Hygroscopic sonographically detectable clips form characteristic breast and lymph node pseudocysts.

The use of hygroscopic sonographically detectable clips (HSDCs) has dramatically increased during the last years, especially in breast cancer patients who undergo neoadjuvant chemotherapy. The aims of this study are to define the appearance of HSDC sites in histopathological specimens, and to enable pathologists to recognize these sites and differentiate them from other lesions. We examined 124 breast cancer specimens in which the application of HSDCs was documented, 88 breast tissues and 36 lymph nodes, and analyzed the appearance of the clip site in these tissues. The clip site was clearly detected histologically in 79/88 (90%) of the breast specimens and in 29/36 (81%) of lymph node specimens. In most of the specimens, the HSDC site had a specific characteristic appearance of a pseudocyst, lined by layers of epithelioid histiocytes, sometimes with pseudopapillary formation, and with minimal or no fibrosis. This was the appearance in 69 of the breast specimens and in 23 of the lymph node specimens. In other specimens, scarring, scattered foamy macrophages and abundant siderophages were the predominant findings, as usually found in sites of other clips. As non-palpable breast lesions become more frequent, clips play a major role in the treatment of breast cancer, making them an important component of the communication among radiologists, surgeons, pathologists, and oncologists. HSDCs in tissues have a characteristic appearance with an epithelioid component. Pathologists should be able to recognize this finding, differentiate it from other breast lesions and include it in the pathology report.