Solitary myofibroma in adults: clinicopathological analysis of a series

Solitary myofibroma is a recently described, benign neoplasm of superficial soft tissue, which represents the adult counterpart of infantile myofibromatosis and is poorly recognized. Eleven new cases are presented herein. The patients were mostly adults with ages ranging from 13-64 years. They presented with a solitary, usually painless nodule of variable duration in the skin or oral cavity. Histologically, each lesion had a biphasic pattern with spindle cells forming fascicular or whorled areas and rounded, more primitive cells arranged around small vessels, forming haemangiopericytoma-like areas. The characteristic zonation of infantile myofibromatosis was often less marked in adult lesions and there was a haphazard arrangement of the fascicular and pericytic areas in some cases. Hyalinization, especially of the peripheral spindle-celled areas, was frequent. Immunohistochemically, the spindle cells were desmin negative but muscle actin (HHF-35 and IA4) positive. The rounded cells were both desmin and actin negative. Electronmicroscopy confirmed the myofibroblastic/fibroblastic nature of tumour cells in two cases. Although vascular invasion was seen in two cases, solitary adult-type myofibroma pursues a benign clinical course.

Artifactual distortion of cells simulating metastatic small cell carcinoma in the bone marrow

Artifactual distortion of hematopoietic elements in histologic preparations and smears of bone marrow aspirates simulating metastatic small cell carcinoma has been recently described. The clinical, pathologic, and immunohistochemical features in 12 such cases have been studied by us. In all these cases, bone marrow smears and histologic sections showed multiple small clusters of atypical, hyperchromatic cells suspicious for metastatic small cell carcinoma. Immunohistochemical stains showed focal positivity of the suspicious cells for leukocyte common antigen (LCA), anti-hemoglobin A (Hem A) and anti-erythrocyte membrane antigen (ERM), and negative staining for epithelial membrane antigen (EMA) and neuron specific enolase (NSE). Clinical follow-up of two years did not demonstrate any evidence of a primary small cell carcinoma in the lung or elsewhere. Comparison of these 12 cases with four cases of transbronchial biopsy-proven metastatic small cell carcinoma to the bone marrow showed that this artifact had a tendency to be located at the periphery of the marrow particles, unlike the true metastatic carcinoma cells which were predominantly found within the marrow particles and replacing the hematopoietic elements. The results of our immunohistochemical studies appear to indicate that these cells correspond to aggregated nuclei and cytoplasmic remnants from erythroid as well as myeloid and lymphoid cells. The main importance of identifying this artifact lies in avoiding confusion with metastatic small cell carcinoma, a distinction that may be very difficult to establish on morphologic grounds alone. Immunohistochemical stains and a thorough clinical follow-up are necessary for arriving at the correct diagnosis.

Acinic cell carcinoma of the lung ("Fechner tumor"). A clinicopathologic, immunohistochemical, and ultrastructural study of five cases

The clinical, pathological, immunohistochemical, and ultrastructural features in five cases of primary acinic cell carcinoma of the lung are presented. The patients' ages ranged from 44 to 75 years (mean, 56); four were women and one a man. The lesions were discovered incidentally on routine chest x-ray and ranged from 1.2 to 4 cm in greatest diameter. Three tumors were located in the right middle lobe, one in the right upper lobe, and one in the left upper lobe. In three cases, the lesions presented as asymptomatic subpleural nodules in proximity to secondary bronchi, one case presented as an endobronchial tumor that led to obstructive symptoms, and one case as a well-circumscribed deep parenchymal nodule. Histologically, the tumors were composed of clear cells with abundant granular cytoplasm growing as solid sheets with focal acinar, microcystic, and papillocystic areas. Immunohistochemical stains showed strong positivity of the tumor cells for low-molecular-weight cytokeratins and epithelial membrane antigen (EMA). Focal weak cytoplasmic positivity was observed in three cases with alpha-1-antichymotrypsin and in one case with amylase. Stains for vimentin, S-100 protein, chromogranin, and lysozyme were negative in all cases examined. Electron microscopy performed in four cases showed abundant zymogen-type cytoplasmic granules of variable electron density characteristic of acinar-type secretory cells. All patients were treated by lobectomy alone. Follow-up of 3 to 10 years in four cases revealed that all patients were alive and well, with no evidence of recurrence or metastases. Because of their relatively indolent behavior and favorable prognosis, primary acinic cell carcinoma of the lung must be distinguished from other primary and metastatic clear cell tumors of the lung.

