Mesotheliomas of the tunica vaginalis propria and peritoneum in Fischer rats

Nine mesotheliomas were found in a group of 384 mature, male, Fischer-derived rats maintained on various experimental diets in long-term feeding studies. The tumors apparently were unrelated to any of the test materials. They ranged from solid, raised serosal growths to delicate papillary structures, and occurred primarily on the tunica vaginalis propria of the testis, epididymis and spermatic cord. Four of the nine cases were unusual because there was mesotheliomatous involvement of the peritoneal as well as of the genital mesothelium.     

Immunohistochemical features of canine ovarian papillary adenocarcinoma and utility of cell block technique for detecting neoplastic cells in body cavity effusions

Dogs with ovarian papillary adenocarcinoma occasionally present with ascites and/or pleural effusion. These aspirated fluids often contain a large number of cells, and distinction between neoplastic cells and activated mesothelial cells can be difficult. In this study, 7 cases of canine ovarian papillary adenocarcinoma, including 3 with ascites and pleural effusion, were immunohistochemically examined. Ovarian tumor cells were positive for cytokeratin CAM5.2 (CAM5.2), Wilms’ tumor 1 (WT-1) and progesterone receptor (PR) in all 7 cases. A metastatic lesion of the mediastinum in one case was also positive for CAM5.2, WT-1 and PR. Immunohistochemistry on cell blocks obtained from ascites and/or pleural effusion of 2 cases revealed the presence of PR-positive epithelial cells. Whereas, activated mesothelial cells in ascites or pleural effusion collected from dogs without neoplastic lesions were negative for PR. In addition, surface epithelium and subsurface epithelial structures (SES) of normal canine ovaries, that are considered to be the cell of origin for ovarian papillary adenocarcinoma, were also positive for CAM5.2, WT-1 and PR. These results indicate that, together with CAM5.2, WT-1 and PR is a useful diagnostic marker for canine ovarian papillary adenocarcinoma. Expression of PR may be associated with progesterone-dependent nature of canine ovarian papillary adenocarcinoma.     

A scanning electron microscopic study of the peritoneal mesothelium covering the genital tract and its ligaments in the cow

This study was undertaken to describe the surface features of the peritoneal mesothelium covering the genital tract and adjacent ligaments of the cow during the oestrous cycle. The relationship between mesothelial surface and spermatozoa was also evaluated after intra-uterine and intraperitoneal insemination. Surface features of mesothelial cells from 25 cyclic cows were examined by scanning electron microscopy and by image analysis. Presence of spermatozoa was evaluated by scanning electron microscopy in seven additional cows. In the external side of the infundibulum, the oviductal mucosa exceeds the free margin, forming a continuous band measuring 2.5-10 mm in width. This oviductal epithelium shows cyclical variations with a predominance of ciliated cells during the follicular phase. In respect of the mesothelium, no clear morphological differences were observed associated with the side of ovarian bursa (internal versus external), or with the phase of the oestrous cycle. Mesothelial cells covering the uterus and mesometrium have a higher microvilli density and length and a smaller cell surface area than in the oviduct and adjacent structures. The presence of solitary cilia in the mesosalpinx and mesotubarium superius (infundibulo-cornual ligament) of some specimens was also observed. When samples were processed without postfixation in osmium tetroxide, a layer of amorphous material covered all surfaces. After intra-uterine insemination of five cows, no spermatozoa were found on their peritoneal mesothelium. Numerous spermatozoa were found after intraperitoneal insemination being attached throughout mesothelial surfaces. These results indicate that there are morphological differences between regions, but no cyclic changes, in the surface features of mesothelial cells covering the genital tract and adjacent ligaments of the cow, and that spermatozoa can bind to mesothelial surfaces after intraperitoneal insemination.     

An ultrastructural study of malignant mesotheliomas in two cows

Malignant mesotheliomas of two Holstein cows were examined by light and electron microscopy. These tumours were derived from peritoneal surfaces and were of biphasic type composed of mesothelial lining cells and submesothelial mesenchymal cells. Ultrastructurally, the neoplastic mesothelial cells were characterized by intermediate filaments, microvilli, desmosomes, tight junctions and basal laminae. The neoplastic submesothelial cells were closely associated with collagen filaments and some cells had several resemblance to the neoplastic mesothelial cells. The ultrastructural features of the mesotheliomas are discussed in comparison with those of adenocarcinomas and fibroblastic neoplasms. In one case of malignant granulosa cell tumour involved the left ovary and its morphology was apparently different from that of the mesothelioma. Multiple primary tumours are uncommon in cattle.     

