case_images: PMC10551808_01
case_images: (A) Radiograph Knee lateral view. Black star: chondroid lesion in the distal femur. Black arrow: Soft tissue lesion visible without any calcifications in the lesion. Black arrowhead: Smooth regular thickening of the endosteum. Discreet periosteal reaction, single layered. (B) MRI T1 TSE fat saturated after Gadolinium transversal view. White arrow: After Gadolinium heterogenous uptake of the contrast agent, the T2 hyperintense areas do not enhance, only the T2 hypointense areas show enhancement. (C) MRI T1 TSE subtraction after Gadolinium coronal view. White arrow: After Gadolinium the hypointense border shows discreet peripheral enhancement. Heterogenous enhancement of the lesion, the T2 hyperintense areas do not enhance.
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case_images: PMC10551808_01_acc-10-03-10261-g001.jpg
case_images: f1
case_images: An X-ray showed a mass suspicious for enchondroma in the distal left femur as well as a more proximal non-calcified soft tissue lesion with discreet thickening of the endosteum and a discreet periosteal reaction (Figure 1A). A subsequent MRI of the left knee showed a well defined soft tissue lesion with suspected focal invasion of cortical bone (Figure 1B-C).
case_images: Microscopic examination showed sheets of foamy histiocytes (A) (HE, x100), Touton giant cells (B, arrowhead) (HE, x200), osteoclast-like giant cells (C-E) (HE, x200) and scattered bland mononuclear cells with eosinophilic cytoplasm (F) (HE, x400). The tumor was surrounded by a fibrous capsule containing lymphoid tissue (G) (HE x50) and focally infiltrated the resected cortical bone (H) (HE, x50).
case_images: acc-10-03-10261-g002.jpg
case_images: PMC10551808_01_acc-10-03-10261-g002.jpg
case_images: f2
case_images: Microscopic examination of the core biopsy showed sheets of foamy histiocytes, osteoclast-like giant cells and Touton giant cells as well as scattered mononuclear cells with eosinophilic cytoplasm without cytological atypia and with no evident mitotic activity (Figure 2A-B). Subsequent examination of the resected mass further revealed a fibrous capsule containing lymphoid tissue as well as focal infiltration of the resected cortical bone (Figure 2C-H).
case_images: On immunohistochemistry, the scattered eosinophilic cells stained positively for pancytokeratin (A) (anti-CKAE1/AE3 Ab, x100) and CK7 (B) (anti-CK7 Ab, x100) and negatively for EpCAM (C) (anti-EpCAM Ab, x100).
case_images: acc-10-03-10261-g003.jpg
case_images: PMC10551808_01_acc-10-03-10261-g003.jpg
case_images: f3
case_images: The scattered mononuclear cells with eosinophilic cytoplasm stained positively for pancytokeratin and CK7 (Figure 3).