Pleural mesothelioma in a California sea lion (Zalophus californianus)

A 25-year-old female California sea lion (Zalophus californianus) reared in an aquarium died following a history of anorexia, lethargy, abnormal protrusion of the skin, and oral respiration. At necropsy, multiple yellowish-white nodules with diameters of 0.1-0.5 cm were disseminated in the thoracic cavity and lungs. Histopathologically, the nodules were continuous with normal mesothelium and were characterized by the proliferation of spindle-shaped to polygonal neoplastic cells with prominent atypia. The neoplastic cells exhibited diffuse, strong staining for vimentin and partial, weak to moderate staining for cytokeratin AE1/AE3. Based on these findings, the lesions were diagnosed as pleural mesothelioma. This study reports the first case of pleural mesothelioma in California sea lion.

Pulmonary alveolar microlithiasis with concurrent pleural mesothelioma in a dog

Pulmonary alveolar microlithiasis (PAM) is a rare pulmonary disorder characterized by the accumulation of calcium phosphate microliths within the alveoli, with only a few cases described in animals. A 10-year-old female Bulldog was euthanized due to history of dyspnea and recurrent pleural and pericardial effusions. At necropsy, numerous multifocal to coalescent protruding nodules of 1-5 mm in diameter were scattered throughout the thoracic serosal surfaces. Moreover, lungs showed a diffuse pale gray color and had a generalized fine grainy consistency. Histological investigations revealed abundant intra-alveolar laminated microliths that stained positive with periodic acid-Schiff and von Kossa stains. The pulmonary interstitium showed multifocal, mild to moderate thickening, due to collagen deposition and mild hyperplasia of type 2 pneumocytes. The pulmonary lesion was not associated with any inflammatory response, and mineral deposition was not observed in any other organ or tissue. In addition, pulmonary, pericardial, and pleural surfaces were extensively infiltrated by an epithelioid mesothelioma. Immunohistochemical staining revealed neoplastic cells that strongly coexpressed vimentin and cytokeratin, supporting the diagnosis of mesothelioma. An overview of PAM, including pathogenesis and histological characteristics, are discussed in relation to the concurrent pleural mesothelioma. The potential cause and effect relationship between the 2 conditions could neither be established nor ruled out.

A case of biphasic mesothelioma with osseous and chondromatous differentiation in a cat

An 11-year-old domestic short hair cat with dyspnea, cyanosis, and pleural effusion died. Necropsy revealed several nodules and masses on the parietal pleura, pericardium, and diaphragm. The tumor contained epithelial and mesenchymal components and displayed osseous and chondromatous differentiation. Tumors cells were positive for pancytokeratin and vimentin. This is the first report of a biphasic mesothelioma with osseous and chondromatous differentiation in this species.

A biphasic malignant mesothelioma of the peritoneum and pleura in a horse

This report describes the macroscopic, histologic, immunohistologic and ultrastructural characteristics ofa biphasic malignant mesothelioma in the peritoneal and pleural cavity of a 13-year-old Icelandic pony mare, which exhibited recurrent ascites clinically. Immunohistology was performed employing multiple monoclonal antibodies against cytokeratins (CK) and vimentin. The ultrastructural examination included the quantitative evaluation of the length to diameter ratio of the microvilli. Post mortem examination revealed a severe ascites and hydrothorax. The serosal surfaces of the peritoneum and pleura displayed poorly-demarcated, multifocal to coalescing laminar masses and small nodules. Histology revealed a bimorphic mass consisting of spindle-shaped cells and microcystic epithelioid areas. A transcoelomic and local invasive growth pattern as well as lymph node metastases were noticed. Immunohistology revealed a strong expression of CK. Though a low and moderate expression of CK5/6 and CK20 was present, respectively, CK7 and CK10-antigens were lacking. Ultrastructurally, the epithelioid mesothelioma cells displayed long microvilli, cytoplasmic tonofilaments, and desmosomes. Quantitative evaluation of the length to diameter ratio of the 10 longest microvilli revealed a mean value of approximately 16.2. Summarized, this report described the case of a malignant biphasic mesothelioma with an atypical CK20 expression but a characteristic ultrastructural morphology including long microvilli.

