This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
[{'content': 'Third-nerve palsy can result from pathology at all of the following, EXCEPT: \nSelect and explain. \nA. Brainstem, B. Subarachnoid space, C. Cavernous sinus, D. None of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: A third-nerve palsy can result from pathology anywhere along its anatomic pathway, beginning with the brainstem, continuing within the subarachnoid space, traversing the cavernous sinus, and terminating within the orbit. Impoant: Contralateral hemiplegia suggests brainstem involvement. In cases of isolated oculomotor palsy, the subarachnoid space is the most likely site of pathology. The differential includes a posterior communicating aery aneurysm, uncal herniation, compressive neoplasms, inflammatory lesions, or trauma. Causes for third-nerve palsy within the cavernous sinus include neoplasms, carotid aery aneurysm, cavernous sinus thrombosis, and carotid-cavernous fistula. Orbital lesions causing third-nerve palsies may be due to inflammation, trauma, neoplasms, and mucoceles. Isolated third-nerve palsy is common with diabetic or hypeensive disease, likely due to microvascular ischemia. In this situation, the palsy rarely affects the pupil, and may be extremely painful. Ref: Levsky M.E., DeFlorio P. (2010). Chapter 2. Ophthalmologic Conditions. In K.J. Knoop, L.B. Stack, A.B. Storrow, R.J. Thurman (Eds), The Atlas of Emergency Medicine, 3e.', 'role': 'assistant'}]