Giant dissecting aneurysm of basilar artery in a child – treated by flow reversal: A case report

Abstract

Although intracranial aneurysms are rare in the paediatric population, the proportion of those involving posterior circulation is higher than that of adults (approximately 25% vs. 8%, respectively). Moreover, posterior circulation aneurysms in kids tend to be larger in size, many of them being giant dissecting types, and treatment of them is often challenging. Treatment of giant dissecting aneurysms, especially involving the Basilar artery is difficult due to strategic location and haemodynamic factors. Use of reconstructive techniques viz. flow-diverters and braided stents is difficult in children because of the lack of standard protocol for use of antiplatelet therapy and the need for prolonged use of the same. Continuous growth of parent vessel is also suggested as a pitfall for the use of a flow diverter/ braided stent which has a fixed caliber. Carefully planned endovascular parent or feeder branch artery occlusion (FAO) is a time-tested method to achieve flow reversal or favourable flow modifications in an arterial segment harbouring dissecting aneurysm. Here, in this case report, we describe a case of a ruptured distal giant basilar artery dissecting aneurysm in a 10-year-old boy treated with flow diversion by FAO. The dominant left vertebral artery was occluded, thereby diverting flow from the right vertebral artery towards the left posterior inferior cerebellar artery and decreasing flow through the aneurysm. On 1-year follow-up, the patient was asymptomatic and on check angiography, there was complete involution of the aneurysm with increased flow through bilateral posterior communicating arteries to distal posterior circulation which proved our hypothesis correct.

Introduction

Although intracranial aneurysms are rare in the paediatric population, the proportion of those involving posterior circulation is higher than that of adults (approximately 25% vs. 8%, respectively). ¹ Moreover, posterior circulation aneurysms in kids tend to be larger in size, many of them being giant dissecting types ² and treatment of them is often challenging. The usefulness of endovascular reconstructive techniques using flow diverters or braided stents has not been well established in children though a few authors have attempted the same recently. ³ The problems associated with the deploying of a metallic device (e.g. flow diverter) of relatively fixed diameter in a growing vessel of a child and the need for dual antiplatelet therapy are some of the confounding issues not fully addressed yet.

On the other hand, dissecting aneurysm is basically a disease of the arterial wall and flow reversal is known to cause healing of the disease. Carefully planned endovascular parent artery or a relevant feeder branch occlusion is a time-tested method to achieve flow reversal or favourable flow modifications in an arterial segment harbouring dissecting aneurysm. ⁴ Here, we intend to illustrate this principle with an example of a 10-year-old boy who presented to us with a ruptured giant basilar artery dissecting aneurysm and was successfully treated by occlusion of one of the vertebral arteries.

Case report

A 10-year-old boy presented with a sudden severe headache, vomiting, and altered sensorium to a private hospital where his urgent non-contrast computed tomography (NCCT)-head followed by magnetic resonance imaging (MRI) was performed. The imaging evaluation revealed diffuse subarachnoid haemorrhage in the basal cisterns with intraventricular extension (modified Fischer's grade II) and a giant aneurysm occupying interpeduncular and prepontine cisterns, causing mass effect over the brainstem and obstructive hydrocephalus (Figure 1(a)). Soon the patient experienced two episodes of generalised tonic-clonic seizures (GTCS) followed by left hemiparesis and a further dip in sensorium and hence was intubated. After that, the patient was referred to our hospital for further management. He was received at our hospital in a state of depressed sensorium with a Glasgow coma scale of E₄V_TM₅. Further examination revealed left hemiparesis and left partial third nerve palsy in the form of ptosis and left anisocoria.

Figure 1.

Axial NCCT (a) at the time of presentation shows a large hyperdense lesion in a prepontine cistern (arrow) with diffuse SAH in basal cisterns and bilateral Sylvian fissures with IVH. A significant mass effect on the brainstem is also noted. IADSA images: left VA angiogram in anteroposterior view (b), lateral view (c) and right VA angiogram in anteroposterior view (d) showing a giant distal basilar trunk dissecting aneurysm. A note is made of normal opacification of bilateral PCA (long arrows in (b)) with prominent left PICA (small arrow in (b)). Right PICA (arrow) is filling from right VA (d). Balloon occlusion test (arrow) with left V2 VA occlusion (e) and sequential ICA injections shows moderate flow through the right P-com artery (arrow) (f) and mild flow through the left P-com artery (not shown here). Subsequently, feeder branch artery occlusion (g) was done by coiling (arrow) in the left distal V2–V3 segment of VA. Immediate post-procedure, right VA angiogram (h), shows filling of the left PICA too.

