Metastases outnumber primary brain tumors four to one
A brain tumor is a mass of cells growing beyond control inside the skull—malignant or benign. Causes are usually unknown, though imaging radiation may explain a small share of cases. Secondary tumors from elsewhere are roughly four times as common as primaries.
Most tumours found in the brain did not start there. Metastases that travel in from elsewhere outnumber primary growths by about four to one, and around half of them originate in the lungs. Primary brain tumours strike about 250,000 people worldwide each year and account for under 2 percent of all cancers, yet in children under 15 only acute lymphoblastic leukaemia is more common.
Symptoms track geography more than malignancy. A benign mass can cause as much trouble as a cancerous one, and a small growth in Wernicke's area may disable language more than a large one in the frontal lobe. Frontal tumours can erode planning and inhibition, temporal ones can affect memory and hearing, occipital ones can dim sight, and cerebellar ones upset balance and posture. Headache from rising pressure is a warning only in company: on its own it is rare, and doctors watch for headaches that wake a sleeper, worsen in the morning or ease after vomiting.
Cause is usually a mystery. Ionizing radiation is an established culprit, with CT scans blamed for roughly 4 percent of brain cancers in the general population, and inherited syndromes such as neurofibromatosis type 2 and tuberous sclerosis carry high risk. The mobile phone scare rests on older studies of heavy 2G users that saw a slight rise in glioma; studies have shown no clear link, 3G handsets emit about 1 percent of that energy, and the WHO keeps phone radiation in Group 2B as possibly carcinogenic.
Diagnosis is hampered by the blood-brain barrier, which blocks many imaging tracers until a tumour breaks it down; that breach, seen on MRI or CT, is the main sign of malignant gliomas and metastases. Contrast-enhanced MRI is the preferred test. Treatment mixes surgery, radiotherapy and chemotherapy, with dexamethasone to cut swelling, while some slow growers need only watching.
Source: Brain tumor
