An<unk>  is usually diagnosed by physical exam,<unk>  ultrasound, or CT scan. Plain<unk>  radiographs may show the outline of an<unk>  when its walls are calcified. However, the outline will be visible on Xray in less than half of all<unk> s. Ultrasonography is used to screen for<unk> s and to determine the size of any present. Additionally, free peritoneal fluid can be detected. It is noninvasive and sensitive, but the presence of bowel gas or obesity may limit its usefulness. CT scan has a nearly 100% sensitivity for an<unk>  and is also useful in preoperative planning, detailing the anatomy and possibility for endovascular repair. In the case of suspected rupture, it can also reliably detect retroperitoneal fluid. Alternative less often used methods for visualization of an<unk>  include MRI and angiography. An<unk>  ruptures if the mechanical stress (tension per area) exceeds the local wall strength; consequently, peak wall stress (PWS) and peak wall rupture risk (PWRR) have been found to be more reliable parameters than diameter to assess<unk>  rupture risk. Medical software allows computing these rupture risk indices from standard clinical CT data and provides a patient-specific<unk>  rupture risk diagnosis. This type of biomechanical approach has been shown to accurately predict the location of<unk>  rupture. File:Ultrasonographic measurement of<unk>  diameter at the navel.Aortic measurement on<unk>  ultrasonography in the axial plane between the outer margins of the<unk>  wall. File:Ultrasonography of<unk>  in sagittal plane, annotated.Ultrasonography in the sagittal plane, showing axial plane measure (dashed red line), as well as maximal diameter (dotted yellow line) which is preferred. Image:RupturedAAA.A ruptured<unk>  with an open arrow marking the<unk>  and the closed arrow marking the free blood in the abdomen Image:Sagital<unk> .Sagittal CT image of an<unk>  Image:AAA_rupture_risk.Biomechanical<unk>  rupture risk prediction Image:Contrast-enhanced CT scan demonstrating<unk> .An axial contrast-enhanced CT scan demonstrating an<unk>  of 4.8 by 3.8 cm Image:RupturedAAAXray.The faint outline of the calcified wall of an<unk>  as seen on plain X-ray Image:Abdominal<unk><unk> .Abdominal<unk><unk> s (3.4 cm) File:AneursymCTMark.An<unk><unk>  as seen on CT with a small area of remaining blood flow File:UOTW 35 - Ultrasound of the Week 1.Ultrasound showing a previously repaired<unk>  that is leaking with flow around the graft File:Ultrasonography of<unk>  with mural thrombus.Ultrasonography of an<unk>  with a mural thrombus. Classification +Size classification Ectatic ormild dilatation >2.0 cm and 5.0 or 5.5 cm<unk> s are commonly divided according to their size and symptomatology. An<unk>  is usually defined as an outer<unk>  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<unk>  is considered to be large. Ruptured<unk>  should be suspected in any older (age >60) person with collapse, unexplained low blood pressure, or sudden-onset back or<unk>  pain.<unk>  pain, shock, and a pulsatile mass is only present in a minority of cases. Although an unstable person with a known<unk>  may undergo surgery without further imaging, the diagnosis will usually be confirmed using CT or ultrasound scanning. The suprarenal aorta normally measures about 0.5 cm larger than the infrarenal aorta. Differential diagnosis<unk><unk>  rupture may be mistaken for the pain of kidney stones, or muscle related back pain.
Abdominal aortic aneurysm
Appendicitis
Superior mesenteric artery syndrome
Splenic infarction
Aortoenteric fistula
Postcholecystectomy syndrome
Renal vein thrombosis
Spontaneous bacterial peritonitis