Myofibroblastoma of the meninges

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; im-munostaining 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.

Intracranial Cystic Myofibroblastoma: a Case Report with Literature Review

BACKGROUND

Myofibroblastoma is a rare benign soft tissue tumor comprised of contractile myiod cells mostly in mammary gland. Only 4 prior cases arising in the central nervous system have been reported in the literature. We present a case of myofibroblastoma with a cystic component.

CASE DESCRIPTION

The patient is a 76-year-old man with a history of Parkinson disease. The tumor was found incidentally after a minor fall. Magnetic resonance imaging revealed a 6.7-cm well-circumscribed, partly cystic mass with a 2.4-cm calcified central nodule located at the left sylvian fissure. The frontal dural base showed avid enhancing after gadolinium injection. Gross total resection was achieved. The tumor was marked by dense collagenous tissue and bland spindled cells in pathology review. The spindled cells demonstrated positive staining with antibodies to CD34, estrogen receptor, and smooth muscle actin. A blush of immunoreactivity is observed in scattered cells with antibody to progesterone receptor. Patient recovered well postoperatively.

CONCLUSIONS

This is a rare condition of a benign soft tissue tumor of mammary gland presented primarily in the brain. The literature on myofibroblastomas arising in the central nervous system is reviewed.

‘Sclerosing’ Perineurioma: A Tumor Variant?

We describe two examples of soft tissue perineurioma, a hard tumor, 1.7 cm in diameter, involving the dermis and superficial subcutaneous tissue of the left thumb, and the other a massive, lobulated lesion of the pelvis. Both occurred in 49-year-old men. Both were mobile and well demarcated but unencapsulated. Their cut surfaces were white and collagenous. Microscopically, each consisted of spindle-shaped or epithelioid tumor cells in a dense stroma of haphazardly oriented collagen bundles. Spindle-shaped cells were individually distributed, whereas epithelioid cells were often arranged in cords or clusters. Cytologic atypia was conspicuous in the massive tumor, but no mitotic activity was observed. Immunostains showed diffuse reactivity for vimentin, membrane pattern staining for epithelial membrane antigen and type IV collagen, as well as patchy CD34 reactivity. Stains for S-100 protein, Leu-7, smooth muscle actin, desmin, and cytokeratin were negative. Ultrastructural studies showed perineurial cell characteristics, including slender cytoplasmic processes, numerous pinocytotic vesicles, occasional tight junctions, and discontinuous surface basement membrane. Perineuriomas featuring marked stromal sclerosis often occur in the hands of young adults, as has recently been reported; the authors considered it a clinicopathologic variant. Herein we report two sclerotic perineuriomas, one a small tumor of the thumb and the other a centrally situated, massive pelvic tumor with sclerosis and degenerative cytologic atypia. We believe that exaggerated collagen deposition in perineuriomas, occasionally associated with degenerative nuclear changes, is not a manifestation of a unique, clinically relevant tumor variant but rather a manifestation of chronicity akin to that seen in “ancient schwannoma” and ‘atypical neurofibroma.’

Meningeal myofibroblastoma in the frontal lobe: A case report

Myofibroblastoma is a benign tumor composed of spindle cells in clusters and fascicles. To date, only three cases of intracranial myofibroblastoma have been reported. The present study reports the case of a 47-year-old female with meningeal myofibroblastoma. The patient had a history of ovarian cyst resection and presented with paroxysmal mild headaches that had been apparent for 4 years. Magnetic resonance imaging disclosed a well-circumscribed mass in the left frontal lobe. A resection of the mass was performed. Abundant fascicular clusters of spindle- and oval-shaped cells were found by conventional histopathology. Immunohistochemical staining demonstrated that these cells were strongly positive for smooth muscle actin, weakly positive for epithelial membrane antigen and negative for cluster of differentiation (CD)117, CD34, S-100 or desmin, with a Ki-67 index of >10%. These results supported the diagnosis of myofibroblastoma. No recurrence of the mass was found during the 24-month follow-up period. Overall, the patient exhibited a rare type of meningeal neoplasm. Resection of the tumor proved to be successful and no recurrence were found. Histopathological and immunohistochemical staining is crucial to form a diagnosis. To the best of our knowledge, the present study is the first to show the presence of myofibroblastoma in the left frontal lobe.

