Ultrasonographic characterization of the liver, caudal vena cava, portal vein, and gallbladder in goats

Ueli Braun Department of Farm Animals, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, CH-8057 Zurich, Switzerland.

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Kathrin Steininger Department of Farm Animals, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, CH-8057 Zurich, Switzerland.

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Abstract

Objective—To characterize the localization, visible extent (ie, measurement of selected dimensions), and appearance of the liver, caudal vena cava, portal vein, and gallbladder during ultrasonography in healthy goats.

Animals—27 female Saanen goats.

Procedures—A 5.0-MHz linear transducer was used to ultrasonographically examine the localization, visible extent of various dimensions, and appearance of the liver, caudal vena cava, portal vein, and gallbladder from the right side of each goat.

Results—Images of the liver were obtained in all goats. The dorsal margin of the liver extended in a cranioventral to caudodorsal direction parallel to the caudal margin of the lungs. The greatest visible extent of the liver was evident at the seventh and eighth intercostal spaces (mean value, 15.9 cm), and width was evident at the 10th intercostal space (mean value, 5.2 cm). The caudal vena cava had a triangular shape on cross section; the maximum width in cross section, circumference, and surface area ranged from 1.2 to 1.8 cm, 4.8 to 5.2 cm, and 0.8 to 1.1 cm2, respectively. The portal vein was round on cross section (diameter, 0.8 to 1.7 cm) with stellate ramifications into the liver parenchyma. The gallbladder was pear-shaped and variable in size; it extended beyond the ventral margin of the liver to a variable degree depending on the amount of bile.

Conclusions and Clinical Relevance—Results provided information regarding the ultrasonographic appearance of the liver, caudal vena cava, portal vein, and gallbladder in healthy goats; these data may be useful during examination of goats with suspected liver disease.

Abstract

Objective—To characterize the localization, visible extent (ie, measurement of selected dimensions), and appearance of the liver, caudal vena cava, portal vein, and gallbladder during ultrasonography in healthy goats.

Animals—27 female Saanen goats.

Procedures—A 5.0-MHz linear transducer was used to ultrasonographically examine the localization, visible extent of various dimensions, and appearance of the liver, caudal vena cava, portal vein, and gallbladder from the right side of each goat.

Results—Images of the liver were obtained in all goats. The dorsal margin of the liver extended in a cranioventral to caudodorsal direction parallel to the caudal margin of the lungs. The greatest visible extent of the liver was evident at the seventh and eighth intercostal spaces (mean value, 15.9 cm), and width was evident at the 10th intercostal space (mean value, 5.2 cm). The caudal vena cava had a triangular shape on cross section; the maximum width in cross section, circumference, and surface area ranged from 1.2 to 1.8 cm, 4.8 to 5.2 cm, and 0.8 to 1.1 cm2, respectively. The portal vein was round on cross section (diameter, 0.8 to 1.7 cm) with stellate ramifications into the liver parenchyma. The gallbladder was pear-shaped and variable in size; it extended beyond the ventral margin of the liver to a variable degree depending on the amount of bile.

Conclusions and Clinical Relevance—Results provided information regarding the ultrasonographic appearance of the liver, caudal vena cava, portal vein, and gallbladder in healthy goats; these data may be useful during examination of goats with suspected liver disease.

Ultrasonography is an established technique used in the diagnosis of liver disease in cattle and sheep. A recent review article1 summarized the results of numerous reports of the ultrasonographic findings in healthy cattle and cattle with liver disease. Detailed information regarding ultrasonographic appearance of the liver in sheep is also available.2,a However, in goats, ultrasonography has been limited to use as a screening method for identification of hydatid cysts of Echinococcus granulosus (canine tapeworm).3–5 Yet, ultrasonographic findings could be used to diagnose other liver disorders in goats, such as abscesses, tumors, hepatomegaly, and fascioliasis. Identification of liver disease via ultrasonography is based on a thorough knowledge of the normal appearance of the organ. The purpose of the study reported here was to characterize ultrasonographically the localization, visible extent (ie, measurement of selected dimensions), and appearance of the liver, caudal vena cava, portal vein, and gallbladder in healthy goats.

