Normal Anatomy and Anatomic Variants of the Paranasal Sinuses on Computed Tomography




It is imperative for all imaging specialists to be familiar with detailed multiplanar CT anatomy of the paranasal sinuses and adjacent structures. This article reviews the radiologically relevant embryology of this complex region and discusses the region-specific CT anatomy of the paranasal sinuses and surrounding structures. Radiologists also need to know the clinical implications of identifying preoperatively the numerous anatomic variations encountered in this region and prepare a structured report according to the expectations of the referring clinician.








Anatomic concepts of the paranasal sinuses have been known since the late nineteenth and early twentieth centuries. These have assumed greater significance in recent times due to advances in functional endoscopic sinus surgery (FESS) and imaging technology. Multiplanar high-resolution CT (HRCT) of the paranasal sinuses provides a precise and reliable preoperative roadmap for the endoscopic sinus surgeon. All radiologists should be familiar with the 3-D anatomy of the paranasal sinuses and the anatomic variants that surgeons are likely to encounter. This article reviews the embryology of the paranasal sinuses and outlines the CT technique/protocols for imaging this region. CT anatomy of the nasal cavity and paranasal sinuses is described in detail together with the anatomic variants encountered in each region.




Knowledge of relevant embryologic events in paranasal sinus development can avoid pitfalls in diagnosis. Sinus pathologies in children younger than 4 years are uncommon except in the ethmoid sinuses because these are the only sinuses that are pneumatized at birth.






The mucosal lining over the nasal septum and the nasal turbinates is influenced by the nasal cycle, which is responsible for alternating changes in the turbinate sizes due to mucosal engorgement. This cyclic and physiologic enlargement of the turbinates alternates between both nasal cavities every 45 minutes to 1 hour and should not be mistaken for pathology.




  • 2.

    Septal pneumatization: pneumatization may occur anteriorly from the crista galli or posteriorly from the sphenoid sinus. Posterior septal pneumatization may occasionally narrow the sphenoethmoidal recess and impede access to the sphenoid ostium.




  • 4.

    Pneumatized basal lamella: may be mistaken for an anterior ethmoidal air cell leading to incomplete exploration of the posterior ethmoid sinuses.




  • 3.

    The suprabullar and retrobullar recesses can be identified while viewing the lamellar anatomy in the sagittal plane.




    • Rarely, the uncinate process may be entirely absent.




    Bony margins of the infraorbital nerve canal may be dehiscent in up to 14% of cases, which exposes the nerve to sinus pathology.








    Inadvertent intracranial penetration can be avoided during FESS by preoperative CT identification of a low ethmoid skull base, presence of a frontal bullar cell, Keros type 1 and type 3 olfactory fossae and asymmetric olfactory fossae.





  • E: Ethmoidal (anterior) artery anatomy


    • References



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