Sharon Redrobe
M- mode
To perform M-mode echocardiography, the apical pulse is identified and the transducer placed at the same intercostal space. Images of the left AV valves are obtained first. Standard views are then obtained (Figure 8.9) at the apex, left AV valve, cranial left AV leaflet, aortic root, right AV valve and pulmonic valve.
Echocardiographic M-mode measurements re - p or ted for dogs vary proportionately with body size (weight) and therefore type or breed, whereas those reported for ferrets and chinchillas do not vary greatly, perhaps because these species are simi-lar in size. In rabbit studies published so far, no sig nificant associations between bodyweight and
Parasternal view showing the hypoechoic lumen of the ascending aorta.
8.7 Parasternal short axis view showing right (RV)
and left (LV) ventricles.
8.8
ECG TW RV IS LV PW
mv
aml av Ao
LA per
1 2 3 4
The four main positions for M-mode measurements. aml = anterior mitral leaflet Ao aorta av aortic valve
electrocardiogram
S interventricular septum A left atrium left ventricle mv mitral valve per pericardium
posterior wall right ventricle T thoracic wall.
(Reproduced with permission from Tello de Meneses et al., 1989)
8.9
echocardiographic measurements have been re - p orted. However, individual rabbits and breeds of rabbit do vary considerably in size, and perhaps there are yet too few studies to establish whether the meas-urements may be different in larger or smaller breeds.
The results from one M-mode examination in a rabbit (Figure 8.10; Tello de Meneses et al., 1989) yielded the following results:
• Mean ± standard deviation (SD) heart rate = 155
± 29 beats/min
• Mean ± SD measurements in diastole and systole for interventricular septum thickness, left ventricular internal diameter, and left ventricular free wall thickness were: 2.03 ± 0.37 mm and 3.05 ± 0.45 mm; 14.37 ± 1.49 mm and 10.25 ± 1.22 mm; and 2.16 ± 0.25 and 3.48 ± 0.55 mm, respectively
• Mean ± SD of the ratio of the left atrial to aortic diameter was 1.17 ± 0.14, and the mean ± SD mitral valve E-point to septal separation interval was 1.71 ± 0.29 mm
• Mean ± SD for fractional shortening and ejection fraction were 30.13 ± 2.98% and 61.29 ± 4.66%, respectively
• Mean ± SD maximal aortic and pulmonary artery outflow velocities were 0.85 ± 0.11 m/s and 0.59 ± 0.10 m/s, respectively. The peak E to peak A wave velocity ratio of the mitral valve was 2.19 ± 0.46.
Ultrasonography of the eye
Ultrasonography is a valuable technique for oph-thalmic evaluation in the rabbit (Figure 8.11). The conscious rabbit will tolerate scanning of the globe following topical anaesthesia to the eye and seda-tion is rarely required. A high detail, high-frequency probe is required, typically a 10 MHz sector probe.
Normal measurements of the various structures of the eye can be taken using ultrasonography (Figure 8.12).
R
SSS
RVDD LVDD
LVSD E
F EFS
SSPAW LAD
PEP EP
Diagram summari ing mode measurements. slope early diastolic posterior motion of mitral valve ejection period AD left atrial interval dimension DD left ventricular end diastolic dimension SD left ventricular end systolic dimension pre ejection period DD right ventricular end diastolic dimension SS A systolic slope of the posterior aortic wall SSS systolic slope of the septum. eproduced with permission from Tello de Meneses et al., 1989)
8.10
(a) Position of probe used to obtain an image of the globe.
(b) Normal ultrasonographic appearance of the rabbit globe.
8.11
(a) (b)
Ultrasonographic appearance of a retrobulbar abscess in a rabbit, obtained using a 10 MHz curvilinear probe.
8.13
ltrasonographic appearance of calcification of the aortic arch of a rabbit with ‘early’
arteriosclerosis, obtained using a 10 MHz curvilinear probe.
8.14
Examples of conditions for which ultrasound examination can be diagnostic
Retrobulbar and intraocular lesions
Exophthalmos in the rabbit should be investigated using ultrasonography of both the eye and the sur-rounding tissues for masses, but the mediastinum should also be examined because thymoma often presents as intermittent or persistent exophthalmos (see Chapter 17). In the typical rabbit with a retro-bulbar abscess, ultrasonography will reveal a mass ventromedial to the eye, with hyperechoic areas that cast an acoustic shadow and appear typically homogeneous (Figure 8.13). If osteomyelitis is also present the bony orbit may appear incomplete, the mass may extend laterally, and the contralateral globe may appear indented by the pressure of the adjacent mass. Tapeworm cysts will appear as large hypoechoic areas representing fluid-filled structures (see Chapter 29). Tumours will be seen as hyper-ec ic s lid’ asses ic are ten eter ene s in appearance.
used to provide a highly specific assessment of cardiac size, arrhythmias, and internal structure and function (dynamics), respectively.
