lower left swelling following bowel movement

I have a mild swelling on the left side of my pelvis that becomes more pronounced (actually protrudes) after bowel movements. It's directly below and to the left of my navel.  It also visibly moves around slowly in waves at that time, and it's sometimes accompanied by a palpable hard nodule-like feeling directly above my navel.   No pain, except sometimes right before BM.  I have had a CT, ultrasound, and MRI because my docs thought the issue was an ovarian cyst on the opposite side. However, the cyst is resolving itself and there's no change in the swelling. It is likely it is an unrelated GI problem, but no masses came up in the tests. BMs are regular, but I have had a change to a vegan diet so consistency is different. I also have tremendous amounts of gas and popping feelings in my pelvis on left side. I should also mention that I'm very thin. I wonder if it could be a gas pocket, as I've been told that air is not seen well on these tests. As far as GI diseases/disorders go, I only know that I have had a borderline result on one of the celiac tests, the IGA I think. My doctors are not very concerned, but they have not seen this strange sight after bowel movements.  They say it's probably just that I'm so thin that the colon is more visible.  I have, however, been this thin before and have never experienced this.  Thanks in advance for any help.

[Kevin Pho, MD]

You have had a pretty comprehensive set of imaging studies to evaluate the symptoms.  

You can consider a colonoscopy as the next test.  Changes in the shape of stool caliber or patterns can indicate an anatomical problem - like a stricture or mass.  The colonoscopy would rule that out.

If the tests continue to be negative, treatment for irritable bowel disease should be considered.  This can include increasing fiber in the diet, antibiotics like Rifaximin, and antispasmodic therapy.  

Testing the stool to rule out malabsorption syndrome scan be done as well.

These options can be discussed with your personal physician.

Followup with your personal physician is essential.

This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.

Kevin, M.D.
kevinmd_

[mandala]

Should also add that I have lost a considerable amount of weight over past months.  This has coincided, however, with starting a vegan diet.  I don't have much muscle tone.