ICA: internal cerebral artery; NCCT: non-contrast computed tomography; PCA: posterior cerebral artery; PICA: posterior inferior cerebellar artery; VA: vertebral artery; SAH: subarachnoid haemorrhage; IVH: intraventricular haemorrhage; IADSA: intra-arterial digital subtraction angiography.

Reviewing the available images, we diagnosed a ruptured upper basilar artery aneurysm and planned an urgent digital subtraction angiography (DSA) under general anaesthesia with the intent of endovascular intervention. DSA confirmed the presence of a giant dissecting distal basilar trunk aneurysm measuring 32 × 12 × 20 mm. The left vertebral artery (VA) was dominant with a large left posterior inferior cerebellar artery (Figure 1(b) to (d)). To further understand the haemodynamics, we proceeded with the balloon occlusion test. The left VA distal V2 segment was occluded by inflating a balloon microcatheter (Figure 1(e)) with a sequential injection of bilateral internal cerebral arteries (ICAs) and the right VA (RVA). Right ICA (RICA) run showed moderate size right posterior communicating (P-com) artery supplying right posterior cerebral artery (PCA) territory (Figure 1(f)). The left ICA run showed a small left P-com artery (P-com A) partially supplying the left PCA territory (Figure 1(g)). The RVA run showed antegrade flow in the basilar artery filling bilateral PCAs with relative stasis in the aneurysm and filling the left posterior inferior cerebellar artery (PICA) through flow reversal in distal left V4 VA. Subsequently, feeder branch artery occlusion (FAO) of the left VA was done by deploying detachable coils in distal V2-proximal V3 segments (Figure 1(h)). Control angiograms showed findings similar to the balloon occlusion test, which included contrast stasis in the aneurysm.

Post-procedure, the patient was kept intubated with rigorous monitoring in the intensive care unit (ICU). He showed rapid improvement in the sensorium and was extubated the next day. His overall neurological status started improving, only to be punctuated by right upper limb weakness (4 of 5) on the third post-procedure day. NCCT showed a recent focal infarct in the left posteromedial parietal cortex. Subsequent MRI confirmed this infarct apart from a few other tiny infarcts in the left cerebellar hemisphere (Figure 2(a)). Relative increase in aneurysmal thrombosis was also noted (Figure 2(b)). The patient’s blood pressure was augmented, suspecting perfusion deficits as the cause of infarcts. He gradually improved in the following weeks. A check computed tomography (CT) at two weeks showed persistent hydrocephalus, though the aneurysm size appeared to be shrinking. A medium-pressure ventriculoperitoneal shunt was performed (Figure 2(c)), following which further improvement in the clinical condition was observed. The patient was discharged with residual deficits of left-side ptosis with anisocoria and mild weakness in bilateral upper limbs (4+/5).

Figure 2.

MRI was done on the sixth post-procedure day. A small acute left parietal infarct is noted on DWI (a). Axial T2 WI (b) shows the appearance of a thrombus in the anterior part of the aneurysm (arrow). Note the significant mass effect on the brainstem is still present with moderate hydrocephalus. NCCT (c) done after 1 week of VP shunt (arrow) shows a decrease in hydrocephalus. Follow-up imaging at 3 months. NCCT (d) shows a decrease in the size of the aneurysm with the appearance of peripheral calcification anteriorly. RVA angiogram – lateral (e) and anteroposterior views (f) show irregular narrowing of the mid-segment of the basilar artery and only partial filling of the aneurysm with a decrease in size as well. Also, note filling of left PICA from RVA. Right ICA angiogram (g) shows augmented flow through the right P-com artery. However, the left P-com artery is not enlarged as much (h).

