Periosteal Chondroma: Ultrasound with Magnetic Resonance Imaging Correlation for Diagnosis of a Bone Surface Tumor

Ultrasound (US) equipped with high-frequency linear transducers is a convenient, first-line imaging modality for evaluating a wide spectrum of musculoskeletal abnormalities. In complex cases, the US findings may need to be correlated with findings on the magnetic resonance (MR) imaging studies to generate an accurate diagnosis. Periosteal chondroma is a rare, benign bone surface tumor arising from the periosteum. The lesions are composed of hyaline cartilage and tend to be small, superficial, and slow-growing. Despite an indolent clinical course, this neoplasm may cause scalloping of the outer bone cortex, necessitating detailed imaging investigation to rule out malignancy. Interestingly, the imaging appearances of periosteal chondroma may overlap with those of chondrosarcoma, and in addition, the histological differentiation of these tumors can be difficult. Sporadic cases of MR imaging findings in periosteal chondroma have been published; however, the usefulness of US in diagnosing surface-based bone tumors has not been adequately studied. In this illustrated case, we describe the US features of periosteal chondroma, emphasizing the versatile role of US for diagnosing a tumor of the bone surface, and the correlation with MR imaging findings.