Anatomic characteristics of primary acquired nasolacrimal duct obstruction: a comparative computed tomography study

BACKGROUND: Studies of local anatomic characteristics of primary acquired nasolacrimal duct obstruction (PANDO) are important for understanding the etiology of PANDO and guiding surgical treatment. The purpose of this study was to review computed tomography (CT) scans to identify the anatomic differences in the obstructed and unobstructed sides of PANDO patients as well as in control patients in a Chinese population. METHODS: In this retrospective comparative observational study, the CT scans of 126 PANDO patients were reviewed. A total of 76 patients who underwent CT examinations for eyeball atrophy or an intraocular foreign body but had a healthy lacrimal drainage system and orbit structure were enrolled as controls. The nasolacrimal canal (NLC) widths, lacrimal sac fossa structures, and nasal abnormalities in the obstructed and unobstructed sides in patients and both sides in controls were evaluated. RESULTS: Both obstructed and unobstructed sides in PANDO patients showed significant differences to the sides of controls in NLC width (obstructed: 3.91±0.90 mm, unobstructed: 3.86±0.83 mm, control: 4.31±0.95 mm; obstructed and control: P<0.01, unobstructed and control: P<0.01, respectively), ethmoid sinusitis (26%, 28%, 16%; P=0.03 and P=0.03, respectively), osteomeatal complex opacification (18%, 14%, 7%; P<0.01 and P=0.04, respectively), and agger nasi cell opacification (22%, 20%, 9%; P<0.01 and P<0.01, respectively). However, although no significant differences (all P>0.05) were found between the obstructed and unobstructed sides of unilateral PANDO patients in these characteristics, there were correlations (r=0.714, 0.209, 0.376, and 0.112; P<0.01, P=0.03, P<0.01, P=0.24, respectively). We also found expanded lacrimal sac fossa width (6.45±1.01 mm) and decreased frontal process proportion (45.9%±15.4%) only in the obstructed sides of PANDO patients compared to the lacrimal sac fossa width in controls (6.08±1.16 mm, P<0.01) and the frontal process proportion in controls (49.9%±15.4%, P=0.03). There was no difference in the positional relationship of the uncinate process (UP) with the lacrimal fossa between patients and controls. CONCLUSIONS: A narrow NLC and nasal inflammation are associated with PANDO, while an expanded lacrimal sac fossa and a decreased frontal process proportion could be pathological changes. The healthy sides of unilateral PANDO patients might have a high risk of developing an obstruction. We also found an increased probability of the UP overlapping the lower lacrimal sac fossa in an Asian population compared to the published European data.