A method of treating diseased ethmoid sinuses in a patient with a therapeutic agent includes providing an injection device comprising an elongate member having a proximal end, a distal tip or end, and a lumen extending between the distal tip or end and the proximal end, the proximal end being operatively coupled to a source of the therapeutic agent. The distal tip or end of the injection device is inserted at least partially within an interior portion of an ethmoid air cell. The therapeutic agent is then injected into the interior portion of the ethmoid air cell using the injection device, the therapeutic agent being delivered via the lumen in the elongate member.