Defining the role of magnetic resonance imaging in unifocal bone lesions of langerhans cell histiocytosis.

Localized Langerhans cell histiocytosis (LCH) of bone often presents as a diagnostic challenge. Magnetic resonance imaging (MRI) is frequently used to better delineate most solitary bony lesions. The authors present two cases that illustrate and better define the role of MRI in the evaluation of solitary bone lesions of LCH. In a 3-year-old boy with left-sided hip pain, MRI showed a focal lesion involving the proximal left femur with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. A tumor was suspected because of the overall imaging characteristics and increased uptake on three-phase nuclear scintigraphy. In a 6-year-old boy with right thigh pain, MRI showed a fluid-containing lesion in the mid-diaphysis of the right femur, suggestive of chronic osteomyelitis and Brodie abscess. MRI was instrumental in showing the extent of the lesions in both cases; however, the final diagnosis of LCH was achieved only with histopathologic confirmation, illustrating the limited diagnostic power of this imaging tool.