Diagnosis of a ruptured cerebral aneurysm is commonly made by finding signs of subarachnoid hemorrhage on a computed tomography (CT) scan. If the CT scan is negative but a ruptured aneurysm is still suspected based on clinical findings, a lumbar puncture can be performed to detect blood in the cerebrospinal fluid. Computed tomography angiography (CTA) is an alternative to traditional angiography and can be performed without the need for arterial catheterization. This test combines a regular CT scan with a contrast dye injected into a vein. Once the dye is injected into a vein, it travels to the cerebral arteries, and images are created using a CT scan. These images show exactly how blood flows into the brain arteries.

The U.S. Preventive Services Task Force recommends a single screening ultrasound for abdominal aortic aneurysm in males age 65 to 75 years who have a history of smoking. There is an estimated number needed to screen of approximately 850 people. It is unclear if screening is useful in women aged 65 to 75 who have smoked and they recommend against screening in women who have never smoked.

Repeat ultrasounds should be carried out in those who have an aortic size greater than 3.0 cm. In those whose aorta is between 3.0 and 3.9 cm this should be every three years, if between 4.0 and 4.4 cm every two year, and if between 4.5 and 5.4 cm every year.

In the United Kingdom one time screening is recommended in all males over 65 years of age. Australia has no guideline on screening.

Once suspected, intracranial aneurysms can be diagnosed radiologically using magnetic resonance or CT angiography. But these methods have limited sensitivity for diagnosis of small aneurysms, and often cannot be used to specifically distinguish them from infundibular dilations without performing a formal angiogram. The determination of whether an aneurysm is ruptured is critical to diagnosis. Lumbar puncture (LP) is the gold standard technique for determining aneurysm rupture (subarachnoid hemorrhage). Once an LP is performed, the CSF is evaluated for RBC count, and presence or absence of xanthochromia.

Screening for an aortic aneurysm so that it may be detected and treated prior to rupture is the best way to reduce the overall mortality of the disease. The most cost-efficient screening test is an abdominal aortic ultrasound study. Noting the results of several large, population-based screening trials, the US Centers for Medicare and Medicaid Services (CMS) now provides payment for one ultrasound study in male or female smokers aged 65 years or older ("SAAAVE Act").

Aortic aneurysms are often discovered during an X-ray, ultrasound, or echocardiogram done for other reasons. IAA may also be found during a routine physical exam by feeling for bulges in the abdominal area. If your doctor thinks you might have an aortic aneurysm, you will likely have a medical history and physical exam. You might have further tests to locate the aneurysm.

When an aneurysm is suspected or diagnosed, it is important to:

- Pinpoint the location of the aneurysm.

- Estimate its size.

- Find out how fast it is growing.

- Find out whether other blood vessels are involved.

- See if there are blood clots or inflammation.

Tests to help find out the location, size, and rate of growth of an aneurysm include:

- Abdominal ultrasound - This imaging allows the doctor to observe growth of the aneurysm. If the aneurysm is large, a monitoring ultrasound may need to occur every 6 to 12 months. If the aneurysm is small, monitoring may occur every 2 to 3 years.

- Computed tomography (CT) and magnetic resonance angiogram (MRA) - These imaging techniques give a more detailed view of the aneurysm. These techniques may be used to gather information about aneurysm's relation to the blood vessels of the kidney or other organs. Your doctor needs this information especially before surgery. CT is used to watch the growth of a thoracic aortic aneurysm.

- Echocardiogram - This ultrasound exam is used to study the heart. A transthoracic echocardiogram (TTE) or a transesophageal echocardiogram (TEE) may also be done to further diagnose thoracic aortic aneurysm.

- Angiogram - An angiogram can help your doctor identify the size of the aneurysm and also examine if there are any aortic dissections, blood clots, or other blood vessel involvement.

Renal aneurysms are very rare consisting of only 0.1–0.09% while rupture is even more rare. Conservative treatment with control of concomitant hypertension being the primary option with aneurysms smaller than 3 cm. If symptoms occur, or enlargement of the aneurysm, then endovascular or open repair should be considered. Pregnant women (due to high rupture risk of up to 80%) should be treated surgically.

2002 the CT scan was assessed for it reliability for imaging inflammatory aortic aneurysms and to quantitatively evaluate its features. The finding were that CT scan was a reliable means to diagnose IAA.

2008 a study was done to test the effectiveness of MRI and FDG-PET tests to detect, diagnose, and measure inflammatory aortic arch syndrome. The results from the study were that MRI and FDG-PET were unreliable techniques due to giant cell arteritis.

2015 following endovascular repair of an aortic aneurysm the type of the endograft’s material used for repair seems to play a role in the inflammatory response associated with IAA.

