Ultrasonography and magnetic resonance imaging of heel fat pad inflammatory-oedematous lesions in rheumatoid arthritis

Objective: To study heel fat pad (HFP) inflammatory-oedematous lesions in selected patients with rheumatoid arthritis (RA) using ultrasonography (US) and power Doppler US (PDUS), to describe and compare US features of these lesions with those obtained with magnetic resonance imaging (MRI), and to describe changes in the lesions after a short-term follow-up with conventional or anti-tumour necrosis factor-alpha (TNFalpha) therapy. Methods: Twelve heels of eight RA outpatients with HFP inflammatory-oedematous lesions were studied by US, PDUS, and unenhanced MRI. All the patients were followed up and US was performed after 3 months. Five patients started on anti-TNFalpha therapy. Results: HFP lesions appeared at US as a heterogeneous and hypoechoic subcalcaneal mass, with loss of normal lobular structure and increased thickness of HFP, because of focal rupture of fibrous septae with oedema and fluid. PDUS showed peripheral vascularization of HFP lesions in 9/12 heels. In 3/12 heels some vascular signals was also detectable inside the lesion, always along the residual echoic septa. No detectable flow was observed within the central fluid-filled spaces. MRI of the HFP lesions showed areas of mean intensity in T1-weighted sequences and high intensity in T2-weighted sequences, with poorly or well-defined margins. After 3 months, PDUS showed reduction in HFP lesion vascularity (associated with reduction in pain) in 10/12 heels, while poor regression of grey-scale US abnormalities was observed. Conclusions: Both US and MRI are capable of demonstrating structural abnormalities in the HFP. PDUS is useful to assess and monitor inflammatory vascularization of the HFP lesions.