Weird lump on top of foot that comes and goes

[GreenLabels]

For a few months, the bridge of my left foot has been quite sore, feeling bruised although I've never to my knowledge knocked it or anything.

I also noticed that when I pinched the skin there, the fat under the skin felt a lot thicker than on my other foot, if that makes sense.

And then, in the last week, whenever I have a shower, it swells up into a hard lump, probably the size of a small plum. It's completely solid to touch. This lump then disappears within 90 minutes of getting out of the shower.

It is totally bizarre. I'm not sure whether it warrants a GP appointment though, especially as - unless I go straight after having a shower - there'll be nothing to see!

Any ideas?

[TeddyIsaHe]

Take a photo of it when it swells to show the dr. I would get it checked out just for peace of mind more than anything.

[blamethecat]

Ganglion cyst ?

[GreenLabels]

Photos never quite seem to capture what it looks like to me, but these are my attempts: