Azygous fissure and vein are normal variant seen in about 1% of the population. Note the thin linear line in the right upper zone. This is azygous fissure. It is categoriesed as accessory fissure. Further down and medially, there is an elliptical shadow within the thin line. This is azygous vein within the fissure.
Azygous fissure or vein has no clinical significance. No treatment or intervention required.