The project will involve multiple units within our Institute (Neurosurgery, Cerebrovascular Diseases, Neurology IV), as well as additional neurosurgical centers across Italy, for the enrollment of patients with saccular intracranial aneurysms (sIA), both ruptured and unruptured. Based on predefined inclusion and exclusion criteria, the recruitment target over a two-year period is 400 patients with sIA (200 ruptured, 200 unruptured) and 200 healthy controls. The study will not alter clinical practice: treatment decisions for unruptured sIA will be made independently by vascular teams according to routine standards.

For each enrolled subject, anonymized clinical data will be collected (age, sex, BMI, lifestyle habits, family history, comorbidities, aneurysmal parameters) to build an integrated database within the Biorepository. Peripheral blood samples will be obtained for genomic analyses, and when available (e.g., during clipping procedures or lumbar puncture), aneurysm wall tissue and/or cerebrospinal fluid (CSF) samples will be collected for expression studies. All materials and data (clinical/genetic) will be coded and stored at the Cryobank of the Fondazione IRCCS Istituto Neurologico Besta.

Genomic analyses: a pathway-based Genome-Wide Association Study (GWAS) is planned.

Phase I: Genotyping of 200 patients (100 with ruptured sIA, 100 with unruptured sIA) and 100 healthy controls, with combined analysis of genetic data and environmental factors related to rupture risk.

Phase II: Validation in an additional cohort of 200 patients (100 ruptured, 100 unruptured) and 100 controls to confirm the associations of identified SNPs.

This observational study aims to identify potential genetic determinants associated with the risk of rupture in saccular intracranial aneurysms (sIA). The study is conducted in collaboration with three Units of the Fondazione IRCCS Istituto Neurologico Carlo Besta in Milan (Neurosurgery Unit II, Cerebrovascular Diseases Unit, Neurology Unit IV), as well as additional neurosurgical centers across Italy, particularly for the enrollment of patients with ruptured sIA who do not present to Besta due to the absence of an Emergency Department.

As an observational study, it does not involve any modification to the routine clinical management of patients with sIA at participating centers. Specifically, the decision to propose surgical or endovascular treatment for patients with ruptured or unruptured aneurysms will be made independently of the study, based on shared criteria discussed during regular multidisciplinary vascular meetings. Furthermore, no additional follow-up is planned beyond what is routinely scheduled for patients undergoing surgical or endovascular treatment for intracranial aneurysms.

Each patient will be asked to provide informed consent through a dedicated form. Once consent is obtained, each participant will be assigned a unique alphanumeric central code, used exclusively for study purposes. Throughout the duration of the project and thereafter, only the responsible physician will be able to link the code to the patient's identity.

Patients will undergo clinical evaluation at the time of enrollment, as part of standard clinical practice. Anonymized clinical data will be recorded in a centralized database and will include: sex, age, height, weight, regular use of illicit substances, alcohol consumption, smoking habits, family history of sIA, arterial hypertension, medical history with particular attention to autoimmune diseases and recent infections, general and neurological assessment, and aneurysmal characteristics (location, maximum diameter, morphology-regular or irregular).

Each patient will also undergo peripheral venous blood sampling for genomic studies. When available (e.g., during clipping procedures or lumbar puncture performed for decompression or other clinical indications), samples of aneurysm wall tissue, subcutaneous arterial wall, and/or cerebrospinal fluid (CSF) will be collected. Biological samples, along with coded clinical and genetic data, will be stored at the Fondazione IRCCS Istituto Neurologico Carlo Besta in separate containers, housed in controlled and locked environments, to establish the first Integrated Italian Biobank for Intracranial Aneurysms.

Regarding genomic analyses, a pathway-based genome-wide association study (GWAS) will be conducted.

• Phase I: DNA extracted and genotyped from 200 patients (100 with ruptured sIA and 100 with unruptured sIA) and 100 healthy controls will be analyzed. Statistical analysis will assess the combined effect of genetic and environmental factors on rupture risk. In this phase, healthy subjects and patients with unruptured sIA will serve as control groups for patients with ruptured sIA.
• Phase II: An additional cohort of 200 patients (100 ruptured, 100 unruptured) and 100 healthy controls will be analyzed to validate the single nucleotide polymorphism (SNP) combinations identified in the preliminary phase.

Finally, the genetic and clinical data obtained from the biostatistical analysis of the entire cohort (400 patients and 200 healthy controls) will be used to develop a user-friendly computational tool aimed at estimating the individual risk of rupture in patients with sIA.

Inclusion Criteria:

• Adults aged 18 to 80 years, of both sexes
• Patients diagnosed with ruptured or unruptured saccular intracranial aneurysms (sIA)

Exclusion Criteria:

• Patients with non-saccular intracranial aneurysms
• Patients unable to provide informed consent due to language impairment or altered consciousness, in the absence of a legally appointed guardian

Patients diagnosed with ruptured or unruptured saccular intracranial aneurysms (sIA)