Injury of trochlear nerve, unspecified side, init encntr

This code signifies damage to the trochlear nerve (cranial nerve IV), which is responsible for innervating the superior oblique muscle of the eye. Such an injury typically results in impaired downward and outward gaze, often leading to vertical diplopia (double vision).

Apply this code when documentation confirms an injury to the trochlear nerve, without specifying laterality (left or right eye), and the patient is receiving active treatment for the acute injury. This is appropriate for initial evaluations and treatments following the onset of the nerve damage.

• Ensure documentation clearly states "injury" to the trochlear nerve, not just a palsy or disorder, to differentiate from non-traumatic etiologies.
• If laterality (left or right) is documented, select a more specific code (S04.21XA or S04.22XA).
• Confirm the "initial encounter" status; subsequent care for the same injury would require a different seventh character (e.g., D for subsequent, S for sequela).