A 65-year-old diabetic woman develops weakness on the left side of the face, right arm,and right leg. She also has diplopia on left lateral gaze. What is the site of lesion?
**Core Concept**
The patient's symptoms suggest a lesion affecting the motor pathways of the brain, resulting in contralateral weakness and a specific pattern of diplopia. This is a classic presentation of a brainstem lesion, given the involvement of cranial nerve VI (abducens nerve), which controls lateral gaze.
**Why the Correct Answer is Right**
The patient's symptoms are consistent with a lesion in the pons, specifically affecting the corticospinal tract and the abducens nerve nucleus. The corticospinal tract is responsible for motor control, while the abducens nerve controls eye movement. The involvement of cranial nerve VI is a key clue, as it is the only cranial nerve that has a nucleus in the pons. The lesion is likely located in the pons, given the involvement of the abducens nerve and the contralateral weakness.
**Why Each Wrong Option is Incorrect**
**Option A:** A lesion in the medulla oblongata would more likely affect the pyramidal tracts and cranial nerve IX, X, and XII, which are not consistent with this patient's symptoms.
**Option B:** A lesion in the midbrain would more likely affect the oculomotor nerve (cranial nerve III) and the trochlear nerve (cranial nerve IV), which control other eye movements.
**Option C:** A lesion in the frontal lobe would more likely affect the motor cortex, resulting in weakness on the opposite side of the body, but not specifically affecting the abducens nerve.
**Clinical Pearl / High-Yield Fact**
When assessing a patient with a brainstem lesion, it's essential to examine for cranial nerve abnormalities, as they can provide critical clues about the location and severity of the lesion.
**Correct Answer:** C. The lesion is likely located in the pons, affecting the corticospinal tract and the abducens nerve nucleus.