Cardiovascular Disease, Lymphoproliferative Disorders, and Thymomas

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 tumors 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 tumor volume reduction during RT, the frequency of replanning during RT, and survival time in rabbit thymomas treated using intensity-modulated/image-guided radiation 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-October 2019. The median progression-free survival was 561days and the median overall survival was 634 days (range: 322-1118 days). The tumor 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<0.001). All subsequent RT fractions did not further reduce the GTV significantly (p>0.06). 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 dyspnea in rabbits. This article is protected by copyright. All rights reserved.

Clinical and pathological findings in rabbits with cardiovascular disease: 59 cases (2001-2018)

OBJECTIVE

To determine epidemiological features of cardiovascular disease in rabbits examined at a veterinary teaching hospital and characterize clinical and pathological findings.

ANIMALS

59 rabbits.

PROCEDURES

Medical records from 2001 to 2018 were reviewed, and data were collected. Echocardiographic images and histologic diagnoses were reviewed.

RESULTS

The prevalence of cardiovascular disease was 2.6% (59/2,249). Clinical signs related to cardiac disease included heart murmur (n = 25 rabbits), arrhythmia (22), tachypnea or dyspnea (13), hyporexia or anorexia (13), and muscle wasting (9). Radiographic (n = 39) abnormalities included cardiomegaly (19) and peritoneal (12) and pleural (11) effusion. Common echocardiographic (n = 37) diagnoses included degenerative valve disease (15), dilated cardiomyopathy (7), unclassified cardiomyopathy (4), restrictive cardiomyopathy (3), and hypertrophic cardiomyopathy (2). On ECG (n = 19), supraventricular arrhythmias (16) were more common than ventricular arrhythmias (12). Thirty-five necropsy reports were available, and diagnoses included cardiomyopathy (n = 14), myocarditis (10), and arteriosclerosis (9). Medical management (n = 20) included a wide range of drugs and dosages with few adverse effects. Survival times (n = 36 rabbits) ranged from 1 to 2,353 days with a median cardiac disease-specific survival time of 306 days.

CONCLUSIONS AND CLINICAL RELEVANCE

The findings provided information on the prevalence of cardiovascular disease in rabbits and survival times for affected rabbits. Right-sided, left-sided, and biventricular congestive heart failure occurred equally. Median survival time was lower than that reported for other species. Further research on the diagnosis and treatment of cardiovascular disease in rabbits is needed.

Ostium secundum type of atrial septal defect in a rabbit

A 14-month-old, female mini rex was referred for a detailed examination because of exercise intolerance with associated dyspnea. The thoracic radiograph demonstrated severe cardiac enlargement and elevation of the trachea. The echocardiography revealed dilatations of the right-side heart and pulmonary artery, and the color flow Doppler echocardiography demonstrated an atrial septum defect with left to right shunt, resulting in a disturbed flow. The rabbit died 19 days after the initial presentation, and a necropsy was performed. At the necropsy, a defect, 5 mm in diameter, was detected in the atrial septum. Based on the location of the defect, an ostium secundum type atrial septal defect was diagnosed. This is the first clinical report of atrial septal defect in rabbits.