Why only 1 anal gland blocked?

Vet said had never had to empty a gland that was so compacted (it was so bad nurse couldn't do it), but the other one was completely empty. Got to go back in a week to check hasn't filled again. Am a bit concerned as to why one only was so full and when I asked whether there could be anything serious causing this, nurse said "shouldn't think so", but didn't sound very definite. I took her to vet 2days after showing symptoms, so it's not as if it built up because I ignored it. Must have been very painful to empty, as still chewing bum.

I automatically ask for Pereg's anal glands to be checked at each vet visit [currently every six months] and only one side has ever needed emptying. Not blocked though, thankfully.

My youngster only needs one side emptying. The vet has done it once and I managed to do it myself as well!

Thanks for replies - wish I wasn't such a worrier!