Cellular features in desmoid fibromatosis and well-differentiated fibrosarcomas: an electron microscopic study

Low-grade sarcomas with CD34-positive fibroblasts and low-grade myofibroblastic sarcomas

A subset of low-grade fibrosarcomas is composed of CD34-positive spindle cells. These include dermatofibrosarcoma, its morphologic variants, and its associated fibrosarcoma, solitary fibrous tumor, hemangiopericytoma and their malignant counterparts, and some cases of myxoinflammatory fibroblastic sarcoma. Dermatofibrosarcoma and related lesions are characterized by a t(17;22)(q22;q13) rearrangement resulting in fusion of the genes COL1A (17q21-22) and PDGFB1 (22q13). Solitary fibrous tumor displays varying cellularity and fibrosis and a peripheral hemangiopericytomatous pattern; most tumors formerly called hemangiopericytoma are now subsumed into the category of solitary fibrous tumor, although a few strictly defined examples are recognized; however, these are probably not composed of pericytes. Myofibroblastic malignancies are best identified by electron microscopy, with which varying degrees of differentiation, including the presence of fibronexus junctions, can be identified. Low-grade sarcomas showing myofibroblastic differentiation include myofibrosarcomas and inflammatory myofibroblastic tumors. Myofibrosarcomas are spindle cell neoplasms that occur in children or adults in the head and neck, trunk, and extremities as infiltrative neoplasms and that display a fascicular or fasciitis-like pattern with focal nuclear atypia and variable expression of myoid antigens. These sarcomas are prone to recurrence and a small number metastasize. Inflammatory myofibroblastic tumor (synonymous with inflammatory fibrosarcoma) is a neoplasm arising predominantly in childhood, and frequently in intraabdominal locations. It has spindle cells in fascicular, fasciitis-like and sclerosing patterns, with heavy chronic inflammation including abundant plasma cells. Many IMT have clonal chromosomal abnormalities involving 2p22-24, and fusion of the ALK gene with tropomyosin 3 (TPM3-ALK) or tropomyosin 4 (TPM4-ALK) is found in a subset.

Desmoidfibromatosen (aggressive Fibromatosen)

Desmoid-type fibromatoses (aggressive fibromatoses) represent infiltrative, locally destructively growing soft tissue tumors with a high potential for recurrence. Desmoid tumors of 33 adult patients were analysed regarding clinical and morphological aspects (sex, age distribution, site, size, mitotic rate, tumor microvessel density, surgical margins, additional radiotherapy). Possible statistical correlations were examined using log-rank-tests. No prognostic significance of tumor microvessel density was evident. A correlation between mitotic index (1 or more mitoses per 50 high power fields) and local relapse rate was notably striking, but not statistically significant (log-rank: 0.17). Additional postoperatively applied radiotherapy proved to be statistically significant to avoid local recurrences (log-rank: 0.01). The presented results may indicate an increased risk for local relapse in those desmoid-type fibromatoses which are mitotically active. Postoperative radiotherapy seems to be effective in the treatment of aggressive fibromatosis to avoid tumor recurrence. Differential diagnosis of desmoid-type fibromatosis/aggressive fibromatosis in adulthood include various fibroblastic/myofibroblastic soft tissue tumors such as nodular fasciitis, fibrosarcoma, low-grade fibromyxoid sarcoma, myofibroblastic sarcoma as well as leiomyosarcoma and soft tissue leiomyoma.

Myofibroblastic malignancies

Malignant tumors composed of myofibroblasts are increasingly being recognized, but their existence remains controversial. Currently accepted examples within this category represent spindle cell or pleomorphic neoplasms of the soft tissues with a spectrum of histological grades. Low- and intermediate-grade myofibrosarcomas are fascicular spindle cell neoplasms resembling fibrosarcoma or leiomyosarcoma. They infiltrate deep soft tissue with disproportionate involvement of head and neck sites and can recur locally but infrequently metastasize. They variably express myoid immunohistochemical markers, and their differential diagnosis includes benign myofibroblastic proliferations such as fasciitis and fibromatosis as well as other types of spindle cell sarcoma. High-grade (pleomorphic) myofibrosarcomas are an ultrastructurally defined subset of malignant fibrous histiocytoma, which they resemble in morphology and behavior. Inflammatory myofibroblastic tumor and infantile fibrosarcoma are neoplasms that have myofibroblastic features and have been included in this category, but they have distinctive genetic findings. This article reviews the concept of myofibrosarcoma and describes its variants.

h-Caldesmon as a specific marker of smooth muscle cell differentiation in some soft tissue tumors of the skin

BACKGROUND

An existing problem in contemporary pathology is the classification and distinction of spindle cell soft tissue tumors of the skin. Markers such as alpha-smooth muscle actin (alpha-SMA) and desmin, considered specific for smooth muscle cell (SMC), have been shown to be expressed in a variety of fibroblastic and myofibroblastic processes. High-molecular-weight caldesmon (h-caldesmon), one of two isoforms, is reported to be expressed exclusively by SMC and has recently been shown to be a specific marker of SMC tumors.

METHODS

Tumors were obtained from 11 patients taken from the surgical pathology archives of the University of South Florida and cases were coded as smooth muscle hamartoma, myofibroma, and dermatomyofibroma.

RESULTS

The case of smooth muscle hamartoma had greater than 90% of tumor cells labeling with anti-h-caldesmon antibodies. Three of three cases of myofibroma had focal areas of positivity representing less than 10% of total tumor cells. Seven of seven dermatomyofibromas showed no apparent labeling with anti-h-caldesmon antibody. Dense reactivity was noted in vascular wall smooth muscle, indicating internal controls.

CONCLUSIONS

We can conclude that h-caldesmon is a specific marker of fully differentiated smooth muscle and that it can serve to differentiate spindled SMC soft tissue tumors of the skin from tumors of myofibroblastic and/or fibroblastic origin.

Feline vaccine-associated fibrosarcoma: morphologic distinctions

Forty-four primary feline vaccine-associated fibrosarcomas and 16 recurrences were examined histologically for detailed morphologic characterization with emphasis on tumor grade, presence of neoplastic multinucleated giant cells, presence and proportion of T and B lymphocytes within the tumor, and thin and intermediate filament contents of neoplastic and stromal cells. The microvascularity and proliferation rates of central and peripheral areas of the tumors were also quantified by computerized image analysis. For primary fibrosarcomas, 11 of 44 (25%) were grade I, 21 of 44 (47.7%) were grade II, and 12 of 44 (27.3%) were grade III. The recurrences followed a similar pattern: 4 of 16 (25%) were grade I, 8 of 16 (50%) were grade II, and 4 of 16 (25%) were grade III. A positive correlation was found between the presence of neoplastic multinucleated giant cells and tumor grade. These cells were present in 9 of 12 (75%) of grade III and none of the grade I tumors. Prominent peritumoral lymphoid aggregates or follicles were present in 59% of the tumors, and many contained high proportions of T lymphocytes, varying from 19 to 87%. All fibrosarcomas were immunoreactive for vimentin and 28 of 44 (64%) were reactive for alpha-smooth muscle actin. The actin-positive cells were either part of the tumor or formed a capsule around tumor nodules. The peripheral vascularity was significantly higher than the central vascular density but no difference was found in tumor cell proliferation rates between the two areas. Centrally located, fluid-filled micro- or macrocavitations were frequently observed in the large vaccine sarcomas and probably formed secondary to rapid tumor growth and central necrosis.

Low-grade myofibroblastic sarcoma: analysis of 18 cases in the spectrum of myofibroblastic tumors

The clinicopathologic, immunohistochemical, and ultrastructural features of a seemingly distinctive low-grade spindle cell sarcoma showing myofibroblastic differentiation have been analyzed in a series of 18 patients. The age range of the patients (7 women and 11 men) was 19-72 years (median: 42 years). A painless, enlarging mass was the most common clinical presentation. Five tumors arose in the oral cavity (including four lesions in the tongue), four in the lower extremities and three in the upper extremities, four cases in the abdominal/pelvic cavity, and two on the trunk. Eight soft-tissue cases involved skeletal muscle, three cases were located in perifascial tissues, and two arose in subcutaneous tissue. Tumor size ranged from 1.4 to 17 cm (median: 4 cm); in six cases (of which four were abdominal/pelvic) the lesion was larger than 5 cm. All patients were treated surgically, and four received additional adjunctive therapy. Histologically, most cases were cellular lesions showing a diffusely infiltrative pattern, and were composed of spindle-shaped tumor cells arranged mainly in fascicles. Tumor cells had poorly defined, palely eosinophilic cytoplasm and fusiform nuclei, which were either tapering and wavy or plumper and vesicular with indentations and small inconspicuous nucleoli. Tumor cells were set in a collagenous matrix often with prominent hyalinization. Mild nuclear atypia was noted in 16 cases; in the other 2 cases, and in the metastases of one other lesion, a greater degree of nuclear atypia was seen. In all but one case, the mitotic rate ranged from 1 to 6 mitoses in 10 HPFs (mean: 2/10 HPFs); in a single case, there were more than 20 mitoses in 10 HPFs. Immunohistochemically, all cases stained positively for at least one myogenic marker; 12 cases were positive for desmin, 11 for alpha-smooth muscle actin, and 6 for muscle actin (HHF35). Seven neoplasms were desmin positive/ alpha-smooth-muscle actin negative, and five cases were desmin negative/alpha-smooth-muscle actin positive emphasizing the variable immunophenotype of myofibroblastic lesions. In addition, 7 of 10 tumors stained at least focally positive for fibronectin. Ultrastructural examination in five cases showed characteristic features of myofibroblasts. Follow-up in 11 patients (median: 29 months) revealed local recurrence in 2 cases, and multiple distant soft-tissue, intraosseous, and pulmonary metastases in one other patient. Low-grade myofibroblastic sarcoma seems to represent a distinct entity in the spectrum of low-grade myofibroblastic neoplasms and is distinguishable from fibromatosis, myofibromatosis, solitary fibrous tumor, fibrosarcoma, and leiomyosarcoma.

