Ultrastructural findings of capillaries in nasal polyps.

The permeability of capillaries in nasal polyps is very high. The continuous capillary is the typical type but the discontinuous type and fenestrated type are also observed. These fenestrated capillaries are found near the stalk region. Although discontinuous capillaries undoubtedly have high permeability, many morphological findings which show this high permeability are observed even if they are continuous capillaries. There are many endothelial projections into the capillary lumen, well-developed marginal folds and pinocytotic vesicles. The endothelial projections complicatedly agglutinate to another part of the endothelium or projections and sometimes form the reticulation. Morphological findings inhibiting the interstitial oedema are also observed. Several layers of basement membrane appear around the capillaries, endothelial projections into the interstitium and the formation of the appositional junction between the pericytes and endothelium. Well-developed basement membrane inhibits the leakage of large molecules. The large spaces which are enclosed by external projections demonstrate the efficient absorption of interstitial fluid. The external projections and the formation of the appositional junction between pericyte and endothelium may support the findings of the rebirth capillaries. The capillaries in nasal polyps are very small in number. If the capillaries or venules were quickly created the interstitial fluid would be efficiently absorbed in the vessels.