Myoid Differentiation Research Articles

Testicular Effects of Vasectomy in Rats: An Ultrastructural and Immunohistochemical Study

Objectives. The correlation between infertility and morphofunctional alterations following vasal occlusion is not clearly understood. Although a correlation has been found between the expression of a high titer of antisperm antibodies and the status of infertility, the relationship between the immunoglobulin (Ig) depositions in the testis and ultrastructural alterations of the peritubular structures has not been clearly established. The objective of this study is to explain the etiopathogenesis of diffuse and focal testicular lesions caused by vasal obstruction. Methods. Unilateral vasectomy was performed on adult male rats. Ultrastructural changes of testicular tissues and immunostaining affinity of peritubular structures with anti-actin, anti-vimentin, anti-laminin, and anti-immunoglobulin G (anti-IgG) antibodies were analyzed. Results. In an ultrastructural study, vasectomized animals presented abundant collagen fibril accumulation in the peritubular area. In testis with intense IgG antibodies, staining revealed weak immunostaining of peritubular myoid cells with anti-actin antibodies, but intense immunostaining with anti-vimentin antibodies. The tubules of rats with no IgG deposition on peritubular structures revealed intense immunostaining with anti-actin antibodies but scant immunostaining with anti-vimentin antibodies. Anti-laminin deposits decreased severely in most of the tubules demonstrating intense IgG deposition. Conclusions. Our findings suggest that spermatogenesis deteriorates more severely in testes with dense IgG deposition. The sclerosis of the lamina propria in cases with vasal occlusion is secondary to alterations in the peritubular myoid cells. With the progressive changes that occur in the peritubular myoid cells or differentiation of the peritubular myoid cells that acquire active cell characteristics, collagen accumulation adjacent to these cells increases markedly. The alterations of the peritubular myoid cells reported here may be caused by alterations in basement membrane structures.

Dermatofibrosarcoma protuberans and its fibrosarcomatous variant with areas of myoid differentiation: a report of three cases

We describe three examples of dermatofibrosarcoma protuberans which demonstrated focal myofibroblastic differentiation, and discuss the nature of myofibroblastic differentiation. We studied three cases of dermatofibrosarcoma protuberans, two of which had fibrosarcomatous portions containing myoid areas, and one which showed myoid areas in ordinary dermatofibrosarcoma protuberans. Myoid areas were recognized histologically as randomly distributed, scattered bundles or small nodules of spindle cells with deeply eosinophilic cytoplasm. Myofibroblastic differentiation was demonstrated immunohistochemically by positive staining for smooth muscle actin and muscle-specific actin, and ultrastructurally by the presence of microfilament bundles with focal dense bodies and pinocytic vesicles. The myoid areas occasionally contained intraneoplastic blood vessels. The presence of myoid areas may be related to reactive hyperplasia of stroma, and its relation to the histogenesis of dermatofibrosarcoma protuberans is uncertain.

Dermatofibrosarcoma protuberans and its fibrosarcomatous variant with areas of myoid differentiation: a report of three cases

Aims We describe three examples of dermatofibrosarcoma protuberans which demonstrated focal myofibroblastic differentiation, and discuss the nature of myofibroblastic differentiation. Methods and results We studied three cases of dermatofibrosarcoma protuberans, two of which had fibrosarcomatous portions containing myoid areas, and one which showed myoid areas in ordinary dermatofibrosarcoma protuberans. Myoid areas were recognized histologically as randomly distributed, scattered bundles or small nodules of spindle cells with deeply eosinophilic cytoplasm. Myofibroblastic differentiation was demonstrated immunohistochemically by positive staining for smooth muscle actin and muscle-specific actin, and ultrastructurally by the presence of microfilament bundles with focal dense bodies and pinocytic vesicles. The myoid areas occasionally contained intraneoplastic blood vessels. Conclusion The presence of myoid areas may be related to reactive hyperplasia of stroma, and its relation to the histogenesis of dermatofibrosarcoma protuberans is uncertain.

