A bump on the head can cause permanent disability -- even months after the injury, a Chicago-area neurologist said.

Dr. Jose Biller, a neurologist at Loyola University Medical Center, said a patient slipped on the ice and bumped her head but she wasn't too concerned until two months later, when she began to experience weakness in her right leg and right arm.

Biller ordered an immediate magnetic resonance imaging scan, which showed a large subdural hematoma -- a mass of blood on the surface of the brain. With the hematoma compressing the brain, the patient was in imminent danger of suffering permanent paralysis or cognitive deficits, similar to disabilities caused by strokes, Biller said.

Biller referred the patient to Loyola neurosurgeon Dr. Douglas Anderson, who performed emergency surgery by drilling two holes in the patient's skull and draining the hematoma -- which was about 2 inches long and 1.5 inches thick. The patient made a full recovery, Biller said.

Subdural hematomas are triggered by head injuries that cause blood vessels between the surface of the brain and its outer covering -- the dura -- to stretch and tear.

The subdural hematomas are usually caused by severe head injuries that cause bleeding, which rapidly fills the brain area. However, less severe head injuries can cause chronic subdural hematomas and these slow bleeds might not cause symptoms for days or weeks, Biller said.