Chordomas of the mediastinum: clinicopathologic, immunohistochemical, and ultrastructural study of six cases presenting as posterior mediastinal masses

Six cases of chordomas presenting as primary posterior mediastinal tumors are described. Three patients were female, and three were male between the ages of 8 and 65 years (mean, 40.6 years). In all cases, the tumors presented radiographically as relatively well-circumscribed, encapsulated soft tissue masses that did not seem to be related to the thoracic or dorsal spine. Only in one case, focal infiltration of bone at the level of T6-T7 was observed at the time of surgery. Histologically, the lesions showed a spectrum of features that ranged from sheets and cords of large cells with abundant vacuolated cytoplasm to small, stellate cells embedded within an abundant mucoid matrix. In one case, the cell population showed more pronounced nuclear atypia with loss of cytoplasmic vacuolization, frequent mitotic figures, necrosis, and solid areas characterized by a perivascular distribution of atypical spindle cells set against a myxoid stroma. Another case showed features of chondroid chordoma, with an immature chondroid-appearing matrix surrounding the atypical tumor cells. Immunohistochemical studies in all cases showed positive staining of the tumor cells with CAM 5.2 and broad-spectrum keratin, epithelial membrane antigen (EMA) and vimentin, and, to a lesser extent, with S-100 protein. Stains for muscle actin, carcinoembryonic antigen (CEA), and desmin were negative. Ultrastructural examination in two cases showed a spectrum of features that varied from large cells with abundant cytoplasm containing scattered ribosomes, glycogen granules, Golgi apparatti, abundant intermediate filaments, and small lumen formation with immature microvilli to smaller cells with elongated cytoplasmic processes, fewer intermediate filaments, rare desmosome type intercellular junctions, and complexes of mitochondria/rough endoplasmic reticulum. On clinical follow-up, two patients died with metastases to the lungs, chest wall, and liver from 1 to 3 years after diagnosis, and two patients are alive and well without evidence of disease after 3 and 16 years. Chordoma should be entertained in the differential diagnosis of posterior mediastinal tumors. Application of immunohistochemical stains or electron microscopy will be of aid in separating them from other conditions that may histologically closely resemble these lesions.

Clear nuclear changes in Hashimoto's thyroiditis. A clinicopathologic study of 12 cases

Histologic sections of thyroid glands resected from 12 patients with Hashimoto's thyroiditis have been studied in which areas were present showing clear nuclear changes such as those seen in papillary carcinoma. The patients' ages ranged from 28 to 78 years (mean = 57.3); 11 were women and one was a man. The lesions presented as focal, ill-defined areas displaying clear nuclear changes of the cells within otherwise well-circumscribed adenomatous nodules, or as small clusters of cells showing the characteristic clear nuclear features randomly admixed with the Hashimoto's elements. Histologically, the lesions were characterized by a range of nuclear features that included optically clear nuclei, prominent cytoplasmic invaginations with intranuclear cytoplasmic inclusions, and occasional nuclear grooves. In two cases, focal papillary formations were seen that were lined by cells with optically clear nuclei. In two other cases, well-circumscribed nodules bearing the architectural features of trabecular hyalinizing adenoma with focal clear nuclear changes were also present. In three cases, small (< 0.5 cm) well-circumscribed nodules bearing cytological features indistinguishable from those of microscopic papillary carcinoma were also present in addition to the areas of clear nuclear change. Follow-up of 1.5 to 19 years (mean = 9 years) showed no evidence of recurrence or metastases in any of our patients. Our study appears to indicate that thyroid follicular epithelium in patients with Hashimoto's thyroiditis may exhibit a range of clear nuclear changes similar to those encountered in papillary carcinoma. Such changes may represent another form of response of follicular epithelium to the underlying autoimmune process with possible premalignant connotation. However, they should be interpreted in context with the rest of the findings within the involved gland to avoid an overdiagnosis of malignancy.

Thymic carcinoid with prominent mucinous stroma. Report of a distinctive morphologic variant of thymic neuroendocrine neoplasm

Four cases are described of a distinctive morphologic variant of thymic carcinoid that was characterized by abundant stromal mucin admixed with the neuroendocrine elements resulting in a histologic picture reminiscent of metastatic mucin-secreting carcinoma. The patients were three men and a woman, aged 22 to 43 years. The tumors presented with symptoms of chest discomfort, cough, and dyspnea and were described as large anterior mediastinal masses on chest radiographs and computerized scans. Histologically, all cases showed nests and strands of tumor cells embedded in an abundant lightly eosinophilic, mucinous stroma with small cellular clusters as well as scattered single tumor cells seen floating in the mucin. The mucinous matrix was negative for periodic acid Schiff's and mucicarmine stains; alcian blue stains at pH 2.5 showed strong positivity of the mucinous material; this reaction was abolished by treatment with hyaluronidase, indicating the presence of nonepithelial stromal mucosubstances. Immunohistochemical stains showed strong positivity of the tumor cells with CAM 5.2, chromogranin, synaptophysin, and neuron-specific enolase, and negative staining with carcinoembyronic antigen and epithelial membrane antigen. Electron microscopy done in one case showed abundant dense-core cytoplasmic neurosecretory granules; there was no evidence of glandular secretory activity by the tumor cells. The tumors in two patients behaved in a highly aggressive fashion, with invasion of the chest wall, recurrence, and metastases to the lungs, pleura, and axillary, retroperitoneal, and mesenteric lymph nodes. Thymic carcinoid should be considered in the differential diagnosis of mediastinal neoplasms displaying prominent mucinous features. Application of immunostains and electron microscopy will be of value for establishing the correct diagnosis in this setting.

Solitary fibrous tumors of soft tissue. A clinicopathologic and immunohistochemical study of 12 cases

We describe 12 cases of primary soft tissue neoplasms that showed the histologic and immunohistochemical features of solitary fibrous tumors of serosal surfaces (solitary fibrous mesothelioma, submesothelial fibroma). Nine patients were women and three were men whose ages ranged from 28 to 83 years. Seven lesions were located in the head and neck region, and the remainder were located in the back, buttock, perineum, and groin. The lesions measured from 1 to 6 cm in greatest diameter and presented grossly as well-circumscribed, unencapsulated, soft to rubbery tissue masses. Histologically they were characterized by a proliferation of spindle cells exhibiting a variety of growth patterns, including storiform, herringbone, neural with wavy nuclei, and hemangiopericytic admixed with areas of sclerosis. In two cases the lesions showed areas of increased cellularity with occasionally scattered mitotic figures. Three cases were located adjacent to a major salivary gland; in one, entrapment of normal salivary gland acini and ducts could be observed at the edges of the lesion. Immunohistochemical studies showed positive staining of the spindle cells with CD34 (anti-HPCA-1) and vimentin antibodies and negative staining with keratin, actin, desmin, S-100 protein, collagen type IV, and factor VIII related antigen. Follow-up from 6 months to 12 years has shown no evidence of recurrence or metastasis in any of our patients. Solitary fibrous tumors appear to represent ubiquitous mesenchymal neoplasms that may not be necessarily restricted to serosal surfaces. Identification of these lesions is of importance to avoid misdiagnosis with other more aggressive conditions in soft tissue locations.

Ectopic poorly differentiated (insular) carcinoma of the thyroid. Report of a case presenting as an anterior mediastinal mass

A case is presented of an anterior mediastinal mass arising in a 64-year-old woman that showed on histologic, immunopathologic, and ultra-structural examination features of a poorly differentiated (insular) thyroid carcinoma. The tumor in this patient most likely arose from ectopically displaced thyroid tissue on the basis of a developmental defect. The clinicopathologic features and differential diagnosis of the lesion in the setting of its mediastinal location are discussed. Ectopic poorly differentiated (insular) carcinoma of the thyroid should be added to the list of mediastinal tumors showing a solid or insular growth pattern.

Mediastinal seminomas with prominent cystic changes. A clinicopathologic study of 10 cases

We present 10 cases of thymic seminomas associated with prominent cystic changes. All patients were males, aged 16 to 79 years (median, 23.5). Clinically, two patients presented with chest pain/four were asymptomatic and the tumors were discovered on routine chest radiographs; one tumor was discovered incidentally at autopsy; and in three patients no clinical information was obtained. Grossly, the tumors were described as multilocular cystic lesions that ranged in size from 7 to 19 cm in greatest dimension, showing small focal areas of induration within the cyst walls. Histologically, the lesions were characterized by cystic spaces lined by squamous or cuboidal epithelium showing severe chronic inflammatory changes with areas of cholesterol cleft granulomas, lymphoid follicular hyperplasia, and scattered foci of residual thymic parenchyma within the walls of the cysts, resulting in a picture indistinguishable from acquired multilocular thymic cysts. Careful examination, however, revealed microscopic foci composed of a neoplastic proliferation of large polygonal cells with slightly eosinophilic to clear cytoplasm and large nuclei with prominent nucleoli. The atypical cells were admixed with an inflammatory background and were often accompanied by a florid granulomatous reaction. Periodic acid-Schiff histochemical reaction with diastase revealed moderate amounts of glycogen within the cytoplasm of the tumor cells. Immunohistochemical studies in five cases showed positive labeling of the tumor cells with placental alkaline phosphatase. Nine patients were treated by complete surgical excision of the mass, and additional postoperative radiation therapy was given to two patients. Follow-up information available for five patients showed all to be alive and well from 2 to 19 years after diagnosis (mean follow-up, 9 years). Four of the patients were lost to follow-up. The pathogenesis of the cystic process in these cases remained unsettled but may represent a reactive change secondary to epithelial hyperplasia of thymic epithelium. Thymic seminoma should be considered in the differential diagnosis of cystic lesions of the anterior mediastinum; extensive sampling of such lesions is therefore recommended for proper evaluation.

