During canal wall down mastoidectomy, the surgeon identifies the 'sentinel cell' (Koerner's septum). What is the surgical significance of this structure?
- A It marks the medial wall of the epitympanum
- B It is a bony partition separating mastoid from petrous apex
- C It is a thin bony plate separating squamosal from petrous mastoid cells ✓
- D It indicates the position of the sigmoid sinus
Correct answer: C. It is a thin bony plate separating squamosal from petrous mastoid cells
Explanation
Koerner's septum (petrosquamous lamina) is a bony plate separating the squamosal mastoid air cells from the petrous air cells. Surgically, it is significant because cells may be hidden medial to it — if the surgeon mistakes these cells for the mastoid antrum, the deeper petrous cells remain undrained, leading to persistent disease. The tegmen is the roof of the epitympanum, not Koerner's septum. The sigmoid sinus is identified by its blue coloration and its 'sigmoid groove' bony surface.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.