Cytokine production by cell cultures from bronchial subepithelial myofibroblasts

Myofibroblasts have been previously described beneath the bronchial epithelium and were found to increase in number proportional to the accumulation of extracellular matrix in the bronchial lamina reticularis in asthma. The aim of this study was to assess further the contribution of these structural cells to allergic inflammation in the bronchial mucosa through their cytokine expression. Cell cultures were established from the lamina reticularis of human bronchial biopsies from asthmatic and non-asthmatic subjects. Cytokine secretion was measured by ELISA in supernatants of cultures with or without tumour necrosis factor-alpha (TNF-alpha). The mRNA levels for granulocyte-macrophage colony-stimulating factor (GM-CSF) in the cultures were examined by ribonuclease protection assays (RPAs). Bronchial myofibroblasts grown from bronchial biopsies were capable of producing GM-CSF, interleukin-6 (IL-6), interleukin-8 (IL-8), and stem cell factor (SCF) constitutively. The GM-CSF production by myofibroblasts was significantly increased in response to TNF-alpha simulation with a corresponding increase in GM-CSF mRNA expression. The enhancement of GM-CSF production by TNF-alpha in myofibroblasts was blocked by the inhibition of RNA synthesis. Prednisolone abolished the GM-CSF production. This study provides evidence for the role of bronchial myofibroblasts in the regulation of inflammatory cell recruitment and activation by interaction in the cytokine network in the bronchial mucosa.

Morphological heterogeneity and phenotypical instability versus metastatic stability in the murine tumor model ER 15-P

At clinical presentation, the majority of malignant tumors are composed of multiple clonal subpopulations of tumor cells with different phenotypic characteristics. Using the experimental tumor model ER 15-P, a methylcholanthrene-induced pleomorphic sarcoma of the C57 Bl6J mouse, we studied a system of long-term in vivo passages of this primary tumor for cell morphological changes, and alterations in the potential for spontaneous lung metastases. Transplants from the primary after the 4th, 20th, 40th and 80th i.m. passage (referred to as T4, T20, T40, and T80 respectively) together with their lung metastases were investigated by light microscopy, immunohistochemistry, and electron microscopy. In addition, the potential for metastasis to the lungs in each group was determined and compared with that of the parent T4 tumors. T4 tumors were mainly composed of spindle-shaped tumor cells with the ultrastructural features of fibroblasts and myofibroblasts, often arranged in a storiform or fasciculated growth pattern, and intermingled with tumor giant cells. Some small areas contained polygonal or rounded tumor cells, ultrastructurally undifferentiated, and sometimes arranged in a hemangiopericytoma-like growth pattern. Although electron-microscopical findings clearly demonstrated the mesenchymal origin of these tumor cells, immunostaining with a polyclonal antibody to vimentin was unspecific in all tumor cells and normal mouse tissue. Monoclonal antibodies to vimentin from different sources were completely negative in tumor cells and murine stromal components. In contrast, myofibroblast-like tumor cells showed immunohistochemically, a moderate to strong co-expression with monoclonal antibodies to desmin, muscle actin and alpha-smooth muscle actin. On the basis of these morphological findings, the primary ER 15-P was classified as a pleomorphic myofibrosarcoma. The lung metastases of T4 tumors were mainly composed of undifferentiated round to polygonal tumor cells, while the number of desmin-positive, muscle- and alpha-smooth muscle-actin-positive cells was reduced. The morphological features of T20 tumors and their lung metastases were the same as in T4, indicating a relative stability of the phenotype up to that stage. In contrast, T40 and T80 tumors and their lung metastases were found to contain almost exclusively undifferentiated tumor cells and many tumor giant cells. While fibroblast-like tumor cells were seen only occasionally, myofibroblast-like tumor cells had almost completely disappeared. The potential for lung metastases was nearly constant in all groups, suggesting metastatic stability. Obviously, the undifferentiated tumor cells of this model are associated with a higher metastatic potential.

Heterogeneity in the gingival fibromatoses

Forty-nine cases of isolated familial and idiopathic gingival fibromatoses, consisting of 12 cases from six families and 37 cases of idiopathic gingival fibromatosis, were reviewed. Pedigrees of five families revealed various penetrances and genetic heterogeneity as suggested by the presence of both autosomal dominant and autosomal recessive inheritances. Ultrastructurally, the lesions were composed of fibroblast-like cells and myofibroblast-like cells, with the former being the predominant cell type. The 267 cases of familial and idiopathic gingival fibromatoses were analyzed, and they with or without hypertrichosis, mental retardation, and/or epilepsy. These included 49 cases seen by the authors, 50 cases from the Japanese literature, and 168 cases from non-Japanese literature. Isolated gingival fibromatosis occurred more frequently after age of 12 years (P less than 0.0074). There was no significant difference in age of onset between generalized and localized forms of the idiopathic gingival fibromatosis. Gingival fibromatosis with hypertrichosis and mental retardation and/or epilepsy occurred frequently before 12 years (P less than 0.069). It has been shown that heterogeneity of the gingival fibromatosis is a result of either histologic heterogeneity, genetic heterogeneity, or a combination with other systemic disorders.

Cytoskeletal characteristics of myofibroblasts in benign neoplastic and reactive fibroblastic lesions

The characteristics of the cytoskeleton of myofibroblasts were examined immunohistochemically in 10 extra-abdominal desmoid tumours, 3 palmar and 2 plantar fibromatoses and 5 nodular fasciitis; in the cultured cells of one desmoid tumour, and also ultrastructurally in 3 desmoid tumours. Polyclonal anti-desmin antibody reacted with the cells in 7 extra-abdominal desmoid tumours, 1 palmar fibromatosis, 1 plantar fibromatosis and 3 nodular fasciitis. Monoclonal antidesmin antibody reacted with cells in only 2 desmoid tumours. Desmin-positive spindle cells were scattered throughout these lesions. There were no marked ultrastructural differences between desmin-positive and desmin-negative desmoids. All specimens except one specimen of nodular fasciitis showed immunoreactivity for alpha-smooth muscle actin and vimentin. Muscle actin-positive cells were observed in all specimens. Cultured cells gave positive reactions with polyclonal desmin antibody as well as to vimentin antibodies and two preparations of actin antibodies, whereas the original tumour did not react with desmin antibody. The present studies suggested that the cytoskeleton of some myofibroblasts in both neoplastic and reactive lesions resembles that of smooth muscle cells.

