INTRODUCTION
Posterior inferior cerebellar artery (PICA) aneurysms constitute 0.5%–3% of all intracranial aneurysms. Aneurysms arising distal to the vertebral artery-PICA junctions are called distal PICA aneurysms and are still rare (0.28%–1.4%). Mirror aneurysms of the PICA are extremely rare with only a few case reports.[1] Mortality due to recurrent bleed, within 48 h after the first rupture of PICA aneurysm is three times more than those of ruptured aneurysms in the anterior circulation. Hence, an early treatment is mandatory to achieve a favourable outcome.[2]
CASE REPORT
A 40-year old female patient presented with a sudden onset of severe headache and was evaluated in a nearby hospital. An emergency plain computerized tomography (CT) of the brain revealed bleed in the fourth ventricle. Magnetic resonance angiography of the brain did not reveal any abnormality and hence was managed conservatively. Ten days later, the patient had a similar episode of sudden severe headache and was referred to our centre.
A repeat CT brain plain revealed new haemorrhage in the fourth ventricle with lateral ventricular extension and moderate ventricular dilatation. CT angiography of the brain revealed mirror aneurysms of the PICA, a saccular aneurysm in the cortical segment of the left PICA and another aneurysm in the cortical segment of the right PICA. The left aneurysm was larger than the right and was projecting inferiorly into the cisterna magna. The patient underwent midline craniotomy and durotomy. There was fresh haemorrhage in the cisterna magna. The left PICA aneurysm was found immediately below the arachnoid. Fibrin plug was adherent to the nipple of the fundus indicating the site of the bleed. A 7 mm straight Yasargil clip was applied to the neck and the fundus was then punctured and shrunk with bipolar coagulation. Indocyanine green (ICG) angiography revealed preserved flow in the distal segment and total exclusion of the aneurysm.
Then, the right PICA was dissected in the cortical region and the aneurysm was exposed. The fundus was partially buried inside the pia of the cerebellum and the neck had a blister aneurysm. After subpial dissection, the neck was completely exposed and a straight 7 mm Yasargil clip was applied. During the application of the clip, there was rupture of the aneurysm from the fundus just beyond the neck at the subpial surface. The bleed was controlled by a patty, with gentle pressure at the rupture point, followed by a temporary clip application at the proximal segment. The permanent clip was repositioned at the neck and the temporary clip was removed.
On further dissecting the fundus, there was a healed fibrin at the nipple of the fundus suggesting an old sealed bleed. A mini 5 mm straight clip was applied separately to the blister at the neck of the aneurysm which could not be secured with the earlier permanent clip fearing occlusion of the parent vessel. ICG angiography showed intact distal flow. The fourth ventricle was then irrigated with warm saline and wound closed in layers.
Post-operative period was uneventful and a repeat CT angiography showed complete occlusion of both the aneurysms and preserved parent vessels.
DISCUSSION
Aneurysms occurring bilaterally on similar arteries are called mirror-image aneurysms. It includes <5% of all intracranial aneurysms. The most common locations of mirror aneurysms are the middle cerebral artery followed by the internal carotid and the posterior communicating arteries.[3,4] Mirror aneurysms of PICA are extremely rare with only a few reports and almost all the reported cases of distal PICA mirror aneurysms presented with subarachnoid haemorrhage.[1,5,6] It is more common in females, smokers and hypertensives and there is a role of genetic predisposition.[3] In general, the morphology of the aneurysm and the direction need not always be similar to their mirror counterparts similar to the present case.[3,4]
There are significant treatment dilemmas in managing mirror aneurysms - microsurgical versus endovascular, single stage versus multiple stages, etc., In ruptured mirror aneurysms, the lesion responsible for the rupture takes priority and the other can be managed at a later stage.[4,5] While this applies to most locations distal PICA mirror aneurysms would be ideal candidates for microsurgical clipping in single stage as the surgical exposure is the same and it is difficult to ascertain which one had ruptured based on the pattern of bleed.
Microsurgical clipping has the distinct advantage for these aneurysms, as they are more superficial, proximal to each other and hence easily accessible, surgically unlike in other locations. Moreover, there is less need for retraction, significant dissection and handling of neural tissues. It also gives access for drainage of cerebrospinal fluid (CSF); irrigation of the ventricles and can potentially obviate the need for CSF diversion at a later stage.
According to a retrospective analysis of cases with PICA aneurysms, the recurrence rate of endovascular management is 14.7% and procedure-related complications happened in 11.8% of patients.[7] Moreover, distal PICA aneurysms are tortuous and most interventionists prefer parent artery occlusion rather than selective aneurysm coiling because there are no perforators to the medulla. Although the risk of cerebellar ischaemia is high, most often they remain silent.[8,9] On the contrary, microsurgical clip reconstruction can preserve the parent vessel without the need for its sacrifice.[10]
In the present case, although the left aneurysm was responsible for rupture as evident by the adhesion of the arachnoid to the summit of the fundus and a fibrin plug, the right aneurysm also had a healed chronic fibrin plug at the summit of the fundus suggesting an earlier bleed (sentinel bleed). The patient was a relatively young female and hypertensive, amounting to the common risk factors associated with mirror aneurysms.
To conclude, mirror aneurysms of the distal PICA are extremely rare. Early management, preferably by microsurgical clipping in a single stage provides an excellent long-term outcome.
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Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that their name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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