Myofibromatosis in adults, glomangiopericytoma, and myopericytoma: a spectrum of tumors showing perivascular myoid differentiation.

The clinicopathologic features of 24 tumors showing perivascular myoid differentiation are described. These included tumors with histologic features of "infantile-type" myofibromatosis occurring in adult patients (8 cases), tumors with composite features of "hemangiopericytoma" and glomus tumor (9 cases), and tumors with a distinctive concentric perivascular proliferation of spindle cells (7 cases). Evidence of morphologic overlap among these groups suggests they are closely related neoplasms that form a single spectrum. Age of patients with lesions resembling infantile-type myofibromatosis ranged from 23 to 67 years (median, 37 years). Clinicopathologic manifestations of this disease included multicentricity (4 cases), local recurrence (3 cases), persistence of congenital lesions into adulthood (4 cases), and tumors that were multifocal within the confines of one anatomic region (7 cases). Histologically, all cases showed a biphasic pattern that consisted of fascicles of spindle cells with abundant eosinophilic cytoplasm that resembled smooth muscle, in addition to a population of more primitive spindled cells associated with a hemangiopericytomalike vascular pattern. Six cases showed reversal of the typical zonation seen in pediatric cases in that the primitive component surrounded the more mature fascicular areas. Also described are nine tumors with features that are intermediate between glomus tumor and hemangiopericytoma, which we have designated glomangiopericytoma. These tumors are characterized by prominent branching vessels lined by a single row of endothelial cells surrounded by epithelioid cells with a glomoid appearance. In other areas, the tumors showed typical hemangiopericytomatous foci similar to those in the myofibromatosis cases. The principal points of distinction were a lack of myoid nodules and an absence of small primitive cells with basophilic cytoplasm. Ages of these patients ranged from 17 to 78 years (median, 35 years). All tumors were located in the subcutaneous tissue and the superficial soft tissue of the extremities. Recurrence developed in one of six patients with follow-up information. The recurrent tumor had features of angiomatoid malignant fibrous histiocytoma. Finally, we describe a subset of tumors characterized by concentric periluminal proliferation of bland, round to ovoid cells, which we have designated as myopericytoma. Patient age ranged from 10 to 66 years (median, 40 years). All were located in subcutaneous and superficial soft tissue of distal extremities. One patient had two recurrences in 3 years after initial excision. Our study suggests that these three lesional groups comprise a histologic continuum of tumors that share clinical similarities and that, perhaps, are designated more appropriately as perivascular myomas. The relationship of this family of tumors to so-called hemangiopericytoma is discussed.

Leiomyomatous nodules and bundles of vascular origin in the fibrosarcomatous variant of dermatofibrosarcoma protuberans

We report 5 cases of the fibrosarcomatous variant of dermatofibrosarcoma protuberans, 4 of which presented a morphologic change of intraneoplastic blood vessels not previously recognized. This change consisted of focal proliferation of smooth muscle cells, resulting in hypertrophy, generally eccentric, of vascular walls with reduction and collapsing of vascular lumina. In 3 cases the proliferation was so intense it formed leiomyomatous nodules and bundles. This proliferation may originate in the smooth muscle cells of the vessel walls either by means of a hyperplastic mechanism or in the pericytes via a line of differentiation leading to mature smooth muscle cells. In either case, we believe that it concerns a reactive process of the vessel walls very probably induced by adjacent neoplastic cells. The cases recently reported by Calonje and Fletcher as "myoid differentiation" of neoplastic cells in dermatofibrosarcoma protuberans (DFSP) may well be an expression of the same phenomenon, and therefore the presence of leiomyomatous areas in this tumor should not be used to support the theory of a fibroblastic/myofibroblastic line of differentiation for DFSP.

