Video‐Assisted Thoracoscopic Resection of Noninvasive Thymomas Using One‐Lung Ventilation in Two Dogs

Objective— To report the technique and outcome of video‐assisted thoracoscopic surgery (VATS) for resection of cranial mediastinal thymoma in 2 dogs. Study Design— Case report. Animals— Eleven‐year‐old Labrador Retrievers (n=2). Methods— Two dogs had VATS resection of thymoma. Preoperative computed tomography (CT) scans revealed well‐circumscribed cranial mediastinal masses with dimensions of 4.5 cm × 4.2 cm × 3.7 cm and 2.1 cm × 2.1 cm × 4.1 cm (at the time of resection) without CT evidence of vascular invasion. One‐lung ventilation (OLV) was achieved using a bronchoscopically placed double‐lumen endobronchial tube. A 3‐portal technique was used for VATS access to the thorax. Thymomas were dissected from the tissues of the cranial mediastinum with the aid of a harmonic scalpel and retrieved in specimen retrieval bags. Results— Two cranial mediastinal thymomas were resected successfully, with their capsules intact, using a VATS technique. One dog developed aspiration pneumonia postoperatively which resolved with treatment and remains healthy 18 months postoperatively with no radiographic evidence of tumor recurrence. The second dog was diagnosed with myasthenia gravis, megaesophagus, and aspiration pneumonia preoperatively and despite recovering well from the procedure had a second episode of aspiration pneumonia 5 days postoperatively and was euthanatized. Conclusions— VATS resection of modestly sized noninvasive thymoma is possible in dogs. Careful case selection and preoperative imaging are the keys. Clinical Relevance— Thoracoscopic resection of modestly sized mediastinal masses forms part of an increasingly expansive set of indications for minimally invasive surgery in select veterinary patients.     

Dosimetric benefit of adaptive radiotherapy in the neoadjuvant management of canine and feline thymoma—An exploratory case series

While surgery is the treatment of choice for thymomas, complete excision is not possible in a significant proportion of cases. For these patients, radiotherapy can be used as neoadjunctive, post‐operative adjunctive or sole therapy. During radiotherapy, rapid biological clearance of tumour cells is often observed, requiring adaptation of the treatment plan. Adaptive radiation therapy (RT) is a dynamic process, whereby the treatment plan is altered throughout the treatment course due to changes in morphologic, functional or positioning changes. With the hypothesis, that individually adapted replanning will massively reduce the dose to organs at risk (OAR) in a fast‐changing environment such as a rapidly responding thymoma, the dosimetric impact of adaptive treatment planning in 5 patients with large thymoma was measured. In all patients rapid tumour‐shrinkage of the gross tumour volume was observed after 1 week of therapy, with a mean shrinkage of 31.0% ± 15.2%, or a tumour regression of 5.2% per day. In consequence, there was a considerable change in position of organs such as heart and lung, both of them moving cranially into the high dose area upon tumour regression. After mid‐therapy replanning, the dose to OAR was significantly reduced, with ?18.2% in the mean heart dose and ?27.9% in the V20 lung dose. Adaptive planning led to a significantly reduced radiation dose and hence protection of OAR for these patients. It can be concluded that adaptive replanning should be considered for canine and feline thymoma patients receiving fractionated RT.     

A comparison between the cytological and histological characteristics in thirteen canine and feline thymomas

Cytological smears and histological sections collected from histologically diagnosed cases of thymoma in nine dogs and four cats were reviewed. Most of the histological features were apparent in the cytological specimens with two notable differences. The epithelial component was underestimated and Hassal's corpuscles were not observed using Wright's-stained cytological preparations. Features of thymoma were recognized in seven of the nine cases in which fine needle aspiration biopsy was done. Therefore, cytology, and specifically fine needle aspiration biopsy, has the potential to be a useful aid in the rapid diagnosis of canine and feline thymomas.     

Results of excision of thymoma in cats and dogs: 20 cases (1984-2005)

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.     

Thymoma-associated exfoliative dermatitis in cats

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.     

