Imaging Features of Periosteal Chondroma Manifesting as a Subcutaneous Mass in the Index Finger

Periosteal chondroma is a rare benign hyaline cartilage neoplasm that occurs most commonly in the metaphases of long tubular bones. We present a unique case of periosteal chondroma arising in the proximal phalanx of the left index finger in a 12-year-old boy. Physical examination revealed a slightly protuberant, subcutaneous mass. Plain radiographs and computed tomography scans showed a periosteal lesion producing saucerization of the cortex and subjacent cortical sclerosis, without internal matrix calcification. On magnetic resonance imaging, the lesion exhibited intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Contrast-enhanced fat-suppressed T1-weighted images demonstrated peripheral and septal enhancement. The patient underwent a marginal excision with curettage of the underlying bone cortex. Histological examination confirmed the diagnosis of periosteal chondroma. There has been no evidence of local recurrence eight months after surgery. Periosteal chondroma can protrude into the subcutaneous soft tissue causing a palpable mass. Recognition of the typical radiological features can lead to an accurate diagnosis of this rare condition. 1. Introduction Periosteal chondroma, also known as juxtacortical chondroma, is a rare benign cartilaginous neoplasm of bone surface that occurs predominantly in the metaphases of long tubular bones, particularly, the proximal humerus and distal femur. The small tubular bones are also common sites. It presents as a swelling or palpable mass that may be painful in children and young adults, with a slight male predominance [1]. Histologically, periosteal chondroma consists of lobulated hyaline cartilage with variable cellularity. The chondrocytes frequently show mild nuclear atypia with hyperchromasia and binucleation [2], mimicking chondrosarcoma. Surgical excision is the treatment of choice. Malignant transformation has not been reported. We herein present the imaging features of periosteal chondroma involving the proximal phalanx of the left index finger in an adolescent boy and provide a brief review of the relevant literature. 2. Case Presentation A 12-year-old boy presented with a 1-year history of a slow-growing, painless mass in the radial aspect of the proximal phalanx of the left index finger. The patient’s past medical history was unremarkable. Physical examination revealed a 2？cm, firm, immobile, nontender, subcutaneous mass (Figure 1). There was no limitation of motion in neighboring joints. Neurovascular examinations were normal. Laboratory data were