Calcifying Aponeurotic Fibroma: Case Report with Radiographic and MR Features
A 67-year-old healthy man presented with a 20-year history of a painless, slow growing mass in the dorsum of his right wrist. Physical examinations showed a firm, non-tender, palpable mass, measuring 1.5-cm, and overlying the carpal bones in the dorsum of his wrist. Radiographs demonstrated a relatively ill-defined soft tissue mass with speckled calcifications on the dorsal ulnar aspect of the wrist. Cortical scalloping of the underlying carpal bones was demonstrated (). MRI showed an ill-defined rounded subcutaneous soft tissue mass partially encasing the tendons of the extensor carpi ulnaris (ECU) and the extensor digiti minimi (EDM) on the dorsum of the wrist. MRI revealed low to intermediate signal intensity on the T1-weighted image (T1WI) and heterogeneous mixtures of low and high signal intensity on the T2-weighted image (T2WI). The mass showed heterogeneous intense contrast enhancement after intravenous gadolinium administration. The lesion had a poorly demarcated margin and was associated with edema like signal changes in the adjacent soft tissues on MR images (). In view of the radiographic and MR findings, the preoperative differential diagnosis included soft tissue chondroma, bizarre paraosteal osteochondromatous proliferation (BPOP), giant cell tumor (GCT) of the tendon sheath, fibroma of the tendon sheath, nodular fasciitis and a small sized synovial sarcoma. The mass was excised and was revealed to be an off-white colored, firm lesion. The mass adhered to and involved the tendon sheaths of ECU and EDM, the adjacent extensor retinaculum, and the wrist joint capsule with the intracapsular extension. The triquetral and hamate cortical bone erosions were seen. However, the mass could be excised without any resection of the bones or tendons. Microscopically, an ill-defined tumor mass showed multifocal calcifications surrounded by dense fibrous stroma. The fibrous stroma revealed mixed cellular areas near the calcification and lesser cellular fibromatosis-like areas in the background. Multilayers of fibroblasts with small round nuclei, histiocytes and multinucleated giant cells in the cellular areas were adjacent to the calcification. Lesser cellular and densely collagenous areas showed early chondoid metaplasia-like cellular changes such as small round nuclei and perinucler clear spaces in the hyalinized stroma. There were neither cellular atypism nor mitosis in the fibroblasts (). A pathologic diagnosis of calcifying aponeurotic fibroma was made.