Epithelioid and spindle-cell hemangioendothelioma of the spleen. Report of a distinctive splenic vascular neoplasm of childhood

A case of a distinctive vascular neoplasm of the spleen in a 3-year-old boy is described. The tumor was characterized histologically by a biphasic growth pattern, with discrete nodular areas composed of atypical round, epithelioid cells with large nuclei and prominent nucleoli, and areas showing an intricate proliferation of vascular channels lined by elongated spindle cells. Immunohistochemical studies showed cytoplasmic staining of the tumor cells with factor VIII-related antigen, Ulex europaeus lectin, and vimentin antibodies. Stains for keratin, actin, desmin, lysozyme, and S-100 protein were negative in the tumor cells. Electron microscopy revealed a fairly cohesive population of cells that contained mature and immature cell junctions, basal lamina material, and surface pinocytotic activity consistent with vascular endothelial cells. Five-year follow-up has shown the patient to be alive and free of disease. This case appears to represent a previously unreported primary vascular neoplasm of the spleen showing combined features of epithelioid and spindle-cell hemangioendothelioma. The lesion should be distinguished from other benign and malignant vascular proliferations of the spleen such as Kaposi's sarcoma, angiosarcoma, and the recently described littoral-cell angioma.

Large cell lymphoma of the mediastinum with marked tropism for germinal centers

The cases are presented of three patients with large cell malignant lymphoma of the mediastinum with a distinctive growth pattern characterized by marked tropism of tumor cells for germinal centers. The patients' ages ranged from 35 to 70 years; one was a woman, and two were men. Histologically, the lesions were characterized by a proliferation of large atypical cells arranged in clusters that encroached on mantle zones and invaded germinal centers. Immunohistochemical studies showed positive staining of the tumor cells for leukocyte common antigen, L-26 (pan-B-cell antigen), and lambda light chain restriction and negative staining with Leu-M1, UCHL-1 (pan-T-cell antigen), Ber-H2 (Ki-1 antigen), S-100 protein, HMB-45, low-molecular weight keratins, epithelial membrane antigen, carcinoembryonic antigen, and placental alkaline phosphatase. Electron microscopy done on one specimen showed cells with abundant cytoplasm, some of them containing surface microvilli, scant organelles, and scattered polyribosomes consistent with lymphoid cells. Because of their unusual growth pattern and morphology, these tumors can be mistaken for primary or metastatic carcinomas, germ cell tumors (particularly seminomas), and metastatic malignant melanomas. It is proposed that the "germinotropic" features observed in these lesions are the result of active colonization of germinal centers by the tumor cells. The possible pathogenetic implications of this phenomenon are discussed.

The spectrum of histologic growth patterns in benign and malignant fibrous tumors of the pleura

A review of the histologic growth patterns in 50 cases of benign and malignant fibrous tumors of the pleura (localized or solitary fibrous tumor, fibrous mesothelioma) is presented. Two major histologic growth patterns were observed admixed in various proportions: solid spindle and diffuse sclerosing. The solid spindle growth pattern assumed various configurations, including fascicular areas, storiform and herringbone formations, angiofibroma and hemangiopericytoma-like areas, synovial sarcoma-like areas, and neural-type palisading, thus simulating a variety of soft-tissue neoplasms. The diffuse sclerosing pattern, although rarely assuming a dominant role, was present in varying proportions in virtually all cases. In areas with extensive sclerosis, focal degeneration of collagen simulating tumor necrosis was often present. Other less frequently observed features were the formation of "amianthoid" fibers, multinucleated giant cells, and foci of metaplastic ossification. On ultrastructural and immunohistochemical examination, the tumor cells showed nondistinct features. Due to the extreme variability in morphologic appearances and the lack of distinctive ultrastructural or immunohistochemical characteristics, these tumors can pose a significant diagnostic problem. Familiarity with their histologic appearances and correlation with the gross findings and clinical setting are essential for arriving at the correct diagnosis.