ICA: internal cerebral artery; NCCT: non-contrast computed tomography; PICA: posterior inferior cerebellar artery; RVA: right vertebral artery; WI: weighted image; VP: ventriculoperitoneal; DWI: diffusion-weighted imaging; MRI: magnetic resonance imaging; P-com: posterior communicating.

The patient had to be readmitted, five days after discharge, with altered sensorium following an episode of GTCS. CT scan showed no fresh bleed though an increase in the hyperdensity within the aneurysm indicating thrombosis was noted. Check DSA revealed a change in the morphology of the aneurysm now, filling only about 50% of its initial size. Significant narrowing and luminal irregularity were noted in the mid-basilar artery (Figure 2(e) and (f)). Flow through both P-coms appeared to have increased, and the left PICA was filling from the RVA (Figure 2(g) and (h)). The patient recovered with an escalation in his antiepileptics and was discharged with the same residual deficits as were seen at the time of previous discharge.

During the entire critical period, the patient was kept in the ICU with rigorous monitoring of vitals and when MRI showed tiny infarcts in the left parietal cortex and cerebellar hemisphere, the patient's blood pressure was increased to augment the perfusion pressure.

At three months of follow-up, he recovered entirely with no residual neurological deficits. NCCT revealed a significant decrease in the size of the aneurysm with peripheral calcification along its anterior wall. On the one-year follow-up CT, the aneurysm had shrunken completely, appearing as a calcified nodule with complete resolution of mass effect (Figure 3(a)). DSA at this point revealed no evidence of the aneurysm with gradual tapering and occlusion of the mid-basilar segment. ICA angiograms showed a significantly enlarged right P-com artery supplying bilateral posterior cerebral and superior cerebellar arteries, with a prominent distal basilar artery (Figure 3(b) to (d)).

Figure 3.

Follow-up imaging at 1 year: NCCT (a) shows small, calcified nodules (arrow) representing the erstwhile aneurysm. RVA angiogram anteroposterior (b), and lateral views (c) show smooth tapering and occlusion of mid basilar artery with no evidence of an aneurysm. Note the filling of the left PICA. RICA angiogram lateral view (d) shows complete reorganisation of distal basilar circulation through prominent P-com. Note the prominent basilar top (arrow).

NCCT: non-contrast computed tomography; PICA: posterior inferior cerebellar artery; RICA: right internal cerebral artery; RVA: right vertebral artery; P-com: posterior communicating.

Discussion

Giant posterior circulation dissecting aneurysms, especially those involving basilar artery, pose significant challenges for treatment by any method because of their strategic location and haemodynamic factors.

Currently, endovascular reconstructive techniques, using flow-diverters and overlapping braided stents, are increasingly used with reasonable success in managing such aneurysms in adults. However, the same cannot be extrapolated to the paediatric population in whom the following are major limitations:

1. Lack of standard protocols for antiplatelet therapy in children, especially regarding dosage and duration.^5,6

2. The response of an artery that continues to grow and re-model as the child grows, to a metallic implant like the flow diverter is largely unknown yet. ⁷

3. Long-term follow-up data is unavailable for neointimal hyperproliferation following the use of low diverters in children. ⁸

In view of these limitations in paediatric populations, strategic parent artery or FAO can induce flow reversal in the involved arterial segment and promote healing of dissecting aneurysms. This hypothesis is best illustrated in our case.

In our case, the mid-basilar giant artery aneurysm was fed by both vertebral arteries; however, the left VA was dominant with a large left PICA. We hypothesised that occluding left VA proximal will cause left PICA to draw from RVA, thereby reducing forward flow in the basilar artery and hence the distending pressure in the aneurysm. Also, P-com arteries were expected to enlarge and take over upper basilar circulation. Findings of the balloon occlusion test reinforced these contentions (Figure 4). The final long-term outcome of the patient proved our convictions correct.

Figure 4.

Schematic diagram showing flow dynamics before and after feeder branch artery occlusion, size of arrows representing the quantity of flow. Note, for example, decreased flow through the aneurysm and increased flow via posterior communicating (P-com) arteries after feeder branch occlusion.

Conclusion

Giant posterior circulation aneurysms in kids can present with life-threatening emergencies. Flow reversal by FAO can be an elegant and efficient solution, as illustrated by our case.