Endovascular management of a ruptured aneurysm associated with distal PICA fenestration

Abstract

Fenestrations are rare but well-known arterial anatomic variations in which a segment of artery divides into two parallel channels that reunite distally. Although fenestrations as such are asymptomatic, they have gained clinical significance because of their association with aneurysms and other intracranial vascular pathologies. Here we present a 35-year-old woman with history of sudden severe occipital headache and vomiting. Imaging revealed a ruptured aneurysm in the distal posterior inferior cerebellar artery arising from one of the limbs of the fenestration. The aneurysm was successfully managed by coiling, and the patient made complete recovery without neurological sequelae.

Introduction

Fenestrations are rare but well-known arterial anatomic variations in which a segment of artery divides into two parallel channels that reunite distally. They result from incomplete fusion of the early embryonic plexiform network which unite to form mature cerebral arteries.¹ According to Lasjaunias et al., fenestrations are due to incomplete cell selection and apoptosis during vasculogenesis and point to an incomplete maturation of the arterial wall.² Although fenestrations as such are asymptomatic, they have gained clinical significance because of their association with aneurysms and other intracranial vascular pathologies.³ Imaging and autopsy studies report a prevalence varying from 0.7% to 60%.^4–8 Commonly involved vessels include the vertebral, basilar and anterior communicating artery.^1,9 Fenestration of the posterior inferior cerebellar artery (PICA) is not as common and its occurrence especially beyond its tonsilomedullary segment is exceedingly rare. To the best of our knowledge, only six cases of PICA fenestration have been reported in the literature.^1,10–14 Among these, only one case report involved PICA fenestration beyond its tonsilomedullary segment.¹⁴ Here we report possibly the second in the literature, a case of distal PICA fenestration with ruptured aneurysm of one of its limbs successfully managed by endovascular coiling. The study was approved by our institute ethics committee.

Case report

A 35-year-old woman presented to the emergency department with a history of acute severe occipital headache and vomiting. There was no history of loss of consciousness or seizure. At the time of presentation the patient's Glasgow Coma Scale was 15. Neurological examination was normal except for mild neck rigidity. The patient was otherwise healthy with no comorbidities. Computed tomography of the head showed dense subarachnoid haemorrhage (SAH) around the medulla and inferior cerebellum with extension into the fourth ventricle and mild hydrocephalus (Figure 1(a)). Subsequently digital subtraction angiography (DSA) showed left PICA fenestration in the telovenotonsilar segment with an aneurysm measuring approximately 3 × 4 mm arising from one of the limbs of the fenestration (Figure 1(b–d)). The aneurysm was successfully accessed with the use of a Headway 17 (MicroVention) and occluded with detachable coils. A post-embolization control angiogram showed complete occlusion of the aneurysm including its feeding limb (Figure 2 (b, c)). Distal cerebellar cortical branches were seen filling through the unaffected limb. The post-procedure period was uneventful. No new neurological deficit developed although post-procedure computed tomography showed evidence of a small acute infarct in the left inferior cerebellar hemisphere involving PICA territory (Figure 2(d)).

Figure 1.

(a) Axial non-contrast computed tomography section at the level of the pons showing haemorrhage within the fourth ventricle (thick arrow). (b) Digital subtraction angiography (DSA) image of the left vertebral artery (VA) frontal view showing a small saccular aneurysm in the midline arising from the left posterior inferior cerebellar artery (PICA) in the telovelotonsillar segment (arrowhead). (c) DSA of the left VA lateral view showing the same saccular aneurysm arising from the left posterior inferior cerebellar artery with dome directed inferiorly (arrowhead). (d) DSA volumetric three-dimensional reconstructed image of the left VA showing PICA fenestration with aneurysm (arrowhead).

Figure 2.

(a) Digital subtraction angiography (DSA) volumetric three-dimensional reconstruction of the left vertebral artery (VA) showing two limbs of posterior inferior cerebellar artery (PICA) fenestrations (arrowheads) with an aneurysm arising from its medial limb. (b) DSA image of the left VA oblique view post-coiling shows complete non-filling of the aneurysm (asterisk) with good opacification of the distal branch through an unaffected fenestrated limb of PICA (thin arrow). (c) DSA image of the left VA lateral view showing complete occlusion of the aneurysm (asterisk) with good opacification of PICA branches (thin arrow). (d) Follow-up axial computed tomography image at the level of the quadrigeminal cistern shows a small infarct in the left cerebellar hemisphere (long, thin arrow).

Discussion

Fenestrations or partial duplications are rare but well-known arterial anatomic variations in which a segment of an artery is divided into two parallel channels that reunite distally. Fenestrations are commonly described in the vertebrobasilar system, followed by the anterior communicating artery. Basilar artery fenestration results from the failure of fusion of embryologic longitudinal neural arteries during the fifth week of intrauterine life.¹⁵

PICA fenestrations are exceedingly rare, with only six cases reported in the literature.^1,10–14 All reported cases except one showed fenestration in the proximal medullary segment, which is analogous to the radiculopial artery supplying the spinal cord. A proposed embryological basis includes partial regression of a double origin of the PICA or cranial nerve entrapment by circumscribed fenestrations.¹² Fenestration in the distal PICA beyond tonsilomedullary is exceedingly rare. To the best of our knowledge, only a single case of distal PICA fenestration has been reported in the literature.¹⁴ The exact embryological basis of distal PICA fenestration is not known.

Fenestrations are known to be associated with aneurysms and other intracranial vascular pathologies such as stroke and arteriovenous malformations. Reported prevalence of aneurysm in the setting of fenestrations varies from 2.5% to 17%.^3,16 Aneurysms may be anatomically associated with fenestrated limbs or remote from them. Kumar and colleagues¹⁰ reported a case of right PICA and basilar artery fenestration with an unruptured left V4 segment aneurysm. Lesley¹¹ reported PICA fenestration with multiple intracranial aneurysms in the anterior circulation. Theodosopoulos and Lawton¹² reported a case of peri-mesencephalic SAH, in which DSA failed to show any aneurysm except for a right PICA fenestration. The patient underwent a subsequent craniotomy and no aneurysms were documented intraoperatively either. Lee et al.¹³ reported a case of double origin of the left PICA with fenestration of its caudal channel and right V4 segment dissecting aneurysm. Maeda and colleagues¹⁴ reported a case of PICA fenestration with a ruptured aneurysm in the cranial loop of the telovelotonsilar segment that was subsequently managed by endovascular coiling. Our case also showed PICA fenestration distal to the tonsilomedullary segment with a ruptured aneurysm in one of its limbs.

PICA aneurysms are diverse, and management of each one should be individualised considering especially its location and morphology. Common surgical treatment options include clipping, resection, parent vessel occlusion, trapping and bypass. Endovascular treatment options include simple coiling, balloon or stent-assisted coiling and parent vessel occlusion. In general aneurysms of the anterior medullary segment, which are known to be associated with vital brainstem perforators, can be considered for surgical treatment. The choice of endovascular treatment depends on the aneurysm location, morphology and whether it is ruptured. In general, simple coiling is possible for narrow-neck aneurysms whereas wide-neck aneurysms may require stent or balloon assistance. Parent vessel occlusion is considered for a complex dissecting fusiform aneurysm, especially one arising from a distal segment.¹⁷ However, aneurysms of the proximal medullary segment are not suitable for parent vessel occlusion because of risk of occlusion of vital brainstem perforators.¹⁸ Studies have shown that unilateral occlusion of the PICA beyond the medullary segment is unlikely to be associated with large or disabling infarctions.¹⁹ Our patient also developed a small infarct in the posterior cerebellum which might probably be due to microemboli during catheter manipulation in the small branches of the PICA. However, the patient remained completely asymptomatic. In addition, three-dimensional rotational angiography very well-delineated the anatomy of the fenestration, which helped immensely in precise microcatheter and coil placement, thereby possibly reducing the area of infarct.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.