A man of age 30 years came to clinic with inability to close his left eye, tears flowing over the left cheek and saliva dribbling from his left angle of the mouth.
**Core Concept**
The patient's symptoms are indicative of a facial nerve palsy, specifically involving the upper and lower motor neurons of the facial nerve. This condition is characterized by weakness or paralysis of the facial muscles on the affected side, leading to difficulty in closing the eye, tearing, and drooling.
**Why the Correct Answer is Right**
The patient's symptoms are consistent with a lower motor neuron lesion of the facial nerve, which is responsible for controlling the muscles of facial expression. The facial nerve is a mixed nerve that carries both sensory and motor fibers. The motor fibers are responsible for controlling the muscles of facial expression, including the orbicularis oculi, which closes the eye. The patient's inability to close his left eye suggests a lesion affecting the motor fibers of the facial nerve. The tearing and drooling are also consistent with a facial nerve palsy, as the nerve also carries parasympathetic fibers that stimulate tear production and saliva secretion.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it suggests a lesion affecting the trigeminal nerve, which is responsible for facial sensation and motor control of mastication. The patient's symptoms do not suggest a trigeminal nerve lesion.
**Option B:** This option is incorrect as it suggests a lesion affecting the cranial nerves III, IV, and VI, which control eye movements. The patient's symptoms do not suggest a lesion affecting these nerves.
**Option C:** This option is incorrect as it suggests a lesion affecting the hypoglossal nerve, which controls tongue movements. The patient's symptoms do not suggest a hypoglossal nerve lesion.
**Option D:** This option is incorrect as it suggests a lesion affecting the vagus nerve, which controls various functions including swallowing and vocal cord movement. The patient's symptoms do not suggest a vagus nerve lesion.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of facial nerve palsy is the presence of a Bell's sign, which is the ability to wrinkle the forehead on the affected side. This is due to the fact that the facial nerve is responsible for controlling the muscles of facial expression, including the frontalis muscle.
**Correct Answer: C.**