Histological comparison of malignant epithelioid mesothelioma in young and adult cattle

The histology and immunohistochemistry of pleomorphic and conventional epithelioid mesotheliomas were examined. The former was detected in two young calves aged 2 and 4 months and was characterized by pleomorphic and atypical cells with decreased expression of cytokeratin 7 (CK7). In contrast, the latter was found in a 31-month-old heifer, consisting of tumor cells uniform in size and shape with CK7 expression in nearly all cells. Production of collagen by tumor cells was demonstrated in both histological types, and was considered to be characteristic of bovine epithelioid mesothelioma. Pleomorphic mesothelioma is far more pleomorphic and mitotically active than conventional mesothelioma, and its normal counterpart may be immature mesothelial cells with high proliferation potential, which exist in fetal life and early calfhood.     

Spontaneous ovarian neoplasms of the laboratory rat

A wide range of spontaneous tumors of the ovary are reported in a group of 5903 aged female Sprague-Dawley rats of the CD and CFY strains examined since 1978 in this laboratory. The most commonly observed tumor was the tubular adenoma. Others recorded were tubular adenocarcinoma, papillary cystadenoma, papillary cystadenocarcinoma, a Sertoli's cell tumor, benign and malignant granulosa cell tumors, benign thecal cell tumors, and classical mesotheliomas of ovarian origin. A system of classification and nomenclature of the ovarian tumors from this group is advanced.     

Mesothelial cells of peritoneal fluid

Cells in the peritoneal fluid from 159 horses were examined in Giemsa stained preparations using light microscopy. Normal mesothelial cells showed an oval nucleus with finely reticular chromatin and pale blue cytoplasm. Activated mesothelial cells occurred in fluids derived from mesothelium under acute or subacute, non-septic stimulus and were remarkable for their pleomorphism and intense basophilia which may mimic neoplasia. Transformed mesothelial cells seen in chronic inflammatory fluids were sometimes phagocytic and showed conspicuous cytoplasmic vacuolation.     

Feinstruktur des groβen Netzes von Schaf und Ziege

The ultrastructure of the adipose tissue connective tissue, mesothelium and milky spots forming the greater cmentum of sheep and goats was studied.
The mixture of connective tissue fibers and adipose tissue is arranged in submesothelial, marginal, and central layers. – The mesothelial cells are covered by a surface coat and are characterized by numerous microvilli and vesicles. The number of milky spots varies greatly. They are commonly found on the surface of the omentum and are covered by modified mesothelial cells; their interior contains macrophages and lymphoid cells.     

Morphology and classification of 96 primary cardiac neoplasms in Fischer 344 rats

Ninety-six primary cardiac neoplasms were identified from 79,971 Fischer 344 (F344) rats used in chronic toxicity and carcinogenicity studies by the National Toxicology Program (NTP) and National Cancer Institute (NCI), for an overall incidence of 0.1%. Neoplasms were classified as: 60 endocardial schwannomas, 23 intramural schwannomas, eight atriocaval mesotheliomas, three paragangliomas, one pericardial mesothelioma, and one hemangioma. Metastases occurred in four rats with endocardial schwannoma. Histological appearance of the endocardial and intramural schwannomas was consistent with origin from nerve sheath. Two of six endocardial schwannomas available for immunohistochemical staining were weakly positive for S-100 antigen. The atriocaval mesotheliomas, while morphologically resembling adenocarcinoma, were positive for vimentin and keratin, indicating mesothelial origin. Seventy of the 96 cardiac neoplasms occurred in rats 2 years of age or older at time of death. There were no sex or treatment-related differences in the incidence of these neoplasms, with the exception of atriocaval mesothelioma, which was more common in males.     

