Malignant Fibrous Histiocytoma: An Ultrastructural Perspective

Malignant fibrous histiocytoma is a frequent diagnosis, but the relationship of the tumors to histologically similar soft tissue neoplasms is controversial. In this study, 157 examples representing the 4 main subtypes were reviewed by light microscopy and each tumor was studied with the electron microscope. Immunohistochemical stains were performed on 77 tumors. Electron micrographs on 100 fibrosarcomas were reviewed for comparison. Malignant fibrous histiocytomas often closely resemble fibrosarcomas at the ultrastructural level and differences between the two are generally of degree only. Evidence for true histiocytic differentiation was not found. The immunohistochemical results did not contradict the authors' impression from electron microscopy that malignant fibrous histiocytoma forms part of the histologic spectrum of tumors of fibroblasts.     

Malignant fibrous histiocytoma of the esophagus

A 78-year-old man presented with an esophageal polyp that was confirmed by Immunohistochemistry and electron microscopy to be malignant fibrous histiocytoma. The tumor was comprised of a proliferation of spindle-shaped cells admixed with bizarre giant cells. These tumor cells were immunoreactive for smooth muscle actin, vimentin, α-1-arrti-chymotrypsin and CD68. Electron microscopic examination revealed the myoflbroblastic and histtocytic features of the tumor cells. No elements of epithelial or myogenic differentiation were found in the tumor. Malignant fibrous histiocytoma of the esophagus is extremely rare, with 10 cases being documented so far in the literature. The differential diagnosis of pteomorphic tumors of the esophagus is discussed.     

软组织肿瘤细胞中的微丝结构

用透射电镜观察了一组18例肿瘤细胞胞浆中有微丝结构的软组织恶性肿瘤,电镜观察结果与光镜诊断不同,主要发生在纤维肉瘤、平滑肌肉瘤和恶性纤维组织细胞瘤中。肿瘤细胞膜下的具有密体的带状微丝可见于上述各种肿瘤中。一些肿瘤细胞也具有特征性的微丝结构。说明上述肿瘤的细胞成分有重叠。提出肿瘤的分类应主要依据大多数肿瘤细胞的分化方向来确定而不是臆测其组织发生和细胞来源。按此方法分类将会出现更多的纤维组织细胞瘤、肌纤维母细胞瘤和肌纤维组织细胞瘤的诊断。     

Myofibroblasts and related cells in malignant fibrous and fibrohistiocytic tumors.

Myofibroblasts were detected by electron microscopy in five of five cases of fibrosarcoma and in five of six cases of malignant fibrous histiocytoma. In some areas myofibroblasts constituted up to 75 per cent of the tumor cells. Most myofibroblasts contained only sheaves of myofilaments along the margins of the cells, but some cells contained larger bundles of myofilaments and very closely resembled smooth muscle cells. An additional related type of cell was seen in several cases; it was large and possessed abundant eosinophilic cytoplasm, resembling a rhabdomyoblast at the light microscopic level. By electron microscopy this type of cell was seen to contain plentiful rough endoplasmic reticulum and large aggregates of fine filaments with rare dense bodies. These findings suggest that fibrosarcomas and malignant fibrous histiocytomas contain cells showing a spectrum of differentiation from fibrocytic to myogenic and that at the ultrastructural level the distinction between fibroblast and smooth muscle tumors may be blurred.     

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.     

Malignant fibrous histiocytoma of bone and osteosarcoma. A comparative light and electron microscopic study.

Malignant fibrous histiocytomas are well-described tumors of the soft tissues. Recent investigations have shown that malignant histiocytoma may also occur as a primary bone tumor. However, difficulties may arise to distinguish malignant histiocytoma of bone from other malignant bone tumors, such as osteosarcoma. In the present study, the ultrastructure of five cases of malignant fibrous histiocytoma of bone is compared with that of osteosarcoma. The results show that malignant fibrous histiocytoma is composed mainly of histiocytic cells and fibroblastic cells. In addition, xanthomatous cells, undifferentiated cells, and giant cells may be observed. By contrast, the predominant cell type in osteosarcoma is the neoplastic osteoblast, characterized by abundant rough endoplasmic reticulum. Signs of matrix calcification in the intercellular matrix between the collagen fibrils are regularly observed in osteosarcoma, but not in malignant histiocytoma. From these results it is concluded that the ultrastructure of malignant fibrous histiocytoma arising in bone is morphologically identical with the soft tissue counterpart of this tumor. The components of the tumor are derived from neoplastic histiocytes. This cytogenesis differs from that of osteosarcoma, which is derived from neoplastic osteoblasts. Therefore, from the ultrastructural point of view, malignant fibrous histiocytoma of bone should be accepted as a distinct histologic entity among bone tumors.     