Central odontogenic fibroma

An example of a central odontogenic fibroma is presented. This is a rare, benign neoplasm which affected the molar region of the left side of the mandible of a 63-year-old female Caucasian. Histologically, it consisted of fibroblast-like cells lying in a rather myxomatous delicate collagenous stroma. Few islands of odontogenic epithelium were also found. At the ultrastructural level, the tumour cells contained large numbers of fine filaments with focal densities similar to those described in smooth muscle cells. They also showed a moderately developed r ER. These features are consistent with cells referred to as myofibroblasts.

Cellular junctions in a spectrum of human malignant tumors

Cellular junctions in tumors are often considered a hallmark of epithelial differentiation. However, junctions are also seen in tumors having a different differentiation. This observation prompted us to study cellular junctions in malignant nonepithelial tumors. We found a variety of cellular junctions in such tumors, although the majority were poorly formed. This observation is of importance for diagnostic purposes. We have also tried to clarify the nomenclature of cellular junctions as applied in tumor diagnosis by proposing a systematic categorization of terms in everyday use by pathologists and by referring more extensively to the term paired subplasmalemmal densities (PSD) for non-well-formed junctions.

Multicentric extra-abdominal 'myofibromatosis': report of a case with ultrastructural findings

A case of multicentric extra-abdominal fibromatosis, a rare entity, arising in a young female is presented. Three separate lesions developed in the same limb over a period of 11 years, one of which recurred on two occasions. Electron microscopy of the most recent tumour showed a predominance of myofibroblasts. The literature regarding extra-abdominal fibromatosis is reviewed and discussed. Redesignation of both abdominal and extra-abdominal fibromatoses as myofibromatoses is suggested.

Feline mammary sarcoma composed of cells resembling myofibroblasts

A recurrent mammary sarcoma from an 11-year-old, female domestic cat was studied by light and electron microscopy and immunohistochemistry. The tumor consisted of interlacing bands of spindle cells with elongated blunt-ended nuclei and variable amounts of stroma. Multinucleated tumor giant cells and mitoses were common. Ultrastructurally, tumor cells had abundant rough endoplasmic reticulum with dilated cisternae, a prominent Golgi complex, frequent mitochondria, bundles of intracytoplasmic filaments with focal densities, and discontinuous basal lamina-like material and cell junctions. These findings suggest that myofibroblast-like cells were the predominant type of tumor cell. Failure to demonstrate immunoreactivity for cytokeratins attested to the non-epithelial origin of these neoplastic cells. Uniform immunoreactivity with anti-vimentin antibodies and specific labelling of some tumor cells with antiserum to actin are compatible with an origin of this tumor from modified fibroblasts (i.e., myofibroblast-like cells). Tumors composed largely of myofibroblasts may be unique and warrant separate classification from other types of fibroblastic tumors in animals.

Aggressive angiomyxoma of pelvic soft parts: a clinicopathologic study of nine cases

Nine cases of aggressive angiomyxoma (AAM) of the pelvic soft parts were studied by light and electron microscopy and immunohistochemistry. The tumors were confined to the vulva, vagina, pelvic floor, and perineum in the seven women. The perineum and the para-anal region were involved in the two men. The patients ranged in age from 18 to 63 years. Aggressive angiomyxoma presented as a slowly growing, polypoid or cyst-like tumor. Six of the nine cases were followed up; all of the tumors recurred within nine to 84 months, and one recurred for the second time at 144 months. Recurrences were attributed to incomplete tumor excision. None of the six patients died or had metastases. The aggressive angiomyxomas had infiltrative borders and rubbery, white or soft, gelatinous cut surfaces. Histologically, the lesions were composed of stellate and spindle-shaped neoplastic cells embedded in a collagenous and hyaluronic acid-containing stroma. Nuclear atypia and mitoses were absent. Typically, the lesions had an important vascular component, often displaying medial hypertrophy and vascular grouping. Ultrastructurally, the neoplastic cells resembled fibroblasts rather than myofibroblasts. They showed strong immunoreactivity for actin but were negative for S-100 protein, Factor VIII, carcinoembryonic antigen, and keratin. The morphoimmunocytochemical characteristics of AAM cells favor a fibroblastic origin and differentiation. Aggressive angiomyxoma should be distinguished from the more common benign and malignant myxoid neoplasms or tumor-like conditions of the pelvic soft parts. Recurrence of AAM may be avoided by wide, local excision.

