as to disease and injury that affects it directly. CAR-
DIOVASCULAR DISEASE(CVD) is perhaps the most sig-
nificant general health risk for the brain.
Conditions such as ATHEROSCLEROSIS, CORONARY
ARTERY DISEASE(CAD), and HEART FAILUREcan dimin-
ish the flow of blood to the brain. HYPERTENSION
(high blood pressure) is the leading cause of
STROKE; stroke, in turn, is the leading cause of irre-
versible brain injury. Conditions that affect the
body’s metabolic state and balance, such as
chronic CIRRHOSIS and DIABETES, may alter the
brain’s biochemical balance to the extent of dis-
rupting brain function (ENCEPHALOPATHY). Direct
injury to the brain may result from INFECTION
(ENCEPHALITIS), BRAIN TUMOR(including metastatic
cancer), traumatic injury, and neurodegenerative
diseases such as ALZHEIMER’S DISEASEand Parkin-
son’s disease.
HEALTH CONDITIONS THAT AFFECT THE BRAINALZHEIMER’S DISEASE BRAIN HEMORRHAGE
BRAIN TUMOR CEREBRAL PALSY
COMA CONCUSSION
CREUTZFELDT-JAKOB DISEASE(CJD) DEMENTIA
DOWN SYNDROME EDWARDS SYNDROME
ENCEPHALITIS ENCEPHALOPATHY
HUNTINGTON’S DISEASE MENINGITIS
MULTIPLE SCLEROSIS NEURAL TUBE DEFECTS
ORGANIC BRAIN SYNDROME PARKINSON’S DISEASE
PATAU SYNDROME PERSISTENT VEGETATIVE STATE
SEIZURE DISORDERS TOURETTE’S SYNDROME
TRAUMATIC BRAIN INJURY(TBI) TREMOR DISORDERS
For further discussion of the brain within the
context of the structures and functions of the
nervous system, please see the overview section
“The Nervous System.”
See also ARTERIOVENOUS MALFORMATION (AV M);
BRAIN DEATH; CIRCLE OF WILLIS; COUGH; SCOTOMA;
SNEEZE.
brain cancer See BRAIN TUMOR.
brain death The permanent cessation of BRAIN
function commonly accepted as the indication that
life has ended. The American Academy of Neurol-
ogy has established guidelines for determining
whether brain death has occurred that form the
basis for the criteria health-care providers in the
United States apply. However, the criteria vary
among states in the United States as well as
among countries. In general doctors make a decla-
ration of brain death only when there is clear and
unquestionable cause for and evidence of irre-
versible loss of brain function, and a series of pro-
cedures consistently support the determination
that all brain function is absent and has no possi-
bility of returning. The concept and establishment
of brain death has medical, legal, ethical, moral,
and for many people religious components.
The need to establish brain death arises when a
person has suffered catastrophic injuries, such as
in a motor vehicle accident, or a catastrophic
health crisis, such as HEART ATTACKor STROKE, that
deprives the brain of oxygen for an extended
period. Emergency treatment may place the per-
son on life support, with MECHANICAL VENTILATIONto
maintain BREATHING. Removing life support gener-
ally requires medical consensus that brain death
has occurred. The declaration of brain death is also
necessary to harvest organs such as the HEARTfor
ORGAN TRANSPLANTATION. In most circumstances a
person’s next of kin, family members, or person
designated with medical power of attorney must
authorize cessation of life support even with a
declaration of brain death.CARDINAL EVIDENCE OF BRAIN DEATH
clear cause for irreversible BRAINdeath
no evidence of drugs or conditions that could suppress brain
function
COMA
no REFLEXresponse to PAIN
no brainstem reflexes
no electrical activity on ELECTROENCEPHALOGRAM(EEG)See also END OF LIFE CONCERNS; QUALITY OF LIFE.brain hemorrhage Significant loss of BLOOD
within the cranium or the tissues of the BRAIN.
Most brain hemorrhages occur suddenly and
unexpectedly. Occasionally brain hemorrhage may
be chronic, such as when slow bleeding takes
place through a small rupture in an ANEURYSM.
Brain hemorrhage has two major conse-
quences, each of which can be life-threatening: It
deprives the brain of vital oxygen and it causes
increased pressure within the skull. Brain hemor-brain hemorrhage 233