Placental intravillous accumulation of sulfated mucosubstances. A reevaluation of so-called hydropic degeneration of villi

A histochemical study was performed on 46 placentas showing so-called hydropic degeneration of villi. The 46 cases included early abortuses (35 cases), incomplete moles (four cases), and complete hydatidiform moles (seven cases). All the specimens showed diffuse, positive staining of the distended villous stroma with alcian blue at pH 1.2 and 2.5 in the areas containing "hydropic changes." The alcian blue positivity was abolished following digestion with hyaluronidase. These findings indicate that so-called "hydropic degeneration of villi" represents an intravillous accumulation of strongly sulfated mucosubstances rather than the result of the accumulation of water. The intravillous accumulation of mucosubstances most likely represents a nonspecific stromal reaction of the connective tissue of the placenta to a variety of noxious stimuli. This finding may have some bearing on the interpretation of the physiologic mechanisms involved in placental villous distention, which has been largely centered in the past on the premise that the villous swelling was related to hemodynamic alterations caused by the accumulation of water.

Cystic thymomas. A clinicopathologic study of ten cases

Cystic degeneration in thymoma is a relatively frequent but focal event. In rare cases, the process proceeds to the extent that most or all of the lesion becomes cystic. The authors studied ten cases of thymoma undergoing cystic degeneration of such degree that the lesions initially were mistaken grossly and microscopically for nonneoplastic thymic cysts. The patients' ages ranged from 23 to 81 years, and the sex distribution was equal. The lesions were characterized by the formation of multiple large cystic cavities filled with clear, hemorrhagic or grumose material. Histologically, residual solid islands showing the characteristic features of thymoma, i.e., biphasic cell population (epithelial cells/lymphocytes), perivascular spaces, and areas of medullary differentiation, were present within the cyst walls. In contrast with nonneoplastic thymic cysts, the walls of the cavities generally were devoid of an epithelial lining; most of the cysts appeared to predominantly result from extreme dilatation and confluence of perivascular spaces. In some instances, the cystic degeneration of the tumor was accompanied by cystic changes of an inflammatory nature in the surrounding, nonneoplastic thymic tissue leading to firm adhesions and apparent infiltration of adjacent mediastinal structures. None of the lesions in the studied patients recurred during follow-up periods of from 2 to 10 years (average follow-up, 5 years). Cystic thymomas should be distinguished from nonneoplastic congenital and acquired thymic cysts and other primary thymic neoplasms undergoing extensive cystic degeneration. It is important not to misinterpret the apparent infiltration of surrounding mediastinal structures that results from the inflammatory changes that often accompany these tumors as evidence of aggressive or malignant behavior.

Myoepithelial differentiation in basal cell carcinoma

Five cases of basal cell carcinomas (BCC) of the skin are described showing morphologic and immunohistochemical features of myoepithelial differentiation. Histologically, they were characterized by a dermal proliferation of tumor cells connected with the epidermis by areas showing the features of conventional BCC, with the deeper portions of the lesion showing a population of oval to spindle cells with eccentric nuclei and homogeneous, ground-glass, or hyaline eosinophilic cytoplasm characteristic of the so-called hyaline cell of myoepithelial tumors of salivary glands. Additionally, scattered cells showing a signet ring configuration were present, and in two cases, focal areas displaying chondromyxoid elements were also seen that appeared to merge imperceptibly with the surrounding spindle cell population. By immunohistochemistry, the tumor cells in the spindle cell component showed strong, diffuse positivity for CAM 5.2 and muscle specific actin, and variable expression of keratin AE1/AE3, vimentin, glial fibrillary acidic protein, and S-100 protein, these findings being consistent with the immunostaining pattern of myoepithelial cells and their neoplasms. A brief review of the literature on the topic is presented, along with a discussion of the possible pathogenesis of this process.

