PMC6335665_01
Lateral and AP views of the left forearm from patient 1 show a mildly expansile lucent lesion in the proximal left radial diaphysis (arrows). The zoomed in view better shows the cortical thinning and internal septations but no periosteal reaction or obvious soft tissue mass.
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fig1
When her symptoms failed to improve with appropriate management, radiographs were obtained, demonstrating a lesion in the proximal radius (Figure 1) characterized as a mildly expansile lucent lesion with a thin zone of transition but no sclerotic rim.
Nuclear medicine bone scan shows marked radiotracer uptake within the lesion in the proximal left radius (orange arrows), within the calvarium (orange arrowhead), and medial left clavicle (black arrowhead).
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Bone scan demonstrated marked radiotracer uptake at the site of the lytic lesion in the proximal left radius as well as at the previously biopsied skull and left clavicle lesions (Figure 2).
Sagittal T1, T2 fat-suppressed, and sagittal and axial T1 fat-suppressed postcontrast images of the left forearm demonstrate a T1 isointense, T2 hyperintense, avidly enhancing lesion (arrows). The axial postcontrast image demonstrates the extent of the cortical thinning with focal areas of cortical breakthrough. There is no surrounding edema or abnormal soft tissue enhancement.
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The MR scan of the left forearm showed a marrow replacing lesion within the proximal diaphysis of the radius (Figure 3).
Histology from open biopsy of the proximal radius lesion demonstrates sheets of pale histiocytic cells in an inflammatory background (a). The histiocytes demonstrate emperipolesis (engulfment of intact lymphocytes within the cytoplasm:arrowheads). The histiocytes express S100 protein by immunohistochemistry, characteristic of Rosai-Dorfman disease (b).
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Lesion histology demonstrated features diagnostic of RDD including emperipolesis (engulfment of intact lymphocytes contained with the cytoplasm of histiocyte cells) and positive S100 immunohistochemical staining (Figure 4).
A follow-up radiograph 8 weeks after surgery demonstrates partial filling in of the lucent lesion with healing bone (dashed circle) following curettage.
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At her follow-up clinic visit 8 weeks after surgery, the patient reported resolution of her left elbow pain, and repeat radiographs demonstrated partial filling in of the lesion with healing bone (Figure 5).
PMC6335665_02
PA and oblique views of the left wrist from patient 2 demonstrate a lucent lesion with numerous internal septations in the distal radial metaphysis and epiphysis. There is marked thinning of the cortex along the radial margin of the distal radius (arrowhead). The cortical thinning is more pronounced and the lesion more aggressive in appearance than in patient 1.
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Left wrist radiographs obtained as part of his initial evaluation (Figure 6) demonstrated a mildly expansile mixed lucent and sclerotic lesion in the distal left radius with multiple internal septations.
Axial and coronal T1 and T2 fat-suppressed images through the left wrist demonstrate the lesion to be isointense on T1 and heterogeneously hyperintense on T2 with numerous internal septations.
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Review of a noncontrast MRI of the left wrist from an outside institution (Figure 7) demonstrated a multilobular, septated marrow replacing lesion in the distal radial metaphysis and epiphysis with more heterogenous signal characteristics than seen in case 1.