The accessory sphenoidal septum (ASS) is an additional bony partition within the sphenoid sinus, separate from the central sphenoidal septum. It may appear as a ridge or complete wall and varies significantly between individuals.

• Located inside the sphenoid sinus, below the sella turcica.
• Unlike the main sphenoidal septum, the ASS:
  • Can be multiple or incomplete.
  • May arise from various sinus walls.
  • Often attaches asymmetrically.
• Important attachments:
  • Optic canal
  • Internal carotid artery (ICA)
  • Lateral opticocarotid recess (LOCR)

• During endoscopic transsphenoidal surgery, the ASS:
  • Can obscure visualization of the LOCR.
  • Serves as a reliable landmark for locating LOCR when it's not directly visible.
• Recognizing the ASS ridge helps avoid injury to:
  • Optic nerve
  • Carotid artery
• The recent anatomical study (Guo et al., 2025) showed that:
  • In cases where LOCR is indistinct, its position can be inferred using the ASS ridge and its prolongation.