Myofibroblasts in fibromatoses. An electron microscopic study

Fifteen cases of fibromatoses were analyzed by electron microscopy, the objective being to compare the incidence and frequency of myofibroblasts in each category. Myofibroblasts were identified in all 15 cases and a considerably large number of these cells appeared in palmar fibromatosis, plantar fibromatosis, and nodular fasciitis. In keloid and cicatricial fibromatosis, however, only a small number of these cells were evident. In seven cases of extra-abdominal desmoid fibromatosis, the frequency of myofibroblasts in the component cells ranged from 10% to 64%, with a mean of 30%. The frequency was high in hypercellular lesions and low in hypocellular lesions, assuming that it would be roughly in parallel to the cellularity of the lesion in extra-abdominal desmoid fibromatosis and in other fibromatoses as well. There appeared to be no particular correlation between the number of myofibroblasts and recurrence of the lesion.

Inflammatory pseudotumor of the lung. Ultrastructural and light microscopic study of a myxomatous variant

A case of a myxomatous variant of an inflammatory pseudotumor of the lung is reported with clinicopathologic findings including its ultrastructure. The pathologic features of inflammatory pseudotumor of the lung are compared with similar tumors arising elsewhere and bear a close resemblance to granulation tissue, which suggests that inflammatory pseudotumors represent a reparative process rather than a neoplastic process. Recognition of this entity is imperative for a correct diagnosis and in order to differentiate it from malignant neoplasm, since only conservative management is necessary for its treatment.

Human osteogenic sarcoma: fine structure of the osteoblastic type

The fine structure of representative regions of 13 osteoblastic osteogenic sarcomas was studied. These regions contained four morphologically distinguishable subtypes of osteoblastlike cells. In addition, fibroblastlike and chondroblastlike cells were present, along with multinucleated giant cells, leukocytes, macrophagelike cells, and small populations of histogenetically unclassifiable (but probably neoplastic) cells. The morphologic evidence was compatible with the view that the variations in appearance among the subgroups of osteoblastlike cells reflected differences in maturation and differentiation of these cells. In at least one subgroup, the morphologic findings suggested that the cells were capable of manufacturing a secretory product. The multinucleated giant cells occurring in genuine tumor areas appeared to be closely related to neoplastic osteoblasts. The presence of chondroblastlike cells in the tissues illustrates that cells with a diverging differentiation can occur in an osteoblast-dominated cell population. This agrees with the view that the neoplastic cells originate from a mesenchymal stem cell with potential for multifaceted differentiation.

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.

Juvenile aponeurotic fibroma: an ultrastructural study

The light and electron microscopic findings in a case of juvenile aponeurotic fibroma are described. The tumor was composed of fibromatosislike areas and cartilagelike islands with characteristic calcification. The ultrastructural study verified the cartilaginous nature of this tumor. The cartilagelike islands were made up of chondrocytic cells embedded in an abundant intercellular matrix containing fine fibrils, spherical granules, and pleomorphic membrane-bound vesicles. The chondrocytic cells had many microvilli, a well-developed granular endoplasmic reticulum, and a prominent Golgi complex. In the periphery of each cartilagelike island was a perichondriumlike structure exhibiting transitional features from fibroblastic cells to chondrocytic cells. The fibromatosislike areas consisted of spindle-shaped fibroblastic cells and occasional myofibroblasts. The morphologic pattern of the tumor somewhat mimics embryonal chondrogenesis, and the fibromatosislike areas may represent an overgrowth of the fibrous layer of the perichondrium. It is possible to regard this tumor as an organoid tumor having a capacity for bidirectional differentiation into cartilage and fibrous tissue.

Inverted papillomas of nasal cavity and paranasal sinuses. Ultrastructural investigations on epithelial-stromal interface

10 cases of inverted papillomas of nasal cavity and paranasal sinuses were examined electron microscopically with particular regard to the epithelial-stromal interface. The papilloma cells were clearly demarcated from the stromal tissue by a basement membrane-like material. However, this structure mainly consisted of two or more layers, occasional breaks in the basement membrane were visible. Within the basal epithelial cells resting on the basement membrane accumulations of actin-like microfilaments could sometimes be observed. Furthermore, in the stromal tissue some myofibroblasts were present in the vicinity of the papillomatous cell complexes and capillary vessels also demonstrated several layers of basement membrane. All the changes presented here are considered to be the result of a permanent interaction between aggressive forces of papilloma cells and the defence mechanism of stromal tissue. The results allow the conclusion that inverted papillomas of nasal cavity and paranasal sinuses are true neoplasms with very low malignancy.

The 'transitional' mucosa adjacent to large bowel carcinoma--electron microscopic features and myofibroblast reaction

An electron microscopic study of the 'transitional' mucosa adjacent to 10 carcinomas of the colon showed impaired maturation of epithelial cells. The pericryptal fibroblast layer was absent, accounting for an increase in the length and distension of crypts. In the tunica propria a massive accumulation of myofibroblasts was noted and was indicative of an intensive fibre-producing activity. Review of the literature identifies various theories concerning the functions of myofibroblasts in respect of contraction, embryonal collagen-fibre formation and non-specific stromal reaction. Of these, the latter two are considered likely in relationship to transitional colonic mucosa.

