Pathognomic features of Maxillary sinusitis is -
Mucopus in the middle meatus
Inferior turbinate hypertrophy
Purulent nasal discharge
Atrophic sinusitis
Characteristic finding of maxillary sinusitis on Rhinoscopy is pus or mucopus in in the middle meatus.
Mucosa and turbinates may appear red and swollen.

Remember: Dental infections are an important source of maxillary sinusitis.