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Original Report |
1
Department of Radiology, Tufts-New England Medical Center, 750 Washington St.,
Boston, MA 02111.
2
Department of Surgery, Tufts-New England Medical Center, Boston, MA
02111.
Received March 30, 2000;
accepted after revision May 24, 2000.
Address correspondence to M. J. Homer.
Abstract
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CONCLUSION. Metallic fragments are commonly present in patients who have surgical clips placed during breast biopsy for both benign and malignant disease. Awareness of this phenomenon may prevent the misidentification of these fragments as microcalcifications and thus avert unnecessary concern or biopsy.
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We have observed that minuscule metallic fragments can appear in association with clip deployment. To our knowledge, this occurrence has not been reported previously in the literature. The purpose of this study was both to report this phenomenon and to note its frequent occurrence. In reviewing 100 cases of patients with metallic clips after breast surgery, we found one patient in whom tiny metallic fragments had been mistaken for microcalcifications and had prompted biopsy. Radiologists should be aware that these tiny metallic fragments occur commonly and may rarely mimic the appearance of breast microcalcifications.
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Subsequently, 100 mammograms of 99 patients who had clips placed at the time of breast biopsy or reexcision for breast cancer were reviewed (one patient had bilateral breast biopsies performed). The patients came from two sources. One source was a list of all patients examined at the Breast Health Center between 1994 and 1997. The mammograms of these patients were interpreted retrospectively. The second source included all patients who were regularly scheduled for follow-up visits to the Breast Health Center and who had undergone a previous biopsy for either benign or malignant disease. The mammograms of these patients were reviewed prospectively.
At our institution, routine images obtained in patients with a history of breast conservation therapy include a craniocaudal, a mediolateral oblique, and a coned-compression magnification image of the biopsy site. Routine mammograms in patients after benign biopsies include oblique and craniocaudal views. In all cases at least two views of the biopsy site were available for review. To be recognized as a fragment originating from clip deployment, the particle had to be of metallic density and had to maintain a fixed relationship to a clip on two images. In some cases, the particle was visible on multiple images on the same day; in other cases, the particle was visible in only one projection but was constant in that projection on multiple prior examinations. The fixed relationship and the metallic nature were judged visually by experienced radiologists. Differentiation of metallic density from calcification is usually not difficult. If doubt existed as to the density or the fixed relationship, because of radiographic technique or intrinsic contrast of the breast, the particle was not counted. We recorded the number of biopsies in which metallic fragments were identified and the results of the breast biopsies.
At our institution, tantalum clips (Weck Hemoclip Ligating Clips; Pilling Weck, Research Triangle Park, NC) were used to mark the surgical bed. Weck Appliers (Pilling Weck) were used for deploying clips in all patients. The biopsies were performed by two surgeons in our Breast Health Center. One surgeon routinely used clips to mark the margins of all biopsy cavities at the time of the initial surgical biopsy, thereby using clips in patients with benign or malignant disease. The other surgeon placed clips only in patients with malignant disease; clips were used to mark the margins of the reexcision cavity as part of breast conservation therapy.
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Intramammary metallic fragments may originate from a variety of sources. Fragments from gunshots [9], sewing needles [2], and transected localization wires [10] are large and therefore not confused with breast microcalcifications. D'Orsi et al. [8] reported only one patient in whom tiny metallic fragments were detected after a braided localization hookwire was cut at the time of surgery for an impalpable mammographic lesion. Korbin et al. [7] reported the presence of metallic particles in the surgical bed after needle localization and excisional biopsy. They observed that the particles did not form during the exchange between the needle and localization wire because they were not present on images after localization. Although they were not certain about the cause of the metallic particles, they postulated that the metallic fragments originated at the time of actual surgical excision. In any event, this occurrence was rare because it was observed in only five of 3500 wire localizations. Gold deposits have been reported to mimic the appearance of microcalcifications [11]. However, these metallic particles have been reported to be present in lymph nodes rather than in breast parenchyma. Their benign origin should be suspected in a patient with rheumatoid arthritis who has been treated with gold injections.