Malignant mesothelioma in urban dogs

Clinical and postmortem materials from six dogs with a diagnosis of malignant mesothelioma were studied retrospectively. The dogs were urban pets with clinical signs of malignant effusions. Two mesotheliomas were pleural, one pericardial, and one peritoneal. Both pleura and pericardium were involved in one dog, and the pleura and peritoneum in another. On gross examination at necropsy, diffuse granular or velvety plaques covering mesothelial surfaces were found in all dogs; firm discrete pleural nodules also were present in two dogs. Neither distant metastases nor areas of deep lung invasion were found. The tumors varied histologically, but the most common type was epithelial with a papillary pattern. Ultrastructurally, the neoplastic cells had prominent surface microvilli, numerous desmosomes, and tonofilaments. Lung tissue from these dogs and from control dogs was evaluated for the presence of ferruginous bodies. Asbestos bodies were found in three of five dogs with mesotheliomas but rarely were found in control dogs. As a group, the mesothelioma cases had significantly more asbestos bodies and total ferruginous bodies than controls. The clinical and morphologic appearance of canine mesothelioma is similar to human mesothelioma and also may be associated with exposure to airborne fibers.     

Lesions and retroviruses associated with naturally occurring ovine pulmonary carcinoma (sheep pulmonary adenomatosis)

Five sheep with ovine pulmonary carcinoma were markedly dyspneic and had sporadic coughing; two had copious watery nasal exudate. In four, lesions consisted of multifocal nodules of neoplastic cuboidal epithelial cells in acinar or papillary patterns. Electron microscopically, cells had microvilli, tight junctions, and cytoplasmic lamellar bodies typical of alveolar type II cells. One sheep had a single lung tumor of nonciliated bronchiolar epithelial cells. Vacuolated alveolar macrophages surrounded adenomatous foci. One sheep had a metastatic lesion in the caudal mediastinal lymph node. All sheep had histologic lesions of lymphoid interstitial pneumonia (LIP, ovine progressive pneumonia) consisting of peribronchiolar and interstitial lymphoid hyperplasia, and fibromuscular proliferation; all had serum precipitating antibodies to ovine lentivirus. Lung fluids or tumor homogenates contained a 26-kd peptide that crossreacted with a primate-derived type D retrovirus as detected by immunoblotting or interspecies competition radioimmunoassay. Ovine lentivirus was isolated from concentrated lung fluids or tumor tissues of four sheep tested and from tumor cell DNA of one animal transfected into ovine muscle cells. These studies document the presence of type D-related retrovirus antigen in ovine pulmonary carcinoma (OPC) in the United States and indicate that lentivirus-induced LIP is a lesion frequently associated with this disease.     

Cytology of diffuse mesothelioma in the thorax of a horse.

Examination of effusions from body cavities must include a search for neoplastic as well as inflammatory cells. Neoplastic cells found in the thorax are generally derived from adenocarcinomas or mesotheliomas. Mesotheliomas are relatively uncommon and the neoplastic cells found in effusions are difficult to differentiate from activated cells in inflammatory effusions. An ante-mortem diagnosis of mesothelioma was made in a mare on the basis of the large volume of fluid produced, the pleomorphic mesothelial cells, the polyp formation and the absence of PAS staining material after digestion of the cell impression with maltase diastase.     

Lectin histochemical pattern on the normal and cystic ovaries of sows

The lectin histochemical pattern (LHP) was characterized and compared in normal and cystic ovaries of sows. Six biotinylated lectins (PNA, SBA, WGA, RCA‐1, DBA and UEA‐1) were used on tissue sections. In the normal ovaries, the reaction to UEA‐1 and SBA was mild to moderate in mesothelial and endothelial cells. RCA‐1 staining was mild to moderate in theca interna of growing follicles, corpora luteum and mesothelium. In addition, this lectin presented strong reaction in endothelial cells, granulosa cells of atretic follicles, zona pellucida of growing follicles and plasma. DBA showed strong intensity in mesothelial and endothelial cells. There was mild to moderate reactivity to WGA in granulosa cells, corpus luteum and theca interna of follicles in development, and moderate in zona pellucida, in granulosa cells of atretic follicles and mesothelium. PNA staining was mild to moderate in oocytes and in the adventitia and media of medullary arteries. Changes in the LHP of the cystic ovaries were noted; however, there were no differences in these findings between the follicular and luteinized cysts. UEA‐1 reactivity in the cystic ovaries was moderately reduced in the mesothelial and endothelial cells, whereas there was mild reduction in the DBA staining in the granulosa cells. Reaction to RCA‐1 and WGA in the cysts also was decreased in theca interna, zona pellucida and granulosa cells of atretic follicles. Furthermore, endothelium and theca interna in the cystic ovaries presented mild reduction of marcation to SBA, whereas there was decreased reactivity to PNA in the oocytes and adventitia and media layers of the medullary arteries. The results of the current study show that cysts modify the LHP in swine ovaries. These changes of glycoconjugates in many ovarian structures could modify diverse process and may be one of the reasons for decreased fertility in sows.     

