Myofibroblasts in central giant cell granuloma of the jaws: an ultrastructural study

The ultrastructure of stromal mononuclear cells and giant cells were studied in two cases of central giant cell granuloma of the jaws. The majority of stromal cells superficially resembled fibroblasts, but also contained intracytoplasmic myofilaments with electron dense bodies similar to smooth muscle cells. These cells were referred to as myofibroblasts. The other type of mononuclear cells resembled macrophages. Many of the myofibroblast type cells appeared close to giant cells and signs of early fusion between them could be demonstrated. It is suggested from these results that the giant cells in central giant cell granuloma form and increase in size through fusion of these cells.     

Undifferentiated (embryonal) sarcoma of the liver in middle-aged adults: smooth muscle differentiation determined by immunohistochemistry and electron microscopy

Undifferentiated (embryonal) sarcoma of the liver (UESL) is a rare pediatric liver malignancy that is extremely uncommon in middle-aged individuals. We studied 2 cases of UESL in middle-aged adults (1 case in a 49-year-old woman and the other in a 62-year-old man) by histology, immunohistochemistry, and electron microscopy to clarify the cellular characteristics of this peculiar tumor. One tumor showed a mixture of spindle cells, polygonal cells, and multinucleated giant cells within a myxoid matrix and also revealed focal areas of a storiform pattern in a metastatic lesion. The other tumor was composed mainly of anaplastic large cells admixed with few fibrous or spindle-shaped components and many multinucleated giant cells. In both cases, some tumor cells contained eosinophilic hyaline globules that were diastase resistant and periodic acid-Schiff positive. Immunohistochemically, the tumor cells showed positive staining for smooth muscle markers, such as desmin, alpha-smooth muscle actin, and muscle-specific actin, and also for histiocytic markers, such as alpha-1-antitrypsin, alpha-1-antichymotrypsin, and CD68. Electron microscope examination revealed thin myofilaments with focal densities and intermediate filaments in the cytoplasm of tumor cells. Our studies suggest that UESL exhibits at least a partial smooth muscle phenotype in middle-aged adults, and this specific differentiation may be more common in this age group than in children. Tumor cells of UESL with smooth muscle differentiation in middle-aged adults show phenotypic diversity comparable to those of malignant fibrous histiocytoma with myofibroblastic differentiation.     

Myofibroblastic differentiation in malignant fibrous histiocytoma (pleomorphic myofibrosarcoma): a clinicopathological study

Myofibroblastic differentiation in malignant fibrous histiocytoma (pleomorphic myofibrosarcoma): a clinicopathological study
Aims : We compared the clinical and pathological features of pleomorphic malignant fibrous histiocytoma (MFH)-like soft tissue sarcomas with and without myofibroblastic differentiation on electron microscopy.
Methods and Results : Fifty-three soft tissue tumours designated as MFH by light and electron microscopy were reassessed. Eighteen were specifically diagnosed and excluded, and follow-up (FU) information obtained for 24 of the other 35 cases. Myofibroblastic ultrastructure was seen in 7/24 (29%). Seventeen of 24 (71%) lacked myofibroblasts on electron microscopy, which showed fibroblastic or undifferentiated cells. Histologically, all tumours but one had storiform-pleomorphic areas; one myofibroblastic neoplasm was fascicular and myxoid. No other morphological differences were seen. In seven myofibroblastic cases, smooth muscle in four cases and muscle-specific actin in two cases, desmin in three cases and S100 in one case were present. In 15 other tumours, smooth muscle in five cases and muscle-specific actin in one case, and desmin in one case were present; none of these cases expressed S100. CD34 was found in the myxoid areas of one myofibrosarcoma and 3/15 other tumours. Positivity for bcl-2 was seen only in non-myofibroblastic sarcomas (4/14). On follow-up (median 41 months), 2/7 (29%) myofibroblastic tumours recurred, 5/7 (71%) metastasized, and 3/7 (43%) patients died of disease. Among the non-myofibroblastic sarcomas, with a median follow-up of 47 months, 6/17 cases (35%) recurred, 10/17 (59%) metastasized, and 7/17 patients (41%) died of disease.
Conclusions : Pleomorphic sarcomas with and without myofibroblastic differentiation on electron microscopy are clinically and histologically similar. The former display myoid immunohistochemical markers more frequently.     