Radiopaque clips placed intraoperatively to define the margins of the tumor bed are helpful in planning radiation for patients who opt for breast conservation. The clips, rather than the lumpectomy scar, are used to delineate the borders of tangential beams, and these markers help avoid the pitfall of underdosing part of the biopsy cavity. This underdosing is more likely to occur with cavities located close to either the medial or lateral edge of the breast [1].
To our knowledge, the presence of minuscule metallic fragments appearing adjacent to the radiopaque clips has not been reported. By obtaining radiographs of breast tissue before and within minutes after clip placement, we have evidence to support the theory that these fragments originate from the metallic clips or their applier at the time of clip deployment. In our review of 100 biopsies, we observed the presence of metallic clips in 57 patients (57%), showing that this is a common occurrence.
One patient in this series underwent a second biopsy because the minuscule metallic fragments were perceived as microcalcifications. A 72-year-old woman underwent excision of a geographic area of microcalcifications. On pathology, the microcalcifications were associated with an invasive ductal carcinoma. One month after surgery, a preirradiation mammogram was obtained. Tiny particles, thought to be microcalcifications, were identified. On the basis of the possibility of residual tumor, needle localization and biopsy were recommended and performed. The specimen radiograph confirmed excision of the particles. Pathologic examination showed no evidence of residual tumor and no residual microcalcifications. In retrospect, the metallic nature of the particles was apparent on the specimen radiograph (Fig. 2). The pathology report did not comment on the presence or absence of metallic fragments because this patient was identified during our retrospective review and the pathologist was focusing on the presence or absence of calcium. It is not surprising that the metallic nature of the particles was obvious on the specimen radiograph, whereas it was not prospectively appreciated on the preceding mammogram. Because of diminished soft-tissue overlap and diminished scatter, it is common to appreciate more detail (e.g., microcalcifications and architectural distortion) on a specimen radiograph than on the corresponding mammogram.
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In some patients it may be difficult to distinguish between a metallic fragment and emulsion pick-off. If the fragment is clearly visible adjacent to a certain clip on both views, this location confirms that it is a metallic fragment rather than pick-off. If uncertainty persists, for example when the fragment is visible on only one image, comparison with a prior examination should reveal whether the fragment is real. In the absence of prior films, a follow-up radiograph obtained in the same projection should make the differentiation straightforward. If the particle maintains a constant relationship to the same metallic clip on the follow-up radiograph, it does not represent emulsion pick-off. Pick-off can sometimes be determined by viewing the emulsion side of the film under reflected light. In our series, if there was doubt as to the density or the fixed relationship, the particle was not counted.
We considered that the fragments might be related to surgical technique. However, we think this cause is unlikely because fragments were seen in patients of both breast surgeons at our institution. This reason does not totally exclude the possibility of surgical technique as the cause of fragments.
We contacted the manufacturer to inquire whether there had been any other reports of metallic fragments appearing at the time of clip deployment. The manufacturer responded that there were no other reports of flaking of radiopaque materials from their ligating clips used in breast biopsy.
Radiologists must be aware that minuscule metallic fragments may appear after deployment of surgical clips in the breast and that these fragments may mimic the appearance of intramammary microcalcifications. This finding is especially important in patients undergoing breast conservation therapy. These women, as a group, receive more careful follow-up than the general population. In addition, the threshold for biopsy of microcalcifications is lower in this high-risk population. In a patient with breast cancer containing microcalcifications who opts for breast conservation therapy, it is a common practice to obtain a preirradiation mammogram after surgery to be certain that there are no residual malignant microcalcifications. In a patient with a noncalcifying breast cancer, we obtain the first mammogram after treatment within 6 months of the completion of radiation therapy [12]. In both clinical settings, the identification of even one residual microcalcification implies the potential presence of tumor. If metallic fragments are mistaken for microcalcifications, an inappropriate intervention might be recommended (Fig. 2).
In summary, metallic fragments may be seen after clip deployment. We now consider their presence part of the usual spectrum of findings in these patients. These fragments sometimes have the potential to be confused with microcalcifications when their metallic nature is not appreciated.
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