Guidelines were issued in March 2010 for early detection of thoracic aortic disease, by the American College of Cardiology, the American Heart Association, and other groups. Among the recommendations:

- First-degree relatives of people with thoracic aortic aneurysm or dissection should have aortic imaging to identify asymptomatic disease.

- People with symptoms suggestive of thoracic aortic dissection should be routinely evaluated "to establish a pretest risk of disease that can then be used to guide diagnostic decisions."

- People diagnosed with Marfan syndrome should immediately have an echocardiogram to measure the aorta, and followed up 6 months later to check for aortic enlargement.

Abdominal aortic aneurysms are commonly divided according to their size and symptomatology. An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm), or more than 50% of normal diameter. If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large.

A ruptured AAA is a clinical diagnosis involving the presence of the triad of abdominal pain, shock, and a pulsatile abdominal mass. If these conditions are present, indicating AAA rupture, no further clinical investigations are needed before surgery.

Diagnosis of IIA is based on finding an intracranial aneurysm on vascular imaging in the presence of predisposing infectious conditions. Positive bacterial cultures from blood or the infected aneurysm wall itself may confirm the diagnosis, however blood cultures are often negative. Other supporting findings include leukocytosis, an elevated erythrocyte sedimentation rate and elevated C-reactive protein in blood.

Emergency treatment for individuals with a ruptured cerebral aneurysm generally includes restoring deteriorating respiration and reducing intracranial pressure. Currently there are two treatment options for securing intracranial aneurysms: surgical clipping or endovascular coiling. If possible, either surgical clipping or endovascular coiling is usually performed within the first 24 hours after bleeding to occlude the ruptured aneurysm and reduce the risk of rebleeding.

While a large meta-analysis found the outcomes and risks of surgical clipping and endovascular coiling to be statistically similar, no consensus has been reached. In particular, the large randomised control trial International Subarachnoid Aneurysm Trial appears to indicate a higher rate of recurrence when intracerebral aneurysms are treated using endovascular coiling. Analysis of data from this trial has indicated a 7% lower eight-year mortality rate with coiling, a high rate of aneurysm recurrence in aneurysms treated with coiling—from 28.6-33.6% within a year, a 6.9 times greater rate of late retreatment for coiled aneurysms, and a rate of rebleeding 8 times higher than surgically-clipped aneurysms.

Cerebral angiography is the diagnostic standard. MRIs are usually normal.

The risk of aneurysm enlargement may be diminished with attention to the patient's blood pressure, smoking and cholesterol levels. There have been proposals to introduce ultrasound scans as a screening tool for those most at risk: men over the age of 65. The tetracycline antibiotic doxycycline is currently being investigated for use as a potential drug in the prevention of aortic aneurysm due to its metalloproteinase inhibitor and collagen stabilizing properties. In contrast, fluoroquinolones antibiotics are being investigated as a potential contributor to aortic aneurysms, given their tendency to break down collagen fibrils.

Anacetrapib is a cholesteryl ester transfer protein inhibitor that raises high-density lipoprotein (HDL) cholesterol and reduces low-density lipoprotein (LDL) cholesterol.

Anacetrapib reduces progression of atherosclerosis, mainly by reducing non-HDL-cholesterol, improves lesion stability and adds to the beneficial effects of atorvastatin

Elevating the amount of HDL cholesterol in the abdominal area of the aortic artery in mice both reduced the size of aneurysms that had already grown and prevented abdominal aortic aneurysms from forming at all. In short, raising HDL cholesterol is beneficial because it induces programmed cell death. The walls of a failing aorta are replaced and strengthened. New lesions should not form at all when using this drug.

AVMs are diagnosed primarily by the following methods:

- Computerized tomography (CT) scan is a noninvasive X-ray to view the anatomical structures within the brain to detect blood in or around the brain. A newer technology called CT angiography involves the injection of contrast into the blood stream to view the arteries of the brain. This type of test provides the best pictures of blood vessels through angiography and soft tissues through CT.

- Magnetic resonance imaging (MRI) scan is a noninvasive test, which uses a magnetic field and radio-frequency waves to give a detailed view of the soft tissues of the brain.

- Magnetic resonance angiography (MRA) – scans created using magnetic resonance imaging to specifically image the blood vessels and structures of the brain. A magnetic resonance angiogram can be an invasive procedure, involving the introduction of contrast dyes (e.g., gadolinium MR contrast agents) into the vasculature of a patient using a catheter inserted into an artery and passed through the blood vessels to the brain. Once the catheter is in place, the contrast dye is injected into the bloodstream and the MR images are taken. Additionally or alternatively, flow-dependent or other contrast-free magnetic resonance imaging techniques can be used to determine the location and other properties of the vasculature.

AVMs can occur in various parts of the body:

- brain (cerebral AV malformation)

- spleen

- lung

- kidney

- spinal cord

- liver

- intercostal space

- iris

- spermatic cord

- extremities – arm, shoulder, etc.