Palliative intravenous cisplatin treatment for concurrent peritoneal and pleural mesothelioma in a dog

A 10-year-old Maltese dog was presented with abdominal distention and dyspnea. Cytological examination of pleural and peritoneal effusion was suggestive of malignant effusion of glandular origin. Numerous, multifocal, tan to white nodules were disseminated throughout the surface of the abdominal organs and peritoneum at biopsy. Histologically, the tumors were revealed to be an epithelial type of mesothelioma. Neoplastic cells co-expressed cytokeratin and vimentin. Intravenous administration of cisplatin was chosen as the treatment. During treatment, the dog's overall body condition improved and the clinical signs were relieved without significant side effects. The survival time from diagnosis to sudden death by unknown cause was 153 days.

Portal site metastasis of invasive mesothelioma after diagnostic thoracoscopy in a dog

CASE DESCRIPTION

A 10-year-old Golden Retriever evaluated because of recurrent pericardial and pleural effusion underwent thoracoscopy with biopsy of the pleura and mediastinum.

CLINICAL FINDINGS

Before thoracoscopy, 5 L of serosanguinous fluid was removed from the pleural cavity via thoracocentesis. During thoracoscopic exploration, it was observed that the parietal pleura and mediastinum were covered by miliary white to tan nodules 1 to 3 mm in diameter. Biopsy specimens were obtained, and partial pericardiectomy was performed. Portal sites were closed routinely. Cytologic evaluation of the pleural fluid revealed high protein concentration and cellularity, with cellular changes consistent with an exfoliating carcinoma. Results of bacterial culture were negative.

TREATMENT AND OUTCOME

Carboplatin was administered via intracavitary instillation, and prednisone was administered orally. Twenty-one days later, 1 firm, irregularly shaped 6.5 x 3-cm mass and 4 smaller masses were detected in the area of the left thoracic wall where the cannula had been inserted during thoracoscopy. Histologic analysis of tissue from the masses collected at necropsy confirmed that they were malignant tumors with similar appearance to the pleural mesothelioma and immunohistochemical staining properties identical to those of the primary tumor.

CLINICAL RELEVANCE

Although thoracoscopy is associated with less postoperative pain, shorter hospitalization times, and faster patient recovery than sternotomy procedures, complications are also possible with minimally invasive endoscopic surgery. Portal site metastasis can develop from contamination of portal sites with cells on instruments or cannulas or via leakage of effusion fluid. Although rare, this potential complication should be discussed with owners prior to performing the procedure.

Ten cases of feline mesothelioma: an immunohistochemical and ultrastructural study

In the cat only 10 cases of mesothelioma, mainly of the peritoneum, have been previously reported. This paper describes a further 10 cases, eight pleural and two peritoneal, in males and females aged 1-17 years. Histologically, five tumours were epithelial, three fibrosarcomatous and two biphasic. Immunohistochemical markers used in human pathology for the identification of mesotheliomas include vimentin, cytokeratin (CK) AE1/AE3, HBME-1, CK 5/6, calretinin, thrombomodulin, carcinoembryonic antigen (CEA), CD15, E-cadherin and desmin. All 10 feline mesotheliomas were positive for vimentin and CK AE1/AE3, six were positive for HBME-1, two for CK5/6, three for CEA and four for E-cadherin. All were negative for desmin and calretinin. Antibodies to thrombomodulin and CD15 failed to cross-react with feline tissues. Electron microscopy, performed in four cases, revealed microvillar structures, desmosomes and intracytoplasmic lumina, confirming its value as a diagnostic tool. The study showed that mesothelial marker antibodies commonly used in human patients can be used for the diagnosis of feline mesothelioma, preferably as a panel of antibodies rather than only one.

Malignant pleural mesothelioma in a woodchuck (Marmota monax)

A spontaneous pleural mesothelioma was observed in a 4-year-old female woodchuck (Marmota monax). At necropsy, multifocal, tan to white, firm discrete nodules, 2 to 40 mm in diameter, were scattered over the ventral parts of the lungs and their corresponding parts of the diaphragm and the thoracic wall. Histopathologically, the tumor cells were large, cuboidal-shaped and variable size, and were weakly positive with PAS and Alcian blue. Immunohistochemically, neoplastic cells were positive for both vimentin and cytokeratin, indicating mesothelial origin. This report represents, as far as we know, the first reported case of a spontaneous mesothelioma in woodchucks.

