Abdominal mass hiding rib osteomyelitis

Background: Rib osteomyelitis is a rare entity, occurring in approximately 1 % or less of all cases of haematogenous osteomyelitis. Given its rarity and clinical heterogeneity, the diagnosis of rib osteomyelitis can be challenging and requires a high index of suspicion. We present a case of acute osteomyelitis of the rib due to community-acquired methicillin-resistant Staphylococcus aureus (MRSA), which occurred in an otherwise healthy 3-month-old infant and mimicked an epigastric hernia at first. Case presentation: An otherwise healthy 3-month-old female infant was sent by her primary care paediatrician to the paediatric emergency department for possible incarcerated epigastric hernia because for 2 days, she had suffered from mild to moderate fever, irritability, poor feeding, and tender epigastric swelling. Ultrasonographic imaging excluded epigastric hernia, and transthoracic echocardiography ruled out endocarditis. However, clinical assessment combined with laboratory criteria classified the child into the high-risk group for having severe bacterial infection. Consequently, awaiting the definitive diagnosis, she was immediately treated with a broad-spectrum regimen of intravenous antibiotic therapy based on vancomycin (40 mg/kg/die in 3 doses) and meropenem (100 mg/kg/die in 3 doses). Three days after admission, the blood culture result was positive for methicillin-resistant Staphylococcus aureus, and vancomycin remained as antibiotic therapy. On day 3, a second swelling appeared at the level of the seventh left rib, 2 cm-wide, non-erythematous, mildly painful. Ultrasonography of the left chest wall on this occasion showed an image consistent with an acute osteomyelitis of the anterior osteo-chondral region of the 7th rib and associated adjacent periosteal and soft tissue collection and magnetic resonance imaging confirmed the osteomyelitis of the anterior middle-distal part of the 7th left rib, near the costochondral junction. Vancomycin was continued up to a total of 6 weeks of therapy, and at the end, the child was discharged in good condition with no relapse during the follow-up. Conclusion: This is one of the few reported cases of paediatric rib osteomyelitis caused by community-acquired MRSA. Timely identification associated with prompt and targeted antibiotic therapy may allow full recovery.