Comparative morphologic and immunohistochemical investigation of spontaneously occurring thymomas in a colony of European hamsters

This study documents the characteristics of a large series of spontaneously occurring thymomas in a laboratory colony of European hamsters (Cricetus cricetus). Thymomas are rare organotypic neoplasms originating from the thymic epithelial compartment. Because the hamster thymomas largely resembled their human counterparts, the recent World Health Organization (WHO) classification of human thymic epithelial tumors was used. Forty hamsters of both sexes aged 3-29 months were examined macroscopically and histologically. In 22 (55%) of the 40 animals, necropsy revealed enormous whitish masses in the anterior mediastinum, with a diameter ranging from 0.5 to 4.5 cm and a lobulated structure. The anatomy of the thymus region was normal in the remaining 18 hamsters. Histologically, the tumors presented as thymuslike organoid structures with areas of medullary and cortical differentiation and a predominance of lymphoid cells. A network of epithelial cells in the cortical areas, demonstrated immunohistochemically with a cross-reactive antibody against pancytokeratin, supported the diagnosis of thymoma. Cortical lymphocytes showed positive staining with cross-reacting antibodies against CD3 and terminal deoxynucleotidyl transferase, characteristic of immature T cells. On the basis of these findings, the tumors were classified as B1 thymomas, in some cases with AB or B2 components, according to the new WHO classification for human thymic epithelial tumors.     

Radiation therapy in the treatment of canine and feline thymomas: a retrospective study (1985-1999)

A retrospective study was performed of 17 dogs and seven cats with various stages of thymoma treated with radiation alone or as an adjunctive therapy. Analysis revealed an overall response rate of 75% (15/20 evaluable cases). Partial (i.e., >50% reduction in tumor size) and complete (i.e., no detectable tumor) responses were included. Complete responses were rare (4/20). Three of five animals with stable disease (i.e., <50% change in tumor size) had improvements in clinical signs, despite lack of measurable response. A median survival time of 248 days (range, 93 to 1,657+ days) was achieved in dogs, and a median survival time of 720 days (range, 485 to 1,825+ days) was achieved in cats. Radiation therapy appears to be useful in the management of invasive thymomas in dogs and cats.     

Myasthenia gravis associated with thymic neoplasia in a cat

Objective: To describe acute myasthenia gravis (MG) in the postoperative period following removal of a thymoma in an adult cat. Case summary: A 6‐year‐old spayed female domestic short haired cat weighing 6.4 kg was referred for workup and treatment of a cranial mediastinal mass. Thoracoscopic biopsies confirmed the diagnosis of thymoma. Median sternotomy was performed and approximately 95% of the mass was surgically excised. Postoperatively the cat became remarkably weak and hypercapneic. A presumptive diagnosis of MG was made following a positive response to edrophonium injection (Tensilon test). An elevated serum acetylcholine receptor antibody level was consistent with a diagnosis of MG. Initial treatment consisted of neostigmine, followed by corticosteroids and pyridostigmine. The cat responded well to therapy. New or unique information provided: This report describes a rare syndrome of postoperative weakness due to development of MG following incomplete removal of a thymoma. Post‐thymectomy weakness associated with MG has been reported in dogs and is not well described in cats.     

Diagnosis of erythema multiforme associated with thymoma in a dog and treated with thymectomy

A 7 yr old Labrador retriever initially presented for severe halitosis, mild ptylism, and depigmentation of the nasal planum. Erythema multiforme was diagnosed based on clinical signs and dermatopathology. Treatment was initiated but the condition did not resolve. Six months later, the dog was diagnosed with a mediastinal mass. Trucut biopsy was performed and histopathologic diagnosis was consistent with a thymoma. A median sternotomy was performed, the thymoma was excised, and the dog recovered well. Four months postoperatively, there were no longer any obvious erythema multiforme lesions and the skin condition was controlled without medication. Erythema multiforme may be a paraneoplastic disorder associated with thymoma in the dog, similar to thymoma-associated exfoliative dermatitis in the cat. Clinical signs of erythema multiforme may warrant performing thoracic radiographs or thoracic CT to rule out thymoma as an underlying cause.     

Invasive thymoma complicated by pneumothorax and haemothorax in a dog

An invasive thymoma associated with pneumothorax and haemothorax is described in a 3^-year-old Labrador Retriever. Diagnosis was based upon radiological and surgical findings and confirmed at autopsy. The case is compared with other thymomas reported in the dog.     

Paraneoplastic T cell lymphocytosis associated with a thymoma in a dog

A four-year-old male neutered Australian shepherd dog was diagnosed with a thymoma and concurrent mature T cell lymphocytosis. The lymphocytosis consisted of a mixed population of T cells expressing either CD4 or CD8 or neither marker, and the result of polymerase chain reaction for antigen receptor rearrangement was negative. The peripheral lymphocytosis resolved within 24 hours following thoracotomy and thymectomy. Similar cases have been reported in man, but the aetiology of the increased circulating lymphocytes remains unclear. Although peripheral lymphocytosis is an uncommon paraneoplastic syndrome associated with thymomas, thymoma should be considered as a differential when the increased lymphocytes consist of a mixed population of T cells.     

