Thymoma

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tonyshuman

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I have some experience with this as my Benjamin suffered from the condition. Here are some x-rays showing the enlarged area near his heart, when we first diagnosed his thymoma.

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The thymus is an organ located very close to the heart, and it has an immune function. Thymoma seems to be common in bunnies, perhaps due to their already strange immune systems.

Some info I have gathered:
http://www.rabbit.org/health/Rabbitthymomas.pdf
http://www.rabbit.org/health/thymomastory.html
http://www.varabbit.com/dusty.html (many embedded links here, other stories)
http://www.ehow.com/facts_6183205_thymoma-rabbits.html
http://www.google.com/url?sa=t&rct=...sg=AFQjCNGQ9lvgwpd2QJhYiskRRxtDHKsA3g&cad=rja

Wonderful site, compiled information and story of a particular bunny's treatment:
http://somecows.com/thymoma/

Journal articles:
http://www.ncbi.nlm.nih.gov/pubmed/16119059
J Small Anim Pract. 2005 Aug;46(8):393-7.Recurrent bilateral exophthalmos associated with metastatic thymic carcinoma in a pet rabbit.Wagner F, Beinecke A, Fehr M, Brunkhorst N, Mischke R, Gruber AD.SourceDepartment of Small Animal Medicine and Surgery, School of Veterinary Medicine Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany.
AbstractA five-year-old, castrated, male chinchilla rabbit was presented for evaluation of recurrent bilateral exophthalmos. Besides a transient and stress-related exophthalmos with protrusion of both third eyelids, the ophthalmological examination was unremarkable. Plain radiography of the thorax revealed a large precardial mass of soft tissue density. Cytological preparations from the thoracic mass were dominated by small, mature lymphocytes with approximately 10 to 20 per cent lymphoblasts. Computed tomography of the head showed a symmetrical laterodorsal deviation of both eyes without evidence of retrobulbar masses. On necropsy a large cystic mass was present in the cranial thorax associated with severe hydrothorax, hydropericardium and ascites. Histology identified the precardial mass as thymic carcinoma with metastases in the kidneys. This case illustrates the difficulty of diagnosing thymic tumours based on cytological or histological features of the primary tumour alone. To the authors' knowledge, this is the first case of recurrent bilateral exophthalmos associated with a metastatic thymic carcinoma in a pet rabbit.


http://www.ncbi.nlm.nih.gov/pubmed/20729825
Lab Anim (NY). 2010 Sep;39(9):262-5.Bilateral exophthalmos in a rabbit. Diagnosis: Thymoma.Pignon C, Jardel N.


http://www.ncbi.nlm.nih.gov/pubmed/9787381
J Am Vet Med Assoc. 1998 Oct 15;213(8):1140-3, 1131.Removal of a thymoma via median sternotomy in a rabbit with recurrent appendicular neurofibrosarcoma.Clippinger TL, Bennett RA, Alleman AR, Ginn PE, Bellah JR.SourceDepartment of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32610-0126, USA.
AbstractA 9-year-old rabbit was evaluated for a mass on the right elbow. As a result of preoperative radiography, another mass was identified in the cranial portion of the mediastinum. Ultrasound guided fine needle aspiration was used for cytologic evaluation of the mass in the mediastinum and resulted in a presumptive diagnosis of thymoma. A median sternotomy approach was chosen to allow wide exposure for meticulous dissection in the cranial portion of the thoracic region. Histologic examination and immunoperoxidase labeling of lymphocytes with CD3 (a T cell marker) confirmed the diagnosis. The mass on the right elbow was subsequently removed and identified as a neurofibrosarcoma. Multiple appendicular masses that developed at separate locations and distinct times were excised and classified as locally invasive primary neurofibrosarcomas. Postmortem examination 9 months after initial evaluation confirmed recurrence of the neurofibrosarcoma at previous surgical sites. Gross or histologic evidence of thymoma was not evident. Prognosis is dismal for incompletely excised soft tissue sarcomas, because they are locally invasive and often recur.


http://www.ncbi.nlm.nih.gov/pubmed/1623725

Cornell Vet. 1992 Apr;82(2):125-9.Thymoma in a domestic rabbit.Kostolich M, Panciera RJ.SourceDepartment of Medicine, College of Veterinary Medicine, Oklahoma State University, Stillwater.
AbstractThymic 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.

http://www.ncbi.nlm.nih.gov/pubmed/7759335

J Am Vet Med Assoc. 1995 Mar 15;206(6):820-2.Thymoma in a geriatric rabbit with hypercalcemia and periodic exophthalmos.Vernau KM, Grahn BH, Clarke-Scott HA, Sullivan N.SourceDepartment of Neurology, Veterinary Medical Teaching Hospital, University of California, Davis 95616, USA.
AbstractAn 8-year-old rabbit was referred to an ophthalmologist because of intermittent bilateral exophthalmos and prolapse of the nictitating membranes. Both eyes could be retropulsed normally, and the exophthalmos was induced with ventroflexion. The rabbit had moderate hypercalcemia and a large mediastinal mass that could be seen on thoracic radiographs. The rabbit's condition was unchanged for 5 months. It was reexamined because of weight loss and paroxysmal coughing and, at that time, was thin and tachypneic, and had reduced thoracic compliance. Thoracotomy was performed, and a 5-cm-diameter encapsulated mass, subsequently determined histologically to be thymoma, was removed. The rabbit was euthanatized after surgery because of complications. The periodic exophthalmos and hypercalcemia in this rabbit were believed to be paraneoplastic syndromes.
http://www.ncbi.nlm.nih.gov/pubmed/22267174

J Am Anim Hosp Assoc. 2012 Mar;48(2):97-104. Epub 2012 Jan 19.Thymomas in rabbits: clinical evaluation, diagnosis, and treatment.Künzel F, Hittmair KM, Hassan J, Dupré G, Russold E, Guija de Arespachochaga A, Fuchs-Baumgartinger A, Bilek A.SourceClinical Department for Small Animals and Horses, University of Veterinary Medicine, Vienna, Austria.
AbstractThymomas 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.
 
Although other diagnostic approaches were taken with Ben, I do not have the files. We did have a CT scan done as well as additional x-rays at the vet school, and a fine needle ultrasound-guided aspiration of the mass. The CT scan showed a large portion of his thoracic cavity full of tumor tissue, with limited space for heart and lungs. This also led to pneumonia without a bacterial cause (just pressure on the lungs causing it) which we tried to alleviate with nebulizing saline treatments, which did appear to cause improvement. The pneumonia made him a bad candidate for radiation treatment due to it putting him at risk under anesthesia. After getting the pneumonia more or less under control, we decided the potential benefits of radiation, even a type called TomoTherapy which uses CT to guide and target the radiation, were not enough to outweigh the discomfort Ben would suffer undergoing such treatment. He lived several months happily with the thymoma diagnosis. After a rapid decline--lethargy and labored breathing that appeared over about 24 hours--he eventually succumbed to cardiopulmonary collapse and the vets were not successful at resuscitating him. It was also decided that it was kinder not to do so. I have the necropsy report but it may take me some time to upload it because it is still emotionally difficult.
 

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