Myofibroblastic sarcoma in meningioma: a new variant of "metaplastic" meningioma

The authors describe a mixed malignant dural tumor composed of meningioma and myofibroblastic sarcoma (MFS). The meningioma component displayed epithelial membrane immunoreactivity and interdigitating cellular processes with desmosomal junctions on electron microscopy. MFS cells were immunoreactive for smooth muscle actin and vimentin, and focally for factor XIIIa, CD31, CD34, and Ulex europeus lectin receptors. Electron microscopy showed collections of intermediate filaments, stress fibers, subsarcolemmal densities of microfilaments, occasional fibronexus fibrils, few pinocytic vesicles, and discontinuous external lamina. After gross total removal, the tumor recurred 1 year later as aggressive MFS only. Development of MFS in continuity with meningioma suggests induction of MFS by meningioma or a divergent differentiation of precursor of the neoplastic arachnoid cell.

Infantile myofibromatosis of the central nervous system

BACKGROUND

Infantile myofibromatosis is the most common fibrous disorder of infancy and childhood. It may occur in two distinct forms: multicentric and solitary. In both cases involvement of the central nervous system (CNS) is unusual: brain myofibromas are usually intracranial in proximity of the dura mater, with infiltration of the calvarial bones and secondary brain compression. Spine myofibromas are exceptional and most of the cases reported in the literature represent secondary locations of visceral lesions. The natural history of myofibromas of the CNS in infantile myofibromatosis is characterized by a period of rapid growth, subsequent stabilization, and spontaneous regression in many cases. On these grounds surgical treatment is reserved for lesions that compress the brain or spinal cord and show an obvious progression. Small lesions or tumor residuals in asymptomatic children without visceral involvement should be closely observed as first choice.

CASE REPORT

We report the case of a 10-month-old child with a solitary intramedullary myofibroma, extended from C7 to the conus. The patient underwent partial surgical removal of this lesion. Control MRI has shown the spontaneous slow reduction of the tumor residual and a progressive improvement of preoperative neurological conditions has been observed. To our knowledge this is the first case in which a solitary myofibroma was localized within the spinal cord.

Myofibroblastoma in the suprasellar region. Case report

Myofibroblastoma is a rare type of benign mesenchymal tumor; only two cases of intracranial myofibroblastoma have been reported in the literature. The authors report on the case of a 34-year-old woman with a myofibroblastoma in the suprasellar region who presented with the complaint of sudden onset of headache followed within 2 weeks by progressively worsening visual disturbance. Computerized tomography scanning demonstrated a mixed low- and high-density mass in the suprasellar region and contrast-enhanced magnetic resonance imaging revealed the mass to be of mixed intensity with heterogeneous enhancement. The tumor was subtotally removed via a right frontobasal translamina-terminalis approach and her vision improved immediately. Histologically, the tumor was characterized by alternating areas of spindle-shaped and round cells that were separated by collagen fibers. The diagnosis of myofibroblastoma was based on the tumor's intense immunoreactivity for alpha-smooth-muscle actin and the ultrastructural identification of myofibroblasts. The tumor was thought to have originated from the meninges in the suprasellar region.

Myofibromas presenting in the oral cavity: a series of 9 cases

OBJECTIVES

Solitary myofibromas are well described in the head and neck, but oral examples are less well known, and jaw lesions are rare. We studied the clinicopathologic features of a series of such lesions.

DESIGN

Nine cases of oral myofibromas were retrieved from archives and studied.

RESULTS

Two cases involved the mandible (intraosseous), 3 involved the gingiva, 2 involved the tongue, and 2, the hard palate. There were 4 men and 5 women, aged 9 months to 50 years (mean, 24 years; median, 27 years). Deep lesions showed typical histology, with paucicellular lobules and intervening hemangiopericytoma-like zones. In ulcerated submucosal lesions, these features blended superficially with cellular fascicles. The tumors expressed smooth muscle actin but lacked desmin and S100 protein. None of the tumors recurred or metastasized.

CONCLUSION

Myofibromas appear in osseous, intramuscular, and submucosal aspects of the oral cavity. Ulceration imparts a fascicular appearance that makes superficial biopsy specimens difficult to interpret.