Materials and Methods

Animals—Twenty-seven clinically normal, nonlactating, female Saanen goats were used in the study. The goats were 2.5 to 6.5 years old (mean age, 4.1 years) and weighed 42 to 86 kg (mean weight, 61.3 kg). The goats were not pregnant and had similar body conditions. They originated from 2 farms and had been sold for slaughter. The study protocol was approved by the Animal Care Committee of the Canton of Zurich, Switzerland.

Ultrasonographic examination of the liver, gallbladder, and blood vessels—A real-time ultrasound machineb with a 5.0-MHz linear transducer was used to examine the liver of each standing, nonsedated goat by use of a method described for cattle,6,7 sheep,2 and goats.c The hair over the right side of the thorax was clipped from the caudal border of the shoulder joint to just caudal to the last rib and from the dorsal midline to the linea alba. After the application of acoustic gel, each intercostal space and the region caudal to the last rib were examined in a dorsal to ventral direction with the transducer held parallel to the ribs.

Subjective ultrasonographic evaluation of the liver, gallbladder, and blood vessels—The liver, gallbladder, caudal vena cava, and portal vein were subjectively assessed via ultrasonography. For the liver, appearance of the surface of the organ and the echogeneity and homogeneity of the hepatic parenchyma were recorded; whether the hepatic blood vessels could be visualized was also noted, and when possible, their appearance was recorded. The location, overall size and shape, and contents of the gallbladder were also assessed and recorded. Visualization of the extrahepatic bile ducts (including the hepatic duct, cystic duct, and the common bile duct [ductus choledochus]) was investigated. The intrahepatic bile ducts were evaluated for calcification.1

Measurements of the liver—At the level of each intercostal space at which the liver could be observed ultrasonographically, half of the abdominal circumference was measured with a tape measure from the mid-line of the dorsum to the linea alba. Then, analogous to studies in cattle6,7 and sheep,2 the dorsal and ventral margins of the liver were determined and used to calculate the extent of the liver. Measurements were made on cross-sectional views of the liver (Figure 1). The positions of the dorsal and ventral borders of the liver were determined in relation to the midline of the dorsum; a tape measure was used to measure the distance between the midline of the dorsum and the dorsal margin and the distance between the midline of the dorsum and the ventral margin of the liver. The visible extent of the liver in a given intercostal space was determined by subtracting the distance between the dorsal liver margin and the midline of the dorsum from the distance between the ventral liver margin and the midline of the dorsum. The thickness of the liver at a given intercostal space was measured electronically at the level of the portal vein by means of the 2 ultrasound machine cursors. The angle between the diaphragmatic and visceral surfaces of the liver was referred to as the angle of the liver. The view that contained the largest angle was printed and measured by use of a protractor. All measurements were made once during maximum inspiration.

Blood vessels—From studies in cattle1 and sheep,2 it is known that the caudal vena cava is consistently situated more dorsally and medially than the portal vein. In each goat, the dorsal margins of the caudal vena cava and portal vein were determined by measuring the distance of each from the dorsal midline by use of a tape measure. The distance between each vessel and the peritoneum, the vessel wall thickness, the maximum width of the caudal vena cava, and the maximum diameter of the portal vein were determined electronically on ultrasonograms by use of the 2 cursors. For the measurement purposes, the ultrasonograms were recorded during maximum inspiration. The circumference and surface area of the caudal vena cava were determined electronically by moving the cursor along the perimeter of the vessel while the image was frozen.

Gallbladder—From studies in cattle1 and sheep,2 it is known that the gallbladder is a pear-shaped cystic structure of variable size and is easy to recognize. The intercostal spaces in which the gallbladder could be visualized were first determined, and then the position of the dorsal margin, length, width, and wall thickness of the gallbladder were determined. The appearance of the contents of the gallbladder and any spontaneous contractions were recorded. Finally, visualization of the intra- and extrahepatic bile ducts was investigated.

