Week 4 - Clinical Correlation: Coma

Question 1

what do the 4 levels of consciousness mean?

• normal
• somnolent
• obtunded
• coma

Answer 1

• no external stimulation needed to maintain wakefulness
• external stimulus needed to wake, but when stop stimulating, falls back asleep
• external stimulus needed, but doesn’t wake up to normal mental status
• no wakefulness

Question 2

how do respiratory patterns differ if there’s a lesion in:

• diencephalon
• midbrain
• pons
• medulla

Answer 2

1. Cheyne-Stokes respiration (waning/waxing episodes of heavy/no breathing)
2. central neurogenic hyperventilation (since near reticular formation, cuts off diaphragm from voluntary contractions, causing deep/regular breaths)
3. apneustic respirations (inspiratory spasms, not organized or coordinated)
4. ataxic respirations

Question 3

how does the pupillary light reaction differ if there’s a lesion in:

1. diencephalon
2. CN III (uncal)
3. midbrain
4. pons
5. tectum

Answer 3

1. small and reactive (normal)
2. one eye is dilated and fixed (consensual is normal, direct is not)
   - not in coma
3. midposition, fixed
   - in coma
4. pinpoint (parasympathetics don’t work)
5. large “fixed”, hippus
   - not in coma

Question 4

how do the occulocephalic and occulovestibular reflexes work? (example with right cochlea)

Answer 4

1. input from R cochlea to R medial vestibular nucleus
2. MVN to R VI nucleus and L pons
3. pons to L lateral rectus and R III nucleus (via MLF)
4. III nucleus to R medial rectus

altogether allows eyes to move together, to the left (fixate eyes on someone when head is moving)

Question 5

what is decorticate posturing? what is this the same as? what does this suggest about the lesion level?

Answer 5

abnormal flexor response of arm (may be wrist and fingers too, with adduction of upper extremity) with extension (may be internal rotation and platarflexion) of legs
-same as spastic hemiparesis, which arises from disconnection of cortex from motor centers, suggesting lesion above level of red nucleus in midbrain

Question 6

what is decerebrate posturing? what is the full form? what is this commonly seen with?

Answer 6

abnormal extensor response of arm and leg

• full form: opisthotonos (extension of trunk/neck), clenching of jaws, stiff limb extension, with internal rotation of arms and plantarflexion of feet
• most common with lesions caudal to red nucleus, due to release of vestibulospinal output

Question 7

what does a bilateral midbrain lesion show in regards to

• respiratory pattern
• pupillary size/reaction
• oculocephalic and oculovestibular response
• motor response to stimulation

Answer 7

1. sustained regular hyperventilation (rarely Cheyne-Stokes)
2. fixed midposition, irregular shape (no reaction)
3. impaired, may be dysconjugate (b/c midbrain, but pons OK)
4. usually motionless, but can be decerebrate rigidity (lesion below red nucleus)

Question 8

what does a bilateral dienceophalic lesion show in regards to

• respiratory pattern
• pupillary size/reaction
• oculocephalic and oculovestibular response
• motor response to stimulation

Answer 8

1. Cheyne-stokes
2. small pupils with small range of contraction (midbrain OK)
3. normal (pons okay)
4. motionless or decorticate (lesion above red nucleus)

Question 9

what does a bilateral pontine lesion show in regards to

• respiratory pattern
• pupillary size/reaction
• oculocephalic and oculovestibular response
• motor response to stimulation

Answer 9

1. ataxic
2. fixed midposition (not pinpoint, b/c going rostral–>caudal)
3. no response (vestibular nucleus can’t stimulate pons or midbrain)
4. no response (motionless and flaccid)

Question 10

what does a unilateral diencephalic lesion show in regards to

• respiratory pattern
• pupillary size/reaction
• oculocephalic and oculovestibular response
• motor response to stimulation

Answer 10

1. Cheyne-stokes
2. small pupils with small range of contraction (midbrain OK)
3. normal (pons and mibrain OK)
4. only one side reacts

Question 11

what does a (late) 3rd nerve lesion show in regards to

• respiratory pattern
• pupillary size/reaction
• oculocephalic and oculovestibular response
• motor response to stimulation

Answer 11

1. regular sustained hyperventilation (midbrain impaired); rarely Cheyne-stokes
2. ipsilateral pupil is widely dilated, but doesn’t constrict (the other eye is fine; shows part of midbrain works)
3. the unaffected eye is fine (pons working, but part of midbrain doesn’t)
4. can have either decorticate or decerebrate responses, or both (one on each side)