KUB: The left psoas muscle shadow is absence, and no evidence of a calculus.
A abdomen CT was performed due to a left psoas mass.

The abdomen CT shows a large abscess with mottled gas over left psoas and iliac region from left renal helium and left upper thigh level. A small right psoas abscess was also noted. There is no evidence of urolithiasis.
After admission, CT-guild drainage was performed, and the milk-like turbid pus grew Staphylococcus aureus. Infecvtive endocarditis (IE) was also surveyed, but no evidence of IE. The final diagnosis was the IV drug abuser with a primary psoas abscess.

1. The primary psaos abscess is a relatively rare disease,

     and can mimic as urolithiasis, sciatica, and APN.
2. The blurred psoas shallow is a hint of psoas mass.
3. The classical clinical triad consisting of fever, back pain,

     and limp is present in only 30% of the patients with

     psoas abscess.
4. The risk factors of primary psoas abscess include DM,

     IV drug abuse, AIDS, renal failure, and

     immunosuppression.