The lumen of a periapical/radicular cyst typically contains which type of fluid?

• A. Serosanguinous fluid with variable necrotic contents.
• B. Pure pus.
• C. Clear, sterile saline.
• D. None; it is air-filled.

Answer: (A)

In a radicular (periapical) cyst, the cavity is a chronic inflammatory space rather than a fresh pus-filled abscess. The fluid inside is typically serosanguinous—a pale, blood-tinged serum—because inflamed capillaries leak fluid and occasional small bleeds occur. The contents can include necrotic debris from the inflammatory process, reflecting tissue breakdown over time. This combination fits a long-standing inflammatory lesion, where the lumen is not simply pus from an acute infection, nor is it sterile saline or air. Hence the lumen commonly contains serosanguinous fluid with variable necrotic contents.