Medic leading operation on extremely squidgy swelling (6)
I believe the answer is:
dropsy
'swelling' is the definition.
(dropsy is a kind of swelling)
'medic leading operation on extremely squidgy' is the wordplay.
'medic' becomes 'dr'.
'leading' is a charade indicator (letters next to each other).
'operation' becomes 'op'.
'on' is a charade indicator (letters next to each other).
'extremely' suggests removing the centre.
'squidgy' with its middle removed is 'sy'.
'dr'+'op'+'sy'='DROPSY'
(Other definitions for dropsy that I've seen before include "illness" , "Oedema (old name)" , "medical condition" , "Accumulation of fluid in a part of the body - oedema" , "fluid build-up" .)