A 58-year-old man has loss of vibration sense and astereognosis affecting the entire right side of the body, with the face spared. Pain and temperature are intact. A lesion in which location best explains these findings?

• A Right nucleus cuneatus of the medulla
• B Left medial lemniscus in the upper pons ✓
• C Right fasciculus gracilis in the cervical cord
• D Left ventral posterolateral nucleus restricted to its medial division

Explanation

Dorsal column second-order neurons cross in the caudal medulla as internal arcuate fibers and ascend as the medial lemniscus. Above the decussation, a unilateral medial lemniscus lesion gives contralateral loss of discriminative touch, vibration and proprioception involving the whole body. Face sparing fits a mid-pons lesion where trigeminal fibers have not yet joined the lemniscus. Option A would give ipsilateral deficits, and C would spare the arm because upper limb fibers travel in the fasciculus cuneatus.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.