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.

Coexistence of anterior choroidal artery and posterior cerebral artery retia mirabilia presenting with subarachnoid hemorrhage: illustrative case

“… 5 This process is called “distal annexation.” 8 The pathogenesis of PCA rete formation has been hypothesized to be the incidence of a remnant of distal annexation between the primitive AchA and the PCA during embryogenesis. 2 , 5 To our knowledge, this is the first report of coexisting AchA and PCA retia mirabilia, supporting the remnant of distal annexation between the primitive AchA and the PCA as the underlying pathogenesis of rete formation at this site.…”

“… 3 , 12–14 With regard to the posterior circulation, retia mirabilia involving the vertebral artery, PCA, and posterior inferior cerebellar artery have been previously reported. 2 , 5–7 , 15 In the two cases of PCA rete mirabile reported earlier, 2 , 5 one was asymptomatic, whereas the patient in the other case died from subarachnoid hemorrhage due to rete mirabile–associated aneurysm. The primitive AchA has cortical branches to the temporal, parietal, and occipital lobes in the early embryonic stage that transform into the P2–4 segments of the PCA distal to the posterior communicating artery.…”

“… 1 The purpose of this distinctive vascular architecture is believed to be related to thermoregulation, pressure absorption, or blood flow regulation. 2 However, rete mirabile is a rare vascular anomaly that does not exist in humans during normal development. The most accepted mechanism suggests that a rete mirabile results from embryonal agenesis, regression, or annexation of normal vessels, which help to compensate for the blood flow.…”

“…6,7 A rete mirabile of the posterior cerebral artery (PCA) is an extremely rare lesion that has been previously reported in only two cases. 2,5 Moreover, the PCA and anterior choroidal artery (AchA) are closely related developmentally. The proximal segment of PCA (P1) is derived from the posterior division of the internal carotid artery (ICA).…”