Smooth muscle tumours presenting as pleural neoplasms

Five smooth muscle tumours presenting as pleural neoplasma are presented. The patients were three women and two men aged between 21 and 69 years (mean = 45 years). Clinically, one patient presented with chest pain, one with empyema and the other three were asymptomatic. Two of the tumours were located in the left side of the chest cavity and three in the right side. In four cases, the lesions presented as solitary pleural-based masses that varied in size from 10-18 cm in greatest dimension: in two of these cases, involvement of the diaphragm was present in addition to the pleural involvement. In one case, the tumour was seen to totally encase the right lung simulating the growth pattern of malignant mesothelioma. Histologically, three cases displayed an atypical spindle cell proliferation with marked cellular pleomorphism, mitoses and areas of hemorrhage and necrosis. The other two cases were characterized by a bland-appearing smooth muscle proliferation of uncertain malignant potential composed of elongated cells with a moderate amount of eosinophilic cytoplasm and cigar-shaped nuclei, lacking significant nuclear pleomorphism or mitotic activity. Immunohistochemical studies showed strong positivity for alpha-smooth muscle actin in all cases, and for desmin in four of five cases, and a focal positive reaction for keratin in one case. Ultrastructural examination in one of the high-grade tumours showed features of smooth muscle differentiation. Three of the patients were treated by complete surgical excision while, in the other two patients, the lesions were incompletely resected.(ABSTRACT TRUNCATED AT 250 WORDS)

Thymolipoma: clinicopathologic review of 33 cases

The clinical, radiologic, and pathologic features of 33 cases of mediastinal thymolipoma are presented. The patients' ages ranged from 2 to 64 (mean, 33) years; 18 were male and 15 were female. Clinically, the majority of patients (18 cases) were asymptomatic. Five patients presented with upper respiratory symptoms, two patients presented with chest pain, two patients with myasthenia gravis, and one patient with a neck mass; no clinical information was available in four patients. All the tumors were located in the anterior mediastinum and in all cases complete surgical resection of the mass was accomplished. Radiographically, 20 cases showed an anterior mediastinal tumor; when available, computed tomography and/or magnetic resonance imaging demonstrated a mixture of fat and soft tissue elements in these tumors. Grossly, the tumors were described as fairly well-circumscribed, soft, yellowish, fatty tumors with focal solid areas. The tumors varied in size from 4.5 to 36 cm in greatest dimension. Histologically, they were characterized by the presence of abundant mature adipose tissue admixed with areas containing remnants of thymic tissue. The fatty tissue consisted of mature adipocytes devoid of atypia, and the thymic tissue component varied from strands of atrophic thymic epithelium to large areas containing thymic parenchyma showing the typical mixed epithelial/lymphocytic architecture with numerous Hassall's corpuscles. Areas of calcification and cystic degeneration of Hassall's corpuscles were quite prominent in a large number of cases. Our study shows that thymolipomas span the age ranges from the very young to adult individuals with a slight prevalence for patients under the age of 40.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary pulmonary rhabdomyosarcomas: a clinicopathologic and immunohistochemical study of three cases

Three cases of primary pulmonary rhabdomyosarcoma in adults are presented. The patients were all men between the ages of 57 and 78 yr (mean 67.5). All patients presented with symptoms referable to their tumors, including cough, shortness of breath, pleuritic chest pain, and weight loss. In one patient, a history of tobacco and alcohol abuse was obtained. Anatomically, two tumors were located in the left upper lobe and one in the left lower lobe. Grossly, the tumors ranged in size from 6 to 11.5 cm and were tan-gray, firm masses with areas of necrosis and hemorrhage. Histologically, the tumors were characterized by a spindle cell proliferation admixed with areas showing a pleomorphic cell population with numerous rhabdomyoblasts and areas of hemorrhage and necrosis. Immunohistochemically, all three tumors showed strong positivity with desmin and myoglobin antibodies and negative staining with antibodies against keratin, epithelial membrane antigen, and S-100 protein. All patients had a fatal outcome. Two patients died a few days after admission with respiratory distress; the third one died 2 years after diagnosis with widely metastatic disease. Autopsy findings in all cases disclosed disseminated metastases to multiple abdominal and thoracic organs. Primary pulmonary rhabdomyosarcoma should be considered in the differential diagnosis of poorly differentiated pulmonary neoplasms in adults and should be distinguished from other primary and metastatic sarcomas.