The ultrastructure of conventional, parosteal, and periosteal osteosarcomas

Twenty-seven osteosarcomas of bone were examined by electron microscopy. Eighteen cases were conventional osteosarcomas, one case was an osteosarcoma that developed in Paget's disease of bone, two cases were metastasis to the lungs of conventional osteosarcomas, five were parosteal osteosarcomas (and the recurrence of one of them), and one was periosteal osteosarcoma. In addition to the basic neoplastic cell, the osteoblast-like tumor cell, seven tumor cell types could be differentiated in varying numbers in the 27 cases examined: (1) chondroblast-like; (2) fibroblast-like; (3) histiocyte-like; (4) myofibroblast; (5) osteoclast-like; (6) malignant multinucleated osteoblast-like; and (7) atypical primitive mesenchymal cells. Moreover, endothelial cells and pericytes were also present. The tumor cells showed common neoplastic features in relation with general cell configuration and fine structures. No cytoplasmic organelle was considered to be cell-specific, and only the amount and distribution of the organelles allowed us to differentiate the above mentioned cell types. The presence of malignant appearing tumor cells with abundant and dilated cisternae of RER, in an intercellular matrix containing collagen fibers with areas of focal collections or puffs of hydroxyapatite crystals, are the most characteristic ultrastructural features of osteosarcoma. However, those features are not pathognomonic and do not allow in all cases the differential diagnosis with osteoid-osteoma and benign osteoblastoma. Fields of chondroblastic, fibroblastic, or fibrohitiocytic character are indistinguishable of chondrosarcomas, fibrosarcomas, or malignant fibrous histiocytoma of bone, respectively. The comparative study of parosteal and conventional osteosarcomas revealed a marked difference in the cell population: fibroblast-like cells and myofibroblasts were the main cell types in parosteal osteosarcoma; on the contrary, myofibroblasts were very scarce or absent in conventional osteosarcomas. This difference may correlate with the better outcome of parosteal osteosarcoma. The ultrastructural features of a periosteal osteosarcoma are reported for the first time. The tumor was comprised mostly of chondroblast-like tumor cells. However, in the more cellular peripheric areas of the neoplasm, the cells were predominantly of the fibroblast-like type and showed anaplastic features.

Fibroma of tendon sheath

A series of nine cases of fibroma of tendon sheath is described including details of the ultrastructural features of two cases. The series was composed of lesions from six males and three females with a mean age of 38 yr. The most common site of involvement was the hand (including fingers) and the mean greater diameter was 19 mm. Typically the tumours were lobulated and microscopically there was a collagenous stroma with spindle and stellate cells in a moderate degree of cellularity. One recurrence was noted in the series. The lesion was distinguished from circumscribed fibromatosis, nodular fasciitis, neurofibroma, leiomyoma, scar tissue, giant cell tumour of tendon sheath (localised nodular tenosynovitis) and fibrous histiocytoma. Ultrastructural studies revealed that the large majority of cells present in the two cases studied were myofibroblasts and fibroma of tendon sheath is therefore the third instance of a benign tumour containing these cells (the other two being dermatofibroma and giant cell fibroma of the oral mucosa).

A tumor composed of myofibroblasts: an ultrastructural study

A subcutaneous tumor of the right temporal region of head was removed from an 8-year-old boy. This tumor was studied by light and electron microscopy. He was found to have had a retroperitoneal inflammatory fibrous histiocytoma which had been excised seven years ago. The subcutaneous tumor histologically consisted of spindle cells in fascicles, which did not arrange in a storiform or herring-bone pattern. Electron microscopically, this tumor was chiefly composed od myofibroblasts. electron microscopy is essential to determine the cell types of a tumor and we have classified this tumor as a tumor of myofibroblasts. The relationship between the retroperitoneal tumor and the head tumor was discussed.

Ultrastructural diagnosis of pleural tumors

The significant association of two kind of mesothelial cells, differentiated and fibroblastoid, caracterises the ultrastructure of malignant pleural mesotheliomas. The differentiated mesothelial cancer cells (MCC's), whether they are observed in fluids or in biopsies, are not caracteristic enough to assert the diagnosis of mesothelioma. They can easily be mistaken for metastatic cells. Therefore, the diagnosis of mesothelioma relies on the identification of fibroblastoid MCC's, whether they are in association with the preceeding form in epithelial-like tumors, or the main component in sarcomatous-like tumors. Since the absence of fibroblastoid MCC's would eliminate the diagnosis of mesothelioma, patient and careful search for these cells must be done in all pleural tumors with a unique differentiation (epithelial-like or sarcomatouslike). This justifies the need for electron microscopy in the diagnosis of these pleural tumors: for this reason, pleural biopsies should routinely be embedded for possible future ultrastructural examination.

Primary sarcoma of the gallbladder. A light and electronmicroscopical study

Six Swedish cases of primary sarcoma of the gallbladder from the period 1958-1973 and 1 case from 1975 were studied by light and electron microscopy. the literature was reviewed for the period after 1970. Ultrastructural features of sarcoma were investigated in order to exclude poorly differentiated carcinoma. One case was considered to be an embryonal rhabdomyosarcoma, three cases leiomyosarcoma and two were diagnosed as fibrosarcoma. One case, diagnosed as sarcoma of the gallbladder by light microscopy, was omitted because electron microscopical examination revealed a squamous cell carcinoma.

