Coma & Herniation

Question 1

If a patient requires a strong painful stimulus in order to evoke a response, what term would you apply to his/her consciousness?

Answer 1

Minimally conscious state (but these terms are vague and should be avoided)

Question 2

“Coma” is often assessed on a scale… but do people usually have normal sleep-wake cycles while in a coma?

Answer 2

Nope.

Question 3

What are the two interconnected systems required to maintain consciousness?

Answer 3

Ascending Reticular Activating System/Thalami

Cerebral Cortices

Question 4

What are 4 coma mimics that you should include on your DDx?

Answer 4

Locked-in syndrome.
Severe neuromuscular dysfunction.
Pyschiatric conditions (catatonia)
Akinetic Mutism (recall: can happen when frontal lobes lesioned)

Question 5

4 major goals of coma examination?

Answer 5

Determine that it’s actually coma.
Exclude coma mimics.
Localize to brainstem vs. cerebral hemispheres.
Monitor progression / response to therapy.

Question 6

In broad terms, what does knowing the localization of the coma in brainstem vs. cerebral hemispheres tell you about the cause of dysfunction?

Answer 6

Brainstem - more likely to be focal

Cerebral hemispheres - more likely to be systemic

Question 7

Four localizing elements of a coma exam?

Answer 7

Pupils
Eye movement
Limb position
Breathing patterns

Question 8

What affect will a lesion in the midbrain causing coma tend to have on the pupil?

Answer 8

Blown (dilated) pupil due to hitting CN III parasympathetics.

Question 9

What do bilateral pons lesion pupils look like?

Answer 9

always constricted

Question 10

What do bilateral midbrain lesion pupils look like?

Answer 10

Always dilated

Question 11

Despite patients in comas not making voluntary eye movement, what information about localization can you get from eye movement?

Answer 11

Occulocephalic and occulovestibular reflexes.
“Eye field” function
General cortical dysfunction.
Occular motor nerve dysfunction.

Question 12

How can you assess if the cortical eye fields are intact? What structure do the eye fields signal to?

Answer 12

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.

Question 13

How is general cortical dysfunction (but an intact brainstem) manifested in the eyes?

Answer 13

Eyes slowly drifting back and forth.

Question 14

What’s better than COWS for remembering how testing for the occulovestibular reflex works?

Answer 14

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.

Question 15

Two ways to assess ICP when looking at the retina?

Answer 15

Papilledema = increased ICP
Pulsing retinal veins = normal ICP
(note some people’s retinal veins don’t pulse, and that can be normal)

Question 16

What can posture tell you about localization?

Answer 16

Extension posture is “decerebrate” - below red nucleus

Flexion posture is “decorticate” - above red nucleus

Question 17

What sort of breathing pattern is consistent with a bilateral injury to the thalamus?

Answer 17

Cheyne-Stokes: hyperventilation alternating with periods of not breathing

Question 18

What’s the localization for hyperventilation?

Answer 18

Pontomesencephalic region

Question 19

What’s apneusis, and what’s its localization?

Answer 19

Slow, yawning breathing.

Lateral tegmentum of lower half of pons

Question 20

Where what is ataxic breathing, and where does it localize?

Answer 20

Really irregular breathing, often with periods of apnea.

Localizes to lower dorsomedial medulla.

Question 21

List 5 types of herniation.

Answer 21

Subfalcine
Uncal
Central (Diencephalic)
External (Transcalvarial)
Tonsilar

Question 22

What kind of herniation is most likely to cause respiratory arrest?

Answer 22

Tonsilar

Question 23

What actually herniates in subfalcine herniation? What is affected in subfalcine herniation?

Answer 23

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!)

Question 24

Signs of uncal herniation? (list 3)

Answer 24

Midbrain compression ->
Ipsilateral CN III deficit
Contralateral weakness
Ipsilateral weakness - though usu. happens after contralateral
(Prof. also noted “panting breathing rhythm” -> hyperventilation?)

Question 25

What can cause diencephalic herniation?

Answer 25

Large frontal or parietal mass lesions.

Question 26

Early signs of diencephalic herniation? (list 4)

Answer 26

Small pupils, somnolence, Cheyne-Stokes breathing, decorticate posturing

Question 27

Intermediate signs of diencephalic herniation? (3 things)

Answer 27

Pupils become mid-sized and non-reactive
Breathing: hyperventilation -> apneusis
Decerebrate posturing

Question 28

Late signs of diencephalic herniation? (2 things)

Answer 28

Oculovestibular/cephalic reflexes disappear.

Breathing: ataxic -> respiratory arrest.

Question 29

Major sign of tonsilar herniation?

Answer 29

Sudden respiratory arrest. It’s bad news.

Question 30

Micro review: 20 yr old woman with fever and somnolence x 2 days. Low blood pressure. Diffuse purpura. Neck rigidity. Mostly likely cause?

Answer 30

Meningicoccal meningitis and meningicoccemia. (just for fun)

Question 31

Would meningitis more likely cause diffuse cortical dysfunction or brainstem dysfunction? How would this be manifested in the eyes?

Answer 31

Cortical dysfunction. Lack of corrective nystagmus in vestibulocephalic reflex.

Question 32

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?

Answer 32

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.

Question 33

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?

Answer 33

Posterior pons. “Locked-in syndrome” secondary to pontine artery hemorrhage from blood pressure spike.