Pleural mesothelioma in a young cat

A mesothelioma was seen as an incidental finding in the thoracic cavity of an eleven-month old female cat. At necropsy, the pale nodular lesions were spread over the ventral parts of the lungs and their corresponding parts of the diaphragm and the thoracic wall. Microscopically, the tumor consisted of mesenchymal tissue with large amounts of collagenous fibers covered by a mainly unilayered, polymorphic, partly vacuolated line of cells with large nuclei. Mitotic figures were rare. Based on morphological appearance the lesion was classified as an early mesothelioma.

Use of thoracoscopy to determine the etiology of pleural effusion in dogs and cats: 18 cases (1998-2001)

OBJECTIVE

To assess use of thoracoscopy to determine causes of pleural effusion in dogs and cats.

DESIGN

Retrospective study.

ANIMALS

15 dogs and 3 cats with pleural effusion.

PROCEDURE

Medical records were reviewed from 1998 to 2001 for dogs and cats that had exploratory thoracoscopy, biopsy, and histologic analysis to determine the etiology of pleural effusion. Intraoperative and postoperative complications were recorded. Surgical biopsy specimens were evaluated for quantity and quality for providing a histologic diagnosis.

RESULTS

Biopsy specimens were deemed adequate in quantity and quality to render a histologic diagnosis in all animals. Etiology of the effusion was neoplasia in 8 animals and non-neoplastic pleuritis in 10 animals. Median survival time of animals with neoplasia was 15 days, whereas those with inflammatory diseases had median survival time of > 785 days. Postoperative pneumothorax was encountered in 2 animals subsequent to pulmonary biopsy. No other major complications were recorded.

CONCLUSIONS AND CLINICAL RELEVANCE

Thoracoscopy is a diagnostic option that provides excellent viewing of intrathoracic structures and adequate biopsy specimens with minimal complications. This technique provides a less invasive alternative to thoracotomy for evaluating the etiology of pleural effusion.

Myofibroblastic sarcoma of the pleura in a pig

An intrathoracic sarcoma from a 7-month-old female pig was studied by light and electron microscopy and immunohistochemistry. The tumor tissue of varied cell density consisted chiefly of spindle-shaped cells, some of which grew around blood vessels in a concentric fashion. Many tumor cells were positive for alpha smooth muscle actin and not for desmin, though some cells were reactive for both antigens. A majority of tumor cells had ultrastructural features characteristic of myofibroblasts, but a few cells resembled vascular smooth muscle cells in the synthetic state. This neoplasm may have arisen from vascular smooth muscle with features indicating a transition to myofibroblasts.

Concurrent multicentric hemangiosarcoma and ovarian teratoma in an aged Père david's deer (Elaphurus davidianus)

A 20-yr-old female Père David's deer (Elaphurus davidianus) died following a 3-wk history of depression, anorexia, and progressive respiratory distress. At necropsy, numerous soft to firm, tan or blood-filled nodular structures, 1-6 cm in diameter, were noted in the lung and the visceral and parietal pleura and within the mediastinum. Similar nodules were also found in the liver, spleen, kidney, and lymph nodes. Histologically, the nodules were diagnosed as hemangiosarcoma. A benign teratoma was present in the left ovary.

Differentiated embryonal rhabdomyosarcoma in a cow

An embryonal rhabdomyosarcoma was found in the pleura of a 2-year-old Holstein cow after first delivery. The most predominant cells in the tumor were relatively small in size, but considerable numbers of more differentiated cells of larger sizes mingled with the small cells. The most differentiated cells were characterized by multinucleation, abundant cytoplasm containing cross-striated fibrils, intense immunoreactivity for desmin, and weak or negative reactivity for vimentin. Such cells, lacking mitotic activity and displaying weak or no reactivity for proliferating cell nuclear antigen, were considered to be malignant counterparts of myotubes or muscle fibers. This neoplasm seems to follow normal skeletal muscle embryogenesis, and to be capable of differentiation into the final stage of muscle development.

Prognosis factors for survival in cats after removal of a primary lung tumor: 21 cases (1979-1994)

OBJECTIVE

To identify possible prognostic factors for survival time in cats with a primary lung tumor after surgical excision.

STUDY DESIGN

Retrospective clinical study.

