Which cranial nerve, when lesioned, causes the tongue to deviate away from the side of the lesion and is associated with the 'Q' sign?

• A. Glossopharyngeal IX
• B. Vagus X
• C. Hypoglossal XII
• D. Accessory XI

Answer: (C)

The key idea is that tongue movement is governed by the hypoglossal nerve (XII). A unilateral XII lesion causes weakness of the ipsilateral tongue muscles, so when a patient tries to protrude the tongue, the healthy side’s muscles pull it toward the side of the lesion. This pattern, sometimes described with signs like the “Q” sign, points to XII involvement. The other nerves listed don’t directly control tongue protrusion, so they don’t produce this focal tongue deviation pattern. Therefore, the cranial nerve most likely involved is the hypoglossal nerve. (Note: deviation toward the lesion is typical for XII palsy, while deviation away from the lesion would suggest a corticobulbar UMN effect; the “Q” sign supports XII-related pathology in this context.)