A chronic thigh mass in a 69-year-old man

Abstract

Amyloidosis is the result of extra-cellular deposits of amyloid fibril proteins and protein derivatives, recognised histologically by the presence on congo red preparations of apple-green birefringence under polarised light microscopy (Fig 1). Amyloid is classified by the fibrillar protein [1]. Type AL is secondary to a plasma cell disorder. Type AA, as in our case, is usually associated with chronic inflammation and our patient had chronic obstructive pulmonary disease. β2 microglobulin deposits are found in patients on long-term haemodialysis. Other forms of amyloidosis are associated with Alzheimer’s and Creutzfeld– Jacob Diseases; hereditary variants include familial polyneuropathy and cardiomyopathy. In our case, MRI showed a 6 × 6.5 × 1.5 cm subcutaneous mass overlying the vastus lateralis muscle. The mass was isointense to muscle on T1-weighted (Fig. 2a) and T2-weighted (Fig. 2b) images, heterogeneous on the STIR sequence, mostly slightly or moderately hyperintense to muscle, but also containing central hypointense areas. It showed patchy, low-grade enhancement on post-contrast fat-suppressed T1-weighted images (Fig. 2c). Extremity soft-tissue amyloidomas are rare. Maheshwari et al. [2] reported a case in the thigh and identified 20 previous reports of extremity amyloidomas, 17 in the lower limbs. In their case [2], the mass was ulcerated, infected and had a purulent discharge. It was large, encapsulated, multilobulated and showed heterogeneous signal on T1and T2-weighted images, including areas identical to fat on T1-weighted images. Intravenous contrast medium was not administered. Amyloidomas in other sites have also been reported to appear heterogeneous on MRI. They are generally of similar intensity to muscle on T1weighted images, heterogeneous and contain low-signal intensity areas on T2-weighted images, and show variable enhancement after intravenous contrast medium administration [2], although one patient had several lesions that were hyperintense on T2-weighted images and showed rim enhancement after intravenous contrast The question can be found at doi: 10.1007/s00256-010-0970-9