Bacterial Pleuritis with Thickened Mesothelial Hyperplasia in a Young Beagle Dog

A five-month-old male beagle dog suddenly became moribund. Bloody fluid accumulated in the thoracic and abdominal cavities, and soft yellow flecks were floating in the thoracic fluid. The mediastinum and pericardium became dark reddish with villous thickening. Other parietal and pulmonary pleurae were rough, and the organs adhered to each other. Histologically, most mediastinal pleura formed papillary projections covered by a single layer of mesothelial cells. Many macrophages and neutrophils infiltrated the submesothelial connective tissue. At the mediastinum adjacent to the pericardium, cuboidal mesothelial cells proliferated solidly and formed a thick surface stratum. The flecks consisted of gram-negative filamentous or small bacillary (coccoid) bacteria. In the right posterior lobe of the lung, neutrophilic infiltration and a large encapsulated abscess including a bacterial colony were present. We diagnosed this case as “bacterial pleuritis with thickened mesothelial hyperplasia”. The cause of the pleuritis might be a chronic pleural infection spread via the lung abscess.     

Malignant pleural mesothelioma in a female Lion (Panthera leo)

An 18-year-old female lion (Panthera leo) was referred to the Department of Animal Pathology of the University of Turin (Italy). At necropsy, multiple nodular, 4-20-mm, confluent white firm nodules were scattered throughout the pleural surfaces of the thoracic wall and of the lungs. Histological lesions were represented by proliferations of papillary structures lined by cuboidal basophilic mesothelial cells with large, oval nuclei and abundant granular eosinophilic cytoplasm. Immunohistochemistry revealed immunoreactivity for pancytokeratin and vimentin. None of the cells expressed calretinin antigen. Asbestos fibers and asbestos bodies were not detected respectively by light microscopy and by Scanning Electron Microscope-Energy Dispersive Spectrometer investigations. On the contrary, chrysotile asbestos were identified in samples from shelter material. Histological and immunohistochemical findings were consistent with the diagnosis of an epithelial malignant mesothelioma. To our best knowledge, this is the first report of a pleural mesothelioma in a lion.     

Loss of p16/Ink4a drives high frequency of rhabdomyosarcoma in a rat model of Duchenne muscular dystrophy

Rhabdomyosarcoma (RMS) is an aggressive type of soft tissue sarcoma, and pleomorphic RMS is a rare subtype of RMS found in adult. p16 is a tumor suppressor which inhibits cell cycle. In human RMS, p16 gene is frequently deleted, but p16-null mice do not develop RMS. We reported that genetic ablation of p16 by the crossbreeding of p16 knock-out rats (p16-KO rats) improved the dystrophic phenotype of a rat model of Duchenne muscular dystrophy (Dmd-KO rats). However, p16/Dmd double knock-out rats (dKO rats) unexpectedly developed sarcoma. In the present study, we raised p16-KO, Dmd-KO, and dKO rats until 11 months of age. Twelve out of 22 dKO rats developed pleomorphic RMS after 9 months of age, while none of p16-KO rats and Dmd-KO rats developed tumor. The neoplasms were connected to skeletal muscle tissue with indistinct borders and characterized by diffuse proliferation of pleomorphic cells which had eosinophilic cytoplasm and atypical nuclei with anisokaryosis. For almost all cases, the tumor cells immunohistochemically expressed myogenic markers including desmin, MyoD, and myogenin. The single cell cloning from tumor primary cells gained 20 individual Pax7-negative MyoD-positive RMS cell clones. Our results demonstrated that double knock-out of p16 and dystrophin in rats leads to the development of pleomorphic RMS, providing an animal model that may be useful to study the developmental mechanism of pleomorphic RMS.     

