LAUSR

Cerebral arteriovenous malformations (AVMs) are rare vascular lesions that rupture at an approximate annual rate of 2–4% [1]. Annual haemorrhage rates range from < 1%, for unruptured superficially located AVMs, up to 33% in ruptured AVMs with deep, location and venous drainage [12, 68]. Once haemorrhage occurs, the probability of experiencing new neurological deficit has been reported to be up to 50% and fatality ~ 10% [28, 66]. Gamma knife radiosurgery (GKRS) is an established intervention predominantly favoured for small (< 3.5 cm), surgically high-risk or complex AVMs. Successful AVM GKRS is contingent on abolishing the risk of intracranial haemorrhage (ICH) via complete nidal obliteration, whilst limiting the development of new neurological deficit from radiation-induced changes (RICs) [9, 26, 69]. The complications of AVM GKRS are mainly two-fold. Firstly, patients remain at risk of haemorrhage during the latency period between GKRS and nidus obliteration. The relative risk of AVM haemorrhage during this latency period versus the natural history of an untreated AVM remains a topic of debate [26, 28]. Secondly, RICs can occur following radiosurgery, influenced by AVM and treatment parameters including AVM volume, location and treatment dose [12]. Approximately 34% of patients develop RICs, ~ 8% of patients develop RIC-related neurological symptoms and ~ 3% will experience permanent neurologic deterioration. However, considerable variations in the reported rates, durations and definition of RICs still remain. Further, delayed adverse effects including radiation necrosis and cyst formation following GKRS have been reported, yet there is a paucity of literature conclusively describing their incidence [38]. A previous systematic review and meta-analysis quantified haemorrhage risk and obliteration rate following AVM stereotactic radiosurgery (SRS), but it had limitations [72]. The review included 69 observational studies, of which, however, approximately only a third solely treated AVMs with GKRS; the majority reporting on linear accelerator (LINAC) or other SRSmodalities. Additionally, the median duration of study followup was less than three years; an arguably limited time-frame to comprehensively analyse clinical outcomes of AVM GKRS, which evolve in a time-dependent manner over a latency period of 2–3 years following radiosurgical intervention [1, 12, 68]. Alongside imaging advancements and increasingly sophisticated radiation delivery systems since the inception of GKRS, there has also been an increasing knowledge base on AVM obliteration, RICs and post-GKRS ICH [12]. Whilst there are several studies that review or report on these outcomes, none are both systematic or comprehensive. We sought to systematically review the current literature and comprehensively quantify the efficacy: complication profile of GKRS for cerebral AVMs. Musa China and Amisha Vastani are joint first authors.