Is anti-h-caldesmon useful for distinguishing smooth muscle and myofibroblastic tumors? An immunohistochemical study

Misinterpretation of positive staining of antibodies to desmin, smooth muscle actin, and muscle actin as representing smooth muscle differentiation in the context of a spindle cell tumor is not uncommon. Anti-h-caldesmon is a promising novel immunohistochemical reagent for more specific smooth muscle differentiation. We studied 72 tumors (11 leiomyosarcomas, 26 malignant fibrous histiocytomas [MFHs], 11 fibromatoses, 11 cellular cutaneous fibrous histiocytomas [CCFHs], 5 malignant peripheral nerve sheath tumors, 4 synovial sarcomas, and 4 cases of nodular fasciitis), the reactive myofibroblastic response in 5 cases of acute cholecystitis, and the desmoplastic response surrounding 5 invasive breast carcinomas. Tissues were examined for expression of h-caldesmon, desmin, smooth muscle actin, and muscle actin. Diffuse staining for h-caldesmon was present only within the leiomyosarcomas. Focal staining for h-caldesmon involving less than 1% of lesional cells was present in 3 of 26 MFHs and 1 of 11 CCFHs. There was overlap in staining for the other "myoid" markers in all of the lesions that contained myofibroblasts. Anti-h-caldesmon seems to be a reliable marker of smooth muscle differentiation, and its inclusion in a panel of myoid immunohistochemical reagents should allow distinction of smooth muscle and myofibroblastic tumors.     

Synthesis of type I collagen by human smooth muscle cells in vitro.

Human vascular smooth muscle cells, derived from explants of medial smooth muscle of a fetal aorta, were grown in vitro and examined with phase and electron microscopy for characteristic morphologic features of smooth muscle cells and for the biosynthesis of connective tissue proteins. Their patterns of growth and ultrastructure were similar to those described for other species of cultured arterial smooth muscle cells. Most cells contained varying amounts of myofilaments interpersed with dense bodies, rough and smooth endoplasmic reticulum, mitochondria, various sized vesicles, lysosomes, and lipid droplets. Extracellularly, small amounts of electron-dense material and microfilaments were observed adjacent to or between the cells. The over-all morphology suggested that the smooth muscle cells were actively engaged in protein synthesis. Although we could not identify banded collagen fibrils in 10- to 14-day-old cultures by electron microscopy, the cells synthesized and secreted a collagen characterized as type I collagen. A hydroxyproline-containing protein composed of two alpha-1 and one alpha-2 chains was extracted from the cell layer. The triple helical precursor of type I collagen, procollagen, was secreted into the medium.     

The intermediate filament cytoskeleton of myofibroblasts: An immunofluorescence and ultrastructural study

Summary The intermediate filament cytoskeleton of stromal myofibroblasts from a series of twenty-eight infiltrating ductal breast carcinomas was examined by transmission electron microscopy (TEM) and indirect immunofluorescence (IF), the latter using antibodies to desmin, vimentin and prekeratin. Three cases of fibromatoses, selected as an additional source of myofibroblasts, were processed in the same manner. Stromal myofibroblasts from invasive ductal breast carcinomas rich in actin and readily identified by IF, were most numerous in the young edematous mesenchyme, areas corresponding to early stromal invasion or the peripheral invasive cellular front. Within the central sclerotic zone wherein clusters of neoplastic epithelial cells were surrounded by abundant collagen, most stromal cells corresponded by TEM to fibroblasts. In like fashion, myofibroblasts were most numerous in cellular, poorly collagenized portions of fibromatoses. By IF the only detectable intermediate filament protein of myofibroblasts in these two settings was vimentin.Since the appearance of stromal myofibroblasts appears to be associated with stromal invasion by malignant epithelium, their development by modulation of pre-existent periductal fibroblasts is postulated. With the exception of vascular smooth muscle cells and endothelial cells, the only periductal mesenchymal cells shown to contain vimentin were fibroblasts. The lack of desmin in myofibroblasts constitutes evidence against an origin from vascular smooth muscle cells. Because the molecular markers (intermediate filament proteins) of stromal cell differentiation presented quantitative but not qualitative modifications, the transformation of fibroblasts into myofibroblasts is quite likely, suggesting that myofibroblasts may be more closely related to fibroblasts than to smooth muscle cells.     