Nasal pleomorphic adenoma with skeletal muscle differentiation: Potential misdiagnosis as rhabdomyosarcoma

Pleomorphic adenoma can show diverse lines of differentiation in the epithelial and myoepithelial elements, such as cartilage, bone, and fat. Myoid differentiation, however, has not been documented. We report an unusual case of nasal pleomorphic adenoma which shows focal skeletal muscle differentiation. The tumor was discovered only after successful radiation therapy for an undifferentiated carcinoma of the nasopharynx. Apart from being of morphological interest, the presence of cells with skeletal muscle differentiation also raises the practical issue of possible confusion with rhabdomyosarcoma in a biopsy. The distinguishing features are lack of cytological atypia and presence of a neoplastic glandular element.

Amianthoid Myofibroblastoma of the Soft Tissues

Myofibroblastoma (MF) is an uncommon, usually benign, mesenchymal tumor infrequently described in soft tissues. We report here on the clinicopathologic findings of a soft tissue MF (STMF) presenting in the neck of a 90-year-old man as a slowly growing and non-painful nodule, 4 cm in greatest diameter. Histology revealed a circumscribed lesion constituted of monomorphous bipolar spindle cells arranged in swirling fascicles with intervening broad bands of hyalinized collagen and well formed "amianthoid" fibers. Immunohistochemistry showed the spindle cells to be immunoreactive for vimentin, smooth muscle actin and muscle specific actin and, focally, for desmin; immunostaining for cytokeratin, epithelial membrane antigen, S-100 protein, factor VIII-related antigen, and CD34 was negative. Based on the present case and on those previously reported in the literature, STMF is characterized by: 1) exclusive incidence in the male sex; 2) variable immunoreactivity of the neoplastic cells for desmin, probably reflecting an origin from a peculiar subset of myofibroblasts, or, alternatively, a further myoid differentiation; 3) variable abundance of (hyalinized) collagen; 4) presence of amianthoid fibers. The combination of desmin immunoreactivity, frequently observed in MF of the breast, and amianthoid fibers, the main feature of MF of the lymph nodes, has never been observed in soft tissue MF. It is important to recognize STMF as a specific clinicopathologic entity to avoid confusion with other types of spindle cell proliferation and to differentiate it from other types of myofibromatosis.

Comparison of Angiomyofibroblastoma and Aggressive Angiomyxoma in Both Sexes: Four Cases Composed of Bimodal CD34 and Factor XIIIa Positive Dendritic Cell Subsets

