The exudate draining through the sinus tract of a chronic apical abscess consists predominantly of which cell type?

Correct answer: C. Neutrophils (polymorphonuclear leukocytes)

• A. Incorrect. Lymphocytes dominate the surrounding CHRONIC granulomatous tissue of a periapical granuloma, but they are not the main constituent of pus.
• B. Incorrect. Plasma cells are prominent in longstanding chronic periapical lesions and produce local antibody, but again they are a tissue finding, not the content of the purulent exudate.
• C. Correct. Pus, by definition, is composed principally of NEUTROPHILS — both viable and degenerating — together with liquefied necrotic tissue, tissue fluid and bacteria. Even though a chronic apical abscess sits within a chronically inflamed periapical lesion, the actively draining purulent exudate itself is a suppurative (neutrophil-rich) process. The neutrophil's lysosomal enzymes are what liquefy the tissue and create the tract.
• D. Incorrect. Eosinophils indicate allergic or parasitic processes and are not a significant component of odontogenic pus.

Note: Terminology check: a chronic apical abscess is defined by its low-grade, often asymptomatic presentation WITH a sinus tract; an acute apical abscess has rapid onset, swelling and pain and usually no established tract.