is medical term describing the infection and inflammation in mucosa( inner part/linning of mouth,sinus
maxillary sinus mucositis- is what u have been asking for i think so..in it the mucosal linning of maxillary sinus is inflammed due to infection..
residual periapical inflammatory lesion- it indicates that any of your extracted tooth (may be rct treated) had some lesion most probably- a cyst
or grannuloma which has not been removed during their extraction or has not resolved yet.. it typically is around the root region of tooth (periapical)..
the treatment for both includes antibiotics both local and oral along with anti-inflammatory medicines, surgical excision/curretage of residual lesion.. and if tooth is present- repeat RCT and Apicectomy.. and in sinus also sometimes surgery is required if lesion extends inside its linning also.
i think u had some periapical lesion in your premolar or molar tooth of upper jaw bone, which has infected your maxillary sinus.. and the size of lesion and tooth existence will decide treatment plan..
you must consult an oral maxillofacial surgeon for surgery...