MRI performed 1 week later demonstrates symmetrical and diffuse marrow oedema involving the pubic symphysis and bilateral superior pubic rami. There is associated patchy loss of fatty marrow signal and avid contrast enhancement of the pubic symphysis. There is also a small amount of fluid within the pubic symphysis with inferolateral extension into the right adductor longus muscle where it forms a 9.3 x 3.2 cm multiloculated collection consistent with an abscess. Some extension into the left adductor longus muscle is also demonstrated. There is minimal subchondral irregularity within the pubic symphysis.
There is surrounding global inflammatory change involving the pelvic floor muscles with a small amount of pelvic free fluid.
Appearances are in keeping with septic arthritis and osteomyelitis of the pubic symphysis with an associated intramuscular abscess on a background of a diffuse inflammatory process consistent with radiation change.