Mucoepidermoid carcinomas of the thymus. A clinicopathologic study of six cases

Six cases of mucoepidermoid carcinoma of the thymus are presented. The patients were two men and four women aged 17 to 66 years (median age, 34.5). Clinically, three patients had symptoms of chest discomfort and three were asymptomatic. Grossly, the tumors in three patients were described as cystic structures varying in size from 7 to 8 cm in greatest dimension, with focal areas of induration within the walls of the cyst that averaged from 1.5 to 3 cm. The other three cases had grossly and radiographically well-circumscribed, homogeneous tumor masses. Histologically, the lesions showed a spectrum of features that ranged from those of well-differentiated, to moderately well-differentiated, to poorly differentiated mucoepidermoid carcinoma, with sheets and solid islands of squamoid cells admixed with mucin-secreting epithelium lining gland-like spaces. In four cases, the tumor was histologically seen in continuity with the epithelial lining of multilocular cystic structures; the nonneoplastic components of the cysts contained abundant inflammation and showed the features of otherwise conventional acquired multilocular thymic cysts. Clinical follow-up showed that the two patients with intermediate and high-grade tumors died within 2 and 7 months after initial diagnosis. One of these patients showed at autopsy residual tumor limited to the mediastinum, whereas the other patient died with metastases to pericardium and myocardium despite postoperative radiation therapy. Two patients with low-grade tumors were alive and well with no residual disease 2 and 3 years after surgery, and the other two were lost to follow-up. Mucoepidermoid carcinoma of the thymus should be included in the differential diagnosis of cystic neoplasms of the thymus. As with their counterparts at other sites, the biologic behavior of these tumors closely correlates with their degree of differentiation and amount of cytologic atypia.

Primary pulmonary sarcomas with features of monophasic synovial sarcoma: a clinicopathological, immunohistochemical, and ultrastructural study of 25 cases

We present 25 cases of a primary pulmonary sarcoma bearing histological, immunohistochemical, and ultrastructural features indistinguishable from those of monophasic synovial sarcoma of soft tissue. The patients were 11 men and 14 women between the ages of 16 and 77 years. Clinically, the most common symptoms were chest pain, cough, shortness of breath, and hemoptysis. The lesions involved all lung segments. Grossly, they varied in size from 0.6 to 20 cm and were described as soft to rubbery tumors with areas of necrosis and hemorrhage, some with cystic changes. Two lesions involved the bronchial wall and in one case the tumor was described as encircling the bronchial tree. Histologically, all of the lesions were characterized by an atypical spindle cell proliferation with a solid growth pattern. Areas of myxoid, neural, hemangiopericytic, and epithelial-like growth pattern were observed. Mitoses, necrosis, and hemorrhage were seen in all lesions in varying proportions. Immunohistochemical studies for epithelial membrane antigen (EMA) and keratin showed strong focal positivity in 25 of 25 and 23 of 25 lesions, respectively. Immunohistochemical study for vimentin showed diffuse strong positivity in all lesions. Other immunostains, including desmin, smooth muscle actin, and S-100 protein, were negative. Electron microscopy in three cases showed spindle cells with elongated nuclei containing abundant cytoplasmic rough endoplasmic reticulum and well developed desmosome type intercellular junctions. Follow-up information ranging from 2 to 20 years was obtained in 18 patients. Six patients died of their tumors, whereas four patients died of unrelated causes without evidence of recurrence or metastases. Eight patients were alive with disease (recurrence and/or metastases) from 1 to 7 years after diagnosis. Four patients were alive and well without evidence of recurrence or metastases from 2 to 20 years (mean follow-up, 12.5 years). The present group of lesions appears to constitute a distinctive and as yet previously undescribed primary sarcoma of the lung, which probably represents the visceral counterpart of monophasic synovial sarcoma of soft tissue in a pulmonary location. Because of their distinctive biology these lesions should be distinguished from a variety of primary and metastatic malignancies of the lung.

Malignant mixed epithelial/mesenchymal neoplasms of the lung

The existence of biphasic neoplasms occurring primarily in the lung is a well-known albeit rare event. The spectrum of malignant tumors displaying a mixed epithelial/mesenchymal growth pattern is rather narrow when these tumors occur primarily in the lung. The two most often encountered neoplasms showing features of epithelial and mesenchymal differentiation are carcinosarcomas and pulmonary blastomas. Tumors with analogous features are of ubiquitous distribution in the human body and have been described in numerous other organs, including the gastrointestinal tract, the genitourinary tract, and the endocrine system. Although the histopathologic features of these tumors may seem simple in most cases, there appear to be numerous pitfalls in their diagnosis; gray areas still remain in the characterization of these tumors, because a certain degree of overlap may be encountered with these two conditions. Such problems are understandable because the incidence of these tumors in the general population is very rare. Therefore, one is expected to find divergent points of view regarding these neoplasms. It is of importance, however, to unify criteria not only for diagnostic purposes, but also to determine the prevalence and behavior of these neoplasms, because such information may provide a rationale for adjustment and improvement in the treatment and diagnosis of these unusual neoplasms. We will review past and current concepts regarding these unusual tumors, as well as their more salient histopathologic features.

