Findings by Location*
Location | Abnormal Findings |
|---|---|
Bilateral hemispheric damage or dysfunction* | Symmetric tone and response (flexor or extensor) to pain Myoclonus (possible) Periodic cycling of breathing |
Supratentorial mass compressing the brain stem | Ipsilateral 3rd cranial nerve palsy with unilateral dilated, fixed pupil and oculomotor paresis Sometimes contralateral homonymous hemianopia and absent blinking response to visual threat Contralateral hemiparesis |
Brain stem lesion | Early abnormal pupillary and oculomotor signs Abnormal oculocephalic reflex Abnormal oculovestibular reflex Asymmetrical motor responses Decorticate rigidity (usually due to an upper brain stem lesion) or decerebrate rigidity (usually due to a bilateral midbrain or pontine lesion) Hyperventilation (due to a midbrain or upper pontine lesion) |
Midbrain (upper brain stem) lesion | Pupils locked in midposition, often unequal in size, with loss of light reflexes (due to a structural or metabolic disorder that causes loss of both sympathetic and parasympathetic pupillary tone) |
Toxic-metabolic dysfunction* | Spontaneous, conjugate roving eye movements in mild coma Fixed eye position in deeper coma Abnormal oculovestibular reflex Multifocal myoclonus Asterixis (may be considered a type of negative myoclonus) Decorticate and decerebrate rigidity or flaccidity |
* Not all of the findings occur in all cases. Brain stem reflexes and pupillary light responses may be intact in patients with bilateral hemispheric damage or dysfunction or toxic-metabolic dysfunction; however, hypothermia, sedative overdose, or use of an anesthetic can cause partial loss of brain stem reflexes. | |