Diagnostic Video

Dr. Aslesha Vijaay Sheth*

Consultant & Clinical Lead, Kauvery Hospital, Trichy, India

*Correspondence: [email protected]

Dr Aslesha Vijaay Sheth Emergency

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Diagnosis: Left paramedian midbraininfarct

A 60 years gentleman, with history of diabetes, hypertension and dyslipidemia, presented to ED with h/o sudden onset giddiness, swaying to right side and with progressive inability to open the left upper eyelid, since 12 hrs.

BP of 220/100 mmHg, all other vital parameters within normal limits.

Neurological examination:

 

  1. GCS – 15/15
  2. Left eye – complete ptosis with deviation of left eye outward & downward
  3. Left eye – medial rectus, superior rectus and inferior rectus palsy(inability to adduct, elevate or depress the left eye)
  4. Vision was intact
  5. Pupil. Left eye – dilated 4 mm, not reacting to light
  6. Power was normal all 4 limbs
  7. DTR was normal in all 4 limbs
  8. Right leg plantar reflex – was mute, left leg plantar reflex was flexor
  9. Mild incoordination in Finger-nose & Finger-Finger test on the left side

In view of suspected 3rd nerve (oculomotor nerve) palsy – An MRI Brain with MRA was done which revealed:

Abnormal focus with altered signal intensity in the left paramedian midbrain appearing hyperintense on T2W/FLAIR with restricted diffusion on DWI – suggestive of acute infarct of left paramedian midbrain.

Why does midbrain infarct cause III cranial nerve palsy? What are the differences between nuclear & fascicular midbrain lesions?

    • The nuclei of the 3rd cranial nerve originate at the level of the superior colliculus.
    • The oculomotor fascicles run ventrally & laterally from the oculomotor complex, pass through and medial to the red nucleus and then exit the brainstem medial to the cerebral peduncles
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  • A 3rd cranial nerve palsy due to midbrain infarction results from either nuclear or fascicular lesion. Such a lesion can be usually differentiated clinically.
  • The subnucleus of the levator palpebrae superioris, the central caudate nucleus is single & midline.
  • The fibres of the superior rectus muscles originate in paramedian nuclei and provide crossed innervation.
  • Lesions of the oculomotor nucleus would result in bilateral ptosis and contralateral upward gaze palsy
  • Lesions affecting the fascicular fibres will result in unilateral third nerve palsy. Pupillary reactions in such cases are variable but its involvement is more common.

Note: As the face conveys many important and educative lessons in clinical diagnosis, we regret that the general features could not be masked.

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