My cat - approx 12 year old male - has a lump on the back of his
neck, between the shoulder blades. It has gradually grown in size over the past 4 months. It is soft, liquid filled - the skin covering it is stretched and transparent looking. It doesn't seem to cause him pain. Yesterday, when the lump was at about the size of half a golf ball, it burst, realeasing a clear liquid. We cleaned it out, but today it appears to be refilling again, quite rapidly. What could this be? Thanks.