The author has detected a ventricular septal defect in a rabbit presenting with chronic dyspnoea.
Cardiomyopathy is a relatively common post-mor-tem finding in aged rabbits. As the lifespan of pet rabbits has increased, the incidence of heart failure and atherosclerosis has also been increasing.
Confirmation is obtained by demonstrating reduced fractional shortening on ultrasonography. Bacterial endocarditis (associated in particular with severe osteomyelitis) and occasional cases of pericardial effusion have all been noted by the author in rabbits presenting with non-specific signs such as anorexia, ei t l ss r eneral illness’ t is li el t at as t is technique becomes more widely used in the rabbit patient, more conditions will be identified in vivo.
Rabbits are prone to arteriosclerosis, either as a result of a high-fat diet (which may be seen in over-fed house rabbits) or associated with renal failure and soft tissue mineralization. The condition may be clinically silent in its early stages or present as leth-argy and inappetence. Ultrasonography is much more sensitive than radiography for detecting the condition. Calcification of the aorta, reportedly asso-ciated it renal ail re and t ere re lac renal calcium clearance in the rabbit) can be detected on ultrasonography (Figure 8.14), even if the calcifica-tion is not yet detectable on radiography.
Dimension Measurement (mm)
rnea t ic ness 0.50 ± 0.12
ens t ic ness 6.28 ± 0.23
Vitreous chamber depth 9.23 ± 0.61
Axial globe length 18.28 ± 0.17
Ocular measurements in the rabbit. Data based on 10 healthy adult rabbits (20 eyes). (Data from Adel, 2011)
8.12
Cardiovascular disease
Echocardiography is recommended for evaluation of the heart in rabbits presenting with exercise intolerance or dyspnoea. Pet rabbits can develop car diovascular disease, and radiography, electro-cardiography and echoelectro-cardiography are useful non-invasive diagnostic procedures that can be
Thymoma
Rabbits with thymoma often show clinical signs of dyspnoea and bilateral exophthalmos. Cytology of samples collected by ultrasound-guided biopsy can be an accurate diagnostic tool for the identifica-tion of thymomas and differentiaidentifica-tion of the type of neoplasia where present. Ultrasonography of the cranial mediastinum via an intercostal approach, with the rabbit in either sternal or lateral recumbency, is used. The thymoma will appear as a hetero -geneous hypoechoic mass cranial to the heart, with
Ultrasonographic appearance of the liver of a rabbit with liver lobe torsion. The right side of the liver was enlarged and heterogeneous. Image obtained using a 10 MHz sector probe.
8.15
Ultrasonographic appearance of a hyperechoic area of the kidney suggestive of
nephrocalcinosis in a rabbit, obtained using a 10 MHz curvilinear probe.
8.16
Ultrasonographic appearance of the kidney of a rabbit showing a marked hyperechoic cortex consistent with nephrocalcinosis and (early) renal failure.
The nephrocalcinosis was not yet visible on plain radiography. This rabbit died 8 months later and renal failure was confirmed on post mortem e amination. mage obtained using a 10 MHz curvilinear probe.
8.17 hypoechoic (cystic) regions of varying size. As the
thymoma is typically large and takes up most of the cranial mediastinum, lung artefacts do not tend to interfere with the image. Larger cystic lesions in the thymoma are sometimes detected (see Chapter 19), which may be aspirated under ultrasound guidance to relieve dyspnoea.
Lung masses
Normal lung fields do not lend themselves to ultra-sonography because the air contained within them interferes with image formation. However, lung pathology related to chronic pneumonia is very common in the pet rabbit and an element of lung consolidation can sometimes be detectable using ultrasonography. In some cases known to the author, the condition has progressed to lung absces-sation, the extent of which can also be traced using ultrasonography.
Liver disease
Liver lobe torsion in rabbits is well known as a cause of ileus, anorexia and depression. Ultrasonographic findings include an enlarged liver with hetero -geneous liver parenchyma in the affected area (Figure 8.15) and free abdominal fluid. Ultrasound-guided fine-needle aspiration of the liver may reveal unremarkable liver cytology, or in some cases be suggestive of neoplasia – such is the extent of hepatocellular disruption. Free anechoic fluid may be found in the cranial abdomen. In some cases a heterogeneous area of liver-like tissue may be iden-tified adjacent to the right kidney, so it is important to scan the whole liver when this condition is sus-pected. Owing to the presence of gas within the stomach and intestinal tract it will be difficult to con-nect this abnormal tissue to the liver. In other cases, the stomach and caecum appear to be distended with luminal gas, resulting in acoustic shadowing.
