Question

A patient was admitted with skull base trauma. The doctor was testing the marked structure in the image. Which of the following nerves was being tested?

• A. Vagus
• B. Facial nerve
• C. Glossopharyngeal nerve
• D. Trigeminal nerve

Hint:

After skull base trauma, look for which nerve exits through the jugular foramen and is tested by the gag reflex and posterior pharyngeal sensation.

Answer 1

The Correct Option is C

Step 1: Identify the image context. The image shows a lateral dissection of the head and neck with a marked structure being tested in a patient with skull base trauma. The marked structure corresponds to the glossopharyngeal nerve (CN IX) based on its anatomical location.

Step 2: Anatomy of the glossopharyngeal nerve. The glossopharyngeal nerve (CN IX) exits the skull through the jugular foramen. It provides:
- Sensory supply to the posterior one-third of the tongue (taste and general sensation)
- Sensory supply to the pharynx, soft palate, and middle ear (tympanic nerve)
- Motor supply to the stylopharyngeus muscle
- Parasympathetic supply to the parotid gland (via lesser petrosal nerve)
- Carotid sinus and carotid body innervation (baroceptors and chemoreceptors)

Step 3: Clinical relevance in skull base trauma. Skull base fractures involving the jugular foramen can injure CN IX (along with CN X and CN XI), causing jugular foramen syndrome (Vernet syndrome). Testing CN IX involves assessing the gag reflex, sensation of the posterior pharyngeal wall, and taste on the posterior third of the tongue.

Step 4: Differentiate from other nerves. The facial nerve exits through the stylomastoid foramen; vagus exits through jugular foramen (but is more inferior); trigeminal nerve exits through foramen ovale/rotundum/spinosum. The marked anatomical position in the image corresponds to CN IX.

Conclusion: The nerve being tested is the glossopharyngeal nerve (CN IX).