Multilocular thymic cysts with pseudoepitheliomatous hyperplasia

Six cases are described of benign thymic cysts of the anterior mediastinum showing focal pseudoepitheliomatous hyperplasia of the lining epithelium. The patients' ages ranged from 11 to 54 years; five cysts occurred in males and one in a female. Histologically, the lesions were characterized by exuberant proliferation of the cyst lining epithelium that grew as sheets and tongues of atypical squamous cells with large, hyperchromatic nuclei, prominent nucleoli, and scattered mitotic figures. The walls of the cyst adjacent to the areas of epithelial proliferation showed abundant hemorrhage, necrosis, and severe inflammatory changes. All cases were treated by local surgical excision. There was no evidence of recurrence or metastases over a follow-up period of up to 8 years (average follow-up, 4 years). It is proposed that pseudoepitheliomatous hyperplasia may develop in thymic cysts as an expression of regeneration of the lining epithelium in response to the inflammatory, hemorrhagic, and necrotizing changes which often accompany these lesions. This should not be mistaken for malignancy, and should be distinguished from the exceptional cases of true thymic neoplasms seen in association with thymic cysts.

Syringomatous squamous tumors of the breast

Four cases are reported of syringomatous squamous tumors of the breast occurring in women aged 37 to 70 years. The lesions were characterized histologically by relatively well-circumscribed tumor-like nodules composed of a proliferation of teardrop or comma-shaped islands of squamous epithelium. The squamous epithelial islands contained central lumens lined by eosinophilic cuticles and were surrounded by a densely cellular fibrous matrix, thus closely resembling the growth pattern of dermal eccrine syringomas. The lesions appeared to arise de novo from breast parenchyma without evidence of transitions with the surrounding normal or hyperplastic mammary epithelium and were not associated with the overlying skin or nipple epidermis. In all cases, the surrounding breast tissue showed fibrocystic and benign proliferative changes, and in one case, the lesion was found in the vicinity of a large cyst surrounded by microcalcifications. All patients were treated by local surgical excision and have shown no evidence of recurrence over a follow-up period of 1 to 6 years. The histologic differential diagnosis and the possible pathogenesis of these lesions are discussed.

Primary thymic epithelial neoplasms in children

Primary epithelial neoplasms of the anterior mediastinum in children are very rare. We have studied 10 cases of thymic epithelial neoplasms in children aged 16 years or less and correlated their histologic features with the clinical outcome. The patients' ages ranged from one to 16 years (mean: 10.2); with a male:female ratio of 1.5:1. Nine patients had symptoms attributable to their tumors; one was asymptomatic. Four patients presented in clinical stage I, one in stage IIb, and five in stage IVb. Histologically, the tumors comprised a heterogenous group displaying a range of morphologic appearances: one tumor had the classic features of lymphocyte-rich thymoma of the adult; four were of the lymphocyte-rich type with associated unusual stromal features; two were spindle cell thymomas with cytologic and architectural atypia; and three displayed obvious cytologic features of malignancy (i.e., thymic carcinoma); two in the last group showed features of small cell carcinoma, and the other was an undifferentiated/anaplastic carcinoma. The epithelial nature of the tumors was supported in six cases by positive staining of the tumor cells with keratin antibodies and in two cases by electron microscopic demonstration of desmosomes and intracytoplasmic bundles of tonofilaments within the tumor cells. The prognosis for these patients correlated well with the degree of atypicality exhibited by the epithelial components; it was very poor in patients with small cell and undifferentiated/anaplastic carcinoma (8 months average survival), better for those with atypical spindle cell thymomas (multiple recurrences and metastases but no fatalities over a 15- to 72-month period), and best in those with lymphocyte-rich thymomas without cytologic atypia (no recurrences or metastases over an 8-month to 3-year follow-up).

Multilocular thymic cyst: an acquired reactive process. Study of 18 cases

The clinical and pathologic features in 18 cases of multilocular thymic cyst (MTC) of the anterior mediastinum unassociated with Hodgkin's disease or seminoma were studied. The majority of cases were asymptomatic and discovered incidentally on routine chest x-ray. Several patients presented with acute symptoms of chest pain or discomfort, sometimes associated with dyspnea. Two cases had an incidental thymoma, and two had an incidental thymic carcinoma. The main histologic features of MTC included the following: multiple cystic cavities partially lined by squamous, columnar, or cuboidal epithelium (some having features of Hassall's corpuscles); scattered nests and islands of non-neoplastic thymic tissue within the cyst walls, often continuous with the cyst lining; severe acute and chronic inflammation accompanied by fibrovascular proliferation, necrosis, hemorrhage, and cholesterol granuloma formation; and reactive lymphoid hyperplasia with prominent germinal centers. These features suggest that MTC most likely results from the cystic transformation of medullary duct epithelium-derived structures (including Hassall's corpuscles) induced by an acquired inflammatory process. The changes are similar to those sometimes seen in association with thymic Hodgkin's disease and thymic seminoma, which are also probably due to the inflammation that accompanies these tumors rather than to the tumors themselves. We believe that MTC is pathogenetically analogous to a variety of cystic conditions of the head and neck region, for which the common denominator seems to be the induction of cystic transformation in ductular epithelial formations of branchial pouch or related derivation by an acquired inflammatory process.

