Material and Method: The cases, both diagnosed as rhabdomyosarcoma or followed with a history of rhabdomyosarcoma, and interpreted with intraoperative consultation (frozen section) between 2000 and 2013 were culled from pathology archives. The diagnoses were confirmed by desmin and myogenin, immunohistochemically. The frozen and final diagnoses were noted of 21 biopsy specimens of 19 patients. Sensitivity and specificity of intraoperative consultation were calculated regarding to the major diagnostic discrepancies leading to a change in surgical management of the patient, after exclusion of the cases deferred to paraffin section.
Results: Of the evaluated 21 biopsy material, 3 (14%) were misdiagnosed: Of the 2 false negative embryonal rhabdomyosarcoma cases, sample was not representative of the tumor, and there was chemo/radiotherapy induced changes in the other case. In the only false positively diagnosed case with a known history of rhabdomyosarcoma, inflammatory cells were misinterpreted as small round cell neoplasm. In 5 (29%) of 21 biopsies, a frozen diagnosis could not be given, and the diagnosis was deferred. Six cases (29%) were evaluated with cytological squash or imprint preparation; none of the misdiagnosed cases was evaluated with adjunct cytological preparation. Six of 8 misdiagnosed or deferred biopsies showed morphological changes secondary to radiotherapy and/or chemotherapy. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated as 85%, 67%, 92% and 50%, respectively.
Conclusion: Intraoperative consultation for rhabdomyosarcoma is a reliable tool with high sensitivity and fair specificity. Cases with treatment effect may lead to diagnostic difficulties, especially false negative results. Understanding the diagnostic algorithm of surgeon may prevent misdiagnosis of frozen specimen. Our results also emphasize the diagnostic role of intraoperative cytology as an adjunct to frozen section.
In this study, we assessed the diagnostic accuracy of intraoperative consultation in RMS in our department. We aimed to emphasize the reasons leading to misdiagnosis, and to define the specific morphologic findings to reach the correct diagnosis.
Only the major differences that change the surgical management were considered for the assessment of diagnostic power (sensitivity, specificity, and predictive values) of frozen-section diagnoses.
Three of the 21 biopsies (14%) were misdiagnosed in intraoperative consultation; 2 had false negative, and 1 had false positive diagnoses (Table I). In one of the false negative cases, tumour was not represented in the small frozen biopsy material sent by surgeon (Figure 1A). Complete examination of the biopsy material sent to pathology department revealed hypercellular areas composed of neoplastic cells having round, monomorphic, hyperchromatic nuclei, and scanty cytoplasm (Figure 1B) besides the hypocellular and hyalinized zones which were seen in frozen section. Immunohistochemically, desmin and myogenin were positive in the neoplastic cells (Figure 1C,D).
Table I: List of deferred and misdiagnosed cases
In the other false negative case, the biopsy showed prominent chemo/radiotherapy related changes (Figure 2A-D), characterized by oedema and fibrosis with inflammatory background, and only a few atypical cells were present (Figure 2A). In the permanent section, atypical cells were present in the background of fibrosis and inflammation (Figure 2B). Atypical cells were in the form of strap cells with unipolar or bipolar eosinophilic cytoplasmic extensions, and hyperchromatic, irregular nuclei. Histological hallmarks, such as broken arrow sign (Figure 2C), and immunohistochemical demonstration of myoid markers desmin and myogenin were diagnostic for RMS (Figure 2C,D).
Only one false positive case, previously diagnosed as RMS, and re-excised because of surgical margin positivity, was evaluated as having small blue round cell tumour in frozen section (Figure 3A,B); however, it turned out to be an intensive inflammatory infiltrate and fibrosis in the permanent section (Figure 3C), and immunohistochemical analysis for myogenin was negative (Figure 3D).
Five biopsies (24%) were reported as indeterminate during intraoperative consultation, and definitive diagnosis was left to permanent paraffin sections (Table I). Six out of 8 patients (75%) who were misdiagnosed or had inconclusive result during frozen section previously received chemotherapy or radiotherapy, and biopsies of these patients showed significant treatment related morphological changes, such as fibrosis, hyalinization, and inflammatory reaction (Figure 4A-D).
Sensitivity, specificity, positive and negative predictive values of intraoperative consultation diagnosis for RMS were calculated as 85%, 67%, 92%, and 50%, respectively.
Six of 21 cases (29%) were evaluated with cytological preparations, and none of them was misdiagnosed in the intraoperative consultation. Also, squash smear examination was not performed in none of the cases with false frozen diagnoses. Microscopically cytological preparations were hypercellular, and had neoplastic cells with small, round, hyperchromatic nuclei, and scanty cytoplasm (Figure 5A,B).
In soft tissue tumours, intraoperative consultation is useful in determining the surgical procedure, in assessing if the tumour is present and in constructing a differential diagnosis that can direct the proper triage of tissue for flow cytometry, electron microscopy, and molecular studies/ cytogenetics, particularly for neuroblastoma and RMS[2]. Tissue triage is optimally performed at the time of frozen section. In many cases, it is important that a portion of tissue be submitted for ancillary studies, even from fineneedle aspiration (FNA) and core needle biopsy specimens, after sufficient tissue has been submitted for histological evaluation[5].
Frozen diagnosis for RMS is found to be highly sensitive, reaching 85%; however, specificity is lacking, slightly better than flipping a coin. Therefore, it’s recommended to be more careful while one decides to give “negative” result in frozen sections because of low specificity and negative predictive value. One should be especially careful about morphological pathognomonic clues, such as broken arrow sign and cross-striations, and a cytological squash preparation should be used as an auxiliary technique in order to prevent false negative results. Also, a complete understanding of the surgeon’s treatment algorithm is recommended before rendering a frozen section diagnosis[6]. According to the algorithm determination, the case could be released to paraffin embedded sections.
In our series, treatment-related morphological changes seem to have an important role leading to a false frozen section diagnosis. It is important to get the clinical history of patient if he/she had a working diagnosis of RMS previously or had received treatment. A variety of therapy-related histological changes ranging from necrosis, chronic inflammation, fibrosis to atrophic or regenerating nonneoplastic skeletal muscle have been reported in most RMSs, especially the embryonal subtype[7]. Posttreatment specimens can show fibrosis, inflammation with macrophages and lymphocytes, and scattered neoplastic cells simulating reactive fibroblasts. Interpretation of therapy-induced differentiations is a great challenge for the pathologists and it is quite difficult to evaluate them in the frozen sections. The use of cytological preparations as an adjunct to frozen section is highly reliable tool[8], and may be quite useful for the differentiation of chronic inflammatory cells from small round rhabdomyoblasts and for the straightaway appreciation of the morphological details of the neoplastic cells.
Finally, we conclude that intraoperative consultation for RMS is a quite reliable tool with high sensitivity and fair specificity. Pathologists dealing with frozen section should be aware of treatment effect that may lead to diagnostic difficulties, especially false negative results. Understanding the diagnostic algorithm of the surgeon is highly recommended to prevent misdiagnosis. Our findings also encourage the use of intraoperative cytology as an adjunct to frozen section.
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