Myofibroblastic tumours: neoplasias with divergent behaviour. Ultrastructural and flow cytometric analysis

Myofibroblasts are spindle cells having ultrastructural features in common with smooth muscle cells and fibroblasts. In the last few years, tumours have been described in which myofibroblasts represent not only a reactive mechanism but also a true neoplastic component. They constitute new nosologic entities which might be termed "myofibroblastic tumours". Tumours with benign and, rarely, malignant behaviour are reported to belong to this group of lesions. Recently, a third tumour type with borderline biological course, named "inflammatory myofibroblastic tumour" (IMT), has been identified, a condition that has been regarded as a benign and reactive disorder for a long time. Only in recent reports has been demonstrated that, in spite of an apparently benign morphological pattern, some cases of IMT have a malignant course. In this connection, DNA analysis by flow cytometry is a valuable diagnostic tool, because it allows identification of the ploidy status, a procedure that is often useful for predicting the nature and the biological behaviour of the lesion. In this study, 11 cases of myofibroblastic tumours were examined retrospectively by evaluating clinicopathological features and DNA ploidy status by flow cytometry. The diagnosis of myofibroblastic tumour was confirmed by performing histology, immunohistochemistry, and electron microscopy in all patients. In detail, these 11 cases were composed of 1 benign myofibroblastoma, 1 myofibrosarcoma and 9 IMTs. Among these myofibroblastic tumours, all those with local recurrence or distant metastases (one myofibrosarcoma and three IMT) showed an aneuploid cell population demonstrable by flow cytometric analysis, whereas the other cases with benign course (one benign myofibroblastoma and six IMT) exhibited an euploid DNA content. These data suggest the following: a) Besides the rare myofibroblastomas and myofibrosarcomas, IMTs represent a larger group of lesions with potentially different biological and clinical course. b) DNA flow cytometric analysis is a reliable tool that support histopathological examination in characterizing those cases of IMT that, though being malignant, mimic benign lesions. Consequently, it establishes the basis for a different therapeutic approach according to the euploid or aneuploid DNA content.

Spindle cell tumours of the breast: practical approach to diagnosis

Spindle cell tumours of the breast are uncommon and often present diagnostic challenges. The most important is the sarcomatoid/metaplastic carcinoma, which has monophasic and biphasic variants. Each of these groups presents special diagnostic difficulties. In the monophasic variant the mesenchymal component predominates and the epithelial element forms a minor component often detected only after immunohistochemical study. The spindle cell areas may be bland and therefore under-diagnosed as nodular fasciitis or fibromatosis. Alternatively they may be highly malignant with a pattern that is misinterpreted as primary sarcoma of the breast. In the biphasic variant, the difficulty is in distinguishing between sarcomatoid carcinoma, myoepithelial carcinoma or malignant phyllodes tumour. Other spindle cell lesions of the breast include the various myofibroblastic tumours, the spindle cell variant of adenomyoepithelioma, the varied primary breast sarcomas, metastatic tumours with spindle cell morphology and, finally, the very rare follicular dendritic cell tumour. A simple practical approach to the diagnosis of spindle cell lesions is presented to help the general surgical pathologist to compile a differential diagnosis and to arrive at the correct conclusion

Intranodal palisaded myofibroblastoma with so-called amianthoid fibers: a report of two cases with a review of the literature

Two cases of intranodal myofibroblastoma, a rare primary spindle cell tumor of the lymph node, are described. The tumors arose in the inguinal or proximal region of the thigh of one middle-aged and one elderly Japanese male. The tumors were well-demarcated and composed of a fascicular proliferation of spindle cells with focal nuclear palisading and acellular stellate-shaped collagen-rich areas (so-called amianthoid fibers), and were associated with hemorrhagic areas. Immunohistochemically, the tumor cells were positive for vimentin and muscle actin. Together with ultrastructural findings of intracytoplasmic microfilaments with focal densities and profiles of well-developed, rough endoplasmic reticulum, these features reinforced the conclusion of myofibroblastic or smooth muscle differentiation of the tumor cells. One of the tumors was analyzed by flow cytometry and was shown to be DNA diploid. The present report provides clinicopathological findings of the first two Japanese cases of intranodal myofibroblastoma.

