Findings are in keeping with left psoas muscle  abscess. Left superior lumbar hernia is an incidental finding in this patient.

It is often necessary for psoas abscesses to be drained and they are usually amenable to CT guided percutaneous drainage, with the patient in the prone position. On occasion, ultrasound-guided percutaneous abscess drainage is also undertaken.

An important differential is a spontaneous psoas hematoma and tumor, such as a sarcoma, although the clinical scenario may help assist in distinguishing.  Another important consideration is the primary pathology may be a hematoma that becomes secondarily infected.