REVIEW Management of unruptured incidentally found intracranial saccular aneurysms Vikram A. Mehta 1 & Charis A. Spears 1,2 & Jihad Abdelgadir 1 & Timothy Y. Wang 1 & Eric W. Sankey 1 & Andrew Griffin 1 & C. Rory Goodwin 1 & Ali Zomorodi 1 Received: 26 May 2020 /Revised: 22 September 2020 /Accepted: 29 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Unruptured intracranial saccular aneurysms occur in 3–5% of the general population. As the use of diagnostic medical imaging has steadily increased over the past few decades with the increased availability of computed tomography (CT) and magnetic resonance imaging (MRI), so has the detection of incidental aneurysms. The management of an unruptured intracranial saccular aneurysm is challenging for both patients and physicians, as the decision to intervene must weigh the risk of rupture and resultant subarachnoid hemorrhage against the risk inherent to the surgical or endovascular procedure. The purpose of this paper is to provide an overview of factors to be considered in the decision to offer treatment for unruptured intracranial aneurysms in adults. In addition, we review aneurysm and patient characteristics that favor surgical clipping over endovascular intervention and vice versa. Finally, the authors propose a novel, simple, and clinically relevant algorithm for observation versus intervention in unruptured intracranial aneurysms based on the PHASES scoring system. Keywords Intracranial aneurysms . Incidental intracranial aneurysms . Unruptured intracranial aneurysms . Open vascular . Endovascular intervention Introduction Intracranial aneurysms were first reported in the literature in 1761 when Morgagni of Padua described a case of an unruptured carotid aneurysm. [1] Our understanding of intra- cerebral aneurysms has advanced tremendously since that time, especially with the introduction and advancement of endovascular techniques. While intracranial saccular aneu- rysms may present with neurological deficits or other symp- toms, an estimated 59% of unruptured aneurysms are asymp- tomatic. [2] However, with increased utilization of noninva- sive imaging, patients are increasingly likely to have an aneu- rysm be incidentally discovered. The management of unruptured incidental intracranial saccu- lar aneurysms is challenging for both patients and physicians, as the decision to intervene involves balancing the risks of rupture and subarachnoid hemorrhage against the periprocedural risks inherent to surgical or endovascular intervention. Other factors, including the patient ’s potential anxiety regarding living with an unruptured aneurysm, play an unquantifiable role in decision- making. [3] This paper aims to provide an overview of select factors to be considered in the decision to offer intervention for this challenging pathology and to propose a simple treatment algorithm for observation versus intervention. As aneurysmal morphology can be infinitely complex, with various treatment options and protocols for each type, herein, the authors will focus on unruptured, non-enlarging saccular aneurysms. This aneu- rysm type accounts for approximately 90% of intracranial aneu- rysms and is thus most likely to be encountered by a treating physician. Aneurysms with new-onset neurological deficit are considered symptomatic and may warrant more urgent treatment and are therefore not included in this review. Formation of intracranial aneurysms Unruptured intracranial saccular aneurysms occur in 3–5% of the general population. [4] Histopathologically, their hallmark * Vikram A. Mehta Vikram.mehta.a@gmail.com 1 Department of Neurosurgery, Duke University Medical Center, 20 Duke Medicine Circle, Box 3807, Durham, NC 27710, USA 2 Duke University School of Medicine, Durham, NC, USA Neurosurgical Review https://doi.org/10.1007/s10143-020-01407-y