title: Rare presentation of Brodie's abscess in the acromion process and the value of the penumbra sign.
abstract: A 17-year-old male patient presented with a swelling on his right shoulder 1 week after a fall. MRI revealed a superficial fluid collection of the acromion and trapezius muscle, with slight enhancement of the wall. The swelling burst open spontaneously after failed conservative therapy and was treated with surgical drainage and antibiotics. Tissue cultures showed a Staphylococcus aureus 1 year later, he presented with local red discolouration and a recurrent painful swelling that fluctuated at palpation. Radiographs showed a lytic lesion of the acromion process. MRI showed a sinus in the lytic cavity and a penumbra sign, which helped to identify this extremely rare occurrence of Brodie's abscess in the acromion process that was breaking through to the subcutaneous fat. The abscess was treated successfully with surgical drainage and intravenous antibiotics. In retrospect, the first MRI showed a small cortical indentation, with slight oedema of the acromion process.
authors.affiliation: Department of Orthopaedic Surgery, Martini Ziekenhuis, Groningen, The Netherlands.
authors.forename: Jelle
authors.identifier: http://orcid.org/0000-0003-0063-2318
authors.initials: J
authors.lastname: Gorter
authors.affiliation: Department of Orthopaedic Surgery, Martini Ziekenhuis, Groningen, The Netherlands.
authors.forename: Kyrill
authors.initials: K
authors.lastname: Rykov
authors.affiliation: Department of Radiology, Martini Ziekenhuis, Groningen, The Netherlands.
authors.forename: Pieter
authors.initials: P
authors.lastname: Ott
authors.affiliation: Department of Orthopaedic Surgery, Martini Ziekenhuis, Groningen, The Netherlands.
authors.forename: Jos J A M
authors.initials: JJ
authors.lastname: van Raay
mesh_terms: D000038:Abscess / Q000150:complications / Q000000981:diagnostic imaging* / Q000628:therapy; D000174:Acromion / Q000000981:diagnostic imaging*; D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D004322:Drainage; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010019:Osteomyelitis / Q000150:complications / Q000000981:diagnostic imaging* / Q000628:therapy; D011859:Radiography; D013203:Staphylococcal Infections / Q000150:complications / Q000000981:diagnostic imaging* / Q000628:therapy
chemical_list: D000900:Anti-Bacterial Agents