Malignant fibrous histiocytoma: an ultrastructural study of eleven cases

Eleven cases of malignant fibrous histiocytoma were examined electron microscopically. In six of seven cases with storiform-fascicular histologic features and in two cases with a myxoid pattern, no malignant-appearing histiocyte-like cells were identified. The neoplastic cells were fibroblasts and myofibroblasts, occasionally admixed with lymphocytes and benign-appearing histiocytes. Only in the other three cases (two pleomorphic sarcomas and one tumor with a storiform-fascicular pattern) were malignant cells with the features of histiocytes identified. The authors propose that some neoplasms with a storiform-fascicular pattern would be more accurately classified as fibrosarcomas than as histiocytomas and speculate on the possible histogenesis of those tumors that do contain histiocyte-type cells.     

Malignant fibrous histiocytoma of bone

Summary Malignant fibrous histiocytoma (MFH) of bone is a well-defined tumor by light microscopy but no agreement has been achieved concerning its histogenesis. We present the light and electron microscopic findings of four cases of MFH of bone. In case 1 multiple bone tumors were observed and in case 4 the tumor developed after irradiation. It was our aim to document the cytological variability and to arrange the findings in a histogenetic concept of primary intraosseous MFH. We observed some undifferentiated cells but mainly histiocyte- and fibroblast-like cells including intermediate forms, and several types of giant cells. We should emphasize the fact that there were also some large cells with a light microscopic resemblance to rhabdomyoblasts and with electron microscopic characteristics of myoblastic differentiation. From the ultrastructural point of view, therefore, MFHs seem to derive from a primitive mesenchymal stem cell rather than from the ordinary histiocyte. It is suggested that osteosarcoma and MFH of bone may have a common progenitor cell but it is important to make a clear clinico-pathological distinction between the tumors because of differing biological behavior.     

Xanthogranuloma of the rectum

A 46-year-old man with a suspected malignant submucosal tumor received a transabdominoperineal rectal amputation. The histologic diagnosis was xanthogranuloma. The differentiation of xanthogranuloma from malignant fibrous histiocytoma and other histiocytic tumors is difficult in the preoperative stage. Malignant fibrous histiocytoma can be diagnosed histologically by the presence of pleomorphism, mitotic activity, hyperchromatism, and a storiform pattern of cell arrangement. Moreover, some xanthogranulomas are also thought to have malignant potentiality and surgical resection is regarded as the preferred treatment. As for prognosis, the patient has lived for three years after the operation but further follow-up is thought to be necessary.     

XANTHOGRANULOMA OF THE RECTUM

A 46-year-old man with a suspected malignant submucosal tumor received a transabdominoperineal rectal amputation. The histologic diagnosis was xanthogranuloma. The differentiation of xanthogranuloma from malignant fibrous histiocytoma and other histiocytic tumors is difficult in the preoperative stage. Malignant fibrous histiocytoma can be diagnosed histologically by the presence of pleomorphism, mitotic activity, hyperchromatism, and a storiform pattern of cell arrangement. Moreover, some xanthogranulomas are also thought to have malignant potentiality and surgical resection is regarded as the preferred treatment. As for prognosis, the patient has lived for three years after the operation but further follow-up is thought to be necessary.     

Comparative Ultrastructure of Soft-Tissue Myxoid Tumors

This comparative analysis of the characteristic ultrastructural features specific for intramuscular myxoma, myxoid liposarcoma, extraskeletal myxoid chondrosarcoma, myxoid malignant fibrous histiocytoma, myxoid variant of dermatofibrosarcoma protuberans, and myxoid neurilemoma is based on our own studies of 52 cases. In spite of the histologic resemblance frequently observed, these tumors can be easily distinguished on the basis of cytoplasmic and extracellular features by electron microscopy. The value of electron microscopy in the diagnosis of myxoid tumors of soft tissues lies mainly in its potential to provide additional information concerning the cell types involved in the neoplastic process and their line of differentiation.     

Testicular Nodule Incidentally Found in Elderly Male

This comparative analysis of the characteristic ultrastructural features specific for intramuscular myxoma, myxoid liposarcoma, extraskeletal myxoid chondrosarcoma, myxoid malignant fibrous histiocytoma, myxoid variant of dermatofibrosarcoma protuberans, and myxoid neurilemoma is based on our own studies of 52 cases. In spite of the histologic resemblance frequently observed, these tumors can be easily distinguished on the basis of cytoplasmic and extracellular features by electron microscopy. The value of electron microscopy in the diagnosis of myxoid tumors of soft tissues lies mainly in its potential to provide additional information concerning the cell types involved in the neoplastic process and their line of differentiation.     

Liposarcoma of pleural cavity with recurrence as malignant fibrous histiocytoma

The case of a 54-year-old male, with a massive right pleural liposarcoma weighing over 3200 g, is presented. The tumor was found by light and electron microscopy to be of well-differentiated and pleomorphic subtypes, and it apparently represents the sixth reported case of liposarcoma primary to the pleura. Two years after excision of the primary tumor, it recurred as a neoplasm with histologic and ultrastructural features characteristic of malignant fibrous histiocytoma. The histogenetic and pathologic implications of the above findings are discussed, and the literature regarding intrathoracic liposarcoma and malignant fibrous histiocytoma is reviewed.     

