An Unusual Case of Huge Tophaceous Pseudogout Mimicking as a Tumor-Like Lesion around the Ankle Joint: A Case Report and Literature Review

Table 1

Differential diagnosis for the patient in our case report and their distinguishing features.

	Site of origin	Most common distribution	Radiological appearance	Histological appearance
Tumoral pseudogout	Periarticular	Temporomandibular joint, perispinal tissues, joints of extremities	Radiopaque soft tissue mass with varying densities of calcification	Amorphous calcium deposits with numerous refractile radiating rhomboid crystals, demonstrates positive birefringence on polarized microscopy
Tophaceous gout	Periarticular	1st MTP joint, hands and feet	Juxtaarticular punched out erosions with sclerotic margins	Tophi—granulomatous inflammation with plenty of needle-shaped crystals. Negative birefringence on polarized microscopy
Tumoral calcinosis	Periarticular	Around large joints like the hip, shoulder, and elbow	Amorphous multilobulated (cloud-like) appearance	Lobules of calcific material surrounded by histiocytic giant cells
Synovial chondromatosis	Mainly intra-articular, sometimes in bursal tissues and tendon sheaths	Knee joint (70%), hip, shoulder, elbow	Calcified loose bodies in the joint, ring and arc appearances	Cartilage cells with varying degrees of atypia. Varying degrees of calcification and ossification
Myositis ossificans	Large muscle groups of the extremities	Around the knee, hip, and elbow	Circumscribed calcification with a lucent centre	Inner cellular zone, middle zone of woven bone, outer zone of mineralized bone
BPOP	Bony surfaces	Distal extremities, hands and feet	Continuous with the cortex with an underlying intact cortex	Chondro-osteoid matrix containing enlarged, bizarre, binucleated chondrocytes
Lipoma	Typically present in the subcutaneous plane	Usually found over the back, shoulders, and neck region but can be seen in other locations also	Calcifications are seen in 11% of the cases.; Larger lipoma can result in bony erosions due to mass effect	Well-circumscribed encapsulated mass of mature adipocytes. Deeper lipomas may be associated with malignant features
Synovial sarcoma	Soft tissues of the body. In the extremities seen adjacent to large joints	Extremities, trunk, intrathoracic or intra-abdominal	Nonspecific calcification pattern	Biphasic or monophasic forms. Focal calcifications seen in 1/3rd of the cases
Chondrosarcoma	Long bones	Femur, pelvis	Ring and arc (popcorn) types of calcifications	Focal calcifications with no osteoid or bone formation
Parosteal osteosarcoma	Metaphysis of long bones	Distal femur, proximal humerus, proximal tibia	Large lobulated exophytic mass, usually circumferential involvement, central dense ossification; string sign—radiolucent line separating the tumor from the cortex	Low grade tumor. Well-formed bony trabeculae and osteoid deposition with or without osteoblastic rimming; stromal cells show mild cellular atypia and few mitoses