From the Guidelines
Rheumatoid nodules on CT are characterized by well-defined, round to oval soft tissue masses with variable density, often found in subcutaneous tissues near pressure points or extensor surfaces. The CT appearance of rheumatoid nodules is notable for their homogeneous soft tissue attenuation, although central low attenuation representing necrosis may be present 1. These nodules can range in size from a few millimeters to several centimeters and may demonstrate peripheral enhancement following contrast administration. Key characteristics of rheumatoid nodules on CT include:
- Well-defined borders
- Round to oval shape
- Variable density
- Homogeneous soft tissue attenuation
- Possible central low attenuation representing necrosis
- Peripheral enhancement following contrast administration
- Uncommon calcification, but possible in long-standing nodules
- Adjacent bone erosions may be visible when nodules are located near joints It's worth noting that while CT can identify these nodules, other imaging modalities like MRI may provide better soft tissue characterization and can more clearly demonstrate the relationship between nodules and surrounding structures 1. Rheumatoid nodules are present in approximately 20-35% of patients with rheumatoid arthritis and their presence correlates with disease severity and seropositivity.
From the Research
CT Appearance of Rheumatoid Nodules
- The CT appearance of rheumatoid nodules can be characterized by their subpleural location, cavitation, and tendency to occur in clusters 2.
- Rheumatoid lung nodules have distinct CT features compared to malignancy, including multiplicity, smooth border, cavitation, satellite nodules, pleural contact, and a subpleural rind of soft tissue 3.
- The optimal sensitivity and specificity for rheumatoid lung nodules can be obtained with ≥ 3 CT findings, including ≥ 4 nodules, peripheral location, cavitation, satellite nodules, smooth border, and subpleural rind 3.
- Rheumatoid pulmonary nodules may precede RA diagnosis and are mainly located peripherally, in the right lobe, with a high cavitation rate 4.
Key CT Features
- Multiplicity of nodules
- Smooth border
- Cavitation
- Satellite nodules
- Pleural contact
- Subpleural rind of soft tissue
- Peripheral location
Clinical and Imaging Features
- Patients with rheumatoid lung nodules are younger and more likely to manifest subcutaneous rheumatoid nodules and seropositivity 3.
- ACPA positivity is an important independent risk factor for RPN occurrence and progression 4.
- Low-level metabolism and lack of FDG-avid draining lymph nodes are key PET/CT features of rheumatoid lung nodules 3.