Pericardial mesothelioma in a neonatal calf

We encountered an extremely rare tumor, a pericardial mesothelioma, in a neonatal calf. The patient calf showed severe abdominal distention, and died immediately after birth. The thoracic cavity was contained a huge heart with a large amount of pericardial fluid. A number of granular and cobblestone-like nodules were dispersed over the epicardium and pericardium. The nodules consisted of papillary proliferations of neoplastic cells, and the neoplasm occasionally showed mesenchymal proliferations. Immunohistochemistry revealed that they had the characteristics of mesothelial cells (cytokeratin-and vimentin-positive), and the neoplasm was diagnosed as mesothelioma.     

Intracardial mesotheliomas and a gastric papilloma in a giant grouper, Epinephelus itajara (Lichtenstein).

A giant grouper, Epinephelus itajara (Lichtenstein), was found dead in its tank. The principal necropsy findings consisted of multiple tumors in the ventricle of the heart, a tumor mass in the stomach, and protozoa-like organisms in the heart tumor, bile ducts and kidney collecting ducts. The heart tumors were identified as mesotheliomas the stomach tumor as a papilloma. The morphology of the protozoan-like organisms was similar to that of Rhabdospora thelohani (Languesse).     

Surface alterations in the bovine pelvic peritoneum following rectal examination of reproductive organs: a scanning electron microscopy study

The aim of the present study was to evaluate possible injury provoked by an intensive reproductive programme based on rectal palpation in the cow. Alterations to the mesothelial surface of the peritoneum and to the oviductal mucosa were explored by scanning electron microscopy (SEM). Nine multiparous Friesian cows were selected from each of two commercial dairy herds. Cows in herd 1 were maintained on a weekly reproductive health programme, while those in herd 2 were not subjected to gynaecological exploration. Surface features of the mesothelial cells of the reproductive tract and adjacent ligaments, and the oviductal mucosa were explored by SEM observation of tissue specimens from each animal. Six cows in the intensive reproductive programme showed microscopic alterations of the peritoneal surface. Strands were observed in the oviducts and adjacent ligaments in five of these cows. These strands, composed of filaments covered with mesothelial cells, were probably adhesions. Cells with abundant vacuoles on their surface were detected in the mesothelium corresponding to three animals, two of which also showed microscopic strands. No peritoneal surface alterations were observed in the cows from herd 2. No oviductal mucosal modifications were detected in either group. These findings suggest that intensive reproductive programmes based on rectal palpation may increase the risk of peritoneal surface alterations in the cow, but effects on reproductive physiology are unlikely.     

Immunohistochemical characterization of mesothelioma in 6 large felids

Mesothelioma has been reported frequently in large felids. These neoplasms present a diagnostic challenge given their highly variable morphology that mimics carcinomas or sarcomas at different locations. Our goal was to characterize mesotheliomas morphologically and immunohistochemically to determine if a panel of antibodies could be used to more accurately support the diagnosis of these neoplasms in large felids. Mesotheliomas from 6 large felids, including 4 clouded leopards, 1 Bengal tiger, and 1 cheetah, were immunohistochemically labeled for vimentin, E-cadherin, pancytokeratin, Wilms tumor 1 (WT1), MUC-1, and calretinin. The mesotheliomas of the 4 clouded leopards and the tiger were of the epithelial subtype; the mesothelioma from the cheetah was biphasic. All 6 mesotheliomas had strong immunohistochemical labeling for vimentin, E-cadherin, and pancytokeratin. All cases had cytoplasmic labeling for WT1, and 2 also had nuclear labeling. The 3 mesotheliomas with distinct papillary fronds were weakly positive for MUC-1. These and one other epithelial mesothelioma were also positive for calretinin. Our study demonstrates that the morphologic and immunohistochemical phenotypes of mesothelioma that have been identified in humans and domestic species can occur in large felids, and a panel of pancytokeratin, vimentin, WT1, and calretinin can be utilized to support the diagnosis of these neoplasms.