A patient with a midbrain infarct presents with severe bilateral ptosis out of proportion to otherwise mild ocular findings. Which nucleus accounts for bilateral ptosis when damaged?

• A Edinger-Westphal nucleus
• B Central caudal nucleus of the oculomotor complex ✓
• C Subnucleus supplying the superior rectus
• D Nucleus of the posterior commissure

Explanation

The levator palpebrae superioris is supplied by a single midline subnucleus, the central caudal nucleus, which innervates both levators bilaterally. A lesion here therefore causes bilateral ptosis even with a unilateral or small midbrain lesion. The Edinger-Westphal nuclei provide preganglionic parasympathetic fibres affecting the pupil, not the lid. Each superior rectus subnucleus projects to the contralateral muscle, explaining contralateral upgaze weakness rather than ptosis.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.