The heart (left ventricle) will dilate when it is overworked. The overwork can be due to pumping against high resistence. Is the scleroses of the vessels (cause the heart to overwork and enlarge) or is sclerosis of the aorta valve. If it is the valve, that will cause the heart to enlarge due gradient pressure of the left ventricle and the aorta valve.
An athletes's heart enlarges the left ventricle but it is not pathological. The heart has stronger contractions due an increase of heart muscle strength. Stop exercising the heart will return to normal size. An athlete's heart rate will be less than 60 bpm at rest indicating more blood pumped with each stroke than what is considered normal.
I am 60 yrs. old. I had an angiogram 1 1/2 yrs. ago and have clean arteries. But they said I have a very enlarged heart. I don't smoke, etc. You can be thin, eat right and still have an enlarged heart. If you have had blood pressure that was a little higher than normal for years....you can develop an enlarged heart. High blood pressure is a silent killer. Gradually creeps up on you. I know. Now I am on beta blockers, alpha blockers, etc. etc. Wish I hadn't listened to my vegetarian sister who said "never go on high blood pressure pills". Cardiologist said that is the reason I now have "congestive heart failure". I tell everyone. "Take your high blood pressure medicine!!!".
You mentioned you have scoliosis.. Is there any chance that your chest bone is a bit concave?? The reason I mention this is because my son has a concave chest bone and the doc said to keep this in mind because on x-rays his heart would appear to be enlarged from it and to let doctors know.. Although on my son it's very noticeable so I'd imagine they'd realize it themselves.. Anyway, I just thought I'd throw that out there as a possibility.