Aggressive angiomyxoma (AA) is a distinctive, locally aggressive, fibromyxoid tumor of the pelvic and genital soft tissues. AA is of unknown histogenesis but the cytologically bland spindled tumor cells, which surround characteristic variegated blood vessels, show fibroblastic or myofibroblastic features. AA may be related to angiomyofibroblastoma (AMF), another cytologically bland fibromyxoid genital spindle cell tumor with variable myoid differentiation that does not, as a rule, recur. Recently, CD34+ primitive fibroblasts and factor XIIIa+ dendritic histiocytes have been found in varying combination in many fibrovascular, fibrohistiocytic, and myxoid soft tissue tumors. Both cells belong to the microvascular unit, a tissue responsible for stromal repair and remodeling and angiogenesis. To determine if these ubiquitous stromal cells participate in the histogenesis of AA and AMF, we examined two scrotal tumors, one AA with multiple recurrences and one AMF, for the presence of CD34+ and FXIIIa+ dendritic cell subsets. For comparison, a vaginal AMF and a pararectal AA in a woman were included. We also studied actins and desmin to detect myofibroblastic differentiation, and, through double labeling studies, assessed hormone receptors and the cell cycle marker Ki 67 in the different cell subsets. The AA showed unusual cytologic atypia and was initially diagnosed as liposarcoma. It massively recurred four times over 12 years, the first time after seven years. The histologic appearance was fairly constant over the years. The scrotal AMF was a circumscribed 6 cm mass in a 37 year old man. In both cases, most tumor cells were wavy and fibrillar, spindled, stellate, or polygonal fibroblast-like CD34+ dendritic cells. Depending on the area examined, a 20-50% subset of dendritic cells showed both nuclear and cytoplasmic staining for FXIIIa. Actin+ cells were rare but vessels had actin+ myopericytes, although a small focus of the initial male AA was desmin positive. The recurring AA expressed androgen receptors and had Ki 67 index of 10-20% in "hot spots" of the primary and up to 30% in recurrent tumors. The scrotal AMF widely expressed androgen and progesterone receptors with focal estrogen receptor positivity and the Ki 67 index was 10%. Both CD34+ fibroblasts and FXIIIa+ histiocytes were present in the Ki 67+ cycling fraction in both the male AA and AMF and both cell types expressed androgen receptors. The female pararectal AA had more focal CD34 reactivity, particularly in perivascular fibroblasts and these cells were admixed with small FXIIIa+ cells. The vaginal AMF was strongly desmin+ and variably to weakly CD34+ with 20% FXIIIa+ dendritic cells and Ki 67 index of 2%. The vaginal AMF strongly expressed estrogen, progesterone, and androgen receptors. In conclusion our data suggest that at least some AA and AMF are myxoid fibrohistiocytic tumors composed of CD34+ fibroblasts and FXIIIa+ dendritic histiocytes. In our tumors, neoplastic CD34+ dendritic fibroblasts showed predominantly myxo-collagenous differentiation with prominent myofibroblastic differentiation in only one desmin+ vaginal AMF. Our results support the notion that AMF and AA are part of a morphologic and histogenetic continuum of myxofibrous and myoid tumors that may arise due to interactions between microvascular CD34+ fibroblasts and FXIIIa+ histiocytes. CD34 and FXIIIa reactivity may be underappreciated in these tumors and is more important when considered histogenetically and biologically rather than in classifying individual neoplasms. Hormonal stimulation of proliferating pelvico-gential microvascular dendritic cells appears to play a role in the morphogenesis of both tumors.

Myoid differentiation in dermatofibrosarcoma protuberans and its fibrosarcomatous variant: clinicopathologic analysis of 5 cases.

We report a series of five cases of dermatofibrosarcoma protuberans, four of which were fibrosarcomatous and all of which showed histologic and immunohistochemical evidence of focal myoid/myofibroblastic differentiation (accounting for up to 5% of each tumor). These lesions were identified amongst 208 cases of dermatofibrosarcoma protuberans including 24 examples of the fibrosarcomatous variant. Three of the five patients were male and two were females; all were adults (37-72 years). One case arose on the scalp and two cases each on the abdominal wall and upper trunk. All tumors were less than 5cm in diameter and preoperative duration ranged from 2 months to 10 years. In three cases with follow-up there was no recurrence. Histologically, all tumors were typical fibrosarcomatous or ordinary dermatofibrosarcoma protuberans but for the presence of scattered to confluent nodules and bundles of eosinophilic spindle cells associated with well-defined cytoplasmic margins and vesicular nuclei associated with focal stromal hyalinization. While the typical dermatofibrosarcoma protuberans areas were CD34 positive, the myoid areas were negative for this antibody and positive for smooth muscle actin and pan-muscle actin. All tumors were desmin negative. Recognition of myofibroblastic differentiation in fibrosarcomatous dermatofibrosarcoma protuberans is important not only because it gives support to the theory of a fibroblastic/myofibroblastic line of differentiation for this type of tumor, but also because it might be a source of confusion with other myofibroblastic lesions (e.g. myofibromatosis, adult myofibroma), especially when small biopsies are evaluated.

