Kitty's enlarged scrotum

[HimmieMommy]

My mom has a 5 months old neutered himalayan who has an enlarged scrotum. I think it's the scrotum sac but I'm not sure. the protruded sac size is approx 1/4 of his torso length. I don't see or feel it on my 9 months old neutered himmie. My mom's kitty is an overweight boy so I don't know if the weight contributes to the size. The sac isn't hard but rather feels fatty/soft like his tummy. Does anyone know what that is? My mom's going to get an appt w the vet next week but I'm curious/worried to know the results.

More info on the himmie-- he's sleeping quite a bit (about 12 hours a day). When he's up, he's very active, jumping around and playful. And he's appetite is still good and he drinks quite a bit of water.