Spindle-cell thymoma colliding with a bronchogenic cyst in a Yorkshire terrier.

An 8-year-old male Yorkshire terrier was presented to the Tufts Veterinary Hospital for evaluation of increased respiratory effort. A mediastinal mass composed of a spindle-cell thymoma within a bronchogenic cyst was diagnosed with computed tomography thoracic imaging, ultrasound-guided fine-needle aspirate biopsy, and histopathologic evaluation after surgical removal. Histologic evaluation showed a multilocular cyst structure as well as a mass characterized by spindle to polygonal thymic epithelial cells. The cyst was characterized by a lining of ciliated pseudostratified respiratory epithelium. To the authors' knowledge, this is the first report of a spindle-cell thymoma being associated with a mediastinal bronchogenic cyst in a dog.

Adaptive radiation therapy using weekly hypofractionation for thymoma treatment: A retrospective study of 10 rabbits.

Radiation therapy (RT) is being utilized more commonly for rabbit thymomas due to high perioperative mortality rates with surgery. Median overall survival times reported for rabbit thymomas treated with a variety of RT protocols and techniques range from 6 months to greater than 2 years. As thymomas are radiation-responsive tumours and may shrink rapidly after RT, adaptive radiotherapy (ART) is often warranted. The purpose of this single-institution retrospective case series was to investigate the tumour volume reduction during RT, the frequency of replanning during RT, and survival time in rabbit thymomas treated using intensity-modulated/image-guided radiation therapy (IMRT/IGRT) and a weekly hypofractionated protocol delivering a total dose of 30 Gy. Ten rabbits met the inclusion criteria from October 2014 to October 2019. The median progression-free survival was 561 days and the median overall survival was 634 days (range: 322-1118 days). The tumour volume gradually decreased with each RT fraction. On post-hoc analysis, only the first RT fraction was associated with a significant GTV reduction (of more than 50% on average, p < .001). All subsequent RT fractions did not further reduce the GTV significantly (p > .06). Hypofractionated RT using a weekly protocol of 5 fractions of 6 Gy is a reasonable option to treat rabbit thymomas and replanning should be anticipated. The results of this study support the use of RT to rapidly relieve thymoma-induced dyspnoea in rabbits.

Type A thymoma in a pet rabbit.

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.

Thymic squamous cell carcinoma in a cat.

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.

Thymoma originating from the cervical component of the thymus in a degu.

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.

Outcomes of dogs with thymoma treated with intensity modulated stereotactic body radiation therapy or non-modulated hypofractionated radiation therapy.

Canine thymomas are routinely treated with radiotherapy (RT). In this study, we investigate the response and toxicity of canine thymoma treated with intensity-modulated stereotactic body radiation therapy (SBRT) relative to dogs treated with hypofractionated non-modulated radiation therapy (NMRT). A retrospective study was performed of dogs with thymoma treated with RT (total: n = 15; SBRT: n = 8, NMRT: n = 7). Tumour response was evaluated in six dogs (40%); following SBRT, three dogs (100%) experienced stable disease (SD); following NMRT, one dog (33%) had a PR, and two dogs (67%) had SD. Median PFS was 116 days (range 66-727 days) for the SBRT group and 134 days (range 10-405 days) for the NMRT group. The MST for the SBRT group was 250 days (range 1-727 days) and 155 days (range 10-405 days) for NMRT. Median disease-specific survival was 250 days (range 1-727 days) for the SBRT group and 169 days (range 20-405 days) for the NMRT group. No significant differences in survival data were found between the treatment groups, however the results from the small number of dogs analysed are likely underpowered for statistical comparisons. Reported acute and late side effects were limited to the lungs and heart and were statistically significantly more common in the NMRT (71%) compared to the SBRT group (25%) (p = .04). We suggest similar treatment efficacy may be provided for canine thymoma treated with either approach, but SBRT could provide the clinical benefit of reduced incidence of radiation-induced toxicity and completion of RT in a shorter time frame.

Acquired myasthenia gravis with concurrent polymyositis and myocarditis secondary to a thymoma in a dog.

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.

Comorbidity of ectopic thymoma-associated exfoliative dermatitis and pemphigus foliaceus in a cat.

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.

