A 28-year-old man comes to the clinic for 6 days of worsening nasal congestion and thick, yellow-green nasal discharge. He initially had a “bad cold” with sore throat and cough that improved after 2 days, but he then developed increasing right-sided facial pain and pressure that worsens when he leans forward. He reports subjective fever and a diffuse headache. Physical examination shows tenderness to palpation over the right cheek. The clinician suspects acute rhinosinusitis due to obstruction of normal sinus drainage. Which of the following anatomic sites is most commonly involved in adults with this condition?

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