This is Barry Bellosis, one of the musculoskeletal radiology fellows at Stanford University. 42 year old man with history of gout presents the clinic following a left knee injury, concern for gout. On imaging, gout can present with eccentric, asymmetrical deposits of calcium urate, tophi, that may calcify. Punch out erosions and overhanging edges are typical characteristics of gout. For instance, at this first MTP joint, we can see some soft tissue swelling with some erosions at the margin. When we do magnify this, we can see the typical punch out erosion with overhanging edges. This is in a different patient. On the knee, marginal erosions could be seen in the tibia and femoral condyle. On this specific case, we can see the gouty tophi at the tibial tubercle, characterized by the soft tissue lesion with some calcification in it. Briefly, gout on radiograph will demonstrate with nonspecific soft tissue swelling, joint effusion, and a well-defined punched out lesion. CPPD, on the other hand, typically presents with dense, fine linear, with punctate calcification. Here, on a different patient with CPPD, we can see chondrocalcinosis in the medial compartment of the right knee, right here, and in the lateral compartment of the left knee. This is in a different patient with gout. We can see this marginal erosion at the 4-digit PIP joint, which may be suspicious for gout. On MRI, this patient presents with the soft tissue lesion that is hypo-intense on our coronal T1, and heterogeneously T2 hyper-intense on our T2 fluid-sensitive images. Additional lesions are also seen in the first MTP joint, as seen here, and in the second MTP joint, as seen here. In the first MTP joint, we can see the characteristic punched out erosion with overhanging edges, as you see here. In today's imaging, we can further evaluate this lesion to prove the presence of gouty deposit. CT dual energy, without contrast, allows for differentiating the deposits by their different X-ray spectra, using the principle that attenuation of tissues depend not only on their density, but also on their atomic number. By convention, the deposits of gouts are colored green. This is our CT dual energy 3D reconstruction. We can see multiple green deposits predominantly involving the first MTP joint, the second MTP joint, and to a lesser degree in the fourth PIP joint. A small deposit here on the distal fibula is also seen, consistent with uric acid deposits. Other looks of gout, for instance, here in our elbow, we can see the olecranon tophus, likely in the olecranon bursa. In the hand, we have multiple gouty tophi here, characterized by this increased soft tissue density in multiple interphalangeal and MTP joints. When we magnify the interphalangeal joints, we can see this typical punched out erosions along the margin of the joint.

2nd Edition, CASE 45

2nd Edition

Rheumatology

gout

imaging

tophi

CT dual energy

erosions