Thymoma in a domestic rabbit.

Thymic tumors are uncommon in small domestic animals, and thymomas are infrequently reported in rabbits. This report presents a 7-year-old Netherland dwarf rabbit with an anterior mediastinal mass which caused hyperpnea, open-mouth breathing, swelling of the head, and exophthalmos. The mass was composed predominantly of lymphocytes, but the presence of thymic epithelial cells established the histologic diagnosis of thymoma.     

Thymomas in rabbits: clinical evaluation, diagnosis, and treatment

Thymomas are rarely recorded in rabbits, and the literature includes comparatively few cases. Medical records were reviewed to identify all pet rabbits in which a mediastinal mass was diagnosed between Feb 2007 and Jan 2010. Signalment, history, clinical signs, diagnostic work-up (including laboratory data, diagnostic imaging, and ultrasound-guided fine-needle aspiration of the mediastinal mass), treatment modalities, survival time, and histologic findings were evaluated. Cytologic and/or histopathologic examinations revealed thymomas in all rabbits with mediastinal masses (n=13). Rabbits with thymomas showed clinical signs of dyspnea (76.9%), exercise intolerance (53.9%), and bilateral exophthalmos (46.2%). In seven rabbits the thymoma was removed surgically. Two rabbits were treated conservatively, and four rabbits were euthanized because of their poor clinical condition. The two rabbits that underwent surgery were euthanized 6 mo and 34 mo later. Mediastinal masses in rabbits appear to be more common than previously believed and consist primarily of thymomas rather than thymic lymphomas. Cytology of samples collected by ultrasound-guided fine-needle aspiration is an accurate diagnostic tool for the identification of thymomas in rabbits. Due to a high rate of perioperative mortality, intensive perioperative care and the provision of a low-stress environment are recommended for a successful thoracotomy.     

Mixed Thymoma in a Young Cynomolgus Monkey (Macaca fascicularis)

A mass with a diameter of 1.5 cm was found in the thymus of a 4-year and 3-month-old male cynomolgus monkey. Microscopically, the mass consisted of two different patterns of proliferation, dense or fascicular proliferation of elongated spindle cells in a sporadic storiform pattern and dense proliferation of thymic cortex-like lymphoid cells in which the multifocal pale nests resembling the thymic medulla were distributed. In these pale nests, large dendriform cells sometimes forming Hassall's corpuscles were present. The proliferating spindle cells were positive for cytokeratin. The lymphoid cells in the mass were positive for CD3. We concluded that the mass consisted of the neoplastic thymic epithelium with thymocytes proliferation containing medullary differentiation. The mass was diagnosed as a mixed thymoma according to the WHO classification of thymomas in humans. Mixed thymoma is characterized as a mixture of two types of proliferative lesions, spindle-shaped epithelial proliferation and a lymphocyte predominant lesion with or without medullary differentiation. To the best of our knowledge, this is the first report concerning thymoma in monkeys.     

Intranasal melanoma treated with radiation therapy in three dogs

Three dogs were investigated for chronic unilateral nasal discharge. In all cases CT imaging showed an intranasal mass causing turbinate lysis and no evidence of metastasis. Cytology in cases 1 (a 14-year-old neutered male crossbreed dog) and 2 (a five-year-old neutered male German Shepherd dog) demonstrated a pleomorphic cell population with variable intracellular pigment suspicious of melanocytic neoplasia. Histopathology with immunohistochemistry (Melan-A and vimentin, plus PNL-2 in one case) confirmed the diagnosis of melanoma in all dogs. All dogs were treated with megavoltage radiotherapy using linear accelerators. Cases 1 and 3 (a nine-year-old neutered female beagle dog) received a hypofractionated (4 × 8 Gy) protocol and case 2 received a definitive (12 × 4 Gy) protocol. Complete remission was demonstrated on repeat CT scan five months after diagnosis in case 1 and seven months in case 2. Stable disease was documented on CT at four months for case 3; however, clinical signs in this dog remained controlled for 10 months in total. Case 1 died of unrelated causes five months after diagnosis, case 2 was euthanased due to the development of seizures 13 months after diagnosis, and case 3 was lost to follow-up 12 months after diagnosis. Melanoma should be considered as a rare differential diagnosis for primary nasal neoplasia in the dog and radiation therapy can be used as effective local therapy.     

