### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
I have a lump on my back that feels like a large air pocket, it isn t swollen nor does it hurt, no crackling sound when touched, and is about the area of a tennis ball or smaller. the lump doesn t feel like it contains a fluid, just air like. i do have pain to the left of the lump or swollen area, but it feels like a tight muscle. any ideas?

### output:

Hi, Dear thanks for the query to Chat Doctor virtual clinic. I studied your query in full details updated from you. I understood your health concerns. Based on your query data, In my opinion, Dear You seem to suffer from Back Lipoma mostly as its non-tender and is common site for Big Lipoma. Sebaceous Cyst needs to be ruled out by USG study of the lump and by a Second Opinion from Surgeon. If the lump is on the heels as said in the heading, which exposes the confusion by oversight/or typing mistake. Still if it is in the back of heel, TendoAchilles Bursa needs to be ruled out, from or tho Surgeon. Treatment-Would vary depending on the cause of the lump on the back or on the back of the heels. Surgical excision if it troubles you is advisable. Else it is a benign tumor and need not worry unless its of cosmetic or pressure symptoms, for which I would suggest you. Hope this would resolve your query and worry and Anxiety accompanied by it. Welcome for any further query in this regard to ME. I would love to help you out.Awaiting any further query. Wish you fast recovery from this intriguing health problem. Have a Good Day. Chat Doctor. N.M.S. Genl-CVTS -Senior Surgical Consultant