Angiomyofibroblastoma of the vulva: A clinicopathologic study of seven cases

A clinicopathologic and immunohistochemical review was made of seven cases of angiomyofibroblastoma. The patients were middle-aged women who had a slowly growing mass, measuring 1.5-6 cm in maximum dimension, located subcutaneously in the vulva. The tumors were well-demarcated and characterized by well-vascularized, alternating hypercellular and hypocellular edematous areas composed of bland, plump spindle- or oval-shaped stromal cells frequently aggregated around small blood vessels. An epithelioid appearance of the stromal cells was seen in two cases. Immunohistochemically, the stromal cells were consistently positive for vimentin and desmin, but negative for muscle specific actin, alpha-smooth muscle actin, myosin, cytokeratins, S-100 protein or von Willebrand factor. Ultrastructurally, the plump stromal cells had a small amount of peripherally located rough endoplasmic reticulum, numerous pinocytotic vesicles and abundant intermediate filaments, on which immunogold probes for desmin were localized, whereas fine filaments were few and there were no electron dense plaques. Thus, while the proliferating stromal cells expressed an immunohistochemical profile of peculiar myoid differentiation, ultrastructural findings differed from those of smooth muscle cells or those seen in typical myofibroblasts. At 1-4 years after surgery, there was no evidence of recurrence.

Immunohistochemical identification and characterization of a special type of desmin-producing stromal cells in human placenta and other fetal tissues

Abstract An unusual type of stromal cells has been found to be abundantly present in chorionic villi of human placenta of gestational weeks 6, 17, 35–42 and in tissues of early stages of fetal development (gestational weeks 16–21). These mesenchymal cells are loosely arranged throughout the villous interior and contain the intermediate filament (IF) proteins vimentin and desmin; however the smooth muscle (sm) markers sm-α-actin and sm-myosin are absent. Typical myoid stromal cells that are positive for both desmin and sm-α-actin also occur in this tissue but are restricted to certain dispersed cell clusters associated with blood vessels. Similar disperse desmin-positive, sm-α-actin-negative stromal cells have also been identified, although more sparsely, in the chorionic plate of the placenta and in other diverse fetal tissues such as the interstitium of the kidney, of testis and epididymis, and in cells surrounding Hassall bodies of thymus. The biological nature of these desmin-containing but sm-α-actin-negative stromal cells is discussed in relation to myoid cell differentiation. It is emphasized that despite their synthesis of considerable amounts of desmin they cannot be considered myogenic as the occurrence of desmin in the cells may represent an isolated expression of an individual IF protein gene, independent of the synthesis of other muscle proteins.

Haemangiopericytoma — A dying breed? Reappraisal of an ‘entity’ and its variants: a hypothesis

Haemangiopericytoma has been generally accepted for half a century as a distinctive histological type of soft tissue tumour. However, it has become apparent that many other types of tumour may closely mimic haemangiopericytoma, and that haemangiopericytoma itself shows, at best, only a limited morphological relationship to normal pericytes. Therefore this entire diagnostic concept has become controversial and requires reassessment: in particular there are no positive criteria by which to make this diagnosis, thereby bringing into doubt its very existence. With regard to the distinctive clinical and topographic subsets of haemangiopericytoma, there is good evidence that the infantile (or congenital) type represents the same entity as infantile myofibromatosis; the sinonasal type, which is almost always benign, appears to show evidence of myoid differentiation in some cases and may be more closely related to glomus tumour; the meningeal type, which was formerly misclassified as angioblastic meningioma, remains as difficult to categorise as the minority of soft tissue haemangiopericytomas which present in adulthood and which cannot easily be allocated to alternative diagnostic categories with more reproducible features.

Aggressive angiomyxoma of the pelvioperineal region. Immunohistological and ultrastructural study of seven cases.

We describe seven cases of aggressive angiomyxoma of the pelvioperineal region. In three cases, we observed immunohistochemical signs of myoid differentiation in the tumor cells. In one of these cases, we could confirm the myoid differentiation at the ultrastructural level. The other four cases were devoid of this differentiation. We further discuss the relationship of aggressive angiomyxoma to the recently described angiomyofibroblastoma of the vulva.

