When asked to protrude the tongue, deviation toward the right indicates a lesion of which structure?

• A. Right cranial nerve XII
• B. Left cranial nerve XII
• C. Medulla bilaterally
• D. Pons bilaterally

Answer: (A)

Focus on what protruding the tongue tests: the hypoglossal nerve (cranial nerve XII) and the tongue muscles it powers, especially the genioglossus which protrudes the tongue. When a unilateral hypoglossal nerve is damaged, the muscles on that side are weak. The intact side’s genioglossus then pulls the tongue toward the weakened side, so the tongue deviates toward the side of the lesion. If the tongue deviates to the right when asked to protrude, that points to a lesion of the right hypoglossal nerve. A left lesion would cause deviation to the left. Bilateral brainstem lesions (in the medulla or pons) would produce more widespread deficits and not produce a simple, unilateral tongue deviation.