[Agenesis of the internal carotid artery--report of a case combined with arachnoid cyst in a child].

A case of agenesis of the internal carotid artery combined with arachnoid cyst is reported. This 11-year-old boy had occasionally complained headache and nausea since he was of 9 years old. He was admitted to our hospital because of an epileptic seizure. Physical and neurological examinations on admission were normal. A CT scan showed a cystic mass in retrocerebellar region. MRI suggested absence of flow void area indicating internal carotid artery in the cavernous sinus on left side. Left common carotid angiogram showed absence of the internal carotid artery. Bilateral A2 segments were supplied by right A1 with tortuous anterior communicating artery. Left middle cerebral artery and left ophthalmic artery were supplied via dilated left posterior communicating artery on left vertebral angiogram. Thin slice, axial target image of the CT revealed absence of the left bony carotid canal. MRI by 3D TOF method confirmed no blood flow in this area. MR angiography provided sufficient information about cervical vessels non-invasively. 123I-IMP SPECT image ascertained no hypoperfusion area in left cerebral hemisphere. Convulsion was controlled with sodium valproate. Association of agenesis of the internal carotid artery and arachnoid cyst could be a coincidence.