Monophasic synovial sarcoma, epithelioid sarcoma and chordoid sarcoma: ultrastructural evidence for a common histogenesis, despite light microscopic diversity

Ultrastructural examination of six rare sarcomas--four monophasic spindle cell tumours, one epithelioid sarcoma, one chordoid sarcoma--has revealed marked similarities at the electron microscopic level despite widely divergent light microscopic appearances. These features consisted of: 1 the presence of two cell types, viz. a clear cell and a cell resembling the fibroblast; 2 pseudoglandular spaces with projecting microvilli or filopodia, and with related tight junctions; 3 an amorphous intercellular ground substance with focal condensation into recognizable basement membrane. The findings suggest a common maturation of these diverse tumours to synovial-like tissue, and support the proposal of Hajdu Shiu & Fortner (1977) that these be considered variants of synovial sarcoma. Published ultrastructural studies of synovial, epithelioid and chordoid sarcoma are reviewed in the light of these findings. The ultrastructural differentiation of synovial sarcoma from extraskeletal myxoid chondrosarcoma, chordoma and the spectrum of malignant spindle cell tumours is discussed.

Aggressive fibromatosis involving the paramandibular soft tissues. A study with the aid of electron microscopy

The distinction at the level of light microscopy between aggressive fibromatosis and low-grade malignancies with fibroblastic features may be difficult. An electron microscopic study of four cases of aggressive fibromatosis of the mandibular soft tissue was undertaken to determine whether any ultrastructural characteristics could be identified that would aid in a more uniform distinction between these lesions. The pertinent findings include the identification of cells of fibroblastic derivation showing a range of organelle-poor to organelle-rich features, cytoplasmic microfibrils, and dilated rough endoplasmic reticulum profiles. These features are discussed in the light of previously published findings of other forms of aggressive fibromatosis and closely related lesions. The study reaffirms that although electron microscopy may be useful in confirming the cell of origin in these lesions, the accurate diagnosis of fibrous tumors still rests with the proper correlation of clinical and light microscopic features. Clinical follow-up of the cases supports both the diagnosis of aggressive fibromatosis and the recommended treatment of adequate local excision.

Perifollicular, perisinusal and trabecular myofibroblasts in the human fetal spleen

Electron microscopic studies of the human fetal spleen were performed on 22 embryos and fetuses from 31 days to 32 weeks of age. In the course of splenic development myofibroblasts were frequently observed in the perifollicular and perisinusal regions and within the trabeculae. The perifollicular cells were flattened and markedly elongated in shape and had distinct bundles of microfilaments in their cytoplasm. The perisinusal cells under the sinal basement membrane had microfilaments found in particular beneath the plasmalemma. They were attached to each other and constituted a cellular network throughout the splenic cords. The trabecular myofibroblasts, embedded among the abundant collagen fibers, had elongated and often indented nuclei. The cytoplasm contained well developed Golgi apparatus, abundant rough surfaced ER cisternae and massive bundles of myofilaments. These cells showed cell-to-cell and cell-to-stroma connections and were assumed to play a role in the excretion of lymphocytes from the follicles and in pumping blood from the sinuses by their contraction.

Myofibroblasts in fibrous tumors and fibrosis in various organs

The morphology and population of myofibroblasts detected by electron microscopy in fibrous tumors and fibrosis in various organs have been examined. The myofibroblast was identified by characteristic features of the indented nucleus, bundles of abundant microfilaments with dense bodies, focal basal lamina and well-developed rough endoplasmic reticulum. It has been observed that myofibroblasts in a variety of fibrous tumors and fibrosis appeared predominantly in fibromatosis and reparative process of deep fibrous tissues and organs particularly in the lesions involving the fascia and subcutaneous tissue. It was suggested that myofibroblasts would be modified fibroblasts to which fibroblasts in the fascia and deeply situated fibrous tissue transformed during proliferation and differentiation.

Differential diagnosis of spindle cell tumours by electron microscopy--personal experience and a review

Electron microscopy has its value and its limitations in refining the histogenetic diagnosis of certain spindle cell tumours. The ultrastructural diagnostic features of neural tumours, muscle tumours, fibrous histiocytomas, fibrosarcomas, monophasic synovial sarcoma and spindle-cell squamous carcinoma are reviewed and illustrated.

Fibromatosis of dura presenting as infantile spasms

A 6-month-old boy developed emprosthotonic infantile spasms and right hemiparesis. CT scan revealed a large mass related to a distended right temporal horn which on craniotomy proved to be a hard white tumour of the tentorium cerebelli which could be only incompletely resected. Microscopically and ultrastructurally, this lesion proved to be a typical fibromatosis containing myofibroblasts which invaded the brain. The child made an excellent recovery and is well a year after surgery. This case is another example which argues for full investigation of cases of infantile spasms which usually carry such a dismal prognosis.

A study of the cellularity and ultrastructure of congenital mesoblastic nephroma

This study reported 10 cases of congenital mesoblastic nephroma (CMN) from Children's Hospital of Pittsburgh: five were the typical fibromatous lesion, two were the cellular variant, and three had both components. Six cases occurred in infants less than one week of age. The degree of cellularity had no correlation with patient or tumor size. Three- to 10-year follow-ups of nine patients showed neither local recurrence nor metastasis. One infant died of generalized bleeding post nephrectomy. Ultrastructural study of seven cases showed mesenchymal cells with varying degrees of fibroblastic and/or myofibroblastic differentiation.

Myofibroblasts in connective tissue capsules around implanted dental materials

For testing the biocompatibility of dental materials in an experimental animal model the capsular tissues around the implanted dental materials were examined light and electron microscopically. The exudative inflammation and fibrosis at different times after implantation were thought to be the indicators of the degree of the compatibility. Starting from the knowledge of the occurrence of myofibroblasts in reparative granulation tissue we looked for such cells in the capsular tissues. Myofibroblasts were especially found at three weeks after onset of the experiments. Structural peculiarities of this fibroblast modulation are emphasized. Myofibroblasts are considered as an essential link between the early exudative reaction and the late fiber formation in tissue reactions after mechanical injury.

