Cyst or abscess?

[BonBon2010]

Truffles has had a small marble sized 1cm painless lump behind her hip for a while now, never bothered her, and i've left alone.Today it had a small opening in it, so I squeezed it slightly to see if anything was coming out and a black substance, with grey and white cheesy type stuff mixed in started to come out, so i've got it all out and i've given it a clean with salt water. Lump has totally disappeared. Think a vet visit on monday with a view to having the capsule removed so it doesn't come back. This is the guinea pig who suffered alopecia at two and lost almost all her fur midrift, apart from legs, belly, rump and shoulders upwards. She's had a steady regrowth of some of her hair since being paired up with my neutered male Hovis, albeit is a long way from having a full coat, but a friend the other day commented she defo has more hair than the last time she saw her.
Am I right in saying its a sebaceous cyst and not an abscess? I would have thought if an abscess, it would have burst long ago, and she'd have been poorly with it..

 

[Merab]

Only a vet can confirm what it is but cleaning it out daily is a good move.
Hope it’s nothing serious

 

[BonBon2010]

She sat on my lap and never complained once about me flushing it out, nothing else followed, and to look at all you can see is a 1mm hole where the offending crap came out, I think she quite enjoyed that part, as she sat licking my hand as I did it, it's not even worth a photo now, as there's nothing to see, but the tissues were covered in a black substance (I presume because she's black skinned).

 

[Lady Kelly]

It sounds very much like a sebaceous cyst as the pus does tend to reflect the skin colour. You would know if it were an abscess from the absolute foul smell they produce, seriously I nearly passed out in the vets from it!