Clinical findings:
(1) fever
(2) lower abdominal and/or back pain (tuberculosis may be painless)
(3) pain the hip or knee
(4) possible limp
(5) possible flexion deformity of the hip
(6) positive iliopsoas test (with the patient supine and the knee extended, the patient is asked to flex/lift the thigh against resistance)
(7) possible palpable mass
(7a) beneath the inguinal ligament with a mass in the iliac fossa
(7b) in the buttock
(8) clinical findings of the adjacent infection that is the source for the abscess (osteomyelitis, septic arthritis, intra-abdominal abscess, other)
Imaging findings:
(1) a mass effect may be present in the muscle
(2) gas may be present
(3) calcifications may be present (suggests tuberculosis)
(4) a circumscribed, low-density fluid collection is seen on CT scan if an abscess is present; a diffuse enlargement of the muscle on CT scan suggests a phlegmon
Differential diagnosis:
(1) septic arthritis of the hip
