The study is designed to evaluate the efficacy and safety of minimally invasive neurosurgical techniques for patients with incidental cerebral aneurysms of the anterior circulation in the Hospital das Clínicas of the University of São Paulo Medical School.

Minimally Invasive Neurosurgery is a inexorable tendency and it is already a reality in many centers of the world. It is a broad and relative concept and there is few consistent medical data to validate its benefits. In this manner, this is the first clinical trial in Brazil questioning the safety of the of minimally invasive surgery to treat incidental cerebral aneurysms of the anterior circulation. For countries like Brazil, the indirect demonstration of reduction in hospital costs through lower hospital stays is a breakthrough to provide better health for the entire population.

Patients with the diagnosis of incidental brain aneurysms of the anterior circulation will be recruited from the spontaneous demand of the Hospital das Clínicas of University of São Paulo Medical School. The investigators expect to recruit 60 patients for the experimental group and 60 for the control group.

In the study group patients will be submitted to a minimally invasive approach (transpalpebral mini fronto-orbital craniotomy or modified minipterional craniotomy). All patients in this group will be submitted to surgery starting at 8 o'clock in the morning. After 6 hours of the end of surgery, all patients will have a control CT scan and if the result is adequate, they are going to be discharged from the ICU with no IV drugs. The hospital discharge will be in the next day. The control group are patients that will be submitted to a classical pterional craniotomy with hospital discharge occurring in 4-5 days.

All patients will be submitted to the standard care offered by the Hospital das Clinicas. All surgical and ambulatory data will be collected by the main investigators (Dr. Mauricio Mandel and Dr. Eberval Figueiredo). The adverse events will be promptly reported to the chair of the department and to the CAPPESQ (the ethics committee of the hospital).

Ambulatory data will be collected during the regular post operative medical appointments and a web based questionnaire. The post operative follow-up is unified in only one ambulatory center and day (thursdays mornings).

Statistical analysis will compare primary and secondary objectives of the two groups, as specified in the study protocol.

Inclusion Criteria:

• Patients with the diagnosis of incidental unruptured cerebral aneurysms (4mm to 2cm)

Exclusion Criteria:

• Patients who do not have adequate family care during the immediate post-operative period (the patient's family must commit to stay with the patient in the first five days after hospital discharge)
• Patients who are unable to communicate by telephone
• People with cardiovascular disease, liver or kidney failure.
• Pregnant women or breastfeeding
• Patients with coagulation abnormalities
• Patients with High Surgical Risk evaluated by different risk scores (ASA, AHA, Goldman, Detsky)