The mechanism of malignant tumor induction by nickel subsulfide

Experiments were performed to study the earliest changes and their sequence in the development of malignant tumors following implantation of 10 mg of nickel subsulfide (Ni3S2) into the right quadriceps muscle of seven male Fischer rats. Biopsies were performed when nodules reached one to three mm, and, later, when they were five to seven mm, and, finally, at sacrifice, to confirm the fully developed tumor pattern. Light microscopy of the earliest samples showed groups of cells clumped and scattered among degenerating muscle fibers. Mitoses were seen and inflammatory cells were not a feature. Electron microscopy showed individual degenerating muscle fibers, but also cells with characteristic features of myofibroblasts. In many cells osmium, dense fragments suggestive of crystalline material, were seen in the cytoplasm and nuclei. In the second set of biopsy material, myofibroblasts with well defined and dilated rough endoplasmic reticulum, intracellular membrane-bound collagen, and microfilaments with focal "dense bodies" were numerous. Mitoses were frequent. Immunohistochemistry showed strongly positive reaction to Vimentin and muscle-specific Actin in the tumor cells. In the fully developed tumors, the previously described typical storiform cell pattern with spindle and spheroidal cells with frequent mitoses was seen. Vimentin and muscle-specific Actin stains were strongly positive. The long latent period, the evidence of cell degeneration, necrosis, foreign material (probably of nickel composition), cell invasion, and subsequent rapid myofibroblast-type cell development, proliferating to malignant tumors highly suggestive of malignant fibrous histiocytoma, seem to suggest an epigenetic form of carcinogenicity of cytotoxic variety. Whether the tumor cells derive from transformed myofibrils or from activated pluripotential mesenchymal cells, or from both, remains in doubt.     

Possible identification of third stromal component in extraadrenal paraganglioma: myofibroblast in fibrous band and capsule

Sustentacular and dendritic cells are known as the stromal components of extraadrenal paraganglioma. We identified a third stromal component in such a case. A 66-year-old Japanese woman complained of abdominal pain. The tumor was discovered near the right adrenal gland in the retroperitoneum. Histologically, the tumor consisting of round to oval neoplastic cells with eosinophilic cytoplasm proliferating with a “zellballen” pattern. Sustentacular cells were positive for S-100. Dendritic cells positive for HLA-DR were seen among the neoplastic nests. Additionally, many alpha-smooth muscle actin (ASMA)-positive and hcaldesmon-negative stromal cells, namely, myofibroblasts, were distributed in the capsule and fibrous band. Ultrastructurally, myofibroblasts contained many myofilaments and dense bodies in the cytoplasm. Finally, we identified the third stromal component, namely, myofibroblasts, in the extraadrenal paraganglioma. These myofibroblasts may play a role in the stromal response of host against neoplasm or the regulation of tumor growth.     

Fibroblast and myofibroblast participation in malignant fibrous histiocytoma (MFH) of bone. Ultrastructural study of eight cases with immunohistochemical support

Eight malignant fibrous histiocytomas (MFH) of bone were studied with immunohistochemistry and electron microscopy. Ultrastructurally, fibroblasts and myofibroblasts were the main tumor cells in four cases and abundant in two other cases; these cells showed immunohistochemical positivity to alpha 1-antitrypsin, vimentin and anti-muscle antigen (HHF 35). Moreover, histiocytic-like tumor cells were electron-microscopically detected in four cases, being the main tumor cell type in two of the cases; immunohistochemically these cells expressed positivity to alpha-1-antichymotrypsin (A1ACT), alpha-1-antitrypsin (A1AT) and vimentin. Present results confirm the cellular heterogeneity of MFH of bone, in which fibroblasts and myofibroblasts transformed cells play a histogenetical role, suggesting the existence of close links with classic fibrosarcoma of bone.     

