Age / Sex : 14 / M

14/M

C.C.: Both heel discomfort (Click to enlarge)

achilles tendon xanthoma

Discussion

Findings:
- Sagittal STIR and modified proton density images show fusiform enlargement of bilateral heterogeneous Achilles tendons, interspersed with linear areas of low signal intensity.
- Axial modified proton density images demonstrate bilaterally enlarged Achilles tendons, with a diffuse reticulated appearance.

Differential Diagnosis:
Xanthoma, Traumatic or degenerative tendinopathy

Diagnosis: Achilles tendon xanthoma

Discussion:
 Xanthomas are grayish-yellow to yellow masses composed of connective tissue and foam cells (foamy macrophages) containing cholesterol, cholesterol esters, triglycerides and phospholipids. When tendon is involved, the foam cells diffusely infiltrate the tendon, spreading apart the collagen fibers. The presence of tendon xanthomas is associated with the familial hyperlipoproteinemias and cerebrotendinous xanthomatosis. In familial hyperlipoproteinemias, plasma lipid levels are elevated. Cerebrotendinous xanthomatosis is a rare autosomal recessive metabolic disorder of bile-acid synthesis with normal serum triglyceride and cholesterol and elevated plasma levels of cholestanol and bile alcohols. The diagnosis of xanthomas of the Achilles tendon can be accomplished with ultrasonography, CT, and MR imaging. Most reports of MR imaging features of such lesions have documented persistent low to intermediate signal intensity on T1-weighted and T2-weighted spin echo MR images and signal inhomogenity. A diffuse speckled or reticulated pattern of intratendinous signal intensity, most obvious on transaxial images and fat-suppressed T1-weighted images, is evident in some cases and may have diagnostic significance. The areas of low signal intensity are likely to represent residual collagen fascicles of the tendon bundles, visualized as round structures in the axial plane and linear trabeculations in the sagittal plane. The reticulated low signal intensity is also made up of free cholesterol and cholesterol esters. The surrounding higher signal intensity between the collagen fibers represents the infiltrating triglycerides. Interfascicular edema or inflammation in response to the infiltrative cholesterol deposition is also thought to contribute to the reticulated MR appearance and areas of high signal on STIR, T2-weighted spin echo and T2* gradient echo images. The presence of an associated inflammatory reaction is supported by contrast enhancement on post-gadolinium T1-weighted images Thickened tendon of an Achilles tendinopathy may be differentiated by a more non-uniform, heterogeneous pattern with geographic regions of intermediate signal intensity on T1-weighted images. Partial tendon tears may be differentiated by geographic regions of linear high signal intensity within the tendon substance, focal discontinuity of the tendon, or edema within Kager’s fat triangle.

References:
1. Smithard A, Lamyman MJ, McCarthy CL, Gibbons CL, Cooke PJ, Athanasou N. Cerebrotendinous xanthomatosis presenting with bilateral Achilles tendon xanthomata. Skeletal Radiol 2007; 36(2):171-175.
2. Resnick D. Lipidoses, histiocytoses, and hyperlipoproteinemias. In Resnick D eds. Diagnosis of bone and joint disorders 3rd ed. Philadelphia: W.B. Saunders Company, 1995; 2233-2235