Postmortem examination—The goats were slaughtered at the slaughter facility of the Vetsuisse Faculty, University of Zurich (n = 12) or euthanized by use of an injection of pentobarbital (15). The method of slaughter or euthanasia was not considered to influence the outcome of the study. A macroscopic postmortem examination of the internal organs in each of the slaughtered goats was carried out. The euthanized goats, which were also used in other studies, were frozen and cut into 1.0- to 1.5-cm-thick transverse whole-body sections. The internal organs in these sections were examined.

Statistical analysis—For each measurement of interest at each intercostal space, a group mean value and SD were calculated from the data collected; however, not all measurements were obtained at each intercostal space in all goats (variable denominator). Frequencies were also calculated for continuous variables, and correlation coefficients were calculated to describe the relationship between selected variables. Statistical analysis was performed by use of a statistics software program.d Values of P < 0.05 were considered significant.

Results

Liver—The liver was viewed ultrasonographically at 3 or more intercostal spaces in all goats. At the seventh to ninth intercostal spaces, it was seen in all goats (Table 1). The parenchymal pattern of the normal liver consisted of numerous fine echoes homogeneously distributed over the entire area of the liver (Figure 2). The diaphragmatic surface of the liver appeared as a smooth, narrow echogenic line, which was positioned immediately adjacent to the peritoneum and moved in synchrony with the diaphragm during respiration. The visceral surface of the liver also appeared as a narrow echogenic line but was not always clearly defined at the 5th to 10th intercostal spaces, where the liver usually bordered on the reticulum and omasum, or at the 11th and 12th intercostal spaces, where the liver was bordered by loops of intestine. Compared with the renal cortex, the liver parenchyma appeared as dense in 13 goats, more dense in 8 goats, and less dense in 6 goats. The dorsal margin of the liver was positioned parallel to the border of the lungs in the cranioventral to caudodorsal direction (Figure 3). The mean ± SD distance of the dorsal margin of the liver from the dorsal midline was 31.4 ± 1.52 cm at the fifth intercostal space, and this distance progressively decreased in a caudal direction as the liver became less obscured by the lungs. The mean distance between the ventral margin of the liver and the dorsal midline was greatest at the sixth intercostal space and shortest at the 12th intercostal space. The mean visible extent of the liver was the largest at the seventh and eighth intercostal spaces and progressively decreased in the cranial and caudal directions. The smallest mean value for liver extent was recorded at the fifth intercostal space. The mean thickness of the liver was smallest at the sixth intercostal space and greatest in the 10th intercostal space. The distal angle of the liver, formed in the ventral portion of the liver by the diaphragmatic and visceral surfaces, ranged from 15.0° to 64.0°.

Table 1—

Results of ultrasonographic examination of the liver and measurement of the hemi-circumference of the abdomen performed at the 5th through 12th right intercostal spaces in 27 female Saanen goats.