Primary leiomyosarcoma of bone

We describe a primary leiomyosarcoma arising in the proximal part of the right tibia of a 65-year-old man. The diagnosis was confirmed by both histochemical and electron microscopical studies. Ultrastructural examination revealed two different neoplastic cell populations. One, the type 1 cell, resembled typical mature smooth muscle cells, whereas the type 2 cells were smaller, more pleomorphic, and contained thick myofilaments in addition to the characteristic thin actin-like filaments. The tumor most likely arose from vascular smooth muscle cells, although origin from perivascular, multipotential, mesenchymal cells cannot be ruled out. Prognosis of reported cases appears to be poor if they are treated by inadequate surgical excision and irradiation but is more promising if wide excision or major amputation is performed.     

The ultrastructure of plexogenic pulmonary arteriopathy

The lungs from 16 cases of plexogenic pulmonary arteriopathy obtained at heart-lung transplantation, half of which had primary pulmonary hypertension, were examined by electron microscopy. From these the probable pathogenesis of pulmonary arterial intimal fibrosis in plexogenic pulmonary arteriopathy was deduced. The earliest detectable change was migration of smooth muscle cells from the media, through the internal elastic lamina into the intima. These cells collected beneath the endothelium and lost many of their myofilaments to become myofibroblasts. They were associated with ground substance but scanty collagen fibrils. As the quantity of interstitial collagen increased, the myofibroblasts reverted to a muscular structure, became elongated, and assumed a regular, circumferential orientation. This later stage coincided with the development of plexiform lesions. At both early and later stages, the muscular pulmonary arteries were contracted but not markedly so, and muscular evaginations were not seen. On the other hand, the cellular intimal proliferations developed early and were occlusive. This suggests that occlusion of small pulmonary arterial vessels by myofibroblasts may be at least as important as vasoconstriction in the early elevation of the pulmonary vascular resistance in primary pulmonary hypertension.     

The ultrastructure of benign and malignant fibrous histiocytomas

Five benign histiocytomas of varying pattern and three malignant fibrous histiocytomas have been studied ultrastructurally. An essentially biphasic pattern of histiocytes and fibroblasts was present. In addition fibrohistiocytes, myofibroblasts and undifferentiated cells were present in some of the tumours. The histogenesis of this group of tumours is discussed. The value of electron microscopy in establishing the diagnosis in difficult cases is emphasized, but it is not considered useful in distinguishing benign from malignant cases.     

Occurrence of myofibroblasts in the different phases of morbus Dupuytren (Dupuytren's contracture)

Twenty-one surgically removed specimens of Morbus Dupuytren (M. D.) were studied by light and electron microscopy. The cell type observed in the proliferative phase shows the basic ultrastructural features of fibroblasts, while the majority of the cells in the involutional phase resemble myofibroblasts. Myofibroblasts exhibit ultrastructural characteristics of both smooth muscle cells and fibroblasts and are said to behave functionally like smooth muscle cells. In the residual phase, typical fibrocytes of connective tissue are found. These findings confirm the concept that fibroblasts are capable of converting into myofibroblasts and demonstrate the myofibroblasts represent an intermediate cell type of transitional cellular differentiation. The significance of myofibroblasts for the development of the contracture of M. D. is discussed.     

h-Caldesmon as a specific marker for smooth muscle tumors. Comparison with other smooth muscle markers in bone tumors

Caldesmon is a protein widely distributed in smooth and non-smooth muscle cells and is thought to regulate cellular contraction. Its isoform, high-molecular-weight caldesmon (h-CD), was demonstrated to be specific for smooth muscle cells and smooth muscle tumors of the soft tissue and to never be expressed in myofibroblasts. We performed an immunohistochemical study to examine h-CD expression in the following bone tumors: conventional and non-conventional osteosarcoma, 13; malignant fibrous histiocytoma of bone, 5; giant cell tumors of bone, 5; chondroblastoma, 3; metastatic leiomyosarcoma, 2; and rhabdomyosarcoma, 1. Frequent immunoreactivity for muscle actin (alpha-smooth muscle actin or muscle-specific actin) was seen in 11 of 13 osteosarcomas and all other tumors, whereas h-CD was expressed intensely only in 2 leiomyosarcomas. h-CD is considered a specific and useful marker to distinguish smooth muscle tumor from bone tumors with myoid differentiation.     