Sclerosing perineurioma: a clinicopathologic study of 19 cases of a distinctive soft tissue lesion with a predilection for the fingers and palms of young adults

This report describes 19 cases of a distinctive sclerosing perineurial tumor of the hands. Fourteen patients were male and five were female (age range 9-55 years; median age 24.5 years). The process typically presented as a painless mass and was present from 6 months to 40 years before resection. Sites of involvement were the thumb (n = 6); index (n = 3), middle (n = 4), and ring (n = 4) fingers; and the palm (n = 2). The lesions were generally well marginated but nonencapsulated. They had a firm, fibrous consistency and ranged in size from 0.7 to 3.3 cm in maximum dimension. Microscopic examination showed abundant dense collagen and variable numbers of small, epithelioid, and spindled cells exhibiting corded, trabecular, and whorled (onion bulblike) growth patterns. Immunoreactivity was present for epithelial membrane antigen (15 of 15); a cytokeratin cocktail containing AE1, AE3, and CK1 (four of 14); CAM 5.2 (one of 12); vimentin (12 of 12); muscle-specific actin (nine of 14); alpha-smooth muscle actin (six of 14); collagen IV (six of six); laminin (five of six); and CD99 (three of five). Ultrastructural features consistent with perineurial cells were noted. All of the lesions were locally excised. Follow-up was obtained for seven patients, with mean and median follow-up intervals of 12 years 7 months and 10 years 6 months, respectively. None of the lesions have recurred. This study advances the morphologic spectrum of perineurioma, a rare tumor of nerve sheath derivation. Familiarity with this distinctive subtype should help to avoid confusion with other processes, including a fibroma of tendon sheath, the sclerotic fibroma associated with Cowden's disease, an epithelioid neurofibroma, a late stage of tenosynovial giant cell tumor, and sclerosing adnexal tumors.

Solitary fibrous tumor of the meninges. Case report and review of the literature

The authors present the case of a left frontal solitary fibrous tumor of the meninges. The gross appearance of the tumor was very similar to that of a fibroblastic meningioma. Histological examination showed a mixture of spindle-shaped and round cells arranged in a collagen matrix. Immunohistochemical staining of the tumor demonstrated diffuse positive staining for CD34 and vimentin. The tumor displayed no positive staining for markers of muscle, epithelial, glial, or neurocrest differentiation or for estrogen and progesterone receptors. The MIB-1 labeling index (the percentage of positive staining tumor cell nuclei), a marker of cellular proliferation, was 1.1%. Ultrastructural studies support attributing a mesenchymal, rather than meningothelial, nature to the tumor. A differential diagnosis is discussed and a review of the literature on these rare tumors is presented.

Soft-tissue perineurioma. Evidence for an abnormality of chromosome 22, criteria for diagnosis, and review of the literature

Reported herein are two examples of soft-tissue perineurioma (STP), one arising in the maxillary sinus and the other in subcutaneous tissue of the thigh. Electron microscopy and immunohistochemistry were performed in both cases. Based on our findings and a critical review of the literature, STPs are generally small, well-circumscribed but not encapsulated tumors. Histologically, most STPs resemble fibroblastic tumors, being composed of elongated, wavy cells. The immunohistochemical reactivity for epithelial membrane antigen, the lack of reactivity for S-100 protein, and the presence of ultrastructural features of perineurial cells are typical of this tumor. To explore the possibility that STP, like the intraneural variety of perineurioma, exhibits an abnormality of chromosome 22, we performed fluorescence in situ hybridization with a probe specific for the M-bcr locus, which maps to the chromosome band 22q11. In both our tumors, a high percentage of nuclei having only one M-bcr signal (44 and 96%) was observed. Our findings indicated deletion of part or all of chromosome 22 and support the view that both soft-tissue and intraneural perineurioma are part of a spectrum of perineurial neoplasia.