There may be minimal bowel motility in the intestinal tract, consistent with ileus.
Contrast agents may be used to enhance the vis-ualization of hepatic and splenic masses, and this technique has been reported to be successful in the
rabbit experimentally. Detection on ultrasonography of dilation of the biliary tree has been associated with hepatic coccidiosis, which is common in pet rabbits though often undiagnosed in clinical practice.
Kidney disease
Early signs of renal failure, where mild renal calcin-osis is present on histology but not yet visible on radio graphy, is easily detected by the hyperechoic appearance of the renal cortex using ultrasonogra-phy, a finding that can be easily noted by even an inexperienced rabbit ultrasonographer (Figures 8.16 and 8.17). Scarring associated with, for example, encephalitozoonosis may be detected as hyper-echoic regions. An ultrasound-guided biopsy of the kidney may be used in order to perform histology and reach a definitive diagnosis.
Ultrasonographic appearance of the bladder and uterine adenocarcinoma, obtained using a 7.5 MHz sector probe.
8.18
Urolithiasis and cystitis
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Pregnancy
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Uterine pathology
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References and further reading
del 2 11 di ensi nal s n rap i etr e al ati n ra its’ e es Global Veterinaria 6 22 222
s rde H Hatip l et al 2 ltras n rap ic e a inati n t e scr tal c ntent in t e ra it Reproduction in Domestic Animals 441 1 1
i itr lad a ta at a st and te an 2 11 ranst racal t di ensi nal ltras n rap ic anat ical st d t e eart in t e ra it Oryctolagus cuniculus Trakia Journal of Sciences 93
i itr 2 12 ltras nd eat res idne s in t e ra it Oryctolagus cuniculus Veterinary World 5 2 2
la H and ils n 1 ia n sis pre nanc and disease ltras nd in e tic species Symposia of the Zoological Society of London 60 13 1
ntes sa r s il a ra et al 2 de and ppler ec cardi rap ic re erence al es r ale e ealand ite ra its American Journal of Veterinary Research 67 1 2 1 2
ienle and as 2 2 c cardi rap n Small Animal Diagnostic Ultrasound, 2nd edn ed land and
att n pp 3 23 a nders iladelp ia
n el Hitt air Hassan et al 2 12 as in ra its clinical e al ati n dia n sis and treat ent Journal of the American Animal Hospital Association 48 1
a rer i ns and r ce 1 rp etric assess ent t ic si e ariati n in la rat r ra its Toxicological Pathology 18
ara i sallane ad adiri and r eni 2 11 ltras n rap ic e al ati n t e rinar s ste in e ealand ite ra it and lai are Veterinary Research Forum 22 113 12
se and 1 c cardi rap and ppler i a in n Textbook of Canine and Feline Cardiology, 2nd edn ed et al pp 13 1 1 a nders iladelp ia rc tt 2 ardiac and respirat r disease in ra its
Proceedings of the British Veterinary Zoological Society, Autumn meeting 2000 pp 3
i i Ha en and eredit 2 nter ittent c lic and int ss scepti n d e t a cecal p l p in a ra it Journal of Exotic Pet Medicine 16 113 11
a er 1 2 nd crin l ical st d testic lar descent in t e ra it Journal of Surgical Research 33 1 1 3
edr e 2 1 a in tec ni es in s all a als Seminars in Avian and Exotic Pet Medicine 10 1 1
r ri e an and la e 2 ltras n rap ic assess ent estati nal a e in ra its Proceedings of the 15th Congress of the Federation of Asian Veterinary Associations, 27–
30 ct er 2 FAVA–OIE Joint Symposium on Emerging Diseases. Bangkok, Thailand pp 3 3
ta at a c e a i itr n a et al 2 12 parati e i a in anat ic st d d estic ra it li er Oryctolagus cuniculus Trakia Journal of Sciences 101 3 ell de eneses esa and n ale 1
c cardi rap ic assess ent cardiac ncti n in t e ra it a preli inar st d Annales de Recherches Vétérinaires 20 1 1as a er ac s et al 1 3 ec endati ns
r standards in transt racic t di ensi nal ec cardi rap in t e d and cat c cardi rap ittee t e pecialt ardi l erican lle e eterinar nternal edicine Journal of Veterinary Internal Medicine 7 2 2 2
ard 2 ia n sis and ana e ent a retr l ar a scess periapical ri in in a d estic ra it Veterinary Clinics of North America: Exotic Animal Practice 9