Pyomyositis on CT and US

A CT scan through the lower pelvis (A) shows a hypodense right-sided obturator externus muscle (asterisk) and a normal right-sided pectineus muscle (P). The left and right pectineus muscles (P) and left obturator externus muscle (OE) show normal soft tissue density. Image B is a magnified view and modified to highlight the difference in density between the hypodense right OE (asterisk) and normal pectineus muscles (P) and the normal left OE. Image C is an ultrasound of the right groin and shows a hypoechoic right obturator externus (asterisk), a normal right pectineus muscle (P), and a needle (arrow) within an hypoechoic abscess in the muscle. Image D is a magnified view of C. Culture of the aspirate grew Staphylococcus.