ANIMAL POPULATION

21 cats with histologically confirmed primary lung tumors removed surgically.

METHODS

Medical records for cats treated between 1979 and 1994 at 14 participating veterinary referral hospitals were reviewed.

RESULTS

After surgical resection and recovery, 18 cats died from metastatic disease with a median survival time of 115 days (range, 13 to 1,526 days). Three cats were lost to follow-up at 119 days, 251 days, and 410 days after the surgical procedure. Contingency table analysis to determine if an association existed between clinical findings (breed, age, gender, body weight, clinical signs, duration of clinical signs, and radiographic findings) or histological features and survival time was performed. Only histological morphology of the primary lung tumor showed a significant association with survival time. Twelve cats with moderately differentiated tumors had a significantly longer survival time (median, 698 days; range, 19 to 1,526 days) than the nine cats with poorly differentiated tumors (median, 75 days; range, 13 to 634 days).

CONCLUSIONS

Surgical resection of a solitary primary lung tumor in cats is indicated.

CLINICAL RELEVANCE

A poor prognosis for long-term survival is warranted for those cats having a poorly differentiated primary lung tumor.

Metastatic malignant mesothelioma in a tiger (Panthera tigris)

An 8-yr-old female tiger (Panthera tigris) died following a 2-wk history of progressive depression, anorexia, respiratory insufficiency, and exercise intolerance. At the time of necropsy, numerous coalescing, 4-20-mm, tan, firm nodules were scattered throughout the pleural surfaces of the thoracic wall and the mediastinum, giving a velvety appearance to these surfaces. Histologically, the nodules were diagnosed as malignant pleural mesothelioma. Secondary metastasis to the regional tracheobronchial and mediastinal lymph nodes was observed.

Primary adenocarcinoma of the gland of the nictitating membrane in a cat

An 11-year-old, neutered, male domestic shorthair was presented with a five-month history of recurrent, unilateral, seromucoid discharge from the right eye. A verrucous mass extended from the posterior aspect of the nictitating membrane. Adenocarcinoma of the gland of the nictitating membrane (GNM) was diagnosed upon biopsy. The cat subsequently developed metastases to the lungs, pleura, mediastinum, liver, and kidneys and died six months after clinical signs first were observed. Little is known about the biological behavior of adenocarcinoma of the GNM in cats. This is the first report that describes the natural progression of this disease.

Other diseases in animals

Experimental inhalation in a number of studies has demonstrated that chrysotile asbestos can cause pulmonary fibrosis and both benign and malignant pulmonary tumours, two lesions which are associated in that the studies reporting high tumour rates also found high levels of asbestosis. One comparison reported that animals with malignant tumours had approximately twice the amount of fibrosis in the lung parenchyma as those of similar age without tumours. Many studies have examined the pathogenicity of asbestos administered by ingestion and most of these included chrysotile asbestos: the results have been universally negative apart from one study with amosite that contained no control animals and is best discarded. Only one inhalation study has reported an examination of the larynxes of animals: this found no pathological changes. In many studies, tumours other than the lung had been listed, but significant numbers of kidney tumours have never been recorded. Injection studies inducing mesothelioma have indicated that fibre geometry is important with long thin fibres (> 8 microns in length and < 0.25 microns in diameter) being the most carcinogenic. This has been difficult to confirm for inhaled fibres although fibres less than 5 microns in length appear to cause neither fibrosis nor pulmonary tumours. Similar results have been found with amosite for fibres up to 10-15 microns although longer fibres do produce these conditions. It is suggested that to produce pulmonary fibrosis and neoplasia fibres may need to be longer than 20 microns. Chrysotile has been shown in many studies to be removed from lung tissue much more rapidly than amphibole fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and pathological features of thoracic neoplasia in the horse

Thirty-eight horses with confirmed thoracic neoplasia included 28 (37.7%) with lymphosarcoma, 4 (10.5%) with metastatic renal cell carcinoma, 2 (5.3%) with primary lung carcinoma, 2 (5.3%) with secondary squamous cell carcinoma from the stomach, 1 (2.6%) with pleural mesothelioma, and 1 (2.6%) with malignant melanoma. The major clinical features included weight loss, inappetence, dyspnoea and coughing, but in cases of lung metastases, they related more to the primary site of tumour formation. Haematological and serum biochemical abnormalities were non-specific. Specific pre-mortem diagnosis was made in 14 horses; this was most readily achieved when exfoliated neoplastic cells were present in pleural fluid.