Desmoplastic reaction of gastric carcinoma: a light- and electron-microscopic immunohistochemical analysis using collagen type-specific antibodies

The desmoplastic reaction in ten cases of gastric carcinoma was investigated light and electron immunohistochemically by using monospecific antibodies to collagen types. In addition to type I and III collagens, type V collagen was constantly recognized in the fibrous stroma, increasingly of the scirrhous carcinoma. Type IV collagen delineated the basement membranes of carcinoma nests linearly with occasional discontinuity, whereas in the scirrhous carcinoma, it was present along the thick bundles of collagenous fibers. Immunoelectron microscopic studies revealed that type I and III collagens were distributed on the collagen fibers, and type V collagen was stained in the margin of these fibers. These antibodies also reacted in the rough endoplasmic reticulum of fibroblasts or myofibroblasts in a few cases. Type IV collagen was localized in the periphery of smooth muscle cells, endothelial cells of collapsed capillaries, and myofibroblasts scattered in the stroma of scirrhous carcinoma. Carcinoma cells were not reactive with any antibodies examined. These findings suggest that type V collagen, as well as type I and III collagens, is involved in the formation of desmoplastic stroma, and that these collagens are reactively synthesized by fibroblasts and myofibroblasts in some interaction with invading carcinoma cells.     

Thick (myosin) filaments in a glomus tumor

An otherwise classic digital glomus tumor is presented with the unusual ultrastructural finding of cytoplasmic thick (myosin) filaments together with thin (actin) filaments in many of the cells. In places, sarcomere-like orientation was seen. It is little appreciated among diagnostic pathologists, but is well-established, that thick (myosin) filaments occur in smooth muscle type cells. They are present in vivo and can be demonstrated ultrastructurally if rather stringent preparative conditions are met. Whether or not the contractile process in smooth muscle is analogous to skeletal muscle is a debated issue. In the context of diagnostic electron microscopy, it is stressed that thick filaments are not, as often stated, pathognomonic of skeletal muscle neoplasms, and may potentially be found in smooth muscle neoplasms and neoplasms of related cell type (glomus tumors, hemangiopericytomas, tumors of myofibroblasts, etc.).     

Elastofibroma: a clinicopathologic and immunohistochemical study of seven cases and literature review

Elastofibroma is a rare fibrous lesion characterized by accumulated abnormal elastic fibers whose etiology remains largely unknown. In this study, we analyzed seven cases of elastofibroma to further explore the characteristics of its cellular composition. Immunohistochemistry was performed for mast cell tryptase, S-100 protein, vimentin, CD34, smooth muscle actin, desmin and collagen type IV. Histochemical staining methods for Gomori's trichrome and Verhoeff elastica-van Gieson were also evaluated. Histopathologically, a haphazard array of collagen, eosinophilic amorphous fibers, and globules in a fibrous tissue was seen. The elastic nature of the fibers was confirmed by elastic stain, and with Gomori's trichrome collagen fibers were also demonstrated. The interspersed spindle or stellate cells were almost consistently positive for vimentin and frequently positive for CD34. Mast cell tryptase-positive cells were present in five of the cases. Collagen type IV immunoreactivity was seen in two cases. No staining was observed with smooth muscle actin, desmin or S-100 protein. Our findings suggest that CD34-positive mesenchymal cells are an integral component of elastofibroma.     

