor symptom involves rhythmic vertical or lateral movements of the eyes. These movements usually occur involuntarily.
Occipital Lobe
The occipital lobes, which lie at the rear of the brain, play a role in processing visual information. A brain tumor in the occipital lobes may cause symptoms involving the sense of sight. These can include visual hallucinations and auras that precede generalized seizures. Other possible symptoms include hemianopia, partial or total blindness in half of the visual field, occurring in one or both eyes, and quadrantanopia, partial or total loss of vision in one-quarter of the visual field.
Brain Stem
The brain stem is part of the hindbrain, that part of the brain that joins the spinal cord and controls vital bodily functions, including respiration and heart rate. A tumor in the brain stem can cause tremors or loss of sensation or motor control on one or both sides of the body. The tumor may cause nerve deficits that result in vertigo, facial weakness, and hearing loss, notes the Merck Manual.
Cranial Nerves
A series of 12 cranial nerves carry information from the brain to the head and neck's motor system as well as information from the sensory systems to other parts of the brain. Tumors in specific nerves can cause specific focal symptoms. A tumor that develops in the second cranial nerve--the optic nerve--can cause blindness. Weakness in the jaw and loss of sensation in the face are possible symptoms of a tumor in the fifth cranial, or trigeminal, nerve.
References
- "A Primer of Brain Tumors"; American Brain Tumor Association; 2004
- "Handbook of Community Cancer Care"; Mark Gaze; 2002
- Stanford School of Medicine: Brain Tumor Center
- Merck Manual for Healthcare Professionals: Common Localizing Manifestations of Brain Tumors
- "Brain Facts, 6th Edition"; Society for Neuroscience; 2008
