title: Frequency of the common canaliculus: a radiological study.
abstract: BACKGROUND
  It is frequently stated in the literature that there is a common canaliculus (CC) in the lacrimal drainage system in about 90% of individuals; in the remaining 10%, the upper and lower canaliculi enter the lacrimal sac separately. To our knowledge, there is no quantitative study supporting this assumption.
  
  
  OBJECTIVE
  To investigate the frequency of the CC and other anatomical types connecting the upper and lower canaliculi to the lacrimal sac.
  
  
  METHODS
  We presumed that there might be 3 different types of anatomical connection between the lacrimal sac and the canaliculi. Digital subtraction macrodacryocystograms obtained from 281 patients with obstructive epiphora were reviewed, and those of 247 patients were included in the study. These patients were grouped according to the anatomical types.
  
  
  RESULTS
  Dacryocystographies were performed on 153 patients unilaterally and 94 bilaterally. We observed a CC in 321 (94.1%) of 341 lacrimal drainage systems. In 13 lacrimal drainage systems (3.8%), the CC was absent, but the upper and lower canaliculi joined at the wall of the lacrimal sac. In only 7 lacrimal drainage systems (2.0%) did the upper and lower canaliculi enter the sac separately. In 2 patients with bilateral dacryocystograms, a CC was seen on one side but not on the other side.
  
  
  CONCLUSIONS
  The frequency of separate drainage of the upper and lower canaliculi into the lacrimal sac is only 2.0%. The CC might not be present bilaterally in all individuals.
authors.affiliation: Department of Ophthalmology, Uludag University School of Medicine, Gorukle Campus, 16059 Bursa, Turkey. byazici@uludag.edu.tr
authors.forename: B
authors.initials: B
authors.lastname: Yazici
authors.forename: Z
authors.initials: Z
authors.lastname: Yazici
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015901:Angiography, Digital Subtraction; D003287:Contrast Media / Q000008:administration & dosage; D003607:Dacryocystitis / Q000000981:diagnostic imaging; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007472:Iohexol / Q000008:administration & dosage; D007765:Lacrimal Apparatus / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D007767:Lacrimal Duct Obstruction / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D009301:Nasolacrimal Duct / Q000033:anatomy & histology / Q000000981:diagnostic imaging*
chemical_list: D003287:Contrast Media; D007472:Iohexol