AVMs may occur in isolation or as a part of another disease (for example, Von Hippel-Lindau disease or hereditary hemorrhagic telangiectasia).

AVMs have been shown to be associated with aortic stenosis.

Bleeding from an AVM can be relatively mild or devastating. It can cause severe and less often fatal strokes. If a cerebral AVM is detected before a stroke occurs, usually the arteries feeding blood into the nidus can be closed off to avert the danger. However, interventional therapy may also be relatively risky.

Diagnosis is often suspected in patients "in extremis" (close to death) with abdominal trauma or with relevant risk-factors. Diagnosis is confirmed quickly in the Emergency room by ultrasound or CT scan.

Mortality from aortic rupture is up to 90%. 65–75% of patients die before they arrive at hospital and up to 90% die before they reach the operating room.

Thoracic abdominal aneurysm is defined as a diameter exceeding the following cutoff:

- 4.5 cm in the United States

- 4.0 cm in South Korea

A diameter of 3.5 cm is generally considered dilated. However, average values vary with age and size of the reference population, as well as different segments of the aorta.

The differentiating presentations are suggestive of FMD being a unique syndrome in respect to the pediatric population. Experienced FMD clinicians warn against relying in the “string of beads” angiography for a diagnosis. In fact, it is suggested that FMD may be both under and over-diagnosed in children with stroke.

It is the lack of specific symptoms and its potential to appear anywhere that makes FMD a challenge to detect early on. The most accurate diagnosis comes from combining clinical presentation and angiographic imaging. According to the Michigan Outcomes Research and Reporting Program (MCORRP, 2013) the length of time from a patient’s first signs or symptoms to diagnosis is commonly 5 years.

FMD is currently diagnosed through the use of both invasive and non-invasive tests. Non-invasive testing includes duplex ultrasonography, magnetic resonance angiography (MRA), and computed tomographic angiography (CTA). Invasive testing through angiography is the gold standard. However, due to the higher risk of complications this is typically not done early on. Occasionally, FMD is diagnosed asymptomatically after an unrelated x-ray presents the classic ‘string of beads’ appearance of the arteries, or when a practitioner investigates an unexpected bruit found during an exam. When a diagnosis of FMD is considered for a patient thorough medical history, family history as well as vascular examination should be completed.

A definitive diagnosis of FMD can only be made with imaging studies. Catheter-based angiography (with contrast) has proven to be the most accurate imaging technique: this test involves a catheter is inserted into a large artery and advanced until it reaches the vessel of question. The catheter allows practitioners to view and measure the pressure of the artery aiding in the categorization and severity of the FMD diseased artery. According to Olin, “catheter-based angiography is the only imaging modality that can accurately identify the changes of FMD, aneurysm formation, and dissection in the branch vessels.” Practitioners believe it is important to utilize IVUS imaging because stenosis can sometimes only be detected through the methods of pressure gradient or IVUS imaging. In addition, computed tomography angiography and magnetic resonance angiography are commonly used to evaluate arteries in the brain. Doppler ultrasound may be used in both the diagnosis and follow-up of FMD.

IIAs are uncommon, accounting for 2.6% to 6% of all intracranial aneurysms in autopsy studies.

The Cognard et al. Classification correlates venous drainage patterns with increasingly aggressive neurological clinical course.

Treatment for brain AVMs can be symptomatic, and patients should be followed by a neurologist for any seizures, headaches, or focal neurologic deficits. AVM-specific treatment may also involve endovascular embolization, neurosurgery or radiosurgery.

Embolization, that is, cutting off the blood supply to the AVM with coils, particles, acrylates, or polymers introduced by a radiographically guided catheter, may be used in addition to neurosurgery or radiosurgery, but is rarely successful in isolation except in smaller AVMs. Gamma knife may also be used.

It should also not be confused with a pseudoaneurysm, coronary artery aneurysm or a myocardial rupture (which involves a hole in the wall, not just a bulge.)

Charcot–Bouchard aneurysms are aneurysms in the small penetrating blood vessels of the brain. They are associated with hypertension. The common artery involved is the lenticulostriate branch of the middle cerebral artery. Common locations of hypertensive hemorrhages include the putamen, caudate, thalamus, pons, and cerebellum.

As with any aneurysm, once formed they have a tendency to expand and eventually rupture, in keeping with the Law of Laplace.

Charcot–Bouchard aneurysms (also known as miliary aneurysms or microaneurysms) are aneurysms of the brain vasculature which occur in small blood vessels (less than 300 micrometre diameter). Charcot–Bouchard aneurysms are most often located in the lenticulostriate vessels of the basal ganglia and are associated with chronic hypertension. Charcot–Bouchard aneurysms are a common cause of cerebral hemorrhage.