Prevalence of Anatomical Variations of the Sinonasal Region and their Relationship with Chronic Rhinosinusitis. 
Background Precise knowledge of anatomic variations of nose and paranasal sinus complex is essential for achieving best surgical results during endoscopic sinus surgery.  Computed tomography is the gold standard investigation for evaluation of paranasal sinuses and adjacent structures.  Objective To study prevalence of anatomical variations of nose, paranasal sinuses and osteomeatal complex and to identify a probable association between anatomical variations and chronic rhinosinusitis.  Method Prospective, analytical study conducted in 218 patients with Chronic rhinosinusitis in Department of Radiology, Dhulikhel Hospital, Kathmandu University Hospital between January 2015 to January 2016.  Volumetric axial CT scan was done in 128 slice CT scanner in 3mm thickness from frontal sinus to floor of maxillary sinus with thin multiplanar reconstruction.  Radiological findings were reviewed and obtained data analyzed with SPSS version 16.  Pearson chi square test and Pearson correlation coefficient were used for statistical analysis.  Result The most common anatomical variation was pneumatized agger nasi cells followed by concha bullosa and deviated nasal septum respectively.  Statistical significance were seen between ipsilateral agger nasi cell and frontal sinusitis (p< 0.001), ipsilateral haller cell and concha bullosa with maxillary sinusitis (p<0.001) and onodi cell with sphenoid sinusitis (p<0.001), However, no obvious statistical correlation was noted between deviated nasal septum with ipsilateral maxillary sinusitis.  Conclusion Precise knowledge of anatomic variations of the paranasal sinuses is important in chronic rhinosinusitis to prevent possible complications during surgery.  Computed tomography is the modality of choice in evaluation of paranasal sinuses and adjacent structures.