Brainstem lesions

aka Neurological Mind-boggler 003

As promised here are some scenarios to try out Gates’ Brainstem Rules of 4 (helpful figures here):

Scenario 1

You are examining a patient with sudden onset left-sided weakness. These are your clinical examination findings:

  • weakness of the left upper and lower limbs, with sparing of the face.
  • tongue deviation to the right, with no ophthalmoplegia.
  • loss of vibration and proprioception in the left upper and lower limbs.

Where is the lesion?

  • weakness of the left upper and lower limbs, with sparing of the face:
    motor (corticospinal pathway) localises the lesion to the contralateral medial brainstem
    (sparing of the face (CN7) means the lesion must be below the upper pons)
  • tongue deviation to the right, with no ophthalmoplegia:
    tongue deviation indicates CN12 involvement, localising the lesion to the ipsilateral medulla
    (sparing of CN3 and CN6 means the midbrain and pons are not involved)
  • loss of vibration and proprioception in the left upper and lower limbs:
    confirms localisation of the lesion to the contralateral medial brainstem

Site of the lesion: right medial medulla. Sometimes, due to the peculiar pattern of blood supply to the medulla, bilateral infarction may occur.

Scenario 2

You are examining a patient with sudden onset right-sided weakness. These are your clinical examination findings:

  • weakness of the right face, upper and lower limbs.
  • the left eye is turned “down and out” and the pupil is dilated.

Where is the lesion?

  • weakness of the right face, upper and lower limbs:
    motor (corticospinal pathway) localises the lesion to the contralateral medial brainstem
    (involvement of the face means the lesion must be at or above the upper pons)
  • the left eye is turned “down and out” and the pupil is dilated:
    CN3 involvement, localising the lesion to the ipsilateral midbrain
    (sparing of CN6 and CN12 means the pons and medulla are not involved)

Site of the lesion: left medial midbrain. A CN3 palsy (from damage to the CN3 nerve fascicle) and contralateral hemiplegia is known as Weber’s syndrome (“basal” infarction) – which can be difficult to distinguish from ‘coning’ if you don’t have a CT scanner available.

Scenario 3

You are examining a patient with vertigo, vomiting, and nystagmus. These are your clinical examination findings:

  • left-sided limb ataxia.
  • left-sided alteration of pain and temperature on the face.
  • left-sided ipsilateral Homer’s syndrome.
  • right-sided alteration of pain and temperature affecting the arm and leg.
  • dysarthria and decreased gag reflex on the left, with the palate pulling up on the right-side.

Where is the lesion?

  • left-sided limb ataxia:
    spinocerebellar pathway localises the lesion to the ipsilateral lateral brainstem.
  • left-sided alteration of pain and temperature on the face:
    Sensory nucleus of the 5th cranial nerve localises the lesion to the ipsilateral lateral brainstem.
  • left-sided ipsilateral Homer’s syndrome:
    Sympathetic pathway localises the lesion to the ipsilateral lateral brainstem.
  • right-sided alteration of pain and temperature affecting the arm and leg:
    Spinothalamic pathway localises the lesion to the contralateral lateral brainstem.
  • dysarthria and decreased gag reflex on the left, with the palate pulling up on the right-side:
    localises the lesion to the medulla affecting the ipsilateral CN9 and 10.

Site of the lesion: left lateral medulla. Also known as Wallenberg’s syndrome, caused by a left vertebral or left posterior inferior cerebellar artery occlusion (blood supply is variable to this region).

Scenario 4

You are examining a patient with right-sided deafness, that was preceded by tinnitus. These are your clinical examination findings:

  • right-sided limb ataxia (predominantly affecting the right upper limb).
  • right-sided facial numbness with loss of the corneal reflex.
  • right-sided hemi-facial spasms.

Where is the lesion?

  • right-sided limb ataxia (predominantly affecting the right upper limb):
    spinocerebellar pathway localises the lesion to the ipsilateral lateral brainstem.
  • right-sided facial numbness with loss of the corneal reflex:
    Sensory nucleus of the 5th cranial nerve localises the lesion to the ipsilateral lateral brainstem.
  • right-sided hemi-facial spasms:
    the lesion involves the pons affecting the ipsilateral CN7.

Site of the lesion: The findings indicate a lesion affecting the right lateral pons with evidence of spinocerebellar involvement. In this case the lesion was not vascular in origin but in fact an example of a cerebropontine angle lesion – an acoustic neuroma (or schwannoma). This demonstrates the broader utility of Gates’ Brainstem Rules of 4.

References

  • Gates, P. The rule of 4 of the brainstem: a simplified method for understanding brainstem anatomy and brainstem vascular syndromes for the non-neurologist. Internal Medicine Journal 2005; 35: 263-266 [pubmed]
  • Goldberg, S. Clinical Neuroanatomy Made Ridiculously Simple. MedMaster Series, 2000 Edition. [betterworldbooks]
  • Patten, J. Neurological Differential Diagnosis. Springer-Verlag, 1995 (2nd edition). [Google books preview]

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Comments

  1. Jimmyjones says

    Cheers from a med student who now understands brainstem lesions -- excellent diagram -- thanks for your efforts.

  2. MR says

    these problems are great, i passed it on to all my friends….real life saver during step 1 studying. thank you so much!!

  3. Med student 1 says

    This post is particularly helpful. After 30-40 minutes of using your blog posts, I have a significantly better understanding of brainstem lesions. Cheers.

  4. JD says

    Minor spelling error -- in the last question you wrote ‘cerebropontine angle lesion’ but I think you meant ‘cerebellopontine angle lesion’. Just mentioning it as I got confused for a sec and had to google it.

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