Chapter 16 Brain Stem Lesions in High Yield Neuroanatomy is your best friend. Best thing to do is break down every single symptom and try to figure out why it is happening. 😉
I made some notes a while back in medical school when I was tutoring this topic with examples. Read the attached file for color coating and stuff. Hope this helps.
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HOW TO APPROACH CASE BASED QUESTIONS FOR BRAIN STEM LESIONS:
1.) Alternating symptoms are a major sign of brain stem lesions
2.) Find out which cranial nerve is damaged to help localize which part of brainstem is affected.
SOME HELPFUL QUESTIONS TO THINK ABOUT DURING STEP 2 of the Approach:
Is there hoarseness in voice? If yes, cranial nerve X is damaged = Lesion in Lateral Medulla
Is there Lateral strabismus? If yes, cranial nerve III is damaged = Lesion in the Midbrain
Is there medial strabismus? If yes, cranial nerve VI is damaged = Lesion in Pons
Is there complete facial paralysis? If yes, example of a LMN type of lesion due to damage of the cranial nerve VII nucleus = Lesion in the pons
Is there facial paralysis of only the lower lip? If yes, example of an UMN type of lesion due to damage of the corticonuclear/corticobulbar fibers innervating the lower half of the cranial nerve VII nucleus. (***In this case the cranial nerve XII may also be damaged and will be found deviating in the contralateral direction of lesion due to an UMN type of damage.***)
3.) Find out which tracts are damaged involving motor symptoms on right or left side.
4.) Find out which tracts are damaged involving sensory symptoms on right or left side.
5.) Although the MLF is found throughout the brainstem, damage to the MLF is USUALLY due to a lesions in the pons.
BLOCK QUESTION #30
A patient with a bullet wound to the head is referred to you for neurological examination. Upon entering the hospital room you find the patient on a respiratory and cardiac monitor. You have difficulty arousing the patient and once awake you note the following: Right pupil is constricted; there is medial strabismus of the right eye and upon attempted right lateral gaze the left eye fails to adduct; loss of pain and temperature sensitivity on the right side of the face and left side of the body; deafness of the right ear; a pronounced intention tremor in the right arm and leg. The deep tendon reflexes on the right side are not as brisk as those on the left and there appears to be a complete facial paralysis on the right side.
The likely site for this lesion is:
A The left internal capsule
B The right caudal pons
C The left cerebellar hemisphere
D The left side of the midbrain at the level of the superior colliculus
E The right side of the medulla at the level of the dorsal column nuclei
- Right pupil constricted means III is working NORMALLY; cranial nerve III function is to constrict the pupil. (If III was damaged, patient would have presented with a dilated pupil.)
Sympathetic plexus is most likely DAMAGED on the right side; Horner's syndrome leads to pupil constriction.
- Medial Strabismus = DAMAGE to the right lateral rectus muscle which is supplied by cranial nerve VI
- The right eye is already deviated to the right, if the MLF was working normally, then the left eye would have adducted. The left eye failing to adduct means that the MLF is DAMAGED; there is DAMAGE to the connection between the right lateral rectus and the left medial rectus.
- Loss of pain and temperature sensitivity on the right side of face means the right trigeminal nucleus is DAMAGED. Loss of pain and temperature on left side of body means right lateral spinothalamic tract is DAMAGED; result of contralateral loss of pain and temperature.
- Right VIII cochlear nerve DAMAGED near MCP (exam questions may mention that MCP is in a region near upper medulla) = Hearing loss on the ipsilateral side.
- Complete facial paralysis on right side = LMN type of lesion to the right facial nucleus leads to ipsilateral symptoms. Cranial nerve VII is found at the level of the facial colliculus at the level of the pons.
- Answer is the B The right caudal pons
BLOCK QUESTION #36
A 55 year old overweight man was brought to the emergency room unconscious after he had collapsed while loading a truck.After he regained consciousness, an exam revealed a paresis of both right limbs with a Babinski sign on the right. The patient's tongue deviated to the left upon protrusion, and he had no vibratory sense on the right side of the body. These findings suggest.
A) A lesion in the medial medulla
B) A lesion in the medial pons
C) An infract PICA
D) A lesion in the lateral medulla
- Left corticospinal tract DAMAGE will lead to contralateral UMN type of lesions.
- Tongue protrusion can be tricky:
The tongue deviates to the SAME side in a LMN type of lesions.
The tongue deviates to the OPPOSITE side in a UMN type of lesion, HOWEVER, this presentation is usually involved with an UMN type of lesion of the VII nerve also in which paralysis of the face is seen only in the lower lips and part of the cheek.
So with that said, this case is most likely presenting with a LMN type of lesion of the XII nerve. The XII nerve is found in the medial portion of the medulla.
- Left medial lemniscus DAMAGE will result in contralateral loss of vibration, touch, pressure, proprioception, two point discrimination, stereognosis
- The answer is A) A lesion in the medial medulla
BLOCK QUESTION #38
A 50 year old woman was diagnosed with paralysis of her right arm and leg that later became spastic with increased deep reflexes and a positive Babinski. There were ataxic movements on the left extremities. The muscle of the lips and the cheeks were weak on the right side but she could tightly close both eyes and wrinkle her forehead symmetrically. An internuclear opthalmoplegia was observed in which the left eye would not adduct on attempted lateral gaze to the right although both eyes converged on near objects. There was loss of vibratory sense and discriminative touch from the right side of the body. When protruded, the tongue deviated towards the right. Where is the site of the lesion?
A Left Medial medullary
B Left Midbrain
C Left Cerebellum
D Left Pons
E To difficulty to diagnose
- Left corticospinal tract DAMAGE will lead to contralateral UMN type of lesions.
- Left cerebellar peduncle lesion results in IPSILATERAL symptoms damage can be ICP, MCP, or SCP (More information is needed to confirm which peduncle is involed.)
- VERY IMPORTANT to note that this patient has DAMAGE to left corticonuclear fibers resulting in a CONTRALATERAL UMN type of lesion on the face. The entire face is not paralyzed, therefore, LMN type of damage to the cranial nerve VII nucleus can be ruled out.
- Internuclear opthalmoplegia USUALLY results to damage of the MLF at the level of the Pons, important to remember USUALLY NOT ALWAYS.
- Left medial lemnisus is DAMAGE results in CONTRALATERAL loss of vibratory sense and discriminative touch.
- This last line may tend to direct your attention that the XII nucleus LMN type of lesion might be present. HOWEVER, in a medial medullary syndrome the facial nerve is not usually involved as a symptom.
- The involvement of the Facial nerve and the MLF can most likely direct this lesion to the Pons.
- The answer is D Left Pons