VariableIntercostal space
 56789101112
No. of goats in which variable was measurable52427272725196
Dorsal margin-to-dorsal midline distance (cm)31.4 ± 1.5228.8 ± 2.8025.1 ± 2.9120.9 ± 2.9417.0 ± 2.5913.5 ± 2.799.7 ± 2.107.9 ± 1.28
(29.0–33.0)(22.0–33.0)(19.0–29.5)(15.5–27.5)(11.0–20.5)(7.0–18.0)(6.0–14.0)(7.0–10.0)
Ventral margin-to-dorsal midline distance (cm)39.1 ± 6.2841.3 ± 4.9841.0 ± 4.2336.8 ± 4.8132.1 ± 4.5327.0 ± 5.3720.9 ± 4.6118.5 ± 3.78
(33.5–49.0)(29.5–51.0)(30.5–50.0)(28.0–46.0)(24.0–41.0)(18.0–43.0)(15.5–35.0)(13.5–23.0)
Visible extent (cm)7.7 ± 6.6612.9 ± 4.1815.9 ± 3.7215.9 ± 4.7415.2 ± 4.1313.5 ± 3.9811.2 ± 4.2110.6 ± 3.35
(0.5–17.0)(6.5–22.5)(10.0–23.5)(9.0–28.5)(6.0–22.0)(7.0–25.0)(4.0–22.0)(6.5–15.5)
Thickness (cm)NE3.9 ± 0.944.6 ± 1.005.0 ± 0.955.0 ± 0.915.2 ± 0.795.0 ± 1.304.5*
(1.9–5.5)(3.3–7.0)(3.5–6.7)(3.5–6.7)(3.5–6.7)(1.4–6.4)
Distal angle (°)29.0 ± 6.5627.5 ± 5.6228.8 ± 5.9632.6 ± 5.9130.5 ± 6.6833.5 ± 8.2635.8 ± 10.5647.4 ± 6.03
(22.0–35.0)(17.0–40.0)(15.0–40.0)(19.0–43.0)(15.0–40.0)(20.0–53.0)(20.0–64.0)(40.0–55.0)
Hemi-circumference of abdomen (cm)44.4 ± 4.9344.6 ± 6.5045.2 ± 6.0146.0 ± 5.5947.4 ± 5.4448.3 ± 5.6949.8 ± 6.3552.6 ± 5.08
(38.0–50.0)(17.5–51.0)(18.0–52.0)(22.0–53.0)(26.0–55.0)(27.0–58.0)(29.0–59.0)(43.0–59.0)

Data are reported as mean ± SD (range). The distances between the midline of the dorsum and the dorsal liver margin and between the midline of the dorsum and the ventral liver margin were measured by use of a tape measure; the visible extent of the liver was determined by subtracting the former value from the latter value. At a given intercostal space, the thickness of the liver was measured electronically at the level of the portal vein by means of the 2 ultrasound machine cursors; the image that contained the largest distal angle of the liver (the angle between diaphragmatic and visceral surfaces of the liver) was printed, and the distal angle was measured by use of a protractor. All measurements were made during maximum inspiration.

At the 12th intercostal space, the thickness of the liver was determined only in 1 goat in which the portal vein was visible.

NE = Not examined because the portal vein could not be seen.

Figure 1—
Figure 1—

Schematic representation of a cross section of the body of a goat at the 11th intercostal space to illustrate the position of the liver, caudal vena cava, portal vein, and gallbladder and measurement of some variables of interest performed as part of the ultrasonographic characterization of the aforementioned organs and vessels in goats. A = Abomasum. CVC = Caudal vena cava. G = Gallbladder. Li = Liver. Lu = Lung. O = Omasum. PV = Portal vein. Ru = Rumen. S = Spleen. 1 = Distance between dorsal margin of the liver and the dorsal midline. 2 = Distance between the ventral margin of the liver and the dorsal midline. 3 = Visible extent of the liver. 4 = Distance between the caudal vena cava and the peritoneum. 5 = Distance between the portal vein and the peritoneum. 6 = Distal angle of the liver (angle between diaphragmatic and visceral surfaces of the liver).

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

Figure 2—
Figure 2—

Ultrasonogram obtained at the 10th intercostal space on the right side in a 3.5-year-old Saanen goat and schematic representation of the image. In this view, the liver parenchyma is visualized. Ds = Dorsal. Md = Medial. Vt = Ventral. 1 = Lateral abdominal wall. 2 = Liver parenchyma. 3 = Portal vein. 4 = Omasum.

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

Figure 3—
Figure 3—

Photograph of the right side of a Saanen goat on which the dorsal and ventral margins of the liver (upper and lower red lines, respectively) between the 5th and 12th intercostal spaces have been marked. The lines were drawn on the basis of the mean values for the distance between the dorsal or ventral margin of the liver and the dorsal midline calculated from data obtained from 27 Saanen goats.

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

The visible extent of the liver and the hemi-circumference of the abdomen were significantly correlated at the 11th (r = 0.29; P = 0.02) and 12th (r = 0.69; P = 0.04) intercostal spaces. The thickness of the liver and hemi-circumference of the abdomen were significantly correlated at the 10th (r = 0.33; P = 0.01) and 11th (r = 0.33; P = 0.02) intercostal spaces.

Blood vessels—The caudal vena cava had a triangular shape on cross section because it is embedded in the sulcus of the vena cava in the liver (Figure 4). The vein was visualized in 20 of 27 goats and was seen at the 10th, 11th, and 12th intercostal spaces in 1, 11, and 10 goats, respectively (Table 2). The caudal vena cava was visible at both the 11th and 12th intercostal spaces in 2 goats. Because of superimposition of the lungs, the caudal vena cava could not be seen at the fifth to ninth intercostal spaces. The vessel coursed in a caudodorsal to cranioventral direction, similar to the positioning of the dorsal margin of the liver. The distance between the dorsal margin of the caudal vena cava and the dorsal midline decreased from the 10th (12.0 cm) to 12th (11.0 cm) intercostal space. The distance between the caudal vena cava and the peritoneum ranged from 5.9 to 6.3 cm. The maximum width of the vessel ranged from 1.2 to 1.8 cm; the circumference and the cross-sectional area ranged from 4.8 to 5.2 cm and from 0.8 to 1.1 cm2, respectively. The mean thickness of the wall of the caudal vena cava was 1.1 mm. The vessels that were seen in cross section medial to the caudal vena cava and outside of the liver parenchyma were the common trunk of the left gastric and splenic veins or veins extending individually from those 2 organs before their junction as a common trunk.8 These veins were usually circular on cross section.

Table 2—

Results of ultrasonographic examination of the caudal vena cava and portal vein performed at the 6th through 12th right intercostal spaces in 27 female Saanen goats.

VesselVariableIntercostal space
  6789101112
Caudal vena cavaNo. of goats in which variable was measurable000011110
Dorsal margin-to-dorsal midline distance (cm)NANANANA12.011.6 ± 1.19 (9.5–13.0)11.0 ± 2.56 (8.5–17.5)
Distance from the peritoneum (cm)NANANANA6.36.1 ± 1.19 (4.4–8.2)5.9 ± 1.44 (4.3–9.0)
Maximum width (cm)NANANANA1.51.8 ± 0.49 (0.8–2.5)1.2 ± 0.51 (0.7–2.1)
Circumference (cm)NANANANA4.35.2 ± 0.87 (3.9–6.4)4.8 ± 0.84 (3.6–6.1)
Cross-sectional area (cm2)NANANANA0.61.1 ± 0.35 (0.5–1.8)0.8 ± 0.26 (0.5–1.2)
Portal veinNo. of goats examined1223262724161
Dorsal margin-to-dorsal midline distance (cm)29.8 ± 2.45 (25.0–32.0)25.6 ± 3.26 (14.5–30.0)22.6 ± 2.9 (17.0–29.0)19.9 ± 1.98 (16.0–25.0)17.8 ± 2.04 (13.5–23.0)15.5 ± 2.29 (11.0–20.0)13.5
Distance from the peritoneum (cm)3.9 ± 1.37 (2.3–6.2)4.5 ± 1.13 (2.2–6.5)4.9 ± 0.86 (3.4–6.7)4.7 ± 0.93 (2.8–6.3)4.3 ± 0.98 (2.8–6.0)4.3 ± 1.07 (2.4–5.9)2.8
Diameter (cm)0.8 ± 0.01 (0.7–1.0)1.0 ± 0.21 (0.6–1.5)1.2 ± 0.22 (0.9–1.6)1.3 ± 0.24 (0.9–1.8)1.5 ± 0.26 (1.1–2.0)1.7 ± 0.33 (1.4–2.5)1.7

Data are reported as mean ± SD (range). The dorsal margins of the caudal vena cava and portal vein were determined by measuring the distance of each from the dorsal midline by use of a tape measure. The distance between each vessel and the peritoneum, the vessel wall thickness, the maximum width of the caudal vena cava, and the maximum diameter of the portal vein were determined electronically on images by use of the 2 ultrasound machine cursors. All images used for measurements were recorded during maximum inspiration.

