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A 17-month-old girl presents with intermittent fever, hip pain and irritability for 2 weeks. She walks with a limp. On examination, temperature is 38°C, and her hip is held in flexion. Passive hip extension, internal rotation, and abduction causes severe pain. WBC is 29,300 cells/microliter. ESR is 66 mm/h. Radiograph, bone scan and CT scan are shown in Figures A through C. What is the diagnosis?
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This child has a right psoas abscess.
Psoas abscess is rare and difficult to differentiate from septic arthritis of the hip. Primary psoas abscess (in the absence of an underlying focus of infection) has a predisposition to children. The most common organism is Staphylococcus aureus. It most commonly presents with hip pain and limp. It is diagnosed on CT and ultrasound. Treatment involves combination of intravenous antibiotics and either open or percutaneous (CT- or ultrasound-guided) extraperitoneal drainage.
Song et al. reviewed the differentiation of psoas abscess from septic arthritis of the hip in children. Signs unique to psoas abscess include sciatica, femoral nerve neuropathy, bladder irritability (from psoas compression). A psoas abscess can give rise to a sympathetic sterile hip effusion.
Dala-ali et al. described septic arthritis secondary to a psoas abscess in an adult. The psoas has a rich blood supply predisposing it to haematogenous spread. Infection can reach the hip via (1) the psoas bursa (connects directly with the hip joint in 15%), or (2) directly between the iliofemoral and iliopubic ligaments. Mortality from septicemia is 100% if left undrained.
Figure A is an AP radiograph of the pelvis demonstrating obscuring of the right sacroiliac joint by the shadow of a psoas abscess (labeled in Illustration A). Figure B is a bone scan showing leftward displacement of the bladder by a large psoas abscess in the right iliac fossa (labeled in Illustration B). Note the absence of activity in the bony tissue. Figure C is a CT scan showing a large right psoas abscess (labeled in Illustration C).
Answer 1: There is no septic arthritis of the hip. The radiograph does not demonstrate joint widening to suggest effusion, nor is there joint subluxation or bony destruction.
Answer 3: Sacroiliitis is not present. There is no increased tracer uptake around the right SI joint. The right SI joint is obscured because of the overlying psoas mass.
Answer 4: Transient synovitis is a diagnosis of exclusion. There is usually no fever and normal ESR. Hip joints may demonstrate a sterile effusion on radiographs but this is also absent.
Answer 5: There is no increased uptake on bone scan to suggest osteomyelitis. There are no late radiographic changes characteristic of osteomyelitis.
Song J, Letts M, Monson R.
Clin Orthop Relat Res. 2001 Oct;(391):258-65. PMID: 11603678 (Link to Abstract)
Song, CORR 2001
Dala-Ali BM, Lloyd MA, Janipireddy SB, Atkinson HD.
J Orthop Surg Res. 2010;5:70. Epub 2010 Sep 16. PMID: 20846379 (Link to Abstract)
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Educational video describing abscess of the iliopsoas muscle.The iliacus and the...
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