Diagnostic Video

Dr. Aslesha Vijaay Sheth*

Consultant & Clinical Lead, Kauvery Hospital, Trichy, India

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:

GCS – 15/15
Left eye – complete ptosis with deviation of left eye outward & downward
Left eye – medial rectus, superior rectus and inferior rectus palsy(inability to adduct, elevate or depress the left eye)
Vision was intact
Pupil. Left eye – dilated 4 mm, not reacting to light
Power was normal all 4 limbs
DTR was normal in all 4 limbs
Right leg plantar reflex – was mute, left leg plantar reflex was flexor
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 3^rd 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

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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