Sudden onset of hemiplegia with contra lateral ophthlamoplegia the probable lesion is in –
**Core Concept**
The sudden onset of hemiplegia with contralateral ophthalmoplegia suggests a lesion affecting the corticospinal tract and the oculomotor nerve (cranial nerve III) on the same side as the lesion, but with the oculomotor nerve involvement on the opposite (contralateral) side. This phenomenon is often referred to as a "crossed paralysis" or "crossed hemiplegia with ophthalmoplegia."
**Why the Correct Answer is Right**
The correct answer is related to the anatomy of the brainstem, specifically the pons. The corticospinal tract, which carries motor signals from the cerebral cortex to the spinal cord, decussates (crosses over) at the medullary pyramids. In contrast, the oculomotor nerve, which controls eye movements, emerges from the brainstem in the midbrain, but its fibers also decussate at the level of the superior colliculus in the midbrain. A lesion in the pons can therefore disrupt the corticospinal tract on the same side as the lesion, while the oculomotor nerve fibers on the opposite side are affected due to their decussation in the midbrain. This results in contralateral ophthalmoplegia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the anatomy and physiology of the corticospinal tract and the oculomotor nerve.
**Option B:** This option is incorrect because it is too general and does not specify the location or type of lesion that would cause the described symptoms.
**Option C:** This option is incorrect because it does not accurately describe the phenomenon of crossed paralysis or crossed hemiplegia with ophthalmoplegia.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the corticospinal tract and the oculomotor nerve have different decussation patterns, which can lead to the phenomenon of crossed paralysis or crossed hemiplegia with ophthalmoplegia. This is an important concept to keep in mind when evaluating patients with sudden onset of hemiplegia and contralateral ophthalmoplegia.
**Correct Answer:** D. Pons