Milan Stevanovic, MD, PhD

An otherwise healthy 3-year-old boy presented to the pediatric urgent care clinic 2 days after his mother noticed left distal forearm swelling in the child without a known inciting event. The patient appeared to have no pain, skin changes or constitutional symptoms. Neurovascular status and range of motion of the wrist were intact. There was mild tenderness to palpation of an approximately 2-cm, firm fixed mass deep to the subcutaneous tissues at the level of the distal radioulnar joint. Laboratory evaluation was unremarkable. Radiographs revealed soft tissue swelling about the wrist without focal calcifications or cortical irregularity (Figure 1). Ultrasound was remarkable for an ill-defined heterogeneous soft-tissue lesion in the left wrist with mild adjacent cortical thickening and minimal periosteal reaction, without evidence of hypervascularity (Figure 2). One week later, the patient underwent MRI with and without gadolinium contrast which demonstrated a 2 cm (anteroposterior) by 2 cm (longitudinal) by 1.3 cm (transverse) heterogeneous non-enhancing mass that was mildly hyperintense on T1 and T2, diffusely bright on short-TI inversion recovery (STIR), with associated inflammatory change interposed between the distal radius and ulna in the volar aspect of the wrist, just distal to the pronator quadratus. There was no bony involvement, but there was reactive bony remodeling of the distal ulna and radius (Figure 3).