Ultrasonography of Osteosarcoma in Dogs
Sonography Atlas of Dogs

Materials and methods

Thirty healthy dogs, males and females, of several breeds obtained from the Veterinary Hospital, College of Veterinary Medicine and Animal Science-FMVZ, São Paulo State University-UNESP, Botucatu, São Paulo State, Brazil, were evaluated. These animals were considered healthy based on physical, hematological and biochemical analyses, as well as on abdominal ultrasonography. Initially there were 42 animals, but seven dogs could not be examined due to the breathing or the behaviour of the animal, and five dogs had abnormal values of clinical laboratory tests. The animals were divided into three groups, with ten dogs in each, according to weight range: Group A, dogs weighed ≤ 10 kg; Group B, dogs weighed 10.1-20 kg; and Group C, dogs weighed ≥ 20.1 kg.

A triplex scan ultrasonographic device (GE, Logic 3 model) was used. It had two multi-frequency transducers, convex from 3.5 to 5 MHz and linear from 6 to 10 MHz.

Dogs were deprived of food for 12 hours before the test and received dimethicone, (Dimeticolin^® 75 mg/ml, Hipolabor Farmacêutica LTDA, Borges Sabará-MG, Brazil), orally, at a dose of 4 drops/kg, three times from the beginning of the fasting period to 20 minutes before the ultrasonographic evaluation. Dimethicone is an antiflatulent and was used to avoid intestinal gas formation. No sedatives were used.

Before Doppler evaluation, the diameter and area of portal vein were measured, the animal was kept in left lateral decubitus position and the transducer was placed on the right lateral body wall, at approximately the 10th or 11th intercostal space, in the porta hepatis region, in which the right kidney was not observed, as previously proposed by other authors [7] (Fig. 1). After diameters were determined, vessel cross-sectional areas were calculated using the following formula (1):

Color and spectral Doppler examination was carried out in the right branch of the portal vein to evaluate blood flow direction and velocity within the vessel (Fig. 2). To access the right branch, the transducer was kept in the previously described position to allow the determination of the portal vein diameter [6] and was moved approximately one intercostal space cranially and the angle was set to obtain longitudinal image of the portal vein right branch, as suggested in literature [7]. The angle between the sound waves and the flow direction in the evaluated vessel was kept less than or equal to 60 degrees in all cases. Mean velocity (Vmean) was assessed through the uniform insonation technique by using the software from the device; angle correction was used in all cases to calculate the velocities accurately.

The experimental design was completely randomized, with three groups and ten replicates per group. For each animal, all measurements had three replicates, from which a mean was calculated. Based on the obtained data, portal CI and average portal blood flow volume (PBFV) were assessed.

A: portal vein area; Vmean: portal vein flow mean velocity

w: body weight

It was necessary to change the unit of the Vmean (cm/sec to cm/min).

Discussion

In human medicine, introduction of Doppler ultrasonography is considered a milestone in the diagnosis of portal hypertension. Nowadays, it is part of the initial examination of such patients, since it is considered extremely important for the diagnosis and prognosis [6].

In veterinary medicine, the Doppler technique has aided the diagnosis of hepatopathies mainly related to vascular alterations such as intra- and extrahepatic portosystemic disorders [4]. However, correlations between vascular alterations and clinical signs are not completely established. Normal values and variations between dogs of different sizes are needed as the normal values described in literature are based on studies involving medium-sized animals only [1, 3].

The correct insonation angle is essential for the accurate assessment of flow velocity. It has been described that in dogs with chronic hepatic diseases there is a decrease in the mean velocity of portal blood flow and this may result in clinically important portal hypertension [1]. Congenital portosystemic shunts increase the mean velocity of the portal blood flow [9]. However, insonation angles greater than 60° can produce erroneous results. This study has shown that, as described for humans [6], smaller insonation angles can be more easily obtained in the right branch of the portal vein, making its use appropriate for flow velocity measurement in dogs, with more accurate results (Fig. 3).

In this work, portal flow velocity did not differ among groups. The mean velocity values obtained in this study for portal vein right branch flow were similar to those obtained in other studies of the main portal vein, in which the normal value was between 14.7 ± 2.5 cm/s and 18.1 ± 7.6 cm/s [1].

The assessment of PBFV is important, since the main portal vein is responsible for carrying, on average, 75% of the total blood received by the liver [5]. The present study showed that the right intra-hepatic portal vein flow changes according to the weight of the dog; small-sized dogs had greater portal blood flow per kilogram body weight, than larger-sized dogs. Comparing with the results of the literature [1], our data indicate that dogs weighing ≤ 10 kg (Group A) have values above the normal range given for the main portal vein (31.2 ± 9.8 ml/min/kg) by other authors.

Thus, this study demonstrated that the portal vein area in small-sized dogs is significantly smaller than that of the larger animals, while mean velocity is similar among dogs of any body weight.

This new data shows values of normality for the right portal vein flow in healthy dogs, and also an important aspect, PBFV and CI were influenced by the body weight. There is reason to believe that also the flow of the main portal vein varies with the size of the dog, and thus the reference values found in the literature [1, 3] may introduce an error, since they are based only on values in medium-sized dogs.

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