Ectopic cervical hamartomatous thymoma showing extensive myoid differentiation

Ectopic 'hamartomatous' thymoma is a rare benign neoplasm. These tumours are found in the neck and are thought to be part of a spectrum of ectopic cervical thymic neoplasia. The clinical and histological features are discussed and the literature is reviewed. An attempt is made to explain in embryological terms why such lesions appear to occur more commonly on the left side.

The mammalian anti-α-smooth muscle actin monoclonal antibody recognizes an α-actin-like protein in planaria ( Dugesia lugubris s.l.)

Abstract The presence of an α-smooth muscle (α-sm) actin-like protein in planaria ( Dugesia lugubris s.l.) is reported. The protein shows a 42 kDa molecular weight determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis and is specifically recognized by the mammalian anti α-sm actin monoclonal antibody. When a planarian is induced to regenerate by head amputation, the immunostaining of the α-sm actin-like molecule becomes important in the area of growing blastema, reaching a maximum between 70–120 hours after injury. Conventional electron microscopy at the 4-day-regeneration stage shows that blastema-forming cells are a homogeneous population whose morphological features resemble those of migrating mesenchyme-like cells; only the myoblasts show a recognizable phenotype. The immunocytochemical localization of α-sm actin-like molecule by immunoperoxidase (light microscopy) and immunogold stains (electron microscopy) was carried out on both intact and injured worms. The antigen was localized mainly at the basal portion of the epidermal cells and in the un differentiated mesenchyme-like cells. Myoblasts, but not differentiated myofibers, were also labelled by this antibody. The results indicate that in the lower Eumetazoan planarians, as well as in vertebrates, the α-sm actin can be considered to be a marker for myoid differentiation. The suggestion that α-sm actin can be used as a marker for mesenchyme-like cells in vertebrates and in invertebrates is also discussed.

Neuromyoblastoma in the rat

We report three tumours arising in the brain stem or adjacent cranial nerves of the Alderley Park rat. Light microscopy with special stains, immunocytochemistry and electron microscopy supported the conclusion that both neuronal and myoid differentiation occurred in all neoplasms. This was shown by the presence in neural cells of axon-like cell processes and in myoblastic cells of striated myofibrils. Although medulloblastomas occur in man and rats the tumours reported here were not related to the cerebellum. We have termed this tumour neuromyoblastoma.

Fibroepithelial polyps of the vagina: are they old granulation tissue polyps?

To study the nature of fibroepithelial polyps of the vagina. Sixty five fibroepithelial polyps of the vagina and 64 granulation tissue polyps diagnosed over 15 years were reviewed histologically. Cytologically benign multinucleated stromal cells were present in large numbers in 19 of the fibroepithelial polyps of the vagina (FEPV). Only one polyp contained atypical stromal cells, a high mitotic count, and abnormal mitoses and was indistinguishable from a malignant tumour. Immunostaining showed the presence of vimentin and desmin positive mono- and multinucleated stromal cells in FEPV and occasional oestrogen receptor positive nuclei. Desmin positive cells could not be shown in granulation tissue polyps. FEPV are common lesions with benign mono- and multinucleated fibroblastic stromal cells in which myoid differentiation is often present. FEPV may develop as a result of a granulation tissue reaction after some local injury of the vaginal mucosa. Hormonal factors may modulate the growth of FEPVs. Delayed differentiation of myofibroblastic cells may explain why granulation tissue sometimes does not contract properly but turns into polyps.

