Electron Microscopy in the Diagnosis of Small Round Cell Tumors of Bone

Small round cell tumors involving bone can present problems in differential diagnosis by light microscopy. In exploring the role of electron microscopy in this situation, seven small cell osteosarcomas and seven mesenchymal chondrosarcomas were examined by electron microscopy and compared with typical and atypical Ewing's sarcomas. There is much overlap in the ultrastructural features of these tumors, but electron microscopy is helpful to establish or confirm a diagnosis of typical Ewing's sarcoma and, if representative matrix is present, of small cell osteosarcoma.     

The role of electron microscopy in the diagnosis of pleomorphic sarcomas of soft tissue

Classification of pleomorphic malignancies is frequently problematic and important with regard to treatment. Their histologic differential diagnosis is extremely wide, including sarcomatoid carcinoma, melanoma, anaplastic lymphoma, and a large number of sarcomas with overlapping light microscopic appearances. Not infrequently, immunohistochemical investigations of such tumors yield conflicting or confusing results. In such cases, electron microscopy remains an invaluable investigative and diagnostic adjunct, revealing certain subcellular features that indicate a specific line of differentiation. Combining ultrastructural and immunohistochemical studies is particularly useful in these tumors. This article focuses on the ultrastructural aspects of certain sarcomas that are predominantly pleomorphic, including high-grade fibrosarcoma, myxofibrosarcoma-malignant fibrous histiocytoma, acral myxoinflammatory fibroblastic sarcoma, pleomorphic liposarcoma, pleomorphic leiomyosarcoma, and pleomorphic rhabdomyosarcoma, as well as certain sarcomas that are occasionally quite pleomorphic, including angiosarcoma, malignant granular cell tumor, alveolar soft part sarcoma, and extraskeletal osteosarcoma. We also briefly comment on the common simulators of pleomorphic sarcomas, including melanoma, carcinoma, and lymphoma.     

Ewing's Sarcoma with Neuroblastoma-like Features

Four tumors with the clinical and light microscopic features of Ewing's sarcoma contained cells that possessed to varying degrees ultrastructural features suggestive of neuroblastoma. These neoplasms were considered to be Ewing's sarcoma of bone by radiologic examination and on clinical grounds, and light microscopy was consistent with the diagnosis in every case. It is suggested that the ultrastructural morphology of Ewing's sarcoma is broader than had been supposed and that the presence of dendritic processes in a small cell tumor of bone should not exclude the diagnosis of Ewing's sarcoma.     

Ewing's Sarcoma with Neuroblastoma-like Features

Four tumors with the clinical and light microscopic features of Ewing's sarcoma contained cells that possessed to varying degrees ultrastructural features suggestive of neuroblastoma. These neoplasms were considered to be Ewing's sarcoma of bone by radiologic examination and on clinical grounds, and light microscopy was consistent with the diagnosis in every case. It is suggested that the ultrastructural morphology of Ewing's sarcoma is broader than had been supposed and that the presence of dendritic processes in a small cell tumor of bone should not exclude the diagnosis of Ewing's sarcoma.     

Synovial sarcoma: ultrastructural study and immunohistochemical analysis by a combined peroxidase-antiperoxidase/avidin-biotin-peroxidase complex procedure

To analyze the purportedly epithelial features of synovial sarcoma, the antigenic profiles of 20 of these neoplasms (including 12 of the monophasic type) were studied by three different immunohistochemical techniques, and the results were correlated with ultrastructural observations in 10 cases. All of the biphasic tumors were immunoreactive for the epithelial markers epithelial membrane antigen (EMA) and cytokeratin (CK) and also had ultrastructural features of epithelial differentiation. In contrast, only one of five monophasic tumors had electron microscopic features suggestive of epithelial differentiation, but eight of the 12 were immunoreactive for CK or EMA by a procedure combining the peroxidase-antiperoxidase and avidin-biotin-peroxidase complex methods. It is concluded that synovial sarcoma, including the monophasic variant, is a mesenchymal tumor with epithelial features. Immunohistochemical studies are more sensitive than ultrastructural analysis for documenting epithelial differentiation.     

Extraosseous Ewing's sarcoma versus primitive rhabdomyosarcoma: diagnostic criteria and clinical correlation

A light and electron microscopic study of 51 cases of Ewing's sarcoma of bone (ESB) and 33 soft tissue sarcomas (carrying a variety of light microscopic diagnoses, including primitive rhabdomyosarcoma) in children and young adults was performed to clarify the similarities and differences among these tumors. Ultrastructural criteria were developed to evaluate the neoplasms. Remarkable ultrastructural uniformity was found in the cases of ESB. In contrast, the soft tissue sarcomas could be divided into two distinct groups on the basis of the ultrastructural criteria: those closely resembling primitive areas of otherwise differentiated rhabdomyosarcomas, and those indistinguishable from ESB. It is proposed that the diagnosis of soft tissue Ewing's sarcoma be reserved for lesions identical to ESB by both light and electron microscopy. The first group of sarcomas may be histogenetically related to rhabdomyosarcoma and should be distinguished from extraosseous Ewing's sarcoma, as their clinical behavior appears to be quite different.     

