What is a sinus septum?

• A. A groove on the lateral wall of the sinus.
• B. A mucosal fold within the sinus.
• C. A nerve within the sinus.
• D. A bony projection from the floor of the sinus.

Answer: (D)

A sinus septum is a bony wall inside a sinus that partitions the cavity into compartments. In the maxillary sinus, these septa typically arise as projections from the floor of the sinus and extend upward toward the sinus roof. This distinguishes it from mucosal folds (soft tissue), grooves on the wall (linear landmarks), or nerves within the sinus (neural structures). So a bony projection from the floor of the sinus best describes a sinus septum.