Thymic carcinoma. A clinicopathologic study of 60 cases

The clinicopathologic features of 60 patients with thymic carcinoma were studied. Patients ranged in age from 10 to 76 years (mean, 46), of whom 24 were females and 36 were males. Overall survival at 1, 3, and 5 years was 56.6%, 40%, and 33.3%, respectively. The following morphologic features were correlated with survival: type of tumor margins; presence or absence of a lobular growth pattern; nuclear atypia; necrosis; mitotic activity; and histologic tumor type and grade. Eighty eight percent of patients with poorly circumscribed/infiltrating neoplasms died of their tumors as compared with 16.6% of patients with well-circumscribed neoplasms (P less than 0.0000). Of patients whose tumors had mitotic counts exceeding 10/10 high-power fields (HPF), 84.3% died, as compared with 21.4% of patients with lower mitotic counts (P less than 0.0000). Of patients whose tumors showed lack of lobular growth pattern, 91.6% died, as compared with 29% of those whose tumors had a lobular growth pattern (P less than 0.0000). Finally, 84.6% of patients whose tumors displayed a high-grade histology (lymphoepithelioma-like carcinoma, small cell/neuroendocrine carcinoma, clear cell carcinoma, sarcomatid carcinoma, and anaplastic/undifferentiated carcinoma) died of tumor, as compared with 0% of patients whose tumors were of low-grade histology (well-differentiated squamous carcinoma, mucoepidermoid carcinoma, and basaloid carcinoma) (P less than 0.0000). Evaluation of the various treatment modalities used to treat these patients did not yield any statistically significant correlations with survival. Two clinically distinct groups of patients were identified: one after a relatively favorable clinical course with long survival, and one after a rapidly fatal outcome. The morphologic features of the tumors in these patients correlated well with their clinical behavior; histologic type (and the grade to which it was assigned) constituted the most reliable and important predictor of prognosis.

Benign mixed tumors (pleomorphic adenomas) of the breast

Six cases of benign mixed tumors of the female breast are described. The tumors were found in three settings: (a) as a de-novo lesion arising from breast parenchyma, (b) as single or multiple nodules arising in a background of benign proliferative epithelial elements, and (c) in association with breast carcinoma. The tumors ranged from 1 to 4 cm in diameter, and were histologically characterized by the admixture in various proportions of benign glandular epithelial and myoepithelial elements and cartilaginous or myxoid components. Immunohistochemical staining supported this interpretation. One of the cases was remarkable for the presence of abundant tyrosine-like crystals, a feature described in benign mixed tumors of salivary glands. None of the tumors has recurred during a follow-up period of 1-7 years. Mixed tumors of the breast are considered to be similar to their dermal and salivary gland counterparts.

Morphometric analysis of germinal centers in nonthymomatous patients with myasthenia gravis

A morphometric analysis of germinal centers (GCs) in the thymus of nonthymomatous patients with myasthenia gravis was performed in 26 patients, including 14 women and 12 men. The GCs were evaluated for number, diameter, perimeter, and cross-sectional area using a computerized interactive morphometric analysis. The GCs ranged from 2 to 19 per case, with an average diameter of 0.02 to 0.43 mm, a perimeter of 0.38 to 1.35 mm, and a cross-sectional area of 0.01 to 0.14 mm2. In thymic sections with fewer than five GCs, the GCs had a mean area of 0.05 mm2, a perimeter of 0.84 mm, and a diameter of 0.24 mm. In thymic sections containing five or more GCs, the GCs had a mean area of 0.04 mm2, a perimeter of 0.62 mm, and a diameter of 0.19 mm. The clinical improvement in these patients inversely correlated with the above parameters, with improvement being observed in patients whose GCs had a mean area of 0.02 mm2, a perimeter of 0.58 mm, and a diameter of 0.17 mm. No correlation was observed between the number of GCs and clinical improvement. The results of our study appear to indicate that computerized interactive morphometric analysis may represent a potentially useful method for the evaluation of the morphometric features of thymic GCs and their correlation with clinical outcome in patients with myasthenia gravis.