Synovial sarcoma: a review and update, with emphasis on the ultrastructural characterization of the nonglandular component.

Classic biphasic synovial sarcoma is usually not a problem in identification, whereas the monophasic spindle cell form continues to be a challenge in the differential diagnosis of spindle cell neoplasms. Most synovial sarcomas do not arise from a joint or tendon sheath, and by electron microscopy and immunohistochemistry they differ in several ways from nonneoplastic synovium. The cell of origin of synovial sarcoma is unknown, but certain features are rather consistently observed in the biphasic tumors and are useful in identifying monophasic samples. These features are apparent by immunohistochemistry and electron microscopy, both of which indicate early epithelial differentiation in the nonglandular component of the neoplasm. With immunohistochemistry, some of these cells stain for keratin. By electron microscopy, a gradient of differentiation from unclassifiable spindle cells to fully differentiated epithelial lining cells is demonstrable. A review and illustration of the ultrastructural characteristics in this spectrum of intermediate cells constitute the main emphasis of the article. The cells tend to be oval and polygonal; to be arranged in clusters surrounded by basal lamina or flocculent matrix; to have junctions, including tight junctions, and to form villuslike filopodia, true microvilli, canaliculi, and microlumina. This range of ultrastructural features is usually diagnostic of the nonglandular phase of synovial sarcoma.     

Synovial Sarcoma: A Review and Update, with Emphasis on the Ultrastructural Characterization of the Nonglandular Component

Classic triphasic synovial sarcoma is usually not a problem in identification, whereas the monophasic spindle cell form continues to be a challenge in the differential diagnosis of spindle cell neoplasms. Most synovial sarcomas do not arise from a joint or tendon sheath, and by electron microscopy and immunohistochemistry they differ in several ways from nonneoplastic synovium. The cell of origin of synovial sarcoma is unknown, but certain features are rather consistently observed in the biphasic tumors and are useful in identifying monophasic samples. These features are apparent by immunohistochemistry and electron microscopy, both of which indicate early epithelial differentiation in the nonglandular component of the neoplasm. With immunohistochemistry, some of these cells stain for keratin. By electron microscopy, a gradient of differentiation from unclassifiable spindle cells to fully differentiated epithelial lining cells is demonstrable. A review and illustration of the ultrastructural characteristics in this spectrum of intermediate cells constitute the main emphasis of the article. The cells tend to be oval and polygonal; to be arranged in clusters surrounded by basal lamina or flocculent matrix; to have junctions, including tight junctions, and to form villuslike filopodia, true microvilli, canaliculi, and microlumina. This range of ultrastructural features is usually diagnostic of the nonglandular phase of synovial sarcoma.     

Synovial Sarcoma: A Review and Update,with Emphasis on the Ultrastructural Characterization of the Nonglandular Component

Classic triphasic synovial sarcoma is usually not a problem in identification, whereas the monophasic spindle cell form continues to be a challenge in the differential diagnosis of spindle cell neoplasms. Most synovial sarcomas do not arise from a joint or tendon sheath, and by electron microscopy and immunohistochemistry they differ in several ways from nonneoplastic synovium. The cell of origin of synovial sarcoma is unknown, but certain features are rather consistently observed in the biphasic tumors and are useful in identifying monophasic samples. These features are apparent by immunohistochemistry and electron microscopy, both of which indicate early epithelial differentiation in the nonglandular component of the neoplasm. With immunohistochemistry, some of these cells stain for keratin. By electron microscopy, a gradient of differentiation from unclassifiable spindle cells to fully differentiated epithelial lining cells is demonstrable. A review and illustration of the ultrastructural characteristics in this spectrum of intermediate cells constitute the main emphasis of the article. The cells tend to be oval and polygonal; to be arranged in clusters surrounded by basal lamina or flocculent matrix; to have junctions, including tight junctions, and to form villuslike filopodia, true microvilli, canaliculi, and microlumina. This range of ultrastructural features is usually diagnostic of the nonglandular phase of synovial sarcoma.     

