Study Design

When an unruptured aneurysm of 3 mm or more is detected in a patient of 20 years or more, the participating hospital registers each patient by using the procedure described below. When data is available, it is acquired through the electronic data capture method.

Initial registration

When an unruptured aneurysm is found, the patients and their families are informed about the disease and the UCAS study. When patients agree to participate in the study, their private information is recorded and the initial information is sent to the UCAS office on Form I.

Periodic data entry

New data are collected at 3 months, 1 year (12 months), and 3 years (36 months) after the initial registration. And if any data are available beyond 36months, additional data are collected.

At each time point, any changes in the patient’s condition are also reported. Changes in physical or neurological findings are recorded on Form C. Information about any treatment is recorded on Form T. Form D is used to transfer data when an imaging study is done.


When an aneurysm ruptures or a patient dies, follow-up of the case ends and an emergency report is sent using Form E.

Registration Form (pdf file)

Protection and safety of clinical information

Data are sent online by using the electronic data capture method with 128-bit encryption. A fax machine is used when an online method is not available. The data are kept as secure as possible. All data are stored in the computer of the UMIN (University Hospital Medical Information Network) situated in the University of Tokyo Hospital. Only UCAS office managers and UMIN administrators have access to this data.
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