[Persistent primitive trigeminal artery presenting with Weber's syndrome: report of a case with three-dimensional CT angiographic evaluations].

We report a rare case of persistent primitive trigeminal artery(PPTA) presenting with brain stem infarction known as Weber's syndrome, and document its unique findings of three-dimensional CT angiography(3 D-CTA). A 69-year-old woman was admitted to our hospital because of gait disturbance and blepharoptosis on the right eye. Neurological examination on admission revealed the right oculomotor nerve palsy, left hemiparesis and dysarthria, all of which indicated the signs and symptoms of Weber's syndrome. Initial CT scan revealed no abnormality, but a subsequent 3 D-CTA demonstrated the PPTA originating from the right internal carotid artery penetrate into the clivus directly to the distal basilar artery, on top of which a small saccular aneurysm was incidentally visualized. Right internal carotid angiograms showed the PPTA run between the cavernous segment of the internal carotid artery and the distal portion of the basilar artery with the filling of both the posterior cerebral and superior cerebellar arteries. However, the proximal portion of the basilar artery was visualized through the right vertebral artery and there was no blood flow to its distal portion. Evidence of infarction was finally confirmed at the right midbrain and thalamus by the MRI performed 5 days after the onset. With a conservative treatment including physical therapy, the patient recovered well from the deficits and could walk by herself with a cane. With regard to the pathogenesis of vertebrobasilar insufficiency in a patient with PPTA, it is generally considered that microembolus from an atherosclerotic carotid artery may be its cause because of the presence of direct communication between the anterior and posterior circulations. In the present case, however, this mechanism may not be applied since there was no evidence of atherosclerotic plaque or stenotic lesions on the carotid arteries. Alternatively, an embolic occlusion may have occurred in the paramedian branches of the posterior cerebral artery since a dilated PPTA itself, which resembled fusiform-aneurysm in appearance, may become the origin of microembolus.