Coiling of a Bihemispheric ACA Aneurysm Associated with Contralateral Persistent Primitive Olfactory Artery

Sir, Bihemispheric anterior cerebral artery (ACA) is an uncommon variant of ACA. When the A2 segment of an ACA supplies ipsilateral callosomarginal and bilateral pericallosal territories, the ACA is called a bihemispheric ACA.[1] The opposite ACA in such cases, lacks a pericallosal branch and supplies only the callosomarginal territory of that side.[1] Aneurysms are frequently found in association with bihemispheric ACA.[2-4] Another uncommon variant of ACA where the primitive olfactory artery persists in adult life and continues as the ACA (A2 segment onwards) is known as the persistent primitive olfactory artery.[1] The A1 segment is absent in such cases.[1] This variant is identified by a hairpin-like bend of the vessel.[5] Aneurysms are often formed in the hairpin bend of the persistent primitive olfactory artery.[5] Here we describe a patient who has a bihemispheric ACA on one side and a persistent primitive olfactory artery on the other side. A 55-year-old hypertensive male presented with acute onset severe headache. On examination, the patient was drowsy. There was no focal neurological deficit or any neck rigidity. A plain CT scan of the brain showed a right frontal lobar bleed and subarachnoid hemorrhage [Figure 1a]. Cerebral angiography revealed a right-sided bihemispheric ACA [Figure 1b-d]. The right callosomarginal artery was absent. The right ACA cortical branches were seen to be arising directly from the A2 segment [Figure 1b]. A 2.8 mm × 4.3 mm bilobed aneurysm was present at the branching point of the right frontal cortical branch [Figure 1b and c]. On the left side, a persistent primitive olfactory artery was seen continuing as the left callosomarginal artery [Figure 1c and e]. Endovascular coiling of the aneurysm was planned and the aneurysm was completely obliterated with two coils. Post-procedure angiography revealed normal opacification of the right ACA and its branches [Figure 1d and f]. There were no periprocedural complications and the patient was discharged after 3 days.Figure 1: (a) Plain CT scan of brain showing right frontal intraparenchymal hemorrhage. (b) Right ICA angiography showing an aneurysm (black arrow) at the branching point of the frontal cortical branch of right ACA. Distal to the aneurysm there is a trifurcation giving rise to bihemispheric pericallosal branches and the right precentral cortical branch. (c) Right ICA angiography showing the aneurysm (black arrow) and a persistent primitive olfactory artery (white arrow) on the oppsosite side filling via the anterior communicating artery (white arrowhead). (d) Right ICA angiography showing the bihemispheric distribution of the right ACA. Black arrowhead showing the coiled aneurysm. (e) Left ICA angiography showing the persistent primitive olfactory artery (white arrow). (f) Post coiling right ICA angiography showing complete obliteration of the aneurysm (black arrowhead) with normal flow into the right ACA and its branchesKnowledge of the anatomical variations of ACA is important. Treating a bihemispheric ACA aneurysm requires special attention as it carries the risk of bilateral ACA territory infarct both in case of coiling as well as clipping. Microcatheter negotiation into the distal ACA through the hairpin bend of a persistent primitive olfactory artery is extremely challenging. Any tortuous anatomy, loops and bends makes distal catheterization difficult and access to the desired site becomes technically demanding which mandates skilful manoeuvring of instruments. Our patient is unique as he has two ACA variants and the coexistence of these two variants in a single person has not been described previously. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.