Unusual manifestations of metastatic tumors to the lungs

Because of the lung's rich capillary bed and central location in the circulatory system, this organ is one of the most frequent recipient sites for metastatic spread of disease. The histopathologic diagnosis in the vast majority of cases is straightforward and usually supported by clinical findings and a prior history of a known primary tumor elsewhere. However, unusual circumstances may arise: a primary tumor may remain occult at the time of pulmonary metastases, the metastasis may develop after a long period of latency, or the histopathologic appearance of the metastasis may assume a form that is uncharacteristic or inconsistent with the suspected primary lesion, which raises the possibility of the emergence of a second primary tumor in the lung. Herein we review a variety of unusual manifestations of metastatic disease to the lungs that may pose difficulties for diagnosis and interpretation. Emphasis is made on the histological differential diagnosis and the clues that may alert the pathologist to recognizing the process as metastatic in origin.

Primary sarcomas of the lung

Primary pulmonary sarcomas are rare tumors. Because the lung is one of the favored metastatic sites for soft tissue sarcomas, care must be taken when evaluating these lesions to rule out the possibility of an alternate primary source by means of thorough clinical history and radiographic evaluation. In addition to the difficulties involved in separating primary from metastatic tumors, pulmonary sarcomas must be distinguished from a number of sarcomalike primary lung neoplasms, including spindle and giant cell (pleomorphic) carcinoma, and from mixed epithelial/mesenchymal lesions such as pulmonary blastoma and carcinosarcoma. The criteria helpful for accomplishing this distinction are discussed, along with a review of primary sarcomas of the lung, with emphasis on clinicopathologic, immunohistochemical, and ultrastructural features that may be of aid for diagnosis. Additionally, recent or newly described entities are also discussed, and evolving concepts on the pathogenesis and terminology of these lesions are underscored.

Histologic spectrum of cutaneous involvement in patients with myelogenous leukemia including the neutrophilic dermatoses

BACKGROUND

Cutaneous manifestations of myeloid leukemia can be specific or nonspecific. The study was designed to determine the prevalence and histologic appearance of cutaneous lesions in patients with myeloid leukemia and various myeloproliferative disorders.

METHODS

The histologic changes of cutaneous lesions in 52 patients with myelodysplastic syndrome, polycythemia vera, and myeloid, myelomonocytic, or monocytic leukemia are presented in this study.

RESULTS

Two types of cellular infiltrates were identified. In the first group, the most common pattern was a diffuse involvement by the leukemic cells through the entire dermis with preservation of a "grenz zone" in the superficial dermis. Two cases exhibited a Kaposi's sarcoma-like pattern, with prominent slit-like blood-filled spaces lined by myeloblasts against a fibrocellular stroma. The second group of lesions was characterized by dense, neutrophilic dermal infiltrates resembling acute neutrophilic dermatosis (Sweet's syndrome) or pyoderma gangrenosum. In two of these cases, scattered immature blast cells admixed with the mature neutrophilic elements were identified.

CONCLUSIONS

Awareness of these different morphologic features and application of special stains are of value in the evaluation of suspicious cutaneous infiltrates in patients with myeloid leukemia and various myeloproliferative disorders.

Mediastinal hemangiomas: a study of 18 cases with emphasis on the spectrum of morphological features

A study of 18 cases of mediastinal hemangiomas is presented. The patients were eight women and 10 men between the ages of newborn to 74 years. Clinically, the most common symptoms included dyspnea, cough, and chest pain. In one patient the mediastinal hemangioma was associated with another hemangioma in the gastrointestinal tract and presented initially with gastrointestinal bleeding. Four patients were asymptomatic. Anatomically, 14 tumors were located in the anterior mediastinum and four in the posterior mediastinum. Surgical resection was the treatment of choice for all patients. Grossly, the lesions were described as well circumscribed, cystic, hemorrhagic tumors that ranged in size from 2 cm to 20 cm in diameter. Histologically, the tumors were divided into two groups, one showing the features of capillary hemangioma characterized by a lobular and solid growth pattern featuring dilated small vessels and a solid proliferation of endothelial cells and another group showing the features of cavernous hemangioma characterized by large dilated vascular spaces with areas showing interstitial inflammatory changes, fibrosis, and smooth muscle proliferation. A few tumors were characterized by prominent regressive changes, including stromal hyalinization, dystrophic ossification, cystic and perivascular myxoid changes, and extensive fatty overgrowth. Some of the tumors showed extreme cellularity with virtual obliteration of vascular lumina due to compression by tumor cells and focal mitotic activity similar to that observed in cutaneous juvenile hemangiomas. Despite their large size, often infiltrating appearance, and sporadic mitotic activity, follow-up ranging from 1 month to 4 years in 11 patients showed all to be alive and well, thus demonstrating the benign nature of these neoplasms. A discussion of the differential diagnosis and a review of the literature on these rare tumors are presented.

