Lateral right maxillary sinus 8 mm ap x 6 mm transverse x 9 mm craniocaudad mucous retention cyst versus polyp. what does that mean?

Cyst in sinus: It means that you have a small soft tissue mass in your right cheek sinus. It if nearly impossible to differentiate solid versus fluid-filled masses on a ct scan. Either way, no treatment is generally necessary for this condition.

Depends: If it is asymptomatic and painless then nothing. A usual finding, especially in asthmatics. If there are symptoms, frequent sinusitis, or it is growing as noted on serial exams then removal is recommended with histological examination (biopsy).