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: Medicine
Third nerve palsy with pupillary sparing is seen in all except: 
Select and explain. 
A. Hypeension, B. Aneurysm of posterior communicating aery, C. Diabetes mellitus, D. Craniopharyngioma
B: Aneurysm of posterior communicating aery
Answer: B: Aneurysm of posterior communicating aery 
Explanation: Answer is B (Aneurysm of posterior communicating aery): If the pupil is entirely normal, with all other components of an occulomotor palsy present aneurysm is so rare that an angiogram is seldom indicated. - Harrison Isolated pupil-sparing occulomotor palsy Most cases are thought to result from microvascular infarction of the nerve. Somewhere along its course from the brainstem to the orbit Major risk factors are: Diabetes Hypeension Vascular disease Major presentation is with pain. Spontaneous recovery over a period of months is the rule.