Working Diagnosis:
Left septic sacroiliitis with adjacent osteomyelitis and abscess formation

Treatment:
CT guided abscess drainage with IV antibiotics

Outcome:
Interventional radiology performed a CT guided abscess drainage, of the most prominent abscess, and the drain was left in place, over the lower left abdomen, for three days. The drain was removed when output was negligible. At the same time, the patient was started on empiric IV clindamycin, which was switched to oral antibiotics at discharge.

Author's Comments:
Pyogenic sacroiliitis is an exceedingly rare condition, accounting for approximately 1-2% of pediatric osteoarticular infections. Its indolent presentation and variable clinical signs and symptoms pose difficulty with timely diagnosis. The etiology in the pediatric population is typically hematogenous spread following trauma and patients often present with non-resolving hip pain causing a limp. MRI provides the highest sensitivity and specificity for diagnosis.
Advocates for early aspiration-biopsy of the joint space note faster recovery; however, there is growing evidence for initial conservative management. Aspiration, then would be used to increase microbial yield in those not responding to conventional parenteral antibiotic therapy. Likewise, there is no consensus on optimal duration of antimicrobial therapy for patients with pyogenic sacroiliitis, but many have documented success with shortened antimicrobial courses (10-14 days).

Editor's Comments:
Pyogenic sacroiliitis is a rare condition that often presents with vague symptoms, often leading to a delay in diagnosis. Approximately 13% of patients present with acute abdominal symptoms. In 40-60% a fever is present with an elevated ESR. Blood cultures are only positive in 60% of people and therefore, if there is a suspicion, joint aspiration should be completed for establishing the causative organism. MRI is the definitive radiologic study for establishing a diagnosis of pyogenic sacroiliitis. Staphylococcus aureus seems to be the most organism isolated, but infections with Salmonella and Pseudomonas species have been reported. Parenteral antibiotics are the main stay of treatment, targeted to the organism isolated. Those who do not show clinical improvement with conservative therapy can be considered for a CT guided abscess drainage or open surgery.

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