Primary iliac muscle abscess due to Staphylococcus aureus

A 55-year-old man presented with a 3-day history of lower back pain and rig ht thigh pain. A diagnosis of discogenic pain had been made at two other ho spitals. He had been admitted to a medical center for acute hepatitis 5 mon ths prior to this admission. Large doses of parenteral hydrocortisone were used for 13 days to treat acute hepatitis. At the present admission, he was unable to stand and refused to move his right leg. There was mild tenderne ss in the light lower abdomen on deep palpation. Passive flexion and rotati on of the right hip produced mild pain, while passive extension of the righ t hip produced severe pain and resistance. The Patrick test was positive an d the psoas sign was present on the right side. The erythrocyte sedimentati on rate (ESR) was 66/hr. The C-reactive protein (CRP) level was 0.161 g/L. Abdominal sonography shelved a lobulated mass ill the right iliac fossa. Ma gnetic resonance imaging shelved severe swelling of the right iliac muscle with a central heterogeneous mass. Debridement, drainage of the abscess, an d application of a septopal chain were performed via an anterior retroperit oneal approach, and parenteral cephazolin and gentamicin were administered. A culture of the abscess grew Staphylococcus aureus. The ESR and CRP conce ntrations decreased to within the normal ranges 3 weeks later. Awareness of this disease entity, careful physical examination, and appropriate imaging studies such as ultrasonography and magnetic resonance imaging are key to making a correct diagnosis.