Human copper deficiency: Ultrastructural studies of the aorta and skin in a child with Menkes' syndrome

This paper reports the first ultrastructural study of the thoracic aorta and dermis of an 18-month-old boy with Menkes' syndrome who had been treated in the year prior to death with intravenous copper. Light microscopy revealed absence of distinct elastic laminae in the inner third of the media, but irregular clumps of elastin were present. In the middle and outer media the elastic laminae were fragmented and discontinuous. The few cells present in the media were irregular in shape and, unlike normal smooth muscle cells, were seen to contain large accumulations of metachromatic material. A large amount of collagen was present throughout the aortic wall.Ultrastructurally, the elastin present was electron dense and surrounded by a prominent sheath of microfibrils approximately 110 Å in diameter. Similar observations were made for skin elastic fibers. The cells of the middle and outer thirds of the aortic wall contained myofilaments displaced peripherally by large aggregates of a flocculent material. These aggregates were largely nonmembrane limited and may represent an intracellular cytoplasmic accumulation of proteoglycan. Skin fibroblasts did not contain such aggregates.The abnormal elastic fibers observed in this child can be explained on the basis of a copper deficiency occurring very early in development, perhaps even in utero. The abnormally large amount of collagen present throughout the aortic wall and the sparse cell population with large cytoplasmic accumulations of metachromatic material are features not previously described. The collagen probably indicates a generalized repair response and may in part account for the sparse cell numbers because of its abundance. However, the nature of the large intracellular aggregates and their relationship to copper deficiency remain uncertain.     

Cellular origins of ultraviolet radiation-induced corneal tumours in the grey, short-tailed South American opossum (Monodelphis domestica)

Corneal tumours were induced in almost 100% of grey, short-tailed South American opossums (Monodelphis domestica) exposed three times weekly to ultraviolet radiation (UVR) for periods of a year or more. Five tumours, representing the morphological spectrum of UVR-induced corneal tumours (two fibrosarcomas, one malignant fibrous histiocytoma, one putative haemangiosarcoma, and one squamous cell carcinoma overlying a sarcoma), were assayed immunohistochemically for reactivity with antibodies against the intermediate filaments vimentin, smooth muscle actin (alpha isoform), muscle-specific actins (alpha and gamma isoforms), desmin and cytokeratin, and with antibodies against the vascular endothelial marker von Willebrand factor. The squamous cell carcinoma was cytokeratin-positive. Other tumours were cytokeratin-negative and vimentin-positive. Three tumours had scattered individual cells and groups of cells immunoreactive with antibodies against smooth muscle actin and muscle-specific actins; two tumours (a fibrosarcoma and the malignant fibrous histiocytoma) had small numbers of desmin-positive cells. The putative haemangiosarcoma contained two populations of neoplastic cells, von Willebrand factor-positive vascular endothelial cells and smooth muscle actin-positive spindle cells. It was concluded (1) that UVR-induced corneal tumours may be composed of cells derived from resident epithelial cells, immigrant vascular endothelial cells, or fibroblast-like cells of unknown origin, and (2) that such tumours may contain more than one neoplastic cell type.     

New data on the histogenesis of connective tissue tumors

The normal skin and adipose subcutaneous tissue, desmoid fibroma, lipomas with varying proliferative activity, fibrosarcoma, malignant fibrous histiocytoma, epithelioid leiomyoma are studied by means of electron microscopy and electron microscopical radioautography. It was found that the walls of the smallest vessels contain cells which are the source of a permanent physiological renewal of a different type of the connective tissue. In proportion to differentiation and gradual removal of these cells from the vascular wall their proliferative and metabolic activity is more and more decreasing. Thus, the vessels represent not only the transport-nutritive system but the central generative structure of the connective tissue as well. Pluripotential mesenchymal cell of the vascular wall which under physiological conditions is differentiating in the direction of fibro-, angio-, lipo- or osteogenesis, due to the influence of oncogenic factors gives rise to the development of benign and malignant tumours of fibrous, vascular (angiomas), smooth muscle, adipose and bone structure. This can be most demonstratively checked using electron-radioautography of tumourlike conditions and relatively slow growing tumours.