The Clinical Utility of the Right Lateral Intercostal Ultrasound Scan Technique in Dogs
When performing abdominal ultrasonography in dogs, the right aspect of the liver, porta hepatis, right kidney, right adrenal gland, pancreas, and duodenum are often not fully visible from a ventral, or subcostal, approach. The right lateral intercostal plane is an alternative approach that allows evaluation of these structures. This report provides multiple case examples that demonstrate the sonographic anatomy via the right intercostal approach. Other cases are included to demonstrate indications for this approach. Animals in which the right intercostal approach may prove most useful include large- and giant-breed dogs; deep-chested dogs; dogs with gas distention of the stomach, duodenum, and colon; dogs with microhepatia; and those with abdominal effusion and pain.
Introduction
For many ultrasonographers, a standard abdominal ultrasound examination in dogs is performed by scanning the ventral abdomen from a subcostal approach, with the animal in dorsal recumbency. Unfortunately, right cranial abdominal structures, such as the right aspect of the liver, porta hepatis (i.e., hepatic lymph nodes, common bile duct, caudal vena cava, and portal vein), right limb and body of the pancreas, duodenum, right kidney, and right adrenal gland are often not completely visible from the standard subcostal approach.1–10 Evaluation of right cranial abdominal organs via the subcostal approach may be difficult in dogs that are deep-chested, have microhepatia or large amounts of gas in the gastrointestinal tract, or have a large volume of peritoneal effusion. To better evaluate the right cranial abdomen, a right lateral intercostal approach is indicated. The purpose of this paper is to describe the technique and usefulness of the right lateral intercostal ultrasonographic scan plane in dogs.
Technique
For the right lateral intercostal approach, the dog can be imaged in either dorsal recumbency or in left lateral recumbency. To avoid acoustic shadowing from the ribs, a transducer with a small footprint may be chosen.1 To find the appropriate window, the transducer is placed in a transverse scan plane, parallel to the ribs, from the ninth to 12th intercostal spaces. If an aerated lung is encountered, the transducer is angled or moved one intercostal space caudally. Dorsal plane or long-axis images can be obtained by turning the transducer 90° from the transverse plane.2
Access to the liver in dogs may be difficult, because portions of the organ are located within the rib cage.2 In large and deep-chested dogs, complete evaluation of the liver may require a right lateral intercostal approach from the last three to four intercostal spaces.3,11 Even with the right lateral approach, there is often only a narrow space between the aerated lung and gas-filled bowel in which the liver can be seen.2
The right lateral intercostal approach allows examination of the aorta, caudal vena cava, portal vein, and common bile duct [Figures 1, 2]. To locate the porta hepatis, the transducer is placed at approximately the 10th or 11th intercostal space, 5 to 10 cm ventral to the spine.2,4,5,11–13 The correct location is found when no aerated lung is seen, the right kidney is not seen, and the triad of the aorta, caudal vena cava, and portal vein is visible. If an aerated lung is seen, the transducer is angled or moved caudally. If the right kidney is seen, the transducer is angled or moved cranially.13 When the transducer is in the correct location, the aorta, caudal vena cava, and portal vein are usually aligned in a single view [Figure 1].4
The aorta is the most dorsal of the vessels in the region of the porta hepatis. It can be found dorsal to the caudal vena cava and the diaphragm.3,4,13 The margin of the diaphragm blends with the ventral wall of the aorta. In some cases, the azygos vein may be seen running parallel and to the right of the aorta.4 Using duplex Doppler ultrasonography (use of real-time, two-dimensional ultrasound and pulsed Doppler simultaneously), aortic flow is high in velocity and pulsatile.6
The caudal vena cava is ventral and to the right of the aorta, and it runs through the foramen vena cavae of the diaphragm to the right of midline in the mid-dorsal diaphragm.2–4 It is surrounded by the caudate lobe on the right and the right lateral liver lobe on the left. The caudal vena cava can be recognized by its course through the liver and entry of the hepatic veins just caudal to the diaphragm. At that level, there are no aortic branches.4 Also, the caudal vena cava often has a flattened shape in cross-section, whereas the aorta is round.3,13 On duplex Doppler ultrasonography, flow in the caudal vena cava is cranially directed and variable, owing to changes in right atrial and intrathoracic pressures.6,14
From the right lateral intercostal window, the portal vein is ventral and slightly to the left of the caudal vena cava and dorsal to the common bile duct.2,3,6,7,11 Portal blood flow characteristics can be evaluated using Doppler ultrasonography via the right lateral intercostal approach.5,12 Flow in the portal vein is normally low in velocity and does not demonstrate pulsatility.12 Caudal to the bifurcation of the main portal vein, the gastroduodenal vein may be seen in some dogs as it enters the ventral aspect of the portal vein from the right. The splenic vein enters the portal vein caudal to this vessel and from the left.13
The common bile duct is ventral and to the right of the portal vein [Figure 2].2,3 The common bile duct may or may not be seen, but it measures <3 mm in diameter in a normal dog.3,15 This structure is often not seen from the standard ventral approach because of artifact created by overlying gastrointestinal gas. With the right lateral intercostal approach, the liver is used as an acoustic window.2
Complete evaluation of the pancreas is difficult from the standard ventral abdominal approach. Dogs with pancreatitis may resist ventral placement of the transducer. Intestinal gas may also prevent evaluation.8 The right lateral intercostal window is useful in evaluating the right lobe and body of the pancreas [Figure 3].8,16,17 From this approach, the right lobe of the pancreas lies ventral to the right kidney, ventrolateral to the portal vein, and dorsal or dorsomedial to the descending duodenum.8,16,17 The body of the pancreas unites the right and left lobes caudal to the pylorus; it lies ventral to the portal vein and craniomedial to the right kidney. 8,16 The pancreaticoduodenal vein, which drains into the portal vein, may be seen centrally within the right lobe of the pancreas, running parallel to the descending duodenum. 6,8 To ensure thorough evaluation of the right lobe of the pancreas, the entire descending duodenum is followed. The colon is caudoventral to the pancreas.8
The right kidney can be difficult to examine from a ventral approach, because it lies dorsal to the duodenum and proximal large intestine. Positioning the dog in left lateral recumbency and placing the transducer dorsally in the intercostal space allows better access to the kidney.18 The right kidney can be found by angling or moving the transducer caudally from the porta hepatis.
