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Objective: Thymoma-associated paraneoplastic syndromes in dogs and cats include myasthenia gravis, hypercalcemia, exfoliative dermatitis, erythema multiforme, T-cell lymphocytosis, myocarditis, anemia, and polymyositis. Paraneoplastic myasthenia gravis (MG) is the most commonly reported paraneoplastic syndrome in dogs with thymic epithelial tumors. The objective of this study was to examine cases of canine thymic-associated MG treated surgically, with the specific objective of providing an updated clinical picture of the preoperative management, postoperative complications, and outcomes of these cases., Animals: Nine dogs with paraneoplastic MG underwent surgical removal of a thymic epithelial tumor., Procedure: Medical records of dogs with MG that received surgical treatment of a thymic epithelial tumor between January 1, 2012 and October 1, 2022 were obtained from 4 veterinary teaching hospitals. Descriptions of perioperative MG management, complications, and outcomes were reported., Results: Six of the 9 dogs received medical therapy for MG, with either a cholinesterase inhibitor (4 dogs) or a cholinesterase inhibitor and immunosuppressive agent (2 dogs), before surgery. The median duration of medical therapy for MG before surgery was 7.5 d (range: 2 to 60 d). Three of 9 dogs experienced immediate postoperative complications and were euthanized. Six of 9 dogs (66.6%) survived to discharge and 3 of 6 dogs that survived to discharge were alive at the time of writing. At the time of writing, 3 of 6 dogs had complete resolution of clinical signs attributable to MG and 2 of 6 had partial resolution. The median time from surgery to resolution of clinical signs of MG in these dogs was 63 d (range: 2 to 515 d)., Conclusion: Dogs with thymic epithelial tumors and paraneoplastic MG are at a high risk for perioperative complications., Clinical Relevance: The findings of this study corroborate previous literature stating that paraneoplastic MG is a poor prognostic indicator for dogs with thymic epithelial tumors, while also highlighting the variation in approaches to clinical management of thymic-associated MG in veterinary medicine and the lack of established protocols guiding perioperative management., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

Background: The most common cranial mediastinal masses affecting dogs and cats include lymphoma and thymic epithelial tumors. In this report, a cat with a cranial mediastinal mass was diagnosed with a thymic carcinoma subtype squamous cell carcinoma, which has rarely been reported in cats. Management of this subtype with a combination of surgery and chemotherapy has so far not been reported. This case report describes the treatment with surgical management followed by intracavitary carboplatin., Case Description: A 12-year-old male neutered domestic short hair cat was referred for lethargy, hyporexia, and weight loss, and was diagnosed with a cranial mediastinal mass radiographically. Initial cytology through fine needle aspirates was suggestive of carcinoma. Computed tomography was performed which did not show evidence of other primary tumor sources or metastases, and hence surgical resection was recommended. Intraoperative findings revealed local invasion of the surrounding tissues, including major vasculature and nerves, although histopathological assessment showed no local lymph node involvement. Intracavitary carboplatin chemotherapy was administered 2 weeks postsurgery. The patient was humanely euthanized 4 weeks postsurgery due to evidence of local recurrence causing significant respiratory compromise., Conclusion: A combination of surgical excision as well as intracavitary carboplatin does not seem to be effective for the treatment of this thymic carcinoma subtype, with evidence of early recurrence and return of clinical signs., Competing Interests: The authors declared no potential conflicts of interests with respect to the research, authorship, and/or publication of this article.

A 4-y-old, spayed female, mixed-breed domesticated rabbit ( Oryctolagus cuniculus domesticus ) was presented because of progressive bilateral exophthalmos, with a large mediastinal mass in the cranial thorax. Palliative radiation therapy was elected, and 4 fractions of 5 Gy were delivered twice weekly under general anesthesia using 3-dimensional conformal radiation therapy for a total dose of 20 Gy, guided by an on-board cone beam CT scan. Quality-of-life and respiratory rate improved before sudden death that followed an episode of dyspnea. The overall survival time following initial diagnosis was 93 d, with 68 d after the first dose of radiation. An autopsy was performed, and the mass was diagnosed as a type A thymoma. The diagnosis was confirmed with positive immunohistochemical labeling of the neoplastic cells for cytokeratin 5/6 and cytokeratin 7.

A 5-y-old, male degu ( Octodon degus ) was presented with a subcutaneous mass in the ventral aspect of the cervical area. The mass was removed surgically. Histologically, the mass was a densely cellular, expansile neoplasm, with compression of thymic tissue to the periphery. The neoplasm consisted of solid sheets of polygonal cells, mixed with fewer small lymphocytes. Rare Hassall bodies were scattered throughout the mass. Polygonal cells were positive for anti-keratin/cytokeratin AE1/AE3 antibody, and small lymphocytes were positive for anti-CD3 antibody. The histopathologic and immunohistochemical findings were consistent with a thymoma. In addition, an autopsy revealed myxosarcoma of the right thoracic wall with metastasis to the lung. To our knowledge, thymoma originating from the cervical component of the thymus has not been documented previously in a rodent species.

