Coma & Herniation Flashcards
If a patient requires a strong painful stimulus in order to evoke a response, what term would you apply to his/her consciousness?
Minimally conscious state (but these terms are vague and should be avoided)
“Coma” is often assessed on a scale… but do people usually have normal sleep-wake cycles while in a coma?
Nope.
What are the two interconnected systems required to maintain consciousness?
Ascending Reticular Activating System/Thalami
Cerebral Cortices
What are 4 coma mimics that you should include on your DDx?
Locked-in syndrome. Severe neuromuscular dysfunction. Pyschiatric conditions (catatonia) Akinetic Mutism (recall: can happen when frontal lobes lesioned)
4 major goals of coma examination?
Determine that it’s actually coma.
Exclude coma mimics.
Localize to brainstem vs. cerebral hemispheres.
Monitor progression / response to therapy.
In broad terms, what does knowing the localization of the coma in brainstem vs. cerebral hemispheres tell you about the cause of dysfunction?
Brainstem - more likely to be focal
Cerebral hemispheres - more likely to be systemic
Four localizing elements of a coma exam?
Pupils
Eye movement
Limb position
Breathing patterns
What affect will a lesion in the midbrain causing coma tend to have on the pupil?
Blown (dilated) pupil due to hitting CN III parasympathetics.
What do bilateral pons lesion pupils look like?
always constricted
What do bilateral midbrain lesion pupils look like?
Always dilated
Despite patients in comas not making voluntary eye movement, what information about localization can you get from eye movement?
Occulocephalic and occulovestibular reflexes.
“Eye field” function
General cortical dysfunction.
Occular motor nerve dysfunction.
How can you assess if the cortical eye fields are intact? What structure do the eye fields signal to?
Eye drive resting eye position away from their side. If both intact, resting eye position would be straight ahead. If lesioned, eyes will deviate horizontally to the lesioned side.
Eye fields signal to the PPRF.
How is general cortical dysfunction (but an intact brainstem) manifested in the eyes?
Eyes slowly drifting back and forth.
What’s better than COWS for remembering how testing for the occulovestibular reflex works?
Cold decreases firing rate, turning away from side decreasing firing rate.
Warm increases firing rate, turning toward side increases firing rate.
Thus eyes will slowly drift toward cold, then fast-beat away to correct.
Eyes will slow slowly drift away from warm, then fast-beat back to correct.
Two ways to assess ICP when looking at the retina?
Papilledema = increased ICP
Pulsing retinal veins = normal ICP
(note some people’s retinal veins don’t pulse, and that can be normal)
What can posture tell you about localization?
Extension posture is “decerebrate” - below red nucleus
Flexion posture is “decorticate” - above red nucleus
What sort of breathing pattern is consistent with a bilateral injury to the thalamus?
Cheyne-Stokes: hyperventilation alternating with periods of not breathing
What’s the localization for hyperventilation?
Pontomesencephalic region
What’s apneusis, and what’s its localization?
Slow, yawning breathing.
Lateral tegmentum of lower half of pons
Where what is ataxic breathing, and where does it localize?
Really irregular breathing, often with periods of apnea.
Localizes to lower dorsomedial medulla.
List 5 types of herniation.
Subfalcine Uncal Central (Diencephalic) External (Transcalvarial) Tonsilar
What kind of herniation is most likely to cause respiratory arrest?
Tonsilar
What actually herniates in subfalcine herniation? What is affected in subfalcine herniation?
The cingulate gyrus herniates under the falx. Often the contralateral ACA is compressed, causing contralateral* lower extremity weakness - a “false localizing sign.” *weakness ipsilateral to the lesion, contralateral to the involved ACA.
(make sure the uninvolved side stays uninvolved!)
Signs of uncal herniation? (list 3)
Midbrain compression ->
Ipsilateral CN III deficit
Contralateral weakness
Ipsilateral weakness - though usu. happens after contralateral
(Prof. also noted “panting breathing rhythm” -> hyperventilation?)
What can cause diencephalic herniation?
Large frontal or parietal mass lesions.
Early signs of diencephalic herniation? (list 4)
Small pupils, somnolence, Cheyne-Stokes breathing, decorticate posturing
Intermediate signs of diencephalic herniation? (3 things)
Pupils become mid-sized and non-reactive
Breathing: hyperventilation -> apneusis
Decerebrate posturing
Late signs of diencephalic herniation? (2 things)
Oculovestibular/cephalic reflexes disappear.
Breathing: ataxic -> respiratory arrest.
Major sign of tonsilar herniation?
Sudden respiratory arrest. It’s bad news.
Micro review: 20 yr old woman with fever and somnolence x 2 days. Low blood pressure. Diffuse purpura. Neck rigidity. Mostly likely cause?
Meningicoccal meningitis and meningicoccemia. (just for fun)
Would meningitis more likely cause diffuse cortical dysfunction or brainstem dysfunction? How would this be manifested in the eyes?
Cortical dysfunction. Lack of corrective nystagmus in vestibulocephalic reflex.
50 yr old man with severe hypertension. Acute severe headache with somnolence and decreasing consciousness x 30 minutes. Left pupil blown. Left eye down-and-out. Left body motor weakness. (right side pain sensation intact) Likely process occurring? Which side?
Uncal herniation secondary to increased ICP due to a large hemorrhage.
Hemorrhage is on left side, compressing the contralateral corticospinal tract / midbrain in the foramen magnum.
24 yr old man lost consciousness while on crack. Can blink and move eyes vertically. Other voluntary eye movement lost. Normal pupils. Eyes don’t move when cold water squirted in ear. No voluntary movement or movement in response to pain in face/body/limbs. Localization of this process?
Posterior pons. “Locked-in syndrome” secondary to pontine artery hemorrhage from blood pressure spike.
