The ultrasound image provided shows a transverse view of the abdominal aorta, with a clearly measured aortic diameter of 5.71 cm. A normal adult abdominal aorta should measure less than 3.0 cm in anterior-posterior diameter. Any measurement exceeding this threshold is defined as an abdominal aortic aneurysm (AAA).

In this case, the dilation is well beyond the 3.0 cm threshold, confirming the presence of an aneurysm. The rounded, anechoic/heterogeneous central lumen surrounded by echogenic arterial wall layers further supports this diagnosis.

Comparison of answer choices:

A. Stenosis: Would show a narrowed lumen with turbulent, aliasing flow on Doppler, not a dilated aorta.

B. Dissection: Typically shows an echogenic intimal flap separating true and false lumens; no flap is visible here.

C. Aneurysm: Correct. The aorta’s transverse diameter (5.71 cm) confirms the presence of an aneurysm.

D. Occlusion: Would appear as a lack of flow with thrombus or echogenic content filling the lumen, not dilation.