A patient with a dorsal pontine lesion presents with right-sided LMN facial palsy and failure of right eye abduction. MRI shows a lesion in the floor of the fourth ventricle at the facial colliculus. Which structures lie at this elevation?
- A Hypoglossal nucleus and fibers of the vagus nerve
- B Abducens nucleus and fibers of the facial nerve looping over it ✓
- C Facial motor nucleus and abducens nerve fascicles
- D Vestibular nuclei and cochlear nuclei
Correct answer: B. Abducens nucleus and fibers of the facial nerve looping over it
Explanation
The facial colliculus in the floor of the fourth ventricle is formed by motor neurons of the abducens nucleus plus the internal genu, the loop of facial nerve fibers winding around the abducens nucleus before exiting the pons. B lesion here damages both, explaining the combined ipsilateral LMN facial palsy and lateral rectus palsy. The facial motor nucleus itself lies more ventrolaterally in the pons.
Reference: Snell's Clinical Neuroanatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.