ULTRASOUND

Historically, in marine mammals, ultrasound has been used predominantly for reproductive studies. However other applications including echocardiology, abdominal evaluation and thyroid evaluation are starting to gain recognition. Researchers have also used ultrasound to determine blubber depth.

One of the biggest obstacles when using ultrasound in marine mammals is the thick blubber layer that is highly reflective and attenuating, and the large size of many animals.

Stranded Cetaceans

Pneumonia is a constant concern in marine mammals and many animals are too large to radiograph or CT. If lung lesions are peripheral they can be seen using ultrasound. This is particularly useful when dealing with beach stranded cetaceans. The orange arrows below delineate consolidated lung. Differentials include atelectasis, pneumonia, abscessation, neoplasia, or peripheral infarcts. Distribution and history of the patient will help determine the most likely etiology. Tissue sampling can be performed using ultrasound guidance. Note: If lesions are not seen with ultrasound this does not mean that the lungs are normal. However if lesions are seen, lung pathology or atelectasis (collapse) is present. This is because ultrasound can ONLY be used to detect peripheral lesions.

In this image the consolidated lung is in the caudodorsal lung field adjacent to the diaphragm. The tissue to the right of the image is liver on the abdominal side of the diaphragm.

This abnormal liver is hyperechoic and hyperattenuating. In small animal medicine this would be most suggestive of fibrosis, steroid hepatopathy or hepatic lipidosis depending on species, although other hepatopathies could not be completely ruled out without tissue sampling. Histopathology confirmed the presence of lipid within hepatocytes.

Histologically abnormal liver:

Histologically normal liver:

These findings suggest that cetaceans may suffer from hepatic lipidosis similarly to domestic cats, with inappropriate mobilization of fat during periods of anorexia. Little information about this condition in whales is currently available in the literature.

But its not all bad news..........every now and then its a happier story. Below are two movies of a stranded dolphin that on ultrasound was determined to be pregnant. Her fetus is fluking in utero and the heart beat can be seen. Both movies have been slowed from real time to allow easier watching. Both mum and calf did well.

The following two movies were obtained and provided by Dr. Michael Moore VetMB PhD of Woods Hole Oceanographic Institute (WHOI). They are displayed on this website with permission from the International Fund for Animal Welfare (IFAW) who provide rescues for stranded marine mammals in the Cape Cod region.

Links to these organizations can be found at contributors and useful links

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California Sea Lions

California sea lions strand for a variety of reasons. Abdominal ultrasound is a really useful method for assessing abdominal structures that are poorly defined on radiographs. It is important to undertake ultrasound examinations in a systematic manner to ensure that all structures are evaluated and lesions are not missed.

Below are some ultrasound images of normal major organs in variably aged California sea lions.

The orange arrows point to the interface between the liver and spleen.

Marine mammals have multireniculate kidneys. Each renule is really a kidney in its own right. Each darker, hypoechoic region is a renule medulla. The cortices are similar in echogenicity to the spleen and similar or slightly hyperechoic to the liver in normal sea lions.

Abnormal California Sea Lion Ultrasound Examinations

Below are ultrasound images of a kidney with moderate hydronephrosis of the renules and nephrolith formation. Compare the images to the normal kidney above. The renules are dilated and abnormally anechoic (black circles). The uroliths, which contain mineral, produce an artifact called “distal acoustic shadowing” due to strong reflection of the sound beam. This helps determine that mineral is present. The orange arrows point to the urolith. The blue arrows point to the artifact that the urolith produces in the ultrasound beam.