Immunohistochemical study of malignant fibrous histiocytoma

Malignant fibrous histiocytomas (MFH) and other soft-tissue tumors were examined immunochemically (by the peroxidase-antiperoxidase technique) for the presence and location of alpha 1-antitrypsin (alpha 1-AT) and alpha 1-antichymotrypsin (alpha 1-ACT). alpha 1-AT and alpha 1-ACT were found in substantial amounts in 19 and 20 of the 20 MFH tumors examined, respectively. In the other soft-tissue tumors, they occurred inconsistently and in less than 50% of cells, mostly those with signs of damage. It is concluded that assays for alpha 1-AT and alpha 1-ACT may aid in the diagnosis and characterization of malignant fibrous histiocytoma.     

DIAGNOSTIC ASPECT OF SPINDLE-CELL SARCOMAS BY ELECTRON MICROSCOPY

Spindle-cell sarcomas in the somatic soft tissue and soft parts, including fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma (MFH), and malignant schwannoma were examined by electron microscopy in order to delineate the most reliable cellular features for their diagnosis. Fibrosarcoma consisted largely of fibroblastic cells and leiomyosarcoma cells were packed in forming small cell groups with constant junctional complexes of nexus and zonula adherens types. MFH showed variable cellular features containing the cells with myofibroblastic and histiocytic differentiation. Malignant schwannoma was characterized by tumor cells having slender cytoplasmic processes with overlapping or interdigitation and thick basement membrane. These ultrastructural features were contributory to the differential diagnosis of the sarcomas examined.     

Role of electron microscopy in the evaluation of soft tissue neoplasms, with emphasis on spindle cell and pleomorphic tumors

The current significant role of transmission electron microscopy in the evaluation of soft tissue tumors when correlated with conventional histological and immunohistochemical studies is discussed for the following entities: myxofibrosarcoma, storiform-pleomorphic fibrosarcoma (malignant fibrous histiocytoma), and myofibrosarcoma; dermatofibrosarcoma protuberans; hemangiopericytoma; monophasic synovial sarcoma; extrarenal rhabdoid tumor; soft tissue perineurioma; and gastrointestinal stromal tumors, notably the so-called autonomic nerve variant.     

Diagnostic aspect of spindle-cell sarcomas by electron microscopy

Spindle-cell sarcomas in the somatic soft tissue and soft parts, including fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma (MFH), and malignant schwannoma were examined by electron microscopy in order to delineate the most reliable cellular features for their diagnosis. Fibrosarcoma consisted largely of fibroblastic cells and leiomyosarcoma cells were packed in forming small cell groups with constant junctional complexes of nexus and zonula adherens types. MFH showed variable cellular features containing the cells with myofibroblastic and histiocytic differentiation. Malignant schwannoma was characterized by tumor cells having slender cytoplasmic processes with overlapping or interdigitation and thick basement membrane. These ultrastructural features were contributory to the differential diagnosis of the sarcomas examined.     

Intracranial benign fibrous histiocytoma mimicking parasagittal meningioma: report of two cases and review of literature

Primary benign fibrous histiocytoma involving the central nervous system is an exceedingly rare tumor with most cases originating from the dura or parenchymal tissue. Diagnosis of primary benign fibrous histiocytoma is difficult due to its confusing histopathological characteristics. Two cases of primary intracranial benign fibrous histiocytoma mimicking parasagittal meningioma are presented in this report. Both tumors were gross totally resected and the patients showed no evidence of recurrence at follow-up of 12 months. The clinical features and prognosis of this rare tumor that were reported previously in the literature were also reviewed. Histopathological examination coupled with immunohistochemical staining is proved to be the convincing diagnostic method for the primary benign fibrous histiocytoma. Surgical resection is the recommendation for the therapy of the tumor.     

Mesenchymal, IMon-Meningothelial Tumors of the Central Nervous System

The spectrum of non-meningothelial mesenchymal tumors that may arise within the central nervous system is presented, based on the current classification of soft tissue tumors. Among malignant types, hemangiopericytoma, rhabdomyosarcoma, mesenchymal chondrosarcoma, and malignant fibrous histiocytoma are the most frequent ones. Rare tumor entities are mentioned. As in soft tissue sarcomas, diagnosis is mainly based on light and electron microscopy, while immunohistochemistry can improve accuracy of diagnosis.     

Ultrastructure of oral sarcoma

Sarcoma of the oral region is extremely rare and ultrastructural studies of the tumor are limited in number. We collected oral sarcomas, such as fibrosarcoma, malignant fibrous histiocytoma, liposarcoma, leiomyosarcoma, rhabdomyosarcoma, angiosarcoma, alveolar soft-part sarcoma, solitary plasmacytoma, and osteosarcoma, and performed ultrastructural studies of these tumors. The value of these studies for an understanding of the biological behavior of the tumors was then investigated. In these studies, electron microscopic examinations of oral sarcoma were of assistance in our attempt to establish correct diagnosis and histogenesis. Data from the studies of oral sarcoma by light microscopy, electron microscopy, and immunohistochemistry should be accumulated.