Myofibroblastic tumor of soft tissue displaying desmin-positive and actin-negative immunophenotypes

Myofibroblasts have ultrastructural and functional characteristics intermediate between fibroblasts and smooth muscle cells. Previous studies indicated that most myofibroblasts express actin and vimentin but not desmin immunophenotypes. Two benign intramuscular myofibroblastic tumors which displayed a desmin-positive and actin-negative immunophenotype are reported. The tumors occurred on the back of a 45 year old man who had neurofibromatosis 1 and the thigh of a 37 year old man without neurofibromatosis. Both tumors were encapsulated and composed of short intersecting bundles of spindle cells in a collagenous background. Although the tumors were cellular, nuclear pleomorphism was minimal and mitotic figures were rare. Characteristically, most tumor cells were immunoreactive strongly for desmin and vimentin but gave negative staining for muscle-specific actin, alpha-smooth muscle actin, alpha-sarcomeric actin, myosin, S-100 protein, cytokeratins, and CD34. On electron microscopy, the tumor cells were characterized by short spindle-indented nuclei, abundant cytoplasmic intermediate filaments, prominent plasmalemmal pinocytosis and frequent cell coverage by basal lamina. Aggregation of thin myofilaments with focal condensations was identified occasionally. Although the tumors showed distinct morphological and immunohistochemical features enabling delimitation from other soft tissue lesions, they may overlap histologically with myofibroblastoma of the breast, lymph node and soft tissue, low grade malignant nerve sheath tumor, leiomyosarcoma, cellular schwannoma, inflammatory fibrosarcoma and nodular fasciitis.

Ultrastructural study of a perineurioma with ribosome-lamella complexes

The participation of the perineurial cell in peripheral nerve tumors is the subject of much debate. The case of a 75-year-old female with a soft tissue tumor on her left shoulder is presented. The tumor had histological, ultrastructural, and immunohistochemical characteristics of a pure perineurial cell neoplasm. Ultrastructurally, distinctive ribosome-lamella complexes were found in the cytoplasm of the perineurial cells. This may be the first time that these structures have been described in perineurioma.

Myofibroblastoma of the axilla

A mass in the axilla of a 47-year-old woman was biopsied and resected. The mass was composed of a loosely distributed population of spindle cells that were immunoreactive for smooth-muscle actin. Ultrastructurally, the cells possessed abundant endoplasmic reticulum, and some contained peripheral smooth muscle myofilaments, establishing that they were myofibroblasts. Mitotic activity was sparse, there was no cytologic atypia, and by flow cytometry the tumor was diploid with a low S phase. A diagnosis of myofibroblastoma was favored, although the possibility of a low-grade sarcoma could not be excluded. There has not been any indication of recurrence over a 4-month period of follow-up.

Perineurioma (storiform perineurial fibroma): clinico-pathological analysis of four cases

Four cases of perineurioma (storiform perineurial fibroma) arising in the dermis, subcutis, or deep soft tissue have been studied. Two patients were female and two were male with ages ranging from 19 to 45 years. One lesion each arose on the chest wall, shoulder, neck, and elbow. Follow-up information in three patients revealed no recurrence. Histologically, the neoplasms were circumscribed but non-encapsulated lesions and were composed of spindle cells with elongated bipolar cytoplasmic processes, inconspicuous fusiform nuclei and well-defined palely eosinophilic cytoplasm. These cells were arranged in whorls or lamellar-like structures and often demonstrated a storiform growth pattern. In areas, the tumour cells appeared larger with more rounded nuclei. Immunohistochemically, most of the tumour cells stained positive for epithelial membrane antigen and vimentin, but failed to stain for S-100 protein, neurofilament, desmoplakin, and CD34. Ultrastructurally, two cases showed fusiform tumour cells with long, thin cell processes separated by abundant collagen bundles. Tumour cells were covered by discontinuous external lamina, showed many pinocytic vesicles and occasionally desmosome-like structures. The morphology and EMA immunopositivity of perineurioma are similar to meningioma, especially to cutaneous meningioma type II. We believe that perineurioma and meningioma are closely related, but morphologically distinguishable, neoplasms.

Brief review of the fibronexus and its significance for myofibroblastic differentiation and tumor diagnosis

