What Could Cause a Lump on the Left Side of My Stomach under the Ribs?

There are a few things that might cause a lump in the left upper abdomen just under the ribs. One possibility is an abdominal intercostal hernia, which can happen when a forceful cough causes a small opening in the muscles between the ribs. This lets a little bit of the inside of your stomach push out and feel like a lump. Another possibility is a growth on the bones of the rib cage. For example, a giant cell tumor is a kind of growth that can develop in the ribs and slowly get bigger. In some cases, a large mass might even start from nearby areas—like the pericardium (the lining around the heart)—and extend into the rib area. Because the causes are so varied, it is important to have a doctor check any new lump. They might use imaging tests, like an ultrasound or CT scan, to see exactly what is causing the lump and decide if you need treatment.