Extramedullary hematopoiesis presenting as posterior mediastinal mass: a study of four cases

We present four cases of extramedullary hematopoiesis occurring in the posterior mediastinum. The patients are two women and two men between the ages of 20 and 87 years. Two patients presented with a history of thalassemia, and one had a history of anemia of undetermined etiology. One patient was asymptomatic, and the posterior mediastinal mass was detected during a routine chest radiographs. Surgical resection of the mass was performed in one patient, whereas a biopsy was performed in the other three. Histologically, all the cases showed the typical features of extramedullary hematopoiesis, namely the presence of numerous lymphocytes admixed with megakaryocytes and red cell precursors. Follow-up information ranging from 2 mo to 3 years showed that all patients are alive and well.

Extramedullary plasmacytomas presenting as mediastinal masses: clinicopathologic study of two cases preceding the onset of multiple myeloma

We present two cases of extramedullary plasmacytoma presenting as a mediastinal mass and preceding the onset of full-blown multiple myeloma. The patients are a 62-year-old woman who presented with progressive dyspnea and left-sided chest pain and a 59-year-old asymptomatic man. In both patients, radiographic studies revealed a posterior and anterior mediastinal mass, respectively. Surgical resection of the tumor was performed in the two cases. The tumors were characterized by a well-circumscribed proliferation of plasma cells surrounded by residual lymph nodal tissue. Immunohistochemical studies on paraffin sections demonstrated lambda light chain restriction. Follow-up in our patients revealed that both of them developed multiple myeloma after 6 months and 2 years, respectively. One patient received treatment with melphalan and prednisone and is currently alive and well without evidence of disease, 2 years after diagnosis. The second patient died 4 years after resection of his tumor with evidence of disease in lumbar spine, skull, and lungs. Extramedullary plasmacytoma presenting as a mediastinal mass may precede the onset of full-blown multiple myeloma; therefore, institution of early systemic therapy in these patients may be of value in preventing further progression of the disease.

Primary intrapulmonary thymoma. A clinicopathologic and immunohistochemical study of eight cases

We describe eight cases of primary intrapulmonary thymoma occurring in seven women and one man between the ages of 25 and 77 years. Clinically, all patients had initial radiographic findings of a parenchymatous intrapulmonary mass without evidence of mediastinal involvement either radiologically or at surgery. The lesions varied from 0.5 to 10 cm in greatest diameter. Five tumors were located close to the hilum, while the other three were discovered deep within the lung and in subpleural locations. In one case, the lesion appeared to arise endobronchially and infiltrate the surrounding parenchyma. In another case, in addition to the main hilar mass, there were two smaller tumor nodules found deep within the same lung. Histologically, the lesions were characterized by the classic biphasic cellular composition of thymomas, i.e., an admixture in varying proportions of epithelial cells and lymphocytes. Four cases were characterized by sheets of lymphocytes admixed with scattered epithelial cells that were separated by fibrous bands into lobules. Three cases were composed predominantly of sheets of epithelial cells admixed with scattered small lymphocytes and containing prominent perivascular spaces. In two of these cases, focal areas of spindling of the cells were noted. One case was composed predominantly of a spindle cell proliferation with perivascular spaces and numerous small lymphocytes. Immunohistochemical stains for keratin and epithelial membrane antigen in six cases highlighted the epithelial cells scattered against the lymphoid cell background. Seven patients were treated by surgery. In one patient the tumor was deemed inoperable at the time of exploration owing to extensive pleural infiltration and was treated by postoperative radiation; the lesion recurred locally in the pleura 8 years later. Clinical follow-up in three patients after surgical incision showed them to ba alive and well without evidence of disease at 10 months, 2 years, and 8 years, respectively. Two of the patients had been followed clinically for 2 and 4 years following discovery of their lung masses on routine chest radiograph before resection of their tumors. Two patients died of unrelated conditions; in one of them, the lesions had been followed clinically for 6 years before surgery; this patient died 6 months later from coronary artery disease, without evidence of recurrence or metastasis. Our findings suggest that intrapulmonary thymomas are slow-growing tumors that may respond well to surgical resection when confined to the lung. As with their mediastinal counterparts, invasive tumors will require additional treatment for the possibility of recurrence of metastasis.

