**1. Introduction**

Tuberous sclerosis complex (TSC) is a rare multiorgan neuroendocrine disease and belongs to the group of phacomatoses. As a multisystemic genetic disorder with an autosomal dominant inheritance, it can affect any organ in the body [1]. In fact, the damage of one of two genes, TSC1 on chromosome 9 or TSC2 on chromosome 16, that produce the tumor suppressors "hamartin" and "tuberin" [2, 3] results in the formation of benign tumors so-called hamartomas, such as subependymal giant cell tumors (SGCT) in the brain. Interestingly, more than 70% of TSC cases are new mutations, and among them, 75% are caused by TSC2 mutations [4].

The Vogt triad, a combination of epilepsy, mental retardation and adenoma sebaceum, is only present in 29% of the cases [5]. Epilepsy and mental retardation are respectively in 25 and 45% of the cases absent [5]. Because of the relatively mild disease manifestations, TSC was underdiagnosed until the 1980s [6].

Cerebral aneurysms, also known as intracranial aneurysms (IA), are usually pouch-like (saccular) or spindle-shaped (fusiform) focal dilations in the wall of major arteries in the circle of Willis [7] that grow and present a certain risk of rupture. To date, arterial wall anomalies in TSC, particularly in aneurysms, were only described in the extracranial vasculature, such as aortic aneurysms or kidney aneurysms that were considered as the result of a congenital defect [8]. The distinct features of IA in these patients have not previously been addressed in the literature. Indeed, there are sporadic cases or small case series that reported the coexistence of IA and suggested their congenital origin.

First cases of TSC and IA were reported in 1974. The first patient was a 24-year old man who died after a subarachnoid hemorrhage (SAH), and the ruptured aneurysm of the right middle cerebral artery was diagnosed at autopsy [9]. The second patient was a 12-year old girl that presented in 1965 with a sudden blurry vision, and bilateral aneurysms of both internal carotid arteries (ICAs) involving the region of the carotid siphon were diagnosed [10].

Heritable connective tissue disorders such as Marfan syndrome, Ehlers-Danlos Syndrome, Loeys-Dietz syndrome and autosomal dominant polycystic kidney disease (ADPKD) are commonly associated with small saccular aneurysms [10]. Our recent systematic review of the English literature [11] is the first to describe the characteristics of IA in TSC in comparison to the features of IA in healthy adults. Despite the eventuality of a congenital origin in TSC, there are some distinct features that characterize IA in TSC and differentiate them from common nonsyndromal IA. The purpose of this book chapter is to give an overview on the particular demographic, clinical, and radiologic features through a case illustration and discuss the possible natural history of IA in TSC patients. Patient informed consent was obtained.
