What is the most likely etiology of a non-comitant deviation following a Traumatic Brain Injury (TBI)?

• A. CN 4 palsy
• B. CN 3 palsy
• C. CN 6 palsy
• D. Convergence insufficiency

Answer: (A)

Noncomitant deviations after a traumatic brain injury point to a focal cranial nerve palsy affecting a single extraocular muscle. The fourth cranial nerve, which innervates the superior oblique, is especially susceptible to injury because of its long, winding intracranial path. When this nerve is compromised, the eye cannot depress properly in adduction, producing a vertical and torsional misalignment that changes with gaze. This gaze-dependent pattern is the hallmark of a superior oblique palsy and explains why the deviation is noncomitant. Clinically, you’d expect hypertropia that worsens when looking toward the affected eye and with head tilt toward the same side. Convergence insufficiency is a near-vision fusional issue and does not explain a gaze-dependent ocular misalignment after head trauma. A third nerve palsy would bring ptosis and broader deficits, while a sixth nerve palsy typically causes horizontal diplopia that doesn’t fit the characteristic vertical/torsional, gaze-dependent pattern of a superior oblique palsy.