PMC5429926_01
Axial T1 (a), coronal T1 (b), axial T2 (c), sagittal T2 (d), axial T1 FS postcontrast (e), coronal T1 FS postcontrast (f), and coronal T1 FS postcontrast (g) images of the involved lumbar spine and pelvis in the 17-year-old boy from case 1. There is unilateral marked expansion of the right gluteal, piriformis, and paraspinal muscles, exhibiting T1 isointensity and T2 hyperintensity. The muscle enlargement results in effacement of intramuscular fat. The postcontrast images demonstrate diffuse striated enhancement, giving an infiltrative appearance. Enhancing nodules are seen in the adjacent subcutaneous tissues. There is also subcutaneous fat stranding (indicated by the arrow, image (g)). Aside for the enlargement, note the overall preservation of muscle morphology and lack of a focal mass.
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fig1
Additionally, small enhancing soft tissue nodules adjacent to the affected muscles were seen in the overlying subcutaneous tissues (Figures 1(a)-1(g)).
Transverse (a) and longitudinal (b) hematoxylin and eosin-stained histologic sections showing an infiltrate of intermediate-sized to large lymphoid cells in the endomysium between muscle fibers and the perimysium investing the fascicles or bundles of these fibers; these slides were prepared from the gluteal muscle biopsy of the 17-year-old boy described in case 1. On high magnification (c) one can observe the intimate association of the lymphoma cells with the individual striated muscle fibers.
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fig2
Ultimately, the lymphoma is perhaps best classified as a high-grade B-cell lymphoma, not otherwise specified, following the 2016 revision of the World Health Organization classification of lymphoid neoplasms (histopathology depicted in Figures 2(a)-2(c)).
Axial (a) and coronal contrast enhanced CT (b) images of the abdomen and pelvis from the 17-year-old boy in case 1. There is striking asymmetric enlargement of the right gluteal and paraspinal muscles, isodense to adjacent muscle.
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fig3
CT scan of the chest, abdomen, and pelvis was obtained for staging purposes and similar to the MRI, there was diffuse unilateral enlargement of the gluteal and paraspinal muscles (Figures 3(a) and 3(b)).
PMC5429926_02
Sagittal T1 (a), axial STIR (b, c), axial T1 fat saturated postcontrast (d, e), and sagittal T1 fat saturated postcontrast (f) images of the involved lower leg in the 55-year-old man with HIV described in case 2. There is marked enlargement of the posterior calf muscles with effacement of the intramuscular fat. The affected muscle demonstrates T2 hyperintense signal and diffuse enhancement on postcontrast sequences. The overall findings should raise the suspicion for an infiltrative process such as lymphoma.
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fig4
Similar to case 1, MRI demonstrated diffuse enlargement of multiple posterior calf muscles, with effacement of intramuscular fat (Figures 4(a)-4(f)). Postcontrast images showed diffuse enhancement of the affected muscles, but no focal mass (Figures 4(d)-4(f)).
The 55-year-old patient's lymphoma from case 2 showed microscopically a more diffuse infiltrate of large cells with abundant mitotic figures (a, b).
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fig5
However, due to persistent symptoms, an open biopsy was performed, which revealed diffuse large B-cell lymphoma of the gastrocnemius muscle; histology is demonstrated in Figures 5(a) and 5(b).
Axial contrast enhanced CT image of the 55-year-old man from case 2 showing diffuse enlargement of the soleus muscle which is homogenously iso- to slightly hypodense relative to adjacent muscle. Note the skin thickening and subcutaneous fat stranding, which can also be seen in lymphoma.
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fig6
CT was subsequently ordered to assess for progression of disease, which redemonstrated diffuse enlargement of the posterior calf musculature and subcutaneous fat stranding of the leg (Figure 6).