Comorbidité de dermatite exfoliative et de pemphigus foliacé associés à un thymome ectopique chez un chat. Un chat de 8 ans a été présenté avec prurit, panaris purulent, desquamation, croûtes et alopécie spontanée. L'histopathologie a révélé une dermatite acantholytique neutrophilique intra-épidermique et une dermatite d'interface cytotoxique hyperkératosique. Aucune masse thoracique n'a été observée sur une radiographie latérale. Un thymome ectopique a été découvert à l'autopsie. Ce cas met en évidence la nécessité d'une investigation approfondie de tout cas de dermatite exfoliative féline et de pemphigus foliacé pour la présence d'un thymome.Message clinique clé :La comorbidité d'une dermatite exfoliative et de pemphigus foliacé chez un chat devrait inciter à une enquête approfondie pour la présence d'un thymome, éventuellement avec des techniques d'imagerie avancées.(Traduit par Dr Serge Messier).

Radiotherapy-induced tumor lysis syndrome in a dog with thymoma.

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.

Thymoma in an aged backyard Leghorn chicken, with reviews of a database and literature.

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.

Orthostatic hypotension secondary to a suspected thymoma in a dog: a case report.

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.

CD4 and CD8 double-negative immunophenotype of thymoma-associated lymphocytes in a dog.

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.

A Novel Retrovirus (Gunnison's Prairie Dog Retrovirus) Associated With Thymic Lymphoma in Gunnison's Prairie Dogs in Colorado, USA.

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.

Thymoma-associated exfoliative dermatitis in a goat: case report and brief literature review.

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.

Malignant thymoma - the most common neoplasm in goats.

In the literature the occurrence of thymomas in goats varies from 0.7 to 25%, depending on the study. Therefore the current investigation was carried out to determine the prevalence of thymoma in goats in Poland. Between 2007 and 2018 at the Warsaw Veterinary Faculty 399 goat autopsies and ultrasound examinations of the chest in other 145 goats were performed. Mediastinal tumors were diagnosed during post mortem examination in 2 goats. Additionally, ultrasound examination of the chest revealed a large mass close to the heart in the thoracic cavity in 1 case. This goat was euthanized and an autopsy confirmed a mediastinal tumor. Histopathological examination, with immunohistochemical tests to anti cytokeratin, p63 and p40 confirmed thymomas in all three cases. In our study thymomas were found in 0.5% (95% CI: 0.1% to 1.8%) of examined goats and they represented the most common malignancy in this species.

Giant Thymoma with Benign Central Cystic Lesions in a 1-Year-Old Pug.

A 14 mo old pug was referred because of a large space occupying mass within the thoracic cavity. The patient was worked up with thoracic radiographs, cytology, and computed tomography. The most likely differential diagnosis was thymoma; therefore, a median sternotomy was performed, and the mass was bluntly dissected from the adjacent tissues. The patient recovered uneventfully from surgery and was discharged the next day. Histopathology diagnosed a thymoma with central cystic lesions. Thymomas usually occur in elderly patients and these patients are usually presented because of paraneoplastic signs. The age and signs at presentation, as well as the histopathologic appearance of the presented patient is quite atypical. According to telephone follow-ups, the patient was doing well 9 mo postoperatively.

CT imaging features of canine thymomas.

Canine thymomas have been evaluated based on clinical features, treatment options, surgical excision, and outcomes with limited information on specific CT features. The objective of this retrospective, descriptive, cross-sectional study was to describe the CT characteristics of confirmed thymomas and to compare these imaging features to outcome. A total of 22 dogs met the inclusion criteria of histologically confirmed thymomas with concurrent CT imaging. Tumor size varied widely ranging from small and well-circumscribed to large and invasive. Delayed-phase, contrast-enhanced CT studies were best for determining the degree of contrast enhancement in tumors. Of these, 19 of 22 masses had heterogeneous enhancement and three of 22 masses had homogeneous enhancement. Vascular invasion was present in seven of 22 cases. Larger tumors were associated with vascular invasion (height: P = .04; width and volume: P = .02). On precontrast CT, larger tumors (16/21) were heterogeneous and cystic, with smaller tumors (5/21) being more homogeneous (all values P < .05). A larger size was associated with recurrence in fully resected masses (height: P = .03), but not a shorter outcome (P > .3 for all size dimensions). Postoperative complications and incomplete tumor resection were associated with shorter outcome (both values P < .01). Metastasis was confirmed in four cases. There were six cases with lymphadenopathy noted on CT; five of the six cases did not have evidence of metastasis. Larger tumors were more likely to be cystic and associated with vascular invasion.

Comparative Incidences and Biological Outcomes for Thymoma in Various Rat Strains in National Toxicology Program Studies.

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.