title: Abdominal mass hiding rib osteomyelitis.
abstract: 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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy.
authors.forename: Genny
authors.initials: G
authors.lastname: Raffaeli
authors.affiliation: Pediatric Radiology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Borzani
authors.affiliation: Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Pinzani
authors.affiliation: Radiology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Giannitto
authors.affiliation: Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Principi
authors.affiliation: Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy. susanna.esposito@unimi.it.
authors.forename: Susanna
authors.initials: S
authors.lastname: Esposito
mesh_terms: D000005:Abdomen; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D003937:Diagnosis, Differential; D003952:Diagnostic Imaging; D005260:Female; D006801:Humans; D007223:Infant; D055624:Methicillin-Resistant Staphylococcus aureus; D010019:Osteomyelitis / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D012272:Ribs; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D014640:Vancomycin / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin
keywords: Bone infection; MRSA; Osteomyelitis; Rib; Staphylococcus aureus