Ductus nasolacrimalis
The nasolacrimal duct (NLD) is the terminal part of the nasolacrimal apparatus.
Gross anatomy
The nasolacrimal duct is the inferior continuation of the lacrimal sac and is ~17 mm in length in total. There are two parts to the nasolacrimal duct:
- intraosseous part (12 mm): enters the lacrimal groove and descends within the nasolacrimal canal of the maxilla
- membranous part (5 mm): runs in the nasal mucosa; terminates below the inferior nasal meatus as a slit-like opening where it is covered by a mucosal fold called the valve of Hasner (or plica lacrimalis)
Valves
Up to eight 'valves' of the nasolacrimal duct have been defined in the literature and are commonly seen in older anatomical texts and monographs. However, it has been contended that some of these are not true mucosal valves but just embryological irregularities in the ductal wall. From craniad to caudad, these 'valves' have been named: Foltz, Bochdalek, Rosenmüller, Huschke, Aubaret, Krause (or Béraud), Taillefer, Hasner (or Cruveilhier/Bianchi)
Therefore a recent retrospective study used digital subtraction dacryocystography (a high spatial resolution technique) to precisely define the intraluminal anatomy of the nasolacrimal duct and determine which of these named structures really represent consistent anatomical features. The researchers used a study group of 92 individuals for whom DS-DCG had previously been reported as normal :
The inferior group of 'valves' were consistently better seen:
- valve of Krause: was visible in 79.3% cases
- valve of Taillefer: 93.5% cases
- valve of Hasner (plica lacrimalis): 98.9% cases
The superior group of 'valves' were inconsistently visualized and were therefore thought to be mucosal irregularities rather than true anatomical valves:
- valve of Foltz and valve of Bochdalek: were visible in 17.1% cases
- valve of Rosenmüller and valve of Huschke: 46.4% cases
- valve of Aubaret: 40% cases
Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Ductus nasolacrimalis: