This is a genetic thing. The first I'd encountered it was in a single WR hen I'd had for years that I got back from a bad situation where she was being kept on cement floors....prior to that I hadn't noticed it in her. I had kept chickens for most of my life and hadn't even known they HAD those little glands in their feet in that location until I discovered them enlarged and impacted in this one hen.
Flash forward to breeding this hen in her 6th year and having two offspring, both pullets, from her. Both of her daughters have these enlarged glands that become impacted in the their feet and these birds are free range on plenty of clean pasture and have deep litter in the coop, so no excess mud, sand, dirt, etc. to cause such a thing.
On forward to their offspring....thus far I've not noted any of their offspring to have it going on, but I haven't done a good foot inspection yet this spring....by just glancing at the birds, none of their feet are showing the impaction of those glands yet but they are just a year old now, so it may show up as they age. The first one didn't show impaction in her first three years either, but after she had been kept on cement it was evident. Her daughter's impactions were more evident in their second year.
Best solution? Don't breed that bird to pass along the propensity to have enlarged and impacted glands in the feet and, for those you have, just keep them cleaned out regularly to keep them comfortable and to avoid infection.
Once they are enlarged, it is probably far too late to prevent or decrease the size of the duct....I tried packing(the cotton from the ends of Qtips soaked in castor oil) and then removing it, etc. and each time the duct seemed to get smaller and smaller but I don't think it's possible to get them to go back to the original size of not even being able to see them and any opening there at all will collect debris and then become enlarged.