This brief review details the structure, nature, and distribution of the fibronexus, and discusses its significance for myofibroblastic differentiation and tumor diagnosis. The fibronexus is a cell surface specialization consisting of intracellular actin filaments and extracellular fibronectin filaments associated with subplasmalemmal plaque material. The fibronexus represents an intercellular junction between myofibroblasts, but in particular is a device for providing contact between myofibroblasts and matrix that mediates continuity between intracellular contractile filaments and extracellular matrix proteins. Immunoelectron microscopy in particular has shown that the intracellular filaments contain actin. The extracellular filaments contain fibronectin and collectively form the fibronectin fibril. The plaque probably contains such proteins as vinculin, talin, alpha-actinin, and integrin. Under appropriate biologic development and fixation conditions, the fibronectin fibril of the fibronexus is characterized by and distinguished from lamina by enhanced density, a rigid appearance, failure to adhere closely to the contours of the cell surface (except focally near the plaque material), and a longitudinally filamentous substructure. Confirmation of the presence of a fibronectin fibril may be obtained by the finding of intense cell surface staining with an antifibronectin antibody. Problems in identifying the fibronexus may be encountered, however, due to poor development and fixation, in which case the filamentous substructure may be inapparent. The fibronexus is such a typical feature of and is often so conspicuous in myofibroblasts that it can be regarded as perhaps essential for the interpretation of myofibroblastic differentiation. Structures with a similar appearance have been documented in fundamentally nonmyofibroblastic cells; these include aortic and scleral spur smooth muscle cells and endothelium. Uncertainties remain in the protein composition of the fibronexus, the nature of its contact with the matrix, and its relationship to similar structures seen in nonmyofibroblastic cells. Immunoelectron microscopy provides a potential means of clarifying some of these questions.

Sclerosing fibrous tumor of the cauda equina: a fibroblastic variant of peripheral nerve tumors?

The case of a 43-year-old man with an unusual mesenchymal tumor of the cauda equina is presented. A well-circumscribed firm tumor was found in the lower spinal canal at L1 level. Although a nerve root was involved, the adjacent dura mater or filum terminale was unrelated to the tumor. Microscopically, the tumor was rich in collagen and made up of irregularly intertwining fascicles of fibroblastic spindle cells lacking in nuclear atypia or mitotic activity. Partial broad hyalinization of collagen was another histological feature of the tumor. Histological and immunohistochemical studies failed to reveal any findings that suggested known fibrous neoplasms, such as schwannoma, neurofibroma and meningioma, originating in the nervous system. Ultrastructural features of the tumor cells were consistent with those of fibroblasts. Hence, the present tumor is regarded as a unique pure fibroblastic tumor (fibroma) derived from the interstitium of a nerve root in the cauda equina.

Plexiform soft tissue tumor composed predominantly of perineurial fibroblasts (perineurioma)

A 15-year-old girl presented with a small, indolent mass near the knee joint. Light microscopy revealed a peculiar myxoid plexiform tumor composed of cytologically bland cells. Interpretation of the initial biopsy material was controversial. Subsequent immunohistochemical studies revealed tumor cells to be strongly reactive for epithelial membrane antigen (EMA) and negative for S-100 protein. Ultrastructural studies revealed tumor cells with long, thin, bipolar cell processes and discontinuous basal laminae. They had no epithelial or histiocytoid features. Admixed among the tumor cells were Schwann cells, but they represented a rare and scattered component of the overall cell population. These features are most consistent with a so-called perineurioma and contrast with those of plexiform neurofibroma and traumatic neuroma (two lesions strongly positive for S-100 protein and showing a distinctive EMA immunoreactivity pattern with focal peripheral staining of neural bundles).

A study of spindle cell sarcomas showing myofibroblastic differentiation

Five diagnostically problematic spindle cell sarcomas showing invasive character, cellular pleomorphism, and high mitotic rate were studied clinically and histopathologically by conventional light microscopy, immunohistochemistry, and transmission electron microscopy. They showed varied clinical courses, with two causing death within 5 years and three showing recurrent and metastatic behavior. All lacked a clearly defined line of differentiation by conventional light microscopy. By immunohistochemistry, all were positive for vimentin and alpha-smooth muscle actin; in addition, one showed focal S-100 protein positivity, and one stained for desmin. All were cytokeratin negative. By electron microscopy, the great majority of spindle cells in all cases showed abundant rough endoplasmic reticulum and fine myofilaments with focal densities; collagen secretion granules were also found in all cases but in fewer cells. The fine structure and immunophenotype were considered consistent with myofibroblastic differentiation; these tumors, therefore, were designated as sarcomas of myofibroblasts or myofibrosarcomas. The suitability of the alternative diagnostic label of myofibroblastic or matrix-secreting variant of leiomyosarcoma is discussed. Comparisons with similar tumors documented in the literature are drawn.

Mesenchymal, non-meningothelial tumors of the central nervous system

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