Thank you for your query.
From what you mention I understand that you can feel a bulge (which has enlarged since the last examination) above the sternal notch which is sore to touch. The bulge is hard like a bone and is associated with cough
of probably 6 week duration. I would like to get the child clinically examined sooner for the swelling and chest and further investigate with:
1. X-ray chest AP & Lat. view
to know more details of the swelling (this shall be based on the clinical examination)
3. Further investigations, if required, like MRI
It is very difficult to tell the cause of the bulge without a clinical examination as a number of structures are present above and behind the sternum
near the sternal notch and swelling may arise from anyone of them. However the cough of 6 weeks duration suggests that something is pressing on the trachea/bronchus
which may be initiating the cough reflex.
I hope I have answered your query to your satisfaction.
Wishing your daughter all the best.
Rajiv K Khandelwal