Imaging Anatomy of the Paranasal Sinuses

Paranasal Sinus Anatomy and Function
📌 The paranasal sinuses are air-filled extensions of the nasal cavity located in the frontal, sphenoid, maxillary, and ethmoid bones, forming four pairs.
👃 The nasal cavity's primary functions are to humidify, heat, and filter inhaled air, facilitated by structures like the conchae (turbinates) which increase mucosal surface area.
💨 Sinuses function to reduce skull weight, add voice resonance, act as a trauma buffer (crumple zone), and contribute to air conditioning (heating/humidifying/filtering).
🦠 The mucosal lining of the sinuses contains goblet cells (producing mucin) and ciliated epithelial cells that propel captured debris and pathogens out of the sinuses.

Sinus Drainage Pathways and the Osteomeatal Complex
➡️ Drainage occurs via two main routes: the sphenoid-ethmoid recess and the Osteomeatal Complex (OMC).
➡️ The OMC drains the frontal, maxillary, and anterior ethmoid sinuses into the middle meatus via the frontal recess, ethmoid bulla, and infundibulum, respectively.
➡️ The inferior meatus drains the nasolacrimal system.

Anatomical Variants Affecting Outflow and Surgical Risk (CLOSE Acronym)
📌 Cribriform plate depth (Keros classification) dictates the risk of damaging the lateral lamella during a FESS procedure, with Type 3 ($\ge 8$ mm deep) being the riskiest.
📌 Lamina papyracea integrity must be checked for defects or orbital fat prolapse; also note the presence of Haller cells (medial orbital wall) and the adherent uncinate process (linked to Silent Sinus Syndrome).
📌 Onodi cells (posterior ethmoid air cells superior/lateral to the sphenoid sinus) are crucial to report due to their close proximity to the optic canal and internal carotid artery.
📌 Sphenoid sinus pneumatization (Conchal, Preller, or Sellar types) and septal insertions (especially contacting the carotid canal) must be evaluated, as Sellar type has a high risk of intracranial perforation.
📌 Ethmoid notch location (Anterior Ethmoidal Artery Notch) must be determined: if bordered by supraorbital ethmoid air cells, there is a risk of arterial hemorrhage and orbital compartment syndrome during surgery.

Nasal Cavity and Septal Variations
🔎 Septal deviation is very frequent (90% prevalence if defined broadly) and can be associated with a paradoxical middle turbinate (Concha Bullosa) on the contralateral side.
💨 The Concha Bullosa (pneumatization of the middle turbinate) is a frequent finding (14% to over 50% of the population) that can narrow the OMC.
📏 Variations in the olfactory fossa depth must be evaluated using the Keros classification, as deeper fossae increase the risk of injury to the lateral lamella during FESS.

Key Points & Insights
➡️ Radiologists must specifically look for and report anatomical variants that narrow sinonasal outflow tracts (like septal deviation or Concha Bullosa) or pose surgical risks during Functional Endoscopic Sinus Surgery (FESS).
➡️ Critical surgical risk structures include the optic nerve (near Onodi cells/pneumatized anterior clinoid processes) and the internal carotid artery (protrusions in extensively pneumatized sphenoid sinuses).
➡️ When evaluating the cribriform plate, use the Keros classification to assess olfactory fossa depth; deeper fossae correlate directly with a higher risk of CSF leak upon lateral lamella injury.
➡️ Always check the lamina papyracea integrity for defects or fat prolapse, and note the presence of supraorbital air cells, as they can cause dangerous arterial hemorrhage if the anterior ethmoidal artery is inadvertently injured.

📸 Video summarized with SummaryTube.com on Feb 08, 2026, 05:46 UTC