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.     

Uncontrolled study assessing the impact of a psyllium-enriched extruded dry diet on faecal consistency in cats with constipation

Two field trials, involving 66 cats (15 trial 1; 51 trial 2) were conducted to assess the efficacy of a psyllium-enriched diet for management of constipation in cats. After investigations and faecal evacuation (by enema if required), all cats were fed on a moderate fibre, psyllium-enriched, dry extruded diet. Additional therapy was either not used (trial 1), or initially allowed but was subsequently withdrawn if possible (trial 2). The diet was well tolerated, and palatability was excellent. Most cases improved after initial therapy (at 2 months; trial 1: 14/15 [93%]; trial 2: 42/51 [82%]), and faecal consistency improved significantly in both trials (P < 0.001). Use of cisapride and lactulose decreased significantly in trial 2 (P < 0.001 for both). The diets used in these pilot studies were efficient in the management of recurrent feline constipation. Randomised control trials are now recommended to examine whether a clinical benefit can be proven.     

Cryptococcosis in captive cheetah (Acinonyx jubatus): two cases

Cryptococcus neoformans is a yeast-like organism associated with pulmonary, meningoencephalitic, or systemic disease. This case report documents 2 cases of cryptococcosis with central nervous system involvement in captive cheetah (Acinonyx jubatus). In both cases the predominant post mortal lesions were pulmonary cryptococcomas and extensive meningoencephalomyelitis. Both cheetahs tested negative for feline immunodeficiency virus and feline leukaemia virus. The organism isolated in Case 2 was classified as Cryptococcus neoformans var. gattii, which is mainly associated with disease in immunocompetent hosts.     

Tumor necrosis factor alpha levels in cats experimentally infected with feline immunodeficiency virus: effects of immunization and feline leukemia virus infection.

Tumor necrosis factor alpha (TNF alpha) levels were determined by enzyme-linked immunosorbent assay (ELISA) and by cell culture bioassay in supernatants of lipopolysaccharide-stimulated feline monocyte cultures and in cat serum samples. There was a good correlation between the results obtained by the two methods. From the fact that TNF alpha was neutralized quantitatively by antibodies to human TNF alpha in feline monocyte supernatants and in feline sera, it was concluded that feline TNF alpha immunologically cross-reacts with human TNF alpha and that the human TNF alpha ELISA can be used to quantitate feline TNF alpha. During the first 6 months after experimental feline immunodeficiency virus (FIV) infection no differences in serum TNF alpha values were observed between infected and non-infected cats. TNF alpha levels increased significantly after primary vaccination with a feline leukemia virus (FeLV) vaccine in FIV infected cats over those in the non-infected controls. During secondary immune response TNF alpha levels rose transiently for a period of a few days in both the FIV positive and the FIV negative cats. After FeLV challenge, TNF alpha levels increased in all animals challenged with virulent FeLV for a period of 3 weeks. This period corresponded to the time necessary to develop persistent FeLV viremia in the control cats. It was concluded from these experiments that in the asymptomatic phase of FIV infection no increased levels of TNF alpha are present, similar to the situation in asymptomatic HIV infected humans. Activation of monocytes/macrophages in FIV infected cats by stimuli such as vaccination or FeLV challenge readily leads to increased levels of TNF alpha.     

Carotid Body Tumors in the Dog Eleven Cases (1978–1988)

Case records of 11 dogs with histologically confirmed carotid body tumors were reviewed. Surgical excision had been attempted in ten dogs with carotid body tumors, and one dog had been euthanatized at diagnosis. There were no intraoperative deaths but perioperative mortality was 40%. Horner's syndrome and laryngeal paralysis were the most common postoperative morbidities. The median survival time after surgery alone in the four dogs that survived the perioperative period was 25.5 months (range, 12-45 months). Two dogs treated with postoperative radiation therapy had survival times of 6 and 27 months. Of the six dogs surviving the perioperative period, two dogs are still alive at 19 and 32 months postoperatively. Of the four dogs that died, one was euthanatized 12 months postoperatively for nontumor-related causes. The remaining three dogs died of distant metastases. The carotid body tumors studied were characterized by local tissue invasion, neurovascular complications after therapy, and a propensity to metastasize to multiple sites in the body.