Ultrasonography for assessment of subcutaneous nodules.

OBJECTIVE: To characterize a variety of subcutaneous lesions by their ultrasonographic (US) appearance, and establish these images as a starting point to measure changes with treatments.
METHODS: Twenty-six patients with 48 subcutaneous nodular swellings of various types were imaged using a portable US machine equipped with a 10 MHz linear transducer. All patients had a known diagnosis of a rheumatic disease. We used US to examine subcutaneous lesions and the underlying cortical surface of the bone or joint. Two measurements of some tophi and rheumatoid nodules were done on different dates to examine reproducibility of the measurements.
RESULTS: Nodular lesions included 20 tophi and 20 rheumatoid nodules, 2 sarcoid nodules, 2 lipomas, and 4 synovial cysts. Tophi most often appeared as heterogeneous masses; hypoechoic areas in 2 tophi were decreased after aspiration of chalky liquid tophaceous material. Occasionally tophi had calcifications appearing hyperechoic with acoustic shadowing. Cortical bone erosions could be seen adjacent to some tophi. The nodules in patients with rheumatoid arthritis were often attached closely to the bone surface and less erosive to bone, allowing the cortical bone to be seen easily. The nodules were more homogeneous. Some showed a central sharply demarcated hypoechoic area, possibly corresponding to necrosis inside the rheumatoid nodules. Nodules were easily measured. The repeated measurements of both tophi and rheumatoid nodules showed excellent reproducibility. Lipomas had different echogenic patterns depending on composition of the associated connective tissue and position of the mass. They could be hypoechogenic, hyperechogenic, or mixed, but were easily distinguished by oval shapes with well demarcated capsules. Synovial cysts seen in this study had a characteristic hypoechoic pattern.
CONCLUSION: Subcutaneous nodules examined by sonography show characteristics and patterns that, although not diagnostic, can be used to help distinguish their etiology. Tophi and rheumatoid nodules can be easily measured and these measurements used to help follow disease progression or response to therapy.