Deciduosis of the appendix

A clinicopathologic and immunohistochemical study of six cases of deciduosis of the appendix is presented. The patients were pregnant women aged 18-40 years. In four cases, the patients presented with signs and symptoms of acute appendicitis during their 26th to 31st week of pregnancy; in the other two, the lesions were discovered incidentally in appendectomy specimens obtained during cesarean section and tubal ligation at term. Histologically, the lesions were characterized by the presence of multiple, irregularly distributed submesothelial deposits of decidualized cells in the serosa of the appendix, without any associated evidence of endometriosis. By immunohistochemistry, the decidualized cells strongly labelled with vimentin antibodies, consistent with their stromal origin. In two cases, coexpression of vimentin and desmin intermediate filaments was observed, suggestive of myoid differentiation. The possible relationship of the lesions with the development of symptoms of peritoneal irritation in these patients is discussed along with a review of the literature on the abdominal complications of ectopic decidua.

Inflammatory fibroid polyp of the small intestine: ultrastructural and immunohistochemical observations

The ultrastructural and immunohistochemical features of a primary tumor of the ileum showing the classic histologic features of an inflammatory fibroid polyp (IFP) of the gastrointestinal tract are presented. Ultrastructurally the proliferating cells showed a combination of fibroblastic and histiocytic features, with abundant rough endoplasmic reticulum and active production of collagen in many of the cells and long, dendritic cytoplasmic projections with large cytoplasmic vacuoles containing remnants of phagocytosed cellular debris in others. Immunohistochemical studies showed strong cytoplasmic positivity in the proliferating cells with vimentin antibodies and scattered positivity with muramidase. Additional findings include the ultrastructural demonstration of oligocilia and occasional primitive intercellular junctions. The findings in this case suggest that IFP may represent a proliferation of primitive submucosal stromal cells exhibiting incomplete fibrohistiocytic differentiation.

Nongranulomatous involvement of the bone marrow in lepromatous leprosy

Bone marrow involvement in lepromatous leprosy has been characterized histologically by a proliferation of foamy histiocytes containing lepra bacilli, the so-called Virchow cells. The authors have studied three patients with biopsy-proven lepromatous leprosy in whom Fite stain, performed on histologic sections of bone marrow aspirates, demonstrated numerous bacilli lying free in the interstitium in the absence of Virchow cells or focal collections of foamy macrophages. Two of the patients had a recent diagnosis of lepromatous leprosy by skin biopsy; the third patient had a 33-year history of lepromatous leprosy that had been treated. Bone marrow aspirates were performed in all three patients for evaluation of anemia. The findings indicate that the bone marrow may act as a reservoir for viable organisms in the absence of a host response in treated and untreated patients with lepromatous leprosy. The persistence of viable organisms in the bone marrow in patients with lepromatous leprosy may account for the high rate of relapse and/or recrudescence of the disease following cessation of specific therapy. Bone marrow examination with the Fite modification of the acid-fast stain is therefore indicated in such patients to evaluate bone marrow involvement and the efficacy of treatment.

Malignant fibrous histiocytoma (giant cell type) of the pancreas. A distinctive variant of osteoclast-type giant cell tumor of the pancreas

Malignant giant cell tumors of the pancreas are rare neoplasms which have been generally thought to represent epithelial malignancies of either acinar or ductal epithelium. The authors have studied a tumor of the pancreas that was characterized histologically by a proliferation of benign-appearing osteoclast-type giant cells in association with atypical, often bizarre mononuclear cells. Immunohistochemical studies demonstrated negative staining of the tumor cells with epithelial markers, including low-molecular weight keratins, carcinoembryonic antigen and epithelial membrane antigen, and positive staining with vimentin antibodies, supporting a fibroblastic line of differentiation. Electron microscopic examination also showed absence of ultrastructural features of epithelial differentiation such as microvilli, intercellular junctions, or desmosomes. The authors believe the current case represents a true sarcoma of the pancreas, currently best classified as a malignant fibrous histiocytoma, giant cell type. This tumor should be distinguished from the epithelial type of osteoclastic giant cell tumor of the pancreas.