Cell‐Cell Interactions and the Regulation of Testis Function

Regulatory interactions have been shown to occur between all the testicular cell types considered. The paracrine factors mediating these interactions generally influence either cellular growth or differentiation. The regulation of cellular growth is essential in the developing testis and is required for the maintenance of spermatogenesis in the adult testis. The rapid rate of germinal cell proliferation and the continuous but slowed growth of the peritubular cells and Leydig cells requires the presence of specific growth factors in the adult. Therefore, cell-cell interactions have evolved that involve growth factors such as IGF, TGF-alpha, TGF-beta and NGF. Other growth factors such as FGF or less characterized components like the seminiferous growth factor (SGF) also may be involved in the paracrine regulation of testis cell growth. An alternate cellular parameter to cell growth to consider is the regulation of cellular function and differentiation. A number of endocrine agents and locally produced paracrine factors have been shown to control and maintain testis cell function and differentiation. Cell-cell interactions mediated by factors such as androgens, POMC peptides, and PModS are all primarily directed at the regulation of cellular differentiation. Therefore, the agents which mediate cell-cell interactions in the testis can generally be categorized into factors that regulate cell growth or those which influence cellular differentiation. The specific cell-cell interactions identified will likely be the first of a large number of cellular interactions yet to be investigated. Although a number of potentially important cell-cell interactions have been identified, future research will require the elucidation of the in vivo physiological significance of these interactions. The existence of different cell types and potential cell-cell interactions in a tissue implies that the actions of an endocrine agent on a tissue will not simply involve a single hormone and single cell. The endocrine regulation of testis function will have effects on cell-cell interactions and be affected by local cell-cell interactions. The ability of LH to influence Leydig cell androgen production promotes a cascade of interactions mediated through several cell types to maintain the process of spermatogenesis. FSH actions on Sertoli cells also promote cell-cell interactions that influence germinal cell development, peritubular myoid cell differentiation and Leydig cell function. Therefore, elucidation of the endocrine regulation of testis function requires an understanding of the local cell-cell interactions in the testis.

Angiomatoid “malignant fibrous histiocytoma”: An immunohistochemical study indicative of myoid differentiation

Six cases of angiomatoid malignant fibrous histiocytoma (MFH), the rarest subtype of MFH, have been studied immunohistochemically using a broad panel of commercially available antisera in formalin-fixed, paraffin-embedded tissue in an attempt to define the pattern of differentiation shown by this unusual tumor. As has been reported in the more common types of MFH, no evidence of histiocytic differentiation was found. However, five cases strongly expressed desmin (DER-11) and two also expressed muscle actin (HHF 35). All tissues examined were negative for myoglobin and α-smooth muscle actin. These results provide good evidence for some sort of myogenic or possibly myofibroblastic differentiation in angiomatoid MFH. Given its clinicopathologically and immunohistochemically distinctive features, which are very different from the other variants of MFH, redesignation of angiomatoid MFH as a low-grade myogenic sarcoma of uncertain histogenesis is tentatively proposed. The new term angiomatoid myosarcoma is suggested.

Cytokeratin-immunoreactive cells of human lymph nodes and spleen in normal and pathological conditions

The occurrence and the distribution of cytokeratin (CK)-immunoreactive reticulum cells in a series of normal and pathological human lymph nodes and spleens are documented. The immunoreactive cells exhibit morphological and immunophenotypic features of so-called fibroblastic reticulum cells, with or without myoid differentiation. They invariably co-express vimentin and, to a lesser extent, desmin and muscle-specific actin isoforms. These CK-immunoreactive cells are apparently a normal subpopulation of reticulum cells, being detectable from the early stages of spleen and lymph node development. They are distributed mainly in the paracortical and medullary regions of the lymph nodes and at the periphery of the white pulp in the spleen. Their number and distribution are highly variable in different neoplastic and non-neoplastic pathological conditions but the changes are not disease specific. CK-immunoreactive reticulum cells are easily identifiable in both frozen and fixed lymphoid tissue and in cytological smears of fine-needle aspirates, provided that monoclonal antibodies whose spectrum of reactivity includes cytokeratins 8 and 18 are used. The awareness of the occurrence of CK-immunoreactive cells in normal lymphoid tissues is of particular relevance in the search for micrometastatic foci using anti-CK antibodies.