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Ultrasonography of the Liver, Spleen, Kidneys, Bladder, and Peritoneal Cavity

Nathan Slovis

McGee Medical and Critical Care Center, Hagyard Equine Medical Institute, Lexington, KY, USA

Liver

The liver (Figures 22.1, 22.2, 22.3, 22.4, 22.5, 22.6, 22.7, 22.8, 22.9, and 22.10) is the largest of the abdominal organs, occupying most of the right quadrant and extending across the midline. The liver can be located in the right cranioventral and midabdomen between the 7th and 14th intercostal spaces (ICS) and dorsally in the 14th ICS. It can also be located on the left side cranioventrally between the 6th and 9th ICS. On the right side, the right dorsal colon (RDC) is deep to the liver and the duodenum is located between the RDC and liver in the mid portion of the abdomen. On the left side, the liver will be in contact with the stomach and the spleen. Because the liver lies superficially in the young animal, a 5 to 7 MHz transducer is optimal, while a 3.5 or even a 2.0 MHz will be necessary in the older, adult horse. Hepatic vessels and bile ducts can be seen diffusely, with the portal vein and caudal vena cava being the largest vessels observed on the right side. The liver is characterized as homogeneously hypoechoic and uniform throughout compared to the spleen.

**Figure 22.2** Normal liver. In this image from the mare in Figure 22.1, the liver has normal, tapered edges (arrow). Rounded edges are abnormal and may occur in cases of hepatitis or hepatic lipidosis. The sonogram was obtained from the right 10th ICS, 5–7 cm ventral to the image of Figure 22.1, using a curvilinear probe operating at 5.0 MHz at a displayed depth of 18 cm. The left side of this image is dorsal and the right side is ventral.

**Figure 22.3** Normal liver. (A) In this image from the mare in Figure 22.1, the portal veins are prominent with a thick, echogenic wall. This is a normal anatomical finding of the liver. The ventral tip of the lung can be visualized “covering” the liver on the left side of this image. The diagram (Dia) is superficial to the liver. Right dorsal colon (RDC) is visible. The sonogram was obtained from the right 8th ICS using a curvilinear probe operating at 5.0 MHz at a depth of 18 cm. The left side of this image is dorsal and the right side is ventral. (B) Color flow Doppler confirms that the linear structure is the portal vein and not a dilated bile duct.

**Figure 22.4** Normal portal vein. This image shows the portal vein in a normal, 3-year-old racehorse. The color Doppler was used to confirm that the liner structure was the portal vein and not a dilated bile duct. With color, Doppler, direction, and velocity of blood flow can be evaluated. Although color may vary with machine, typically, red indicates flow toward the transducer, while blue indicates flow away from the tranducer. Brighter hues indicate faster velocity of blood flow, while duller colors indicate slower velocity of blood flow. Turbulent blood flow produces a mixture of colors. This sonogram was obtained from the right abdomen using a curvilinear probe operating at 3.5 MHz at a depth of 18 cm.

**Figure 22.5** Normal liver and duodenum. This image shows the duodenum (arrows) located medial to the right lobe of the liver in a 12-year-old Thoroughbred gelding. The right dorsal colon (RDC) is medial to the duodenum. The duodenum is easily recognized because of its oval and flattened appearance with a hyperechoic center. During peristalsis, the duodenum will appear to have an oval to round shape. Note the normal homogeneously hypoechoic sonographic appearance of the liver. The sonogram was obtained from the right 14th ICS using a curvilinear probe operating at 3.5 MHz at a displayed depth of 15 cm. The left side of this image is dorsal and the right side is ventral.

**Figure 22.6** Cranioventral abdomen. This image shows the left, cranioventral abdomen obtained from a 12-year-old pregnant Thoroughbred mare. In the normal horse, the spleen is more echogenic and more homogenous than the liver which is located medial to the spleen. If the liver is the same echogenicity as the spleen, cholangiohepatitis or hepatitis should be suspected. The hyperechoic, curvilinear structure adjacent to the liver is the left ventral colon (LVC). The splenic vein (small arrow) is visualized in the spleen. The sonogram was obtained from the left, cranioventral abdomen using a curvilinear probe operating at 5.0 MHz at a displayed depth of 17 cm. The left side of this image is dorsal and the right side is ventral.

**Figure 22.7** Hepatitis. Note the round edges which is different from the tapered edges noted in the normal liver. The image is obtained using a curvilinear probe operating at 4.0 MHz at a displayed depth of 13 cm.