NA = Not applicable.

Figure 4—
Figure 4—

Ultrasonogram obtained at the 12th intercostal space on the right side in a 4-year-old Saanen goat and schematic representation of the image. In this ultrasonographic view, the caudal vena cava is visualized. The caudal vena cava has a triangular shape on cross section. 1 = Lateral abdominal wall. 2 = Caudal vena cava. 3 = Common trunk of left gastric vein and splenic vein. 4 = Liver parenchyma. 5 = Hepatic veins. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

The portal vein was circular to oval on cross section with stellate ramifications into the liver parenchyma (Figure 5). The wall of the portal vein was more distinct than that of the caudal vena cava but had the same mean thickness of 1.1 mm. The wall of the intrahepatic portal vein was more echoic than that of the hepatic vein, but the 2 veins were reliably differentiated only in the region where the portal vein branched. In contrast to the caudal vena cava, the portal vein was visualized at all intercostal spaces at which the liver could be seen (ie, the 6th to 12th intercostal spaces) with the exception of the 5th intercostal space. The portal vein could be seen in the 6th, 7th, 8th, 9th, 10th, 11th, and 12th intercostal spaces in 12, 23, 26, 27, 24, 16, and 1 goat, respectively (Table 2). The mean distance between the dorsal margin of the portal vein and the dorsal midline decreased from the 6th (29.8 cm) to 12th (13.5 cm) intercostal space. The mean diameter of the vein increased from 0.8 cm cranially to 1.7 cm caudally. The mean distance between the portal vein and the peritoneum ranged from 2.8 to 4.9 cm.

Gallbladder and bile ducts—The gallbladder was visualized in 24 of the 27 goats. It was pear shaped and sometimes extended beyond the ventral margin of the liver depending on the amount of bile (Figure 6). The gallbladder was seen at the seventh intercostal space in 2 goats, at the eighth intercostal space in 10 goats, and at the ninth intercostal space in 15 goats. The gallbladder was seen at a single intercostal space in 24 goats and at 2 spaces in 3 goats. The size of the gallbladder varied with the volume of bile. The width ranged from 0.8 to 3.0 cm (mean width, 1.9 ± 0.64 cm), the length ranged from 2.3 to 6.2 cm (mean length, 4.5 ± 1.00 cm), and the wall thickness ranged from 0.9 to 2.6 mm (mean thickness, 1.7 ± 0.42 mm). There were no correlations between the length of the gallbladder and the wall thickness (r = 0.04; P = 0.86) and between the width of the gallbladder and the wall thickness (r = 0.04; P = 0.85). The distance between the dorsal margin of the gallbladder and the dorsal midline ranged from 26.0 to 51.5 cm (mean distance, 31.9 ± 6.11 cm). The content was anechoic in 20 goats and hypoechoic in 4 goats. The intrahepatic bile ducts, the common hepatic duct, and the common bile duct could not be visualized. The junction of the cystic duct and the neck of the gallbladder was evident in 3 goats.

Postmortem examination—The internal organs of each of the 12 slaughtered goats were examined grossly. The internal organs in frozen transverse whole-body sections of each of the 15 euthanized goats were also examined. Postmortem examination of the liver and gallbladder of the examined goats revealed no abnormal findings. In 1 goat, chronic interstitial nephritis of the right kidney was detected.

Figure 5—
Figure 5—

Ultrasonogram obtained at the ninth intercostal space on the right side in a 3-year-old Saanen goat and schematic representation of the image. In this ultrasonographic view, the portal vein is visualized. The portal vein is circular on cross section with 2 ramifications branching into the liver parenchyma. See Figure 2 for key.

