Lethal subarachnoid haemorrhage in a patient with rete mirabile network of the posterior circulation with associated aneurysm

Abstract

Rete mirabile (RM), an arterial network normally existing in some vertebrate animals interconnecting the extracranial and intracranial arterial circulation, can rarely be found in humans whether asymptomatic or presenting with cerebral ischaemia or haemorrhage. Encompassing diverse angiographic characteristics and similarities with other arterial malformations, proper diagnosis and differential diagnosis is challenging. We hereby describe an unusual RM case variant, presenting to us with lethal subarachnoid haemorrhage owing to a ruptured small aneurysm associated with the RM network. Angiography disclosed an absent P1 segment of the posterior cerebral artery (PCA) and an RM network anastomosing the basilar apex with the normal distal PCA. Brain death was confirmed on the fifth day after admission and attributed to the severity of subarachnoid haemorrhage (SAH). This is an exceedingly rare case representing an intradural-to-intradural RM anastomosis in a patient presenting with lethal SAH. RM epidemiology, pathophysiology, presentation, angiographic findings and prognosis are reviewed.

Keywords: neuro ITU; neuroimaging; neurology.

Figure 1

(A) Non-enhanced CT scan revealing severe acute cisternal subarachnoid haemorrhage, especially in the interhemispheric and sylvian compartments, as well as acute brainstem intraparenchymal haemorrhage. (B, C) More rostral slices of the same CT scan demonstrating intraventricular haemorrhage in the third ventricle and frontal horn of the lateral ventricles. (D) CT angiography demonstrating an abnormal vascular network at the tip of the basilar artery and possibly a small aneurysm.

Figure 2

Posterior circulation angiography demonstrating the RM network in anteroposterior (A) and lateral (B) views. Microcatheter angiography of the RM network, with the tip of the microcatheter being at the basilar artery tip. Anteroposterior (C) and lateral (D) views showing no definite normal connection between the basilar artery and the right posterior cerebral artery. RM, rete mirabile.

Figure 3

3D reconstruction of the posterior circulation in anteroposterior (A, B, D) and lateral (C, E, F) views. Left-sided posterior cerebral artery (PCA) has an embryologic origin. On the right side, there is no existing normal connection between the PCA and the basilar tip (C, white arrow). Instead, there is a rete mirabile (RM) network (C, D, F, yellow arrow) interconnecting these vessels. The right PCA demonstrated delayed filling. The aneurysm (red arrow) is associated with the RM network and protrudes caudally and anteriorly.

Figure 4

3D reconstruction of microcatheter-based angiography demonstrating the RM network. Findings are the same as in figure 3. Normal thalamoperforators (A, C–F) are seen emerging form the RM network (green arrows). Aneurysm (red arrow) and its relationship with the RM network (yellow arrow) is demonstrated (B–F). RM, rete mirabile.