Had a. abdominal ultrasound. results said cannot visualize the mid distal aorta. what does this mean? why does this happen? does this mean aneurysm?

It means the technician who obtained the study did not find and include where the site was visible. In the absence of a visible view they can make no comment on the structure at that site. It does not mean something bad, just the study was not able to include this portion at that time. It happens occasionally in ant study of this type.

The quality of ultrasound exams may vary in different persons. Some issues may be related to the individual such as size, obesity, overlying bowel gas causing artifact, and other reasons. Also the experience and skills of the ultrasound technician, or machine itself, can play a role. To "not visualize" a portion of the aorta,does not indicate an abnormality. CT or MRI can be helpful if needed.