Mesothelioma in horses

Pleural mesothelioma and pericardial mesothelioma with spread to the pleural cavity were diagnosed in 2 horses. Clinical signs included respiratory distress, depression and pleural pain. The affected body cavities contained copious, serous effusions containing very large neoplastic mesothelial cells with densely-staining cytoplasm, hyperchromic nuclei and prominent, often multiple, nucleoli. Ultrastructurally, the neoplastic cells appeared as solid aggregates, with profuse microvillous borders and neolumen formation. Cytological examination, together with confirmative ancillary diagnostic tests, including electron microscopy and immunocytochemistry, may be used to obtain an ante-mortem diagnosis of mesothelioma.

Chemotherapy for intrathoracic cancer in dogs and cats

The thoracic cavity contains numerous tissue types from which tumors may arise. Broadly speaking, the cavity is comprised of the pleural surfaces, the mediastinum and its enclosed viscera, and the lungs. Neoplasms arising from these structures are frequently advanced at the time of diagnosis, and surgery is rarely curative for malignant processes. Although reports describing anticancer chemotherapy use in dogs and cats for tumors of the thoracic cavity largely have been anecdotal, as advances are made in the chemotherapeutic management of comparable tumors in human cancer patients and as veterinarians become familiar with these compounds, use of antineoplastics as an adjunct to, or in place of, local treatment modalities should increase. This article reviews the epidemiology, clinical features, and diagnosis of pulmonary neoplasia; mediastinal neoplasia, particularly thymoma; and pleural neoplasia, with emphasis on mesothelioma. In addition, options for chemotherapy, derived from both the human and veterinary literature, are given for each tumor type.

Mesothelioma in cattle: eight cases (1970-1988)

Over an 8-year period, 8 beef cattle with mesothelioma were admitted to the Auburn University College of Veterinary Medicine and the Louisiana State School of Veterinary Medicine. Diagnosis was confirmed by histologic examination of affected tissues. Five bulls, 1 steer, and 2 cows were affected. Four of the bulls had scrotal swelling; 2 cows and 1 bull had ventral abdominal swelling. The peritoneal cavity was involved in 5 cases, the pleural cavity was affected in 2 cases, and in 2 cases, disease was apparently confined to the vaginal cavity. Of the 8 cattle, 6 died or were euthanatized; only cattle with tumor apparently confined to the vaginal cavity survived.

Intracavitary cisplatin chemotherapy experience with six dogs

Six dogs with a median age of 7 years (range = 5-14 years) were presented for signs referable to thoracic or abdominal effusion associated with neoplasia of the body cavities. Intracavitary cisplatin was administered at 50 mg/m2 every 4 weeks for a median of 2.5 treatments (mean = 3, range = 1-6). Three dogs with pleural mesothelioma had complete resolution of effusion for 289, 129, and greater than 306 days without evidence of tumor growth. Resolution of effusion occurred after one treatment in two dogs and after two treatments in one dog. In three dogs with carcinomatosis of unknown origin, complete responses was seen in two dogs after one treatment for 255 and greater than 807 days, respectively. Intracavitary chemotherapy with cisplatin was associated with palliation and control of malignant pleural and/or abdominal effusion in five of six dogs. Toxicity was minimal, and this method of therapy should be further explored in dogs with similar malignancies.

Pleuroscopic diagnosis of disseminated hemangiosarcoma in a horse

A 7-year-old Thoroughbred mare was examined because of persistent bilateral epistaxis and respiratory distress. Evidence of bilateral pleural effusion was found during physical examination, and a large amount of serosanguineous fluid was drained from the right side of the thorax. Cytologic examination and bacteriologic culture of the transtracheal aspirate and pleural fluid did not yield evidence of sepsis. A coagulation profile was unremarkable. Radiographic and echographic changes were seen in the lung parenchyma. Pleuroscopy, with the horse standing, revealed numerous dark nodules on the pleura, diaphragm, and lung surface. On the basis of biopsy and necropsy findings, the histopathologic diagnosis was disseminated hemangiosarcoma.