**Figure 22.8** Acute hepatitis. This image is from an 8-year-old pregnant mare presenting with pyrexia, SDH, and bile acids above the reference range, but GGT within the reference range. The liver is markedly enlarged with multifocal areas of increased echogenicity. The sonogram was obtained from the left cranioventral using a curvilinear probe operating at 5.0 MHz at a displayed depth of 18 cm. The left side of the image is dorsal and the right side is ventral.

**Figure 22.9** Amyloidosis. These images are liver from a 5-year-old Tennessee Walking Horse stallion. The stallion had a history of hyperglobulinemia, anorexia, and intermittent pyrexia for three weeks prior to examination. The animal had been treated with sulfadiazine/trimethoprim (30 mg/kg PO q 12 hours) for three weeks with minimal improvement. (A) A large mass was imaged adjacent to the liver. In this image, ascertaining if the mass is located medial to the liver or in the liver is difficult. The owners declined a biopsy at the time of the initial examination and the horse was, therefore, discharged with Chloramphenicol (50 mg/kg PO q 8 hours) and Metronidazole (15 mg/kg PO q 8 hours). The sonogram was obtained from the right 9th ICS using a curvilinear probe operating at 3.0 MHz at a displayed depth of 21 cm. The left side of this image is dorsal and the right side is ventral. (B) The horse was examined again 19 days later for pyrexia and continued anorexia. The sonogram revealed large, hyperechoic structures (arrows) within the liver’s parenchyma. Based on histopathology of a biopsy sample, the hyperechoic structures were identified as amyloid deposits and the horse was diagnosed with amyloidosis. The owners opted to euthanize the horse. If the amyloid deposits had been more calcified, an acoustic shadow would have been noted from the near surface of the amyloid deposits. The sonogram was obtained from the right 11th ICS using a curvilinear probe operating at 3.0 MHz at a displayed depth of 19 cm. The left side of this image is dorsal and the right side is ventral.

**Figure 22.10** Bile duct stricture. This image shows the liver from a 3-month-old Thoroughbred colt diagnosed with a gastric outflow obstruction (stricture) affecting the proximal duodenum. The stricture also incorporated the common bile duct opening. The bile duct stricture resulted in cholestasis and severe suppurative cholangiohepatitis. (A) Note the enlarged bile duct (small arrow) and the abscesses (large arrows) within the liver’s parenchyma. An acoustic shadow is present medial to the abscess. The foal had a gastrojejunostomy performed and was placed post-operatively on potassium penicillin (22,000 IU/kg IV q 6 hours), metronidazole (15 mg/kg PO q 8 hours), and gentamicin (6 mg/kg IV SID) for 10 days and then changed to chloramphenicol (50 mg/kg PO q 6 hours) along with the metronidazole. The sonogram was obtained from the right 11th ICS using a curvilinear probe operating at 3.5 MHz at a displayed depth of 17 cm. The left side of this image is dorsal and the right side is ventral. (B) The foal was examined 20 days after discharge from the clinic. His clinical condition had improved and he had been afebrile since treatment. The sonogram of the right lobe of the liver in the 12th ICS shows a diffuse area of increased echogenecity in the parenchyma of the superficial right lobe representing an area of hepatic cirrhosis. The suppurative hepatitis was responding to the prescribed treatment program based on the horse’s improved improved blood parameters (white blood cell count, SDH, bile acids, and fibrinogen values in reference range) along with the decreased size of hepatic abscessation (white arrows) from the previous examination. However, the GGT remained above the reference range secondary to chronic scarring and fibrosis in the liver. The sonogram was obtained from the right 12th ICS using a curvilinear probe operating at 3.5 MHz at a depth of 13 cm. The left side of this image is dorsal and the right side is ventral.

Spleen

The spleen (Figures 22.11, 22.12, 22.13, 22.14, 22.15, and 22.16) is imaged between the 7th ICS and the paralumbar fossa (PLF) on the left side and in the 9th ventral ICS on the right side in contact with the liver. The splenic vein is located on the medial aspect of the spleen, caudal and dorsal to the stomach, in the 11th to 12th mid-ICS. The spleen interfaces caudally with the left kidney and is homogenously echogenic, with few vessels seen. The splenic hilar vessels are usually easily seen, while the intrasplenic vessels typically requires Doppler for identification