Malignant melanoma of soft parts: an ultrastructural study of four cases

Malignant melanomas of soft parts from 4 patients were studied by light microscopy, immunocytochemistry for S-100 protein, and electron microscopy. Each patient presented with a deep soft tissue mass in an extremity. Histologically, the tumors were composed of epithelioid and spindle cells, and in one, neoplastic giant cells were present. The tumors did not stain for melanin but were all positive for S-100 protein. Ultrastructurally, premelanosomes were identified in every tumor and in a cell line established from one tumor. Schwann cell features were present in one of the tumors. Although the clinical presentation of malignant melanoma of soft parts is similar to that of epithelioid sarcoma and synovial sarcoma, the combined light microscopic, immunocytochemical, and ultrastructural features should serve to distinguish it from other soft tissue sarcomas.     

Tissue culture as a diagnostic technique for soft-tissue sarcoma of childhood

A case of childhood small cell undifferentiated sarcoma was grown in vitro in a serum-free culture medium. In vivo the tumor showed no evidence of differentiation by light microscopy, electron microscopy, and immunoperoxidase staining for myoglobin or skeletal muscle myosin. After growth in vitro for two weeks in a defined culture medium, the tumor cells formed myotubes and demonstrated ultrastructural myogenic differentiation. This case demonstrates the use of the tissue culture as a diagnostic aid in the recognition of childhood small cell undifferentiated sarcomas. It also raises questions regarding the origin of these tumors and the ability of in vitro growth to induce differentiation.     

透射电镜在活检中的应用——附145例电镜诊断和分析

对145例活检标本进行超微结构观察,96例作出电镜诊断,分析成功的关键。探讨适用范围,如寻找病毒颗粒、免疫复合物,由于电镜高分辨力发现细胞初期分化信息,常能对低分化肿瘤作正确诊断。初步介绍小细胞癌、梭形细胞肉瘤、APUD瘤、恶性淋巴瘤的超微结构特征。并对上述肿瘤的鉴别诊断进行了讨论。     

Ultrastructure of the Ewing's sarcoma family of tumors

Specimens of 47 tumors diagnosed by routine light microscopy as Ewing's sarcoma of bone, and 5 similar soft tissue tumors (extraskeletal Ewing's sarcomas), were examined by transmission electron microscopy. Immunohistochemical stains were performed on all the tumors, and pre-therapy and post-therapy specimens from 5 of the patients were compared. Cell and nuclear areas were assessed in 41 cases by cytomorphometry by using low-magnification electron micrographs. DNA ploidy was determined by static cytometry on 51 of the tumors. None of the methods revealed differences between the bone and soft tissue tumors. The ultrastructural spectrum extended imperceptibly from the typical forms to markedly irregular variants, and was much broader than could be anticipated from the light microscopy. Neural features were observed but they were not common. Comparison of the Ewing's sarcomas with a group of other small round cell tumors (rhabdomyosarcoma, neuroblastoma, small cell carcinoma) using the same techniques showed that they have similar cell and nuclear areas despite the obvious differences in their immunophenotypes and ultrastructure. The collective findings are in keeping with the currently favored view that Ewing's sarcoma and peripheral primitive neuro-ectodermal tumor are the extremes in a morphologic continuum within which neural differentiation ranges from absent to prominent.     

Primary pulmonary sarcoma: a clinicopathologic study of 26 cases.

The clinical and pathologic features of 26 primary pulmonary sarcomas were analyzed. Fourteen patients were male and 12 were female; ranging in age from 18 to 75 years (mean, 48 yr). The tumors measured from 0.9 cm in greatest diameter to filling the entire hemithorax. Thirteen tumors were in the left lung and nine in the right lung; one was bilateral, two were in the pulmonary artery, and the location of one tumor was not available. The histologic diagnoses were malignant fibrous histiocytoma (7), synovial sarcoma (6), malignant peripheral-nerve sheath tumor (3), leiomyosarcoma (3), angiosarcoma (2), intimal sarcoma (2), fibrosarcoma (2), and one case of epithelioid hemangioendothelioma. Immunohistochemical and ultrastructural examination supported these diagnoses. Morphologically, the differential diagnosis often included sarcomatoid carcinoma or desmoplastic malignant mesothelioma Patients were treated with surgery, chemotherapy, radiation therapy, or a combination of these. Follow-up was available for 22 patients and ranged from 2 to 183 months (mean, 45 mo). Fourteen patients are free of disease, four died of disease, three are alive with disease, and one died of surgical complications. A variety of sarcomas, especially malignant fibrous histiocytoma and synovial sarcoma, arise within the pulmonary parenchyma. These tumors have the potential to behave aggressively but can be cured by resection, with or without adjuvant therapy. Immunohistochemistry and electron microscopy can be helpful in distinguishing primary pulmonary sarcoma from other tumors in the differential diagnosis.     

Histiocytic sarcoma in Wistar rats. A light microscopic, immunohistochemical, and ultrastructural study

Histiocytic sarcoma, a recently described tumor entity in rats, was studied by light microscopy in 20 male and female Wistar rats. The tumors originated from subcutaneous tissues; metastasis involved primarily the liver with sinusoidal spread and the lungs with peribronchiolar distribution. The characteristic features of this tumor were the uniform population of tumor cells, palisading necrosis, and abundant multinucleated giant cells. Immunocytochemical and ultrastructural findings confirmed the histiocytic nature of the tumor cells.     

Electron microscopy of fine-needle aspiration biopsies of the mediastinum.

Twenty cases of fine-needle aspiration (FNA) biopsy of mediastinal tumors with ultrastructural studies of the aspirated material were reviewed. The cases were classified according to the cytologic and ultrastructural diagnosis. A specimen insufficient for ultrastructural study was obtained in five cases (25%). Refinement of the cytologic diagnosis was made in three cases (15%) and good correlation between the initial cytologic impression and the ultrastructural studies was seen in the remaining cases (60%). Comparison of different sites of FNA biopsy revealed a higher rate of ultrastructural examination in the cases involving the mediastinum. Illustrative cases of the use of electron microscopy in FNA biopsies of mediastinal tumors are presented.     

Differential diagnosis of undifferentiated malignant tumors with monoclonal antibody T29/33

An immunoperoxidase method for distinguishing lymphomas from nonlymphoid neoplasms with monoclonal antibody T29/33 is described. This antibody recognizes a 200,000-dalton pan-hematopoietic glycoprotein antigen. Staining in nearly 200 hematopoietic tumors was positive for T29/33, although three of six plasmacytomas were negative for this antibody. Five undifferentiated tumors that were proved to be lymphomas by subsequent electron microscopic and immunohistologic studies were positive for T29/33. Conversely, 11 of 12 undifferentiated tumors with ultrastructural and clinical features of carcinoma or sarcoma were T29/33-negative. The only exception was one sarcoma that was T29/33-positive. Thus, monoclonal antibody T29/33 is a valuable tool for characterizing neoplasms that cannot be diagnosed by histopathologic examination alone.     

Malignant soft tissue tumors (malignant fibrous histiocytoma, pleomorphic liposarcoma, and pleomorphic rhabdomyosarcoma): an electron microscopic study.

A comparative ultrastructural analysis of malignant soft tissue tumors (malignant fibrous histiocytoma, pleomorphic liposarcoma, and pleomorphic rhabdomyosarcoma) revealed similar ultrastructural features in this group of tumors. However, by electron microscopy these tumors can be differentiated on the basis of cytoplasmic and extracytoplasmic features (myosin filaments, lipid droplets, and perinuclear intermediate filaments, for example). This is even true of less well differentiated tumors and tumor cells. These findings support and amplify the concept of a common histogenesis for tumors of mesenchymal origin. Paradoxical features observed by light microscopy warrant further study by electron microscopy if the correct diagnosis is to be made in atypical cases, such as apparent malignant fibrous histiocytoma with cross striations.     

Immunohistochemical and ultrastructural investigation of neural differentiation in Ewing sarcoma/PNET of bone and soft tissues

The authors evaluated the role of immunohistochemistry and electron microscopy in defining neural differentiation in 28 cases of Ewing sarcoma/ PNET. The panel of primary antibodies used included vimentin, MIC-2, NSE, S-100 protein, leu7, neurofilaments, GFAP, and chromogranin A. Cases were considered undifferentiated when neural markers were absent, poorly differentiated if one neural marker was present, and well differentiated if two or more markers were observed. Cases were also evaluated for the presence of cytoplasmic processes, microtubules, and neurosecretory granules as ultrastructural features of neural differentiation: the tumor was classified as well differentiated if two of these features were present; and poorly differentiated if one was evident; all other cases were considered undifferentiated. According to immunohistochemistry, 10 cases (35.7%) were undifferentiated, 12 cases (42.9%) were poorly differentiated, and 6 (21.4%) were well differentiated. According to the ultrastructural analysis, 10 tumors were undifferentiated (35.7%), 14 poorly differentiated (50%), and 4 well differentiated (14.3%). The overall concordance between the two techniques was low (35.7%), and both modalities were concordant in classifying only 1 well-differentiated, 5 poorly differentiated, and 4 undifferentiated tumors. In conclusion, the authors suggest that investigations devoted to test the prognostic significance of neural differentiation in these neoplasms should employ both immunohistochemistry and electron microscopy, separately and in combination, to assess what is the most effective choice for predicting the clinical course.