title: Localized Langerhans cell histiocytosis masquerading as Brodie's abscess in a 2-year-old child: a case report.
abstract: Langerhans cell histiocytosis (LCH), formerly known as histiocytosis X, refers to a spectrum of diseases characterized by idiopathic proliferation of histiocytes that produce either focal (localized LCH) or systemic manifestations (Hand-Schüller-Christian disease and Letterer-Siwe disease). Localized LCH accounts for approximately 60-70 % of all LCH cases. Osseous involvement is the most common manifestation and typically involves the flat bones, along with lesions of the skull, pelvis, and ribs. Localized LCH in bone shows a wide spectrum of clinical manifestations and radiologic features that may mimic those of infections as well as benign and malignant tumors. The diagnostic imaging findings of localized LCH are also diverse and challenging. The penumbra sign is a common and characteristic magnetic resonance imaging (MRI) feature of Brodie's abscess, but is rarely seen in localized LCH. In this report, we describe a case of localized LCH misdiagnosed as Brodie's abscess in a 2-year-old child based on clinical symptoms, laboratory findings, and pre-diagnostic MRI findings (penumbra sign). Therefore, the penumbra sign is not sufficient to clearly establish the diagnosis of Brodie's abscess, and the differential diagnosis of localized LCH should be considered when a child with an osteolytic lesion presents with a penumbra sign.
authors.affiliation: Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan; Department of Radiology and Nuclear Medicine, Zuoying Branch of Kaohsiung Armed Forces General Hospital, Kaohsiung, Taiwan.
authors.forename: Wei-Fang
authors.initials: WF
authors.lastname: Chang
authors.affiliation: Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Yi-Chih
authors.initials: YC
authors.lastname: Hsu
authors.affiliation: Department of Radiology, Cathay General Hospital, Taipei, Taiwan.
authors.forename: Yi-Der
authors.initials: YD
authors.lastname: Wu
authors.affiliation: Department of Orthopedic Surgery, Taoyuan Armed Forces General Hospital, Taoyuan County, Taiwan.
authors.forename: Chun-Lang
authors.initials: CL
authors.lastname: Kuo
authors.affiliation: Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Guo-Shu
authors.initials: GS
authors.lastname: Huang
keywords: Brodie's abscess; Langerhans cell histiocytosis; differential diagnosis; knee pain; penumbra sign