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

Figure 6—
Figure 6—

Ultrasonogram obtained at the ninth intercostal space on the right side in a 3-year-old Saanen goat and schematic representation of the image. In this ultrasonographic view, the gallbladder is visualized. The gallbladder is located on the visceral surface of the liver and appears pear-shaped. The cystic duct appears as an echoic structure with a narrow lumen. 1 = Lateral abdominal wall. 2 = Liver parenchyma. 3 = Gallbladder. 4 = Cystic duct. 5 = Omasum. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 72, 2; 10.2460/ajvr.72.2.219

Discussion

In the present study, established methods for ultra-sonographic examination of the liver in cattle6,7 and sheep2 were easily adapted to allow evaluation of the liver in goats. The liver could be seen at the seventh through ninth intercostal spaces in all goats examined. The location at which views of the liver were obtained was slightly more cranial than that in sheep, in which the liver was seen at the 9th and 10th intercostal spaces.2,a In cattle, the liver is best viewed more caudally at the 10th through 12th intercostal spaces.7,e The liver was seen at the 12th intercostal space in only 6 of the 27 goats examined in the present study. The liver has a more vertical position in small ruminants, compared with its position in cattle,9 which could explain why it was not visualized as often at the 2 caudalmost intercostal spaces in the study goats.

The shape and location of the caudal vena cava in goats were similar to findings in cattle and sheep. The vein had a triangular shape in cross section because of its position in the sulcus of the liver and was located dorsally to and more medial than the portal vein. It was best viewed at the 11th and 12th intercostal spaces but was not seen in as many goats (11/27 [41%]) as it was in other studies of cattle (179/186 [96%])7,e and sheep (93/100 [93%]).2,a The discrepancy may be attributable to differences in the visibility of the liver at the 2 caudalmost intercostal spaces in cattle, sheep, and goats. More cranially at the 7th to 10th intercostal spaces, where the liver was visible ultrasonographically in 93% to 100% of goats, the caudal vena cava was not evident because of superimposition of the lungs. There was a wide variation in the maximum width (0.70 to 2.50 cm) of the caudal vena cava; similar variability is present in sheep.2 In humans, the variation in diameter of the caudal vena cava is attributable to changes during respiration; the lumen of the caudal vena cava decreases by approximately 50% during deep expiration.10 In animals with a high respiratory rate, it is difficult to consistently freeze ultrasonographic images exactly at the point of maximum inspiration, which may have led to the large variation in diameter in the goats of the present study. In contrast to findings in cattle and sheep, it was not possible to visualize the junction of the right hepatic vein and caudal vena cava in any of the goats examined, most likely because the liver parenchyma was often obscured from view at the 12th intercostal space by the right kidney.

The portal vein, which transports nutrient-rich blood from the intestine to the liver, was circular on cross section and had stellate ramifications into the liver parenchyma, similar to findings in cattle6,7 and sheep.2 In contrast to the caudal vena cava, the portal vein was seen at the 7th to 10th intercostal spaces in most goats and could be visualized at any intercostal space in which the liver was in view, even at more cranial locations, because there was no superimposition of lung tissue. Similar to findings in cattle6,7 and sheep,2 the wall of the intrahepatic portal vein was more echoic than that of the hepatic vein. The 2 veins could be reliably differentiated only in the region where the portal vein branched.

In the present study, the gallbladder was best visualized at the eighth or ninth intercostal spaces in 24 of the 27 goats. Although its width and length varied greatly, there was no correlation between wall thickness and either of those dimensions. In cattle, the length and width of the gallbladder also vary greatly6; reflex emptying of the gallbladder occurs during feeding and rumination, which is responsible for continual changes in gallbladder size.11 This may explain why the gallbladder could not be viewed ultrasonographically in 3 goats in the present study.

a.

Hausammann K. Sonographic der Leber beim Schaf, Normalbefunde. Dr Med Vet thesis, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland, 1990.

b.

EUB 8500, Hitachi Medical Systems, Zug, Switzerland.

c.

Steininger K. Ultraschalluntersuchung von Leber, Milz, Dünndarm, Dickdarm und Harnapparat bei 30 Ziegen. Dr Med Vet thesis, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland, 2009.

d.

StatView, version 5.1, SAS Institute Inc, Wangen, Switzerland.

e.

Gerber D. Sonographische Befunde an der Leber des Rindes. Dr Med Vet thesis, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland, 1993.

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