The purpose of this study is to examine the percentage of patients who present with abdominal aortic aneurysms (AAA) will also have intracranial aneurysms (IA) and conversely; to examine the percentage of patients who present with intracranial aneurysms will also have abdominal aortic aneurysms.

The investigators have previously generated estimates for cost effectiveness of each arm of this reciprocal screening protocol based on literature dervied estimates of coprevalence and other key factors in a decision tree model to compare costs and outcomes. They measured expected outcomes using quality-adjusted life years (QALY) and the incremental cost-effectiveness ratios (ICER). The current study will involve establishment of the true co-prevalence and recalculation of the ICERs and QALYs. Based on their literature derived models we previously found an ICER of $34.01/QALY for AAA screening in IA patients and an ICER of $6,401.91/QALY for IA screening in AAA patients. Both of these are well below the societal accepted threshold of $60,000/QALY. However, both models were sensitive to co-prevalence. In the current study the investigators will therefore determine the actual cost-effectiveness of performing additional radiographic procedures and genetic counseling. The investigators will also bank DNA and RNA for future research.

Inclusion Criteria:

• Age 18 years or older
• Clinical and radiographic diagnosis of either abdominal aortic aneurysm (AAA) or intracranial cerebral aneurysm (IA). Aneurysm may be symptomatic (s/p rupture or mass effect) or asymptomatic (detected as part of screening or incidentally discovered. Aneurysms int he brain may be multiple. AAA will be defined as >= 3 cm by any imaging modality. IA will be defined as >= 3 mm on any imaging modality.
• Able to provide a valid informed consent (self or legally authorized representative)

Exclusion Criteria:

• Contra-indication for MRI/A (embedded metal, intractable claustrophobia, pacemaker, etc.)
• Intracranial aneurysm associated with arteriovenous malformation
• Clinical or radiographic diagnosis of mycotic aneurysm
• Substantial pre-existing neurological or psychiatric illness that would confound neurological assessment or other outcome assessment.
• Other serious conditions that make the patient unlikely to survive long enough to benefit from the screening program.
• Inability to follow the protocol or return for screening test or genetic counseling.
• Unwilling to have reports from imaging and genetic counselor sent to a clinician (PCP, testing surgeon, etc)

Note: Pregnancy is not a reason to exclude, but imaging done for the study will be postponed until after the subject has given birth.

Patients who have been diagnosed with either a IA or AAA.

Summary data will be shared and published.