Desmoid tumors. An ultrastructural study of eight cases

A prominent ultrastructural finding in eight desmoid tumors was myofibroblastic mesenchymal cells with abundant intercellular collagen. In addition, seven of the tumors had intracytoplasmic collagen fibers. These findings are discussed in relation to other tumors and to nontumorous conditions.

Aggressive fibromatosis of the tongue

Fibromatoses are uncommon, locally aggressive lesions that may involve the structures of the head and neck. They are most commonly found in and along the fascial planes of the neck muscles but can involve other structures, including the oral cavity, nose, nasopharynx or paranasal sinuses. An unusual case of an extra-abdominal desmoid tumor is presented and a review of the anatomical, clinical and pathological features of these tumors is discussed.

Ultrastructural cytology of human osteosarcoma cells

The cytology of 6 osteosarcomas was examined by electron microscopy. In keeping with the varied pattern of osteosarcomas seen by light microscopy several types of tumor cells could be differentiated: osteoblast-like, fibroblast-like, chondroblast-like, osteoclast-like and histiocyte-like cells. Moreover, atypical malignant mesenchymal cells and vascular spaces were present. The individual cytoplasmic organelles are not considered to be specific to particular types of cell as seen from the discussion of the significance of rough endoplasmic reticulum, microfilaments and lysosomes. Only examination of the composite pattern of subcellular organelles allows the differentiation of certain cell types. All tumor cells visible in osteosarcomas are considered as modifications of a transformed common progenitor cell. Because of the variegated cytological picture a multipotent mesenchymal cell rather than an osteoblastic cell is assumed to be the ancestor cell.

[Studies of the mucopolysaccharid metabolism in the juvenile angiofibroma (author's transl)]

The mucopolysaccharide content of juvenile angiofibromas is investigated using histochemical and ultrahistochemical methods (histochemical in ten cases, ultrahistochemical in four cases). The investigations result in typical histochemical features and show the localization of acid mucopolysaccharides at electronmicroscopical level. The endothelium of the vessels exhibits a strong PAS-reaction and also shows acid groups at the cell surfaces. The interstitial tissue demonstrates neutral perjodatreactive substances as well as acid mucopolysaccharides. The latter substances mainly reacted in perifibrillar position. Electronmicroscopically the perjodreactive material was localized in the cytoplasma of typical fibroblasts and their modulations resembling histiocytes. The acid groups of carboxylated and sulfated mucopolysaccharides of the intercellular substance could be determined as hyaluronic acides and chondroitinsulfates (Chondroitin-4 and Chondroitin-6 sulfate) using the critical-electrolyte-concentration method after Scott and Dorling. Ultrastructurally these acid groups are localized as cell coat covering the fibroblasts and between the collagen fibrils. This histochemical investigation also supports the thesis of an organoid growth pattern of juvenile angiofibroma.

[Electron microscopic examination on cytogenesis of juvenile nasopharyngeal angiofibromas (author's transl)]

After the electron miscroscopic examination of tissue samples of juvenile nasopharyngeal angiofibromas obtained from 9 male patients ranging in their age from 7-24 years the problems of cytogenesis and classification are discussed. Besides it is tried to correlate particular morphological findings to certain clinical phenomenons. The vascular component of juvenile nasopharyngeal angiofibromas shows a clear proliferation of the vascular wall cells. Particularly, proliferating pericytes, cells withous peculiar characteristics ("undifferentiated" cells) and cells in various stages of differentiation are to be emphasized. Obviously, vascular wall cells emigrate into the surrounding tissue and transform themselves into small fibroblasts. The second component of juvenil nasopharyngeal angiofibromas is represented by stromal fibroblasts with several cytological variations. Only activated "classical" fibroblasts and fibroblasts with histocyte-like features reveal the nuclear pattern unique for these growths which is characterized by the combination of protrusions of nuclear membrane with formation of nuclear "blebs" and of dense intranuclear granules. Cells with these nuclear characteristics were considered as preexisting fibroblasts. Thus juvenile nasopharyngeal angiofibromas are formed by the proliferation of two tissue components, namely by the proliferation of vascular wall cells and stromal fibroblasts, and can be conceived as reactive hyperplasias. The swelling body-like and organoid appearance, cytological pecularities, characteristic topographic relations (localization and supplying vessesl) and the sex-dependent occurrence speak for a tumor-like hyperplasia of a rudimentary organ unknown till now.

Ultrastructural cytology of regenerating tendon--an experimental study

Cellular differentiations in regenerating tendon tissue of rats and guinea pigs were examined by the aid of the electron microscope. Fibroblasts with certain variations were found as basic cell types. Corresponding to the organelle composition classical fibroblasts, fibroblasts with histiocyte-like features and fibroblasts with myoide differentiations (comparable to the so-called myofibroblasts) were identified. Furthermore, proliferating capillaries with remarkable pericytic activities among other things producing fibroblast-like features must be mentioned. This fact led to the conclusion, that a part of fibroblasts in the proliferating connective tissue during tendon repair may derive from pericytes. Our ultrastructural investigations showed proof of the great plasticity of fibroblasts which function as stem cells in connective tissue regeneration.