Morphometric estimation of superoxide generation in allergen-induced airway hyperresponsiveness

BACKGROUND

We previously reported that the airway hyperresponsiveness (AHR) that follows antigen challenge is mediated, in part, by the generation of reactive oxygen species. The purpose of this study was to provide quantitative morphologic evidence of oxygen radical production in the airways during antigen-induced AHR.

EXPERIMENTAL DESIGN

Allergic sheep with a history of early and late bronchial responses to inhaled Ascaris suum antigen were used. The sheep were either challenged with antigen (N = 5) or saline (N = 5) and then euthanized 24 hours later when AHR had been documented to occur. Complete transverse sections of the right cranial lobar bronchus were obtained from the animals and were washed three times in Tris buffer and then incubated for 20 minutes in an oxygenated solution of diaminobenzidine which, in the presence of superoxide and manganese, forms an insoluble amber reaction product. Superoxide dismutase (SOD, 2250 units/ml) and phorbol ester (phorbol myristate acetate, 0.5 microgram/ml) were added to some tissues and used as negative and positive controls, respectively. The bronchial samples were then fixed and embedded in paraffin for light microscopy. The diaminobenzidine reaction product was quantified by determining the volume fraction of reaction product by point counting with a differential interference contrast microscope without counterstain.

RESULTS

Diaminobenzidine reaction product increased 5-fold (p < 0.05) in challenged animals, and this response was blocked by SOD. The reaction product was localized in and around the airway epithelium. Antigen challenge also resulted in a 2.4- and 2.0-fold increase in eosinophils and metachromatic cells in the airway wall. There were no differences in the number of neutrophils between groups. Pretreatment of animals (N = 2) with the combination of the 5-lipoxygenase inhibitor (zileuton, 10 mg/kg, po) and the platelet-activating factor antagonist (WEB-2086, 3 mg/kg, i.v.) agents, which have been shown to block AHR and antigen-induced inflammation in the sheep model, also blocked the antigen-induced superoxide formation.

CONCLUSIONS

These data suggest that superoxide and increased numbers of mediator-containing inflammatory cells are present in sheep airways 24 hours after antigen challenge. The interaction of this reactive oxygen species with these cells could contribute to the AHR seen at this time.

Malignant thymic neoplasms that may mimic benign conditions

The thymus is a complex, highly specialized organ that is derived from the third and fourth pharyngeal pouches and contains elements that originate from all three germinal layers. As such, it shows certain specific and distinctive reaction patterns to injury that are frequently encountered in a variety of reactive and inflammatory conditions. These reaction patterns, however, can also often be associated with neoplastic diseases arising from this organ, and in some instances, their presence may contribute to obscure the malignant nature of the underlying process. We present a review of the main tumor entities that may be mistaken for benign conditions of the thymus, with emphasis on the three major reaction patterns to injury that may be associated with malignant neoplasms of this organ: prominent cystic changes, stromal fibrosis, and reactive and hyperplastic changes of thymic epithelium. Histologic clues helpful for diagnosis and the differential diagnosis of these lesions are discussed.

Nevoid melanoma: a clinicopathological study of seven cases of malignant melanoma mimicking spindle and epithelioid cell nevus and verrucous dermal nevus

We report seven cases of a distinctive type of malignant melanoma characterized by a deceptively benign histological appearance with an architecture resembling that of benign melanocytic nevi on scanning magnification. Two predominant architectural patterns were observed: a dome-shaped pattern (two specimens) and a verrucoid pattern (five specimens). The specimens with a dome-shaped pattern of growth were characterized by a smooth epidermal surface and a proliferation of epithelioid melanoma cells with an inconspicuous intraepidermal component resembling spindle and epithelioid cell nevi (Spitz nevi). Gradual diminution in the size of dermal nests toward the bases of the lesions simulating the maturation phenomenon of benign nevi was observed; however, the dermal organization in cords and strands of melanoma cells and the persistence of cellular atypia extending to the bases of the tumors allowed their recognition as malignant melanomas. On the other hand, the specimens with a verrucoid growth pattern consisted of broad, exophytic tumors with a verrucous epidermal surface resembling that of papillomatous dermal nevi but distinguished from them by the presence of a continuous proliferation of melanocytes along the dermal-epidermal junction and by confluent sheets of melanoma cells in the dermis without evidence of true maturation. Clinical follow-up showed local recurrence in three patients after intervals ranging from 5 months to 5 years and regional metastasis in one patient after 2 years. The lesions described here may constitute a serious pitfall for diagnosis because of their innocent silhouette on scanning magnification and their superficial resemblance to spindle and/or epithelioid cell nevi and benign verrucous melanocytic nevi. Proper attention to cytological detail and subtle architectural features will aid in recognizing this unusual variant of malignant melanoma.

