CT Assessment of the Nasolacrimal Canal in a Black African Population

Abstract

Black Africans had been identified to have a lower prevalence of primary acquired nasolacrimal duct obstruction (PANDO). This has been attributed to the likely larger size of the nasolacrimal canal. However, there is paucity of studies that have quantitatively measured the dimension of the nasolacrimal canal in a homogeneous black population. The objective of this study was to determine the diameter of the bony nasolacrimal canal by CT in a normal adult Nigerian population. The authors measured the minimum CT diameter of the bony nasolacrimal canal in 401 consecutive eligible adult patients using retrospective axial CT scans obtained between January 2006 and December 2010. The measurements were taken on axial images using a preset bone window algorithm on a standalone computer workstation with a ClearCanvas viewer (width: 2500, level: 480). The software calipers could measure up to a tenth of a millimeter. The CT images were made up of 378 cranial scans and 23 scans of paranasal sinuses. There were 286 male patients and 115 female patients aged 16 to 86 years with a mean age of 48.5 ± 18 years. The mean difference in nasolacrimal canal diameter of 3.52 mm in male patients and 3.36 mm in female patients was found to be statistically significant (t = 2.238, df = 400, p = 0.026). There was no significant difference in the canal diameter across age groups. In addition, there was no significant difference in the diameter between the right and left sides in the authors' study population (t = 1.551, df = 400, p = 0.122). The mean bony nasolacrimal canal diameter as measured by CT in Nigerians is smaller than those reported in African Americans, Asians, and Caucasians despite the reported lower prevalence of PANDO among blacks.