An 8-year-old cat was presented with pruritus, purulent paronychia, scaling, crusting, and spontaneous alopecia. Histopathology revealed intraepidermal neutrophilic pustular acantholytic dermatitis and hyperkeratotic cytotoxic interface dermatitis. No thoracic mass was seen on a lateral radiograph. Ectopic thymoma was discovered on necropsy. This case highlights the necessity for thorough investigation of any case of feline exfoliative dermatitis and pemphigus foliaceus for the presence of thymoma. Key clinical message: Comorbidity of exfoliative dermatitis and pemphigus foliaceus in a cat should prompt a thorough investigation for presence of a thymoma, possibly with advanced imaging techniques., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

A 13-year-old, female, mixed-breed dog with a huge cranial mediastinal mass underwent radiotherapy (RT). On the following day, the dog presented with lethargy and anorexia. Hematological examination revealed elevated levels of blood urea nitrogen, creatinine, inorganic phosphorus, potassium, lactate dehydrogenase, creatine phosphokinase and aspartate aminotransferase, decreased calcium level, and metabolic acidosis. Urine output markedly decreased. The patient recovered with fluid therapy and diuretic therapy; however, died suddenly from an unknown cause 11 days after RT completion. Histopathological examination after necropsy showed thymoma in the cranial mediastinum and extensive tubular necrosis of both kidneys which may be due to RT-induced tumor lysis syndrome (TLS). This report suggests that the risk of TLS should be evaluated in dogs with thymoma who undergo RT.

Background: Canine thymomas are associated with multiple paraneoplastic syndromes, among which myasthenia gravis (MG) is the most common. Acquired MG is an autoimmune disease characterized by the presence of antibodies against acetylcholine receptors (ACHRs). ACHRs antibodies are the most commonly formed, but the production of antistriational antibodies binding to skeletal and cardiac muscle proteins has also been recorded both in humans and dogs. An association between the occurrence of antistriational antibodies and a severe form of myocarditis, giant cell myocarditis, has been described in humans., Case Description: A 4-year-old mixed-breed dog was referred because of 1 month history of exercise-induced weakness, hypersalivation, and regurgitation. The neurologic examination was indicative of a neuromuscular junction disease, and MG was suspected. A computed tomographic scan examination showed the presence of a megaoesophagus and a thymic mass. Serum antibodies against ACHRs confirmed the diagnosis of MG. Treatment with pyridostigmine was started, and the thymic mass was surgically excised, and a diagnosis of thymoma was confirmed by histology. 24 hours after surgery, the dog developed a third-degree atrioventricular block. Severe arrhythmia and increased troponin serum levels suggested myocarditis which rapidly led to cardiopulmonary arrest. Histopathologic examination of the heart, esophagus and diaphragm revealed a lymphocytic and macrophagic infiltration, consistent with myocarditis and polymyositis. Scattered rare giant multinucleated cells were also detected in the myocardium., Conclusion: To the author's knowledge, this is the first report of thymoma-associated MG with concurrent polymyositis and giant cell-like myocarditis in a dog., Competing Interests: The authors declare that they have no conflict of interest.

A 7-y-old backyard Leghorn chicken ( Gallus domesticus ) was submitted to the California Animal Health and Food Safety Laboratory System (CAHFS)-Turlock branch for postmortem examination, with a history of unexpected death. At postmortem examination, a hemorrhagic soft tissue mass was observed in the cervical region. Microscopically, a densely cellular neoplasm of polygonal epithelial cells and small lymphocytes was observed. The microscopic features of the neoplasm in combination with positive immunohistochemistry for pancytokeratin and CD3 were used to classify the lesion as a thymoma. Thymoma was diagnosed in only 5 birds submitted to CAHFS from 1990 to 2019. Thymoma has been described only rarely in birds, and is an unusual diagnosis in backyard chickens.

Persistent small-cell lymphocytosis in dogs with a concurrent mediastinal mass has been associated with both thymoma and small-cell lymphoma. In thymomas, neoplastic thymic epithelial cells induce overproduction and release of polyclonal lymphocytes, whereas thymic lymphoma results in thymic effacement by a clonal expansion of neoplastic lymphocytes and subsequent leukemic phase of lymphoma. Flow cytometry has been used to differentiate these 2 entities by immunophenotyping mediastinal mass aspirates. It has been reported that cases with mediastinal masses in which ≥ 10% of the associated small-cell lymphocytes were double positive for CD4 and CD8 were thymomas, whereas masses associated with < 10% were suggestive of lymphoma. We report a unique case of thymoma-associated lymphocytosis lacking the classic CD4+CD8+ immunophenotype. Our findings suggest that there may be more diversity in the thymoma-associated lymphocyte immunophenotype than has been identified previously; immunophenotyping alone might not be sufficient to differentiate thymic small-cell lymphoma from thymoma-associated lymphocytosis. In dogs with mediastinal masses and peripheral lymphocytosis, employing a variety of testing modalities to avoid misdiagnosis is prudent. These modalities include cytologic and/or histologic evaluation, immunophenotyping, and clonality assessment.

Background: This is the first case report description, to our knowledge, of a cranial mediastinal mass (suspected thymoma) causing orthostatic hypotension in a dog., Case Presentation: A Labrador Retriever presented for urethral stent placement during cystoscopy secondary to transitional cell carcinoma diagnosis. During anesthesia, the patient had unexpected severe and poorly-responsive hypotension following a shift in position. Several days later, an intrathoracic mass was discovered, raising concerns that the position of the mass in relation to the great vessels and heart may have been the cause of the hypotension. The patient returned for a second stent placement, and computed tomography of the chest confirmed a cranial mediastinal mass, most suspected to be thymoma based on the results of cytology. The patient was kept in sternal recumbency, but when re-positioning to left lateral recumbency, there was a dramatic blood pressure drop that corrected with a return to sternal positioning., Conclusions: To our knowledge, orthostatic hypotension has not been described in relation to thymoma in dogs. Thymomas are rare; however, they may be associated with disease of autonomic dysfunction, such as myasthenia gravis, that may lead to orthostatic hypotension. This has been described within the human literature, and we hypothesize it was present in the currently described case. Concurrently, thymomas may grow to a substantial size and cause direct compression of the intrathoracic vasculature. As such, it should be on the differential list for poorly-responsive hypotension following a shift in body positioning under anesthesia.

As part of research and wildlife disease surveillance efforts, we performed necropsy examinations of 125 free-ranging ( n = 114) and captive ( n = 11) prairie dogs in Colorado from 2009 to 2017. From these cases, we identified three cases of thymic lymphoma in free-ranging Gunnison's prairie dogs ( Cynomys gunnisoni ), and we identified a novel retroviral sequence associated with these tumors. The viral sequence is 7700 nucleotides in length and exhibits a genetic organization that is consistent with the characteristics of a type D betaretrovirus. The proposed name of this virus is Gunnison's prairie dog retrovirus (GPDRV). We screened all 125 prairie dogs for the presence of GPDRV using PCR with envelope-specific primers and DNA extracted from spleen samples. Samples were from Gunnison's prairie dogs ( n = 59), black-tailed prairie dogs ( Cynomys ludovicianus ) ( n = 40), and white-tailed prairie dogs ( Cynomys leucurus ) ( n = 26). We identified GPDRV in a total of 7/125 (5.6%) samples including all three of the prairie dogs with thymic lymphoma, as well as spleen from an additional four Gunnison's prairie dogs with no tumors recognized at necropsy. None of the GPDRV-negative Gunnison's prairie dogs had thymic lymphomas. We also identified a related, apparently endogenous retroviral sequence in all prairie dog samples. These results suggest that GPDRV infection may lead to development of thymic lymphoma in Gunnison's prairie dogs.

A Rock Alpine doe ( Capra aegagrus hircus ) was presented to the Colorado State University Veterinary Teaching Hospital because of scaling and ulceration over the withers, coronary bands, and dewclaws. The doe was euthanized because of poor prognosis associated with a radiographically identified cranial mediastinal mass, increased respiratory effort, and discomfort. Autopsy revealed a cranial mediastinal mass, and scaling-to-ulcerative lesions affecting the dorsum, ventrum, pinna, neck, teats, coronary bands, and dewclaws. Histologically, the mediastinal mass was an epithelial neoplasm with admixed non-neoplastic T lymphocytes, consistent with a lymphoepithelial (mixed) thymoma. Sections of affected skin were characterized by hyperkeratotic cell-rich interface dermatitis with transepidermal and follicular apoptosis. Thymoma-associated exfoliative dermatitis has been recognized in cats and a rabbit, but has not been reported previously in a goat, to our knowledge. Given that thymomas are not uncommon in goats, thymoma-associated exfoliative dermatitis should be considered a clinical differential in goats with dermatologic disease.

Thymomas from 277 Fischer 344/N (F344/N), 10 Sprague Dawley (HSD:Sprague Dawley SD) (SD), 129 Wistar Han [Crl:WI(Han)] (WH), and 4 Wistar Outbred (WO) rats were reviewed from long-term studies in the National Toxicology Program (NTP) database. The incidence of thymomas in F344/N rats was slightly higher in males than in females, while the incidences in SD and WH rats were higher in females than in males. Only male WO rats were used in NTP studies. Of the 277 thymomas in F344/N rats, 235 (84.8%) were benign and 42 (15.2%) malignant, 14 of which exhibited metastasis. Of the 10 thymomas in SD rats, 5 (50%) were benign and 5 (50%) were malignant, one of which exhibited metastasis. Of the 129 thymomas in WH rats, 126 (98%) were benign and 3 (2%) were malignant, 1 with metastasis. Of the 4 thymomas in WO rats, 3 (75%) were benign and 1 (25%) was malignant, with no metastases. Malignant thymomas in F344/N and WH rats showed a propensity to be the cause of death and to result in early mortality, whereas the benign thymomas were associated less often with decreased survival. No occurrences of this neoplasm were reported to be related to exposure to any test articles.

A 12-y-old neutered male Portuguese Water dog was presented because of a 1-y history of persistent hyporexia, diarrhea, and recurrent pyelonephritis. Abdominal ultrasound revealed hepatic nodules and diffuse splenomegaly, and radiographs revealed a mediastinal mass. Fine-needle aspirates of the liver, spleen, and mediastinal mass were suspicious for lymphoma. Flow cytometry identified small T cells that co-expressed CD4 and CD8 at all sites, most suspicious for thymoma, but lymphoma could not be ruled out. PCR for antigen receptor rearrangements analysis identified polyclonal amplification of the T-cell receptor genes, more consistent with thymoma than lymphoma. Histopathology of the liver and thymic mass confirmed thymoma with hepatic metastasis.

Thymoma-associated nephropathies have been reported in people but not in dogs. In this report, we describe a dog with thymoma and concurrent renal amyloidosis. A 7-year-old castrated male Weimaraner was presented for progressive anorexia, lethargy, and tachypnea. The dog was diagnosed with azotemia, marked proteinuria, and a thymoma that was surgically removed. Postoperatively, the dog developed a large left ventricular thrombus and was euthanized. Necropsy confirmed the presence of a left ventricular thrombus and histopathology revealed renal amyloidosis. We speculate that the renal amyloidosis occurred secondary to the thymoma, with amyloidosis in turn leading to nephrotic syndrome, hypercoagulability, and ventricular thrombosis. This case illustrates the potential for thymoma-associated nephropathies to occur in dogs and that dogs suspected to have thymoma should have a urinalysis and urine protein creatinine ratio performed as part of the pre-surgical database., (Copyright © 2018 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

OBJECTIVE To determine the anatomic location and clinical signs of thymoma in goats and long-term outcomes in a subset of goats treated by tumor excision. DESIGN Retrospective case series. ANIMALS 13 goats with a histologic diagnosis of thymoma at the Cornell University Hospital for Animals between 1990 and 2014. PROCEDURES Medical records of goats with thymoma were reviewed and data were evaluated regarding signalment, clinical signs, diagnostic imaging results, thymoma size, treatment, and outcome. Follow-up information was obtained via contact with the owners and review of medical records. RESULTS 8 goats had a mediastinal mass, 4 had a palpable ventral cervical mass, and 1 had both types of masses. Median age at the time of diagnosis was 9.5 years (range, 3 to 12 years). Goats with a mediastinal mass had respiratory distress or marked tachypnea. Six goats were treated surgically, including all 5 with a ventral cervical mass. All 5 goats with a ventral cervical mass survived with no tumor recurrence for ≥ 1 year after excision. Only 2 goats with a mediastinal mass survived to hospital discharge. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the prognosis for goats following excision of ventral cervical thymomas was favorable, whereas goats with mediastinal thymomas appeared more likely to have severe clinical signs and a guarded prognosis.

OBJECTIVE To characterize clinical findings, surgical procedures, complications, and outcomes in dogs undergoing extirpation of masses from the cranial mediastinum via video-assisted thoracic surgery (VATS) and establish preliminary guidelines for case selection when considering VATS for thymectomy in dogs. DESIGN Retrospective case series. ANIMALS 18 client-owned dogs that underwent extirpation of a cranial mediastinal mass by means of VATS at 5 academic referral hospitals from 2009 through 2014. PROCEDURES Medical records were reviewed and data extracted regarding signalment, clinical signs, physical examination findings, diagnostic imaging results, surgical approach and duration, cytologic and histologic examination results, complications, outcome, and cause of death, when applicable. RESULTS 16 dogs had a thymoma, 1 had thymic anaplastic carcinoma, and 1 had hemangiosarcoma. Seven had both megaesophagus and myasthenia gravis. Median approximate tumor volume was 113.1 cm 3 (interquartile range, 33.5 to 313.3 cm 3 ). Median duration of VATS was 117.5 minutes (interquartile range, 91.5 to 136.3 minutes). Conversion to an open thoracic surgical procedure was required for 2 dogs, 1 of which died during surgery. Median survival time following VATS for dogs with thymoma and concurrent myasthenia gravis and megaesophagus was 20 days. Dogs with thymoma without paraneoplastic syndrome survived for ≥ 60 days, and none of these dogs died of disease-related causes. CONCLUSIONS AND CLINICAL RELEVANCE VATS appeared to be an acceptable approach for extirpation of masses from the cranial mediastinum in dogs under certain conditions. Dogs with myasthenia gravis and megaesophagus had a poor postoperative outcome.

Neurological signs and serum acetylcholine receptor antibody (AChR-Ab) levels before and after thymectomy were monitored in a 6-year-old male cat with acquired Myasthenia Gravis (MG) as a paraneoplastic syndrome of thymoma. Soon after surgery, the neurological symptoms relapsed, and the cholinesterase inhibitor was administered to control them. The AChR-Ab levels increased postoperatively until 90 days after surgery. This is the first report on long term measurements of serum AChR-Ab levels in a cat with MG. Although thymectomy is valuable for the removal of thymoma, it may not resolve MG symptoms, neurological signs and serum AChR-Ab levels, without medication early after surgery. Also, this case report indicates that the AChR-Ab level might be a guide to detect a deterioration of MG symptoms.

An ~21-year-old female Barbary sheep (Ammotragus lervia) died spontaneously following a lengthy episode of difficulty in walking. An ~6 × 3 × 3 cm, unilocular cystic growth was found in the cranioventral thorax. The fibrotic cystic wall, lined by a single layer of flattened to cuboidal epithelial cells, was invaginated and partially encircled solid masses of fusiform neoplastic cells with multiple intratumoral cystic structures. The fusiform neoplastic cells were intensely positive for cytokeratin (CK) and partially positive for α-smooth muscle actin and vimentin, but negative for thyroid transcription factor-1 (TTF-1) and neuron-specific enolase (NSE). The intratumoral cysts were lined by CK-positive but TTF-1- negative, NSE-negative, flattened, cuboidal to columnar epithelial cells, suggestive of cystically dilated medullary duct epithelium-derived structures. Based on the location and histopathologic findings of the growth, concurrent spindle-cell thymoma and thymic cysts was diagnosed. We also discuss the correlation between thymic cysts and thymoma and review the literature of thymomas in ovine and wildlife species., (© 2016 The Author(s).)

A 7-year-old, castrated male, domestic shorthair cat presented with generalized exfoliative dermatitis, lethargy, anorexia and weight loss. Multiple skin scrapings taken at the time did not reveal any abnormalities. Skin histopathological examination was consistent with sebaceous adenitis or exfoliative dermatitis caused by an underlying thymoma (thymoma-associated feline exfoliative dermatitis). Thoracic radiographs revealed a cranial mediastinal mass, which was removed surgically. Histopathological examinations indicated that it was a thymoma. Within 90 days of surgery, the cutaneous signs had resolved, suggesting a causal relationship between the thymoma and the skin disease. Recurrence of thymoma was detected 24 months after surgery., (© ISFM and AAFP 2014.)

Objective: To describe clinical signs, diagnostic findings, treatment, and outcome and determine factors associated with survival time for dogs with thymoma., Design: Multi-institutional retrospective case series., Animals: 116 dogs with thymoma., Procedures: Medical records were searched for information regarding signalment, physical examination findings, results of laboratory testing and diagnostic imaging, medical and surgical treatment, and survival data., Results: Of the 116 dogs with thymoma, 44 (38%) were Labrador Retrievers and Golden Retrievers. Twenty of 116 (17%) dogs had signs of myasthenia gravis (diagnosis was confirmed for 13 dogs). At the time of thymoma diagnosis, 40 (34%) dogs had hypercalcemia, 8 (7%) dogs had a concurrent immune-mediated disease, and 31 (27%) dogs had another tumor; 16 (14%) dogs developed a second nonthymic tumor at a later date. Tumor excision was performed for 84 dogs, after which 14 (17%) had tumor recurrence; prognosis was good for dogs undergoing a second surgery. Median survival time with and without surgical treatment was 635 and 76 days, respectively. Presence of another tumor at the time of thymoma diagnosis, lack of surgical excision, and higher pathological stage were significantly associated with shorter survival time. Hypercalcemia and presence of myasthenia gravis or megaesophagus at the time of thymoma diagnosis, histopathologic subtype of thymoma, or tumor development at a later date was not associated with survival time., Conclusions and Clinical Relevance: Dogs with thymoma, even those with a large tumor burden or a paraneoplastic syndrome, had a good prognosis following surgery. Surgical treatment, tumor stage, and the presence of a second tumor at diagnosis influenced survival time.

Thymoma is a primary mediastinal neoplasm arising from or exhibiting differentiation towards thymic epithelial cells, typically with the presence of non-neoplastic lymphocytes. A 13-year-old male Mynah bird (acridotheres tristis) was presented for evaluation of a 2.3 × 1.5 × 1.0 cm mass in the left ventrolateral cervical region. The clinical signs, radiology, cytohistopathology and immunohistochimy findings related to the thymoma are presented. These findings indicated that the tumor was a type AB thymoma according to the World Health Organization (WHO) and veterinary classification. Thymomas are rarely reported in avian species and this is the first report in a Mynah bird., Virtual Slides: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1159525819982779.

Two cases of feline thymoma with amyloid deposition were encountered between 1982 and 2010. Neoplastic cells were separated by abundant, pale eosinophilic, homogeneous material that was congophilic and birefringent. Ultrastructurally, the neoplastic cells were connected by desmosomes, and the extracellular deposits were composed of nonbranching, hollow-cored fibrils, 8-10 nm in diameter. In the case with sufficient archived tissue for additional sections, the amyloid remained congophilic following potassium permanganate incubation, and the neoplastic cells were immunoreactive for pancytokeratin. The histologic, histochemical, ultrastructural, and immunohistochemical features of both neoplasms are consistent with epithelial-predominant thymoma with the unusual feature of intratumoral amyloid deposition. The affinity of the amyloid for Congo red following potassium permanganate incubation is consistent with non-AA amyloid. The ultrastructural findings were consistent with amyloid production by the neoplastic epithelial cells.

A 12-year-old male burrowing owl (Athene cunicularia) was presented for evaluation of a mass in the right cervical region. A thymoma was diagnosed after surgical resection and histopathologic evaluation. Extensive adherence of the thymoma to the esophagus and suspected invasion into the right jugular vein contributed to a poor postsurgical outcome. Diagnosis and treatment of thymomas in avian species is similar to that in mammals. Surgical removal of noninvasive thymomas is usually curative. Thymomas are rarely reported in avian species and this is the first report in a strigiform bird.

A single, solid, yellow-white thymic mass was found at necropsy of a two-year-old female cynomolgus macaque from a four-week, repeat-dose toxicity and immunogenicity study. Microscopically, the mass was multilobular and well encapsulated, surrounded by a thick connective tissue capsule, and composed of dense sheets of elongate or spindle-shaped cells and large cystic cavities separated by thick connective tissue stroma. Normal thymus was adjacent to the mass, but it was compressed. Within the mass were abundant interspersed Hassall's corpuscles; individual and small clusters of mature, small lymphocytes; scattered eosinophils; large areas of necrosis; focal mineralization; and cholesterol clefts. An interesting feature was the presence of large multinucleated giant cells, which varied widely in size and nuclear number. Immunohistochemical staining for two lymphocyte markers and two structural proteins confirmed the identity of the neoplastic spindle cells and other cellular components. There was no evidence of vascular invasion or metastasis. Features of the thymoma indicated it was a pre-existing condition and not treatment related.

During a preventive medicine examination on a 13-yr-old intact female African spot-necked otter (Lutra maculicollis), radiographs were obtained and a cranial thoracic mass was noted. Cytology from an ultrasound-guided fine-needle aspirate was suggestive of a thymoma. Surgical removal was performed and this diagnosis was confirmed by histopathology. At a recheck examination 6 mo postsurgery, there was no evidence of recurrence. This case highlights the value of a comprehensive preventive medicine program that resulted in the early detection of a subclinical thymoma and its successful removal.

Thymoma-associated exfoliative dermatitis was suspected in a cat with a cranial mediastinal mass. The dermatopathy resolved with surgical removal of a thymoma. The cat manifested neurologic signs consistent with myasthenia gravis 7 wk after surgery. Exfoliative dermatitis and post-thymectomy myasthenia gravis in the same cat has not been reported previously.

Lymphoepithelial thymoma was diagnosed in a 14-year-old Samoyed dog with clinical symptoms of myasthenia gravis at 6 months of age. At necropsy, dark red-colored mass with many nodular protuberances was found in the anterior mediastinal area. Histologically, the mass consisted of solid proliferation of neoplastic cells with spindle nuclei and cytoplasm and a few lymphocytes, which is separated by an abundant fibrous and adipose tissue. Immunohistochemically, spindle cells were positive for cytokeratin, and infiltrating lymphocytes were positive for CD3. On the basis of these findings, this tumor was diagnosed as lymphoepithelial thymoma, which is morphologically similar to type A thymoma in humans.

This case report describes the clinical, sonographic, computed tomographic and pathological findings in a 9-year-old goat with mediastinal lymphocytic thymoma. The goat was referred to the Department of Farm Animals because of weight loss and dyspnoea. The lead clinical findings were increased heart rate, increased respiratory rate and heart sounds heard only on the right side. Ultrasonographic examination revealed a massive amount of fluid and an echogenic corrugated mass ventral to the lungs in the thoracic cavity on the left side. Computed tomography showed that the mass was very large and diffusely mineralised. A tentative diagnosis of mediastinal neoplasia was made, and the goat was euthanized. Postmortem examination revealed a cauliflower-like, pedunculated tumour, which occupied the entire left thoracic cavity and displaced the left lung. Based on histological evaluation, the tumour was diagnosed as a lymphocytic thymoma.

Objective: To provide long-term follow-up information for a series of dogs and cats with invasive and noninvasive thymomas treated by excision alone., Design: Retrospective case series., Animals: 9 cats and 11 dogs with thymoma., Procedures: Medical records were reviewed. The following factors were analyzed for their effect on prognosis: age of dog or cat, invasiveness of the tumor, percentage of lymphocytes in the mass (percentage lymphocyte composition) on histologic evaluation, and mitotic index of the mass., Results: All patients were treated with excision of the tumor alone. Median overall survival time for the cats was 1,825 days, with a 1-year survival rate of 89% and a 3-year survival rate of 74%. Median overall survival time for the dogs was 790 days, with a 1-year survival rate of 64% and a 3-year survival rate of 42%. Recurrence of thymoma was observed in 2 cats and 1 dog, and a second surgery was performed in each, with subsequent survival times of 5, 3, and 4 years following the first surgery. Percentage lymphocyte composition of the mass was the only factor that was significantly correlated with survival time; animals with a high percentage of lymphocytes lived longer., Conclusions and Clinical Relevance: Results of this study indicated that most cats and dogs with thymomas did well after excision. Even cats and dogs with invasive masses that survived the surgery and the few cats and dogs with recurrent thymomas or paraneoplastic syndromes had a good long-term outcome. Excision should be considered an effective treatment option for dogs and cats with thymomas.

A 16-year-old, spayed female beagle was diagnosed with metastatic thymoma causing a probable paraneoplastic syndrome of generalized acquired myasthenia gravis. Anticholinesterase treatment was initiated; however, 5 days later the dog died.

A neoplastic mass measuring 25 x 8 x 3 cm was found in the mediastinum of a 10-year-old Holstein cow. The neoplasm was encapsulated, multilobulated, and cystic. Several firm adhesions were present between the neoplasm and the right cranial lung lobe and the ipsilateral side of the pericardial sac. Under microscopic examination, the neoplasm was characterized by solid sheets of spindle epithelial cells (pancytokeratin and high molecular weight cytokeratin positive) subdivided by fibrous trabeculae. Numerous individualized or small aggregates of mature T-cell (CD3 positive) lymphocytes were scattered throughout the neoplastic cell population. Based on the gross, histologic, and immunohistochemical findings, the neoplasm was diagnosed as a mixed thymoma.

Background: Biopsy of mediastinal masses can be invasive, but the procedure may be necessary if cytology of a mass aspirate is inconclusive. The 2 most common mediastinal masses, lymphoma and thymoma, may both be comprised of small lymphocytes. We investigated the ability of flow cytometry to distinguish between these 2 neoplasms., Hypothesis: Flow cytometry of mediastinal mass aspirates may provide a definitive diagnosis of thymoma or lymphoma, reducing the need for biopsy., Animals: Dogs with mediastinal masses presenting to the Veterinary Teaching Hospital/Animal Cancer Center were included in the study., Methods: Aspirates obtained over 2 years that met the inclusion criteria (i.e. sufficient viable cells and a definitive diagnosis by means other than flow cytometry) were analyzed by flow cytometry to determine the percentage of cells expressing B- and T-cell markers, and co-expressing CD4 and CD8., Results: All cases of thymoma (n = 6) consisted of > or = 10% lymphocytes coexpressing CD4 and CD8, a phenotype that is characteristic of thymocytes, whereas 6 of 7 lymphomas contained <2% CD4+CD8+ lymphocytes. The CD4+CD8+ lymphoma could be readily distinguished flow cytometrically from thymoma by light scatter properties. The phenotypes of the remaining lymphomas were CD4+ T cell (4), CD34+ (1) and B cell (1)., Conclusions: Our studies demonstrate that flow cytometry is a useful tool for discriminating mediastinal masses. Lymphocyte-rich mediastinal masses could be unambiguously identified by flow cytometry in 13/13 cases.

This article describes the application of the helicoidal tomography for the study of mediastinal and pulmonal affections by small animals. The global presentation is completed by clinical cases that show the interest in this technic. A thymoma, a chronic pleuresia due to thorns and a mediastinal cranio-dorsal neoplasia provoking only lameness signs will be presentated in details.

Differentiation of benign and malignant causes of lymphocytosis in blood or bone marrow can be problematic. In the present study, reports of examinations of bone marrow from cats, submitted over an 8-year period, were reviewed to identify cats with increased numbers of small lymphocytes. Of 203 reports reviewed, 12 (5.9%) indicated increased numbers of small lymphocytes. Diagnoses for these cats included chronic lymphocytic leukemia (CLL; n = 2), pure red cell aplasia (PRCA; n = 4), immune-mediated hemolytic anemia (IMHA; n = 3), thymoma (n = 1), cholangiohepatitis (n = 1), and fever of unknown origin (n = 1). Several factors were identified that could be used to differentiate reactive lymphocytosis from CLL. Cats with CLL tended to be older, and lymphocytes were slightly larger and had cleaved or lobulated nuclei. Reactive lymphocytosis was associated with immune-mediated anemias and inflammatory diseases. In reactive lymphocytosis, the proliferating lymphocytes were organized into lymphoid aggregates in bone marrow and were predominately B cells. Alternatively, in CLL and thymoma, the proliferating lymphocytes were diffusely distributed and were predominately T cells. Therefore, differentiation of the causes of lymphocytosis should include evaluation of signalment, concurrent disease conditions, lymphocyte morphology, lymphocyte distribution in bone marrow, and immunophenotype. Cat age, presence of severe anemia, and evidence of inflammatory disease also should be considered.

Thymolipomas are rare benign thymic neoplasms recognised in humans, composed of mature adipose tissue and thymic tissue. An 8-year-old male domestic shorthair cat presented with anorexia, lethargy and vomiting secondary to the development of a thoracic effusion and an anterior mediastinal tumoral mass with fatty appearance. Histologically, the mass consisted of adipose tissue containing numerous cords and nests of cortical and medullary thymic tissue. No signs of thymic epithelial or lymphoid neoplastic proliferation were detected. The findings in this case are remarkably similar to the macroscopic and histological features of thymolipoma in humans.

A spayed female dog was evaluated because of edema of the ventral cervical region, lethargy, cough, and reduced exercise tolerance. Invasive thymoma and cranial vena cava syndrome were diagnosed by use of ultrasound-guided fine-needle biopsy and contrast-enhanced helical computed tomography. Resection of the cranial vena cava and an autogenous jugular vein graft were used for restoration of normal venous return to the right atrium and alleviation of the cranial vena cava syndrome.

A 14.6-yr-old, female, multiparous polar bear (Ursus maritimus) acutely developed an apparent hind limb weakness. Physical examination and diagnostic tests including a hemogram, serum biochemistry, electrolytes, radiographs, and myelogram did not provide a definitive diagnosis. No improvement in condition was noted during 4 days of supportive care, and the bear was euthanized. An ovoid mass was present in the anterior mediastinum, and a thymoma was confirmed histologically. Compared with control polar bears, elevated serum acetylcholine receptor (AChR) antibodies (0.13 +/- 0.06 nmol/L vs. 0.86 nmol/L) were detected by immunoprecipitation radioimmunoassay, which is consistent with myasthenia gravis (MG) in other species. Although the AChR antibody test has not been validated in the polar bear, we are confident in the postmortem diagnosis of MG, which is commonly associated with thymoma in other species.

Five cases of exfoliative dermatitis in cats were presented from 1996 to 2002 in which a feline thymoma was found by postmortem or postsurgical examination. Besides abundant exfoliation of keratin squames and layers, the histologic picture of the skin revealed a similar pattern of interface dermatitis with predominantly CD3+ lymphocytes and fewer mast cells and plasma cells. In the epidermal basal layer a hydropic degeneration of keratinocytes was present. In all cases an infundibular lymphocytic mural folliculitis and absence of or drastic decrease in the number of sebaceous glands occurred. In addition to the so far described cell-poor type, we also found examples of a cell-rich skin lesion. Together with the clinical observation of generalized exfoliative dermatitis, the histologic pattern of this dermatitis was suggestive of an underlying thymoma. The pathogenesis of this skin disease in association with thymic neoplasia remains obscure, and our results contradict the hypothesis of production of autoantibodies that cross-react with epithelial antigens. The morphology of the thymomas and CD3 expression of the thymocytes varied and did not seem to have an impact on the dermal lesions.

A 12-year-old male Shiba dog showed anemia and the swelling of systemic lymph nodes. X-ray and post mortal examinations revealed a anterior mediastinal mass. Histologically, the tumor mass consisted of four different elements; cord-like proliferation of cuboidal epithelial cells, tubular or cystic structures lined with ciliated epithelial cells, proliferation of large round-shaped epithelial cells with PAS-slightly positive granular cytoplasm, and diffuse proliferation of neoplastic lymphocytes. Epithelial cells in cord-like or cystic structures were strongly positive for cytokeratin. Granular or foamy cells were negative for all markers examined and had myelin-like bodies in the cytoplasm by electron microscopy. The neoplastic lymphocytes in the tumor mass were considered being derived from concurrent multicentric lymphoma. Based on these findings, the present case was diagnosed as thymoma with a part of granular cell proliferation and concurrent lymphoma cells.