Primary cutaneous sarcomas showing rhabdomyoblastic differentiation

Rhabdomyosarcoma is a rare soft tissue neoplasm most commonly encountered in childhood and adolescence which has a predilection for the head and neck area, the genito-urinary tract and the extremities. Primary cutaneous presentation is extremely unusual and has been rarely reported in the literature. Herein, we describe two cases of rhabdomyosarcoma arising in the dermis of a 9-year-old girl and an 86-year-old man. Clinically, the tumours presented as solitary plaque-like or nodular lesions confined to the skin of the nose and chest wall, respectively. Histologically, the tumour in the first patient corresponded to an embryonal rhabdomyosarcoma. The tumour recurred locally four times, and in the last recurrence, showed features resembling those of malignant 'triton' tumour with fascicles of S-100 protein-positive spindle cells admixed with the rhabdomyoblastic components. The tumour in the second patient corresponded to the solid variant of alveolar rhabdomyosarcoma. Immunohistochemical studies in both tumours showed positive labelling for muscle-specific actin, desmin and vimentin. Ultrastructural examination in one case showed clusters of intermediate filaments in the cytoplasm recapitulating abortive sarcomeric structures consistent with rhabdomyoblastic differentiation. Both patients developed repeated recurrences over a period of 2-4 years despite adequate surgical excision, and the second patient had an axillary lymph node metastasis. Primary cutaneous rhabdomyosarcoma should be considered in the evaluation of small 'blue cell' tumours or undifferentiated malignant neoplasms of the skin, and appropriate immunohistochemical studies in conjunction with electron microscopy should be employed for proper evaluation of such lesions.

Gastrointestinal stromal tumors with prominent myxoid matrix. Clinicopathologic, immunohistochemical, and ultrastructural study of nine cases of a distinctive morphologic variant of myogenic stromal tumor

Nine cases are presented of a distinctive morphologic variant of myogenic gastrointestinal stromal tumor characterized by an unusually prominent myxoid stromal background reminiscent of a neural neoplasm but lacking the immunohistochemical or ultrastructural features of peripheral nerve sheath or ganglionic differentiation. The patients included six women and three men aged 42 to 86 years (mean, 70). The lesions occurred in the stomach (seven cases) and small intestine (two cases) and ranged in size from 2.5 to 9.5 cm. They were described grossly as well circumscribed, unencapsulated, with a prominently myxoid and often cystic cut surface. Histologically, the lesions were composed of a proliferation of round, spindle, or stellate cells embedded in an abundant myxoid stroma. Histochemical stains showed strong positive reaction of the myxoid stromal background with alcian blue at pH 2.5; this staining reaction was abolished by treatment with hyaluronidase, indicating an abundance of connective tissue mucosubstances rich in hyaluronic acid. Immunohistochemical stains showed strong positivity of the tumor cells with vimentin antibodies in all cases and focal weak to moderate positive staining with muscle actin (HHF35) in eight cases and with desmin in two. Stains for keratin, S-100; epithelial membrane antigen, and collagen type IV were uniformly negative. Ultrastructural examination carried out in all cases showed features consistent with those previously described for myogenic gastrointestinal stromal tumors, namely, scattered mitochondria and prominent Golgi apparati, strands of rough endoplasmic reticulum, focal accumulation of intracytoplasmic microfilaments with occasional focal condensations, subplasmalemmal attachment plaques and immature cell junctions, focal extracellular basal lamina material, and surface-oriented micropinocytotic activity. The myxoid changes observed in these tumors may represent a secondary, nonspecific reaction pattern of the tumor cells to some noxious stimulus, or they may be a form of degenerative phenomenon such as that commonly observed in smooth-muscle tumors of the uterus and other sites. Myogenic gastrointestinal stromal tumors with prominent myxoid stroma should be distinguished from benign schwannoma of the stomach and gastrointestinal autonomic nerve tumors. Because of the differences in prognosis for these entities, immunohistochemical and ultrastructural examinations are recommended for the evaluation of gastrointestinal stromal neoplasms with prominent myxoid features.

Mixed diquat/paraquat-induced burns

BACKGROUND

Ducatalon is a bipyridylium herbicide containing a mixture of diquat and paraquat, and is used in agriculture. Adverse reactions due to contact of this compound with the skin have rarely been described.

CASE REPORTS

Two men were seen for severe pain due to extensive chemical burns in the perineal and scrotal regions, caused by leaking of Ducatalon from defective equipment used for spraying the herbicide. The lesions responded well to treatment with topical silver sulfadiazine, combined with systemic antibiotics. The damaged skin healed without scarring within a few days. The lesions have not recurred after the faulty spraying apparatus was replaced.

CONCLUSION

Direct contact of the skin with Ducatalon may lead to severe chemical burns. Proper precautions should be taken by the personnel handling this compound, with particular attention to the integrity of the equipment used for spraying the herbicide.