Fig. 2

a Histopathology of capsules from patients who presented with peri-implant effusion, negative for anaplastic large cell lymphoma. Left: Section of capsule lined by synovium-like cells (also referred to as synovial metaplasia). Inset shows detail of synovium-like cells with a cylindrical to cuboidal shape, indistinct cytoplasm, and round to oval nuclei of the luminal side of the capsule. The underlying stroma is loose and lacks inflammatory cells. (Hematoxylin and eosin, ×100; inset ×400). Right: Section of capsule devoid of synovium-like cells, but displays underlying fibrosis, chronic inflammation and small round clear spaces related with silicone material. Inset shows high magnification of the luminal surface, with a thin fibrous layer, almost acellular. (Hematoxylin and eosin, ×100; inset ×400). b Left: Immunohistochemistry for CD30 in a capsule negative for anaplastic large cell lymphoma highlights a single cell in the stroma. No cells are highlighted in the luminal side of the capsule. Inset: A single small lymphocyte is highlighted in the stroma. (Immunohistochemistry for CD30, ×100; inset, immunohistochemistry for CD30, ×400). Right: Cell block of peri-implant effusion shows small lymphocytes, histiocytes and neutrophils. Inset: Immunohistochemistry for CD30 in cell block highlights a single small to intermediate size cell among other inflammatory cells. (Hematoxylin and eosin, ×400; CD30 immunohistochemistry, ×1000)