Arteries that anastomose with the posterior inferior cerebellar artery (PICA) can harbor aneurysms. We present a case of a patient who suffered a subarachnoid hemorrhage as a result from an aneurysm on the left lateral spinal artery (LSA) which anastomosed to the PICA. The aneurysm was surgically treated and the flow between the LSA and PICA was disrupted. The activated anastomotic network created a new anastomosis between the LSA and PICA which was seen at six months follow-up. Careful follow-up is warranted in patients who have an activated anastomotic network because they can potentially develop aneurysms on newly created anastomoses.