Pleural mesothelioma in a European spotted fallow deer (Cervus dama)

An adult, captive European spotted fallow deer (Cervus dama) was submitted for necropsy due to sudden death. Gross lesions consisted of serosanguinous fluid in the thoracic cavity with multiple, often confluent, nodules covering visceral and parietal pleura. Microscopic examination revealed tubular structures lined by cuboidal cells covering a delicate fibrous stroma. Gross and microscopic morphology was consistent with a mesothelioma.

[Case report: adenocarcinoma of the intestines in a goat]

A case of an adenocarcinoma of the gut with multiple metastases in an old female goat is reported.

Intrathoracic granular cell tumour in a dog

Multiple granular cell tumours occurred diffusely throughout the pleura of an adult German Shepherd Dog. The growths were scattered over the surface of the lungs, mediastinum and diaphragm. Histologically, the masses consisted of plump cords of cells with eosinophilic, weakly PAS-positive cytoplasmic granules. Electron microscopically, the granules consisted of a pleomorphic population of electron-dense granules. The predilection site in the dog is the tongue and this is the first report of an intrathoracic, pleural site of granular cell tumours in the dog.

Management of pleural effusion secondary to metastatic adenocarcinoma in a dog

A 4-year-old spayed Collie-type dog was evaluated for pleural effusion secondary to metastatic adenocarcinoma with no identifiable primary tumor. For 48 weeks, chemotherapy and thoracentesis palliated clinical signs associated with pleural effusion. At week 49, 5 mCi of chronic phosphate P32 (32P) suspension was injected into the right pleural space. Pleural effusion was not detected for 14 weeks after 32P administration (week 63). In week 64, 32P suspension was readministered by injecting 7.5 mCi into the right hemithorax and 2.5 mCi into the left. Pleural effusion was again detected 3 weeks later (week 67), and the dog was treated with additional chemotherapy. Death, at week 72, was caused by disseminated intravascular coagulopathy.

Intrathoracic lipoma in a dog

A 0.9 kg lipoma was removed surgically from the cranial mediastinum of an 11-year-old dog. Clinical signs related to the mass consisted of coughing and dyspnea. Postoperative recovery was uncomplicated and the clinical signs diminished immediately. The thoracic cavity is an unusual location for the development of a lipoma.

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.

Exfoliative cytology in the diagnosis of diffuse mesothelioma in the dog. Illustration by a case report

This report deals with a dog which was presented for ascites that appeard to be related to fluid accumulation in the pericardium. Subsequent to resection of the pericardium the ascites disappeared but a few months later there was fluid accumulation in the thorax. Cytological examination of the thoracic fluid revealed the cell aggregates ("cell balls") which are indicative of mesothelioma and this diagnosis was confirmed by the autopsy findings. The initial cytological diagnosis on the pericardial fluid, which was not in agreement with the histology of the excised pericardium, is also discussed.

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.

Ultrastructure of canine carotid body and aortic body tumors. Comparison with tissues of thyroid and parathyroid origin

The microscopic structure of canine carotid and aortic body neoplasms was compared with that of other lesions of the neck and thorax. Carotid and aortic body adenomas consisted of clusters of large, polyhedral cells whose cytoplasm was filled with dense, membrane-bound granules and which lacked the normal relationship to sustentacular, nerve, and vascular cells. Unlike an ectopic thyroid adenoma, they had no thyroid follicles, PAS-stained cytoplasmic granules, acidic mucopolysaccharide foci, or dense tubules within the cisternae of the endoplasmic reticulum. Cells of the aortic body carcinoma were less differentiated than those of the adenoma. They contained fewer dense granules but had greater numbers of microfibrils and Golgi vesicles. Degeneration and necrosis of neoplastic tissue exaggerated differences from the adenomas. Cells from the metastatic tumor (pleural carcinomatosis) did not differ significantly from those of the primary tumor. Cells from thyroid and parathyroid lesions were significantly different ultrastructurally from those of carotid and aortic body tumors. Cells of the ectopic thyroid adenoma and thyroid carcinoma resembled normal follicular cells but were larger and contained characteristic PAS-stained granules and arrays of intracisternal microtubules. The parathyroid adenoma cells had few organelles; the dominant cytoplasmic structures were aggregates of membranes and residual bodies filled with lipofuscin.