Malignant epithelioid schwannoma of the skin. A low-grade neurotropic malignant melanoma?

We studied a polypoid cutaneous neoplasm excised from the left arm of a 23-year-old man by light microscopy, immunohistochemistry, and electron microscopy. Histologically, the tumor was composed of a proliferation of round to oval epithelioid cells that were arranged in fascicles and showed a prominent perineural distribution. Immunohistochemistry revealed the presence of S-100 protein and vimentin within tumor cells. Electron microscopy demonstrated reduplication of basal lamina and abundant long-spacing collagen in intercellular spaces. The findings are consistent with a primary malignant epithelioid schwannoma of the skin. We discuss the relationship of this lesion with other neoplasms in the spectrum of tumors showing schwannian and melanocytic lines of differentiation.

Intranodal hemorrhagic spindle-cell tumor with "amianthoid" fibers. Report of six cases of a distinctive mesenchymal neoplasm of the inguinal region that simulates Kaposi's sarcoma

We describe six cases of a distinctive spindle-cell neoplasm apparently arising from inguinal lymph nodes in adult patients. The lesions were characterized histologically by highly vascularized, interlacing fascicles of spindle cells circumscribed by an irregular band of sclerosis and hemorrhage, and surrounded by a compressed rim of lymph node remnant. A striking feature observed in all cases was the presence of stellate-shaped areas containing thick collagen fibers (so-called amianthoid fibers). Immunohistochemically, the tumor cells were positive for actin, muscle myosin, and vimentin. Electron-microscopic examination demonstrated features indicative of myofibroblastic and smooth-muscle differentiation. Follow-up has shown no evidence of recurrence or metastases. The lesions appear to represent an intranodal neoplastic proliferation of mesenchymal cells exhibiting benign biologic behavior. The inguinal location, presence of amianthoid fibers, and the striking rim of hemorrhage surrounding the spindle-cell proliferation set this tumor apart from other lesions. It is important to distinguish this entity from nodal involvement by Kaposi's sarcoma, a lesion it may closely resemble.

Spindle cell carcinoma of the renal pelvis. Immunohistochemical and ultrastructural study of a case demonstrating coexpression of keratin and vimentin intermediate filaments

A carcinoma of the renal pelvis characterized histologically by a spindle cell sarcomatoid morphological growth pattern was studied by electron microscopy and immunohistochemical techniques. Ultrastructural examination revealed abundant perinuclear cytoplasmic tonofilament bundles in association with prominent rough endoplasmic reticulum. Immunohistochemical study demonstrated coexpression of keratin and vimentin, two intermediate filaments thought to be specific for epithelial and nonepithelial cells, respectively. It is proposed that the spindle transformation of the epithelial cells in such cases may be explained on the basis of the development by the tumor cells of nonepithelial characteristics, such as the expression of vimentin intermediate filaments, that may be responsible for the adoption of the morphological growth pattern characteristic of neoplasms following mesenchyme-derived lines of differentiation.

Immunofluorescent localization of cytokeratin intermediate filaments as a means of defining the presence of recurrent basal cell carcinoma

Intermediate filament subunits are reliable markers of cytogenetic origin for both normal and neoplastic cells. Immunohistochemical localization of cytokeratin filaments offers a sensitive and specific means of identifying basal or reserve cells when studying histologic sections of skin biopsy specimens. We have applied this technique on eighteen cases in which unequivocal diagnosis or recurrent basal cell carcinoma could not be rendered by conventional histologic techniques. In three of the cases studied, microscopic islands of basal cell carcinoma could be demonstrated by positive staining with cytokeratin antibodies. In the remaining fifteen cases, the possibility of recurrent basal cell carcinoma could be conclusively eliminated on the basis of negative staining with this antibody. Immunolabeling with tissue specific cytokeratin antibodies by indirect immunofluorescent examination may thus constitute a reliable and relatively simple technique that may serve to establish a definitive diagnosis in equivocal cases of suspected recurrent basal cell carcinoma.