Because of its cranial location, the right adrenal gland is difficult to access from the standard subcostal ventral approach. The level of difficulty is increased when there is gas in the pylorus and the duodenum, and in dogs weighing >10 kg.9,10 Landmarks for locating the right adrenal gland with the right lateral intercostal approach include the caudal vena cava, the origin of the celiac and cranial mesenteric arteries, and the craniomedial aspect of the right kidney [Figure 4].4,9,10,19 To find the right adrenal gland in long axis, the caudal vena cava is located caudal to the level of the porta hepatis. Then the transducer is angled dorsolaterally. The right adrenal gland lies dorsally or laterally to the caudal vena cava; it is comma or oval-shaped and hypoechoic; and it may have a layered appearance.10,19
Multiple lymph nodes can be assessed from the right lateral intercostal window. The hepatic lymph nodes are found next to the portal vein, 1 to 2 cm caudal to the porta hepatis [Figure 5]. The left hepatic lymph nodes range from 1 to 6 cm in length and are found in the lesser omentum dorsal to the common bile duct. The right hepatic nodes are smaller and are found next to the body of the pancreas. The hepatic lymph nodes drain the stomach, duodenum, pancreas, and liver.20 The pancreaticoduodenal lymph nodes are inconsistently found in the mesoduodenum near the cranial duodenal flexure between the pylorus and right lobe of the pancreas. These lymph nodes drain the pancreas, stomach, and omentum.20 The gastric lymph nodes (which drain the stomach, esophagus, diaphragm, liver, mediastinum, and peritoneum) are inconsistently found in the lesser omentum near the pylorus and right gastric artery.20
Clinical Indications
The right lateral intercostal approach is useful for diseases involving the right lateral, right medial, and caudate lobes of the liver. This view is especially helpful in diseases that cause microhepatia, such as cirrhosis or congenital portosystemic shunts.21 Ultrasonographic findings associated with cirrhosis include microhepatia, hyperechoic parenchyma, irregular margination, ascites, and regenerative nodules [Figure 6].22 Cirrhosis leads to portal hypertension, and portal flow velocity is decreased on duplex Doppler ultrasonography. 6,21 Affected dogs often develop extrahepatic portosystemic shunts.21 Mass and nodular lesions of the liver may also be evaluated from the right lateral intercostal approach, especially in large and deep-chested dogs [Figures 7, 8]. These lesions could easily be missed in these dogs if the examination is limited to the subcostal approach.
Diseases involving the portal vasculature are also indications for use of the right lateral intercostal view. This view is indicated when a portosystemic shunt is suspected [Figures 9A, 9B].3,6,14 Extrahepatic shunts are not usually visible from the standard subcostal approach, especially in large dogs.6 To locate an anomalous vessel connecting the portal vein and caudal vena cava or azygos vein, the porta hepatis is located and the transducer is moved caudally or cranially, keeping the caudal vena cava and portal vein in the same image and following them caudally to the origin of the cranial mesenteric artery.13 In one study of 20 out of 24 dogs with extrahepatic shunts, the shunt vessel entered the caudal vena cava between the right renal and hepatic veins on the right intercostal view.14 With portoazygos shunts, the anomalous vessel courses cranially toward the diaphragm, parallel to the caudal vena cava, but it does not enter the caudal vena cava.6 Ultrasonographic findings associated with congenital portosystemic shunts include decreased liver size, decreased visibility of intrahepatic portal vasculature, an abnormal vessel draining into the caudal vena cava, increased or variable portal flow, a small portal vein, increased renal size, and urinary calculi.6,14 With acquired portosystemic shunts, the hepatic parenchyma may be inhomogeneous in texture; multiple, small, extrahepatic anomalous vessels may be detected; portal flow is decreased; and renal volume is normal.6 Other potential findings include urinary urate calculi, pancreatic edema, portal vein thrombus, and ascites.6 With congenital portosystemic shunts, pressures in the portal vein are similar to those in the caudal vena cava, so its flow characteristics may be similar to the caudal vena cava.6,14 Its diameