Hi,Dear,Thanks for your query to HCM virtual Clinic. I studied your query in all the details put forth by you. I understood your health concerns. I would suggest you to consult a ER Pediatrician or Pediatric-Surgeon or ER Pediatric Oncologist if need be ,before doing CT scan(avoiding unwanted radiation exposure) or MRI-as the baby is very small for her age and may need sedation which would risk her body. So on mere brother s non-medical advise you should avoid CT/MRI scans for a painful lump with 1 weeks fever off and on. As there are many causes of a painful lump under the left rib cage,without the first hand information I would not be able to advise you for your baby niece. I would advise therefore to consult a Er Pediatrician before doing this test,who would rule out the other causes as Lymphoma/or other neonatal tumors besides infective skin/subcutaneous lumps with fever and would treat it accordingly with- Sponging for the control of fever if need be, Antipyretic drops / antibiotic drop and needful medicines as need be. Remedy- So till the time you consult ER Pediatrician and get his definitive opinion ,DON T WORRY AT ALL about it being tumor,but you need to be worried as it would complicate into other problem associated with it. And act fast on the above suggestions,which helps you to plan treatment with your ER Surgeon. Hope this would resolve your query with full satisfaction. Welcome for any further query in this regard to ME by direct question at HCM. Write excellent review and hit thanks, to narrate your experience ,which would improve my rating for many other visitor s to HCM. Wishing you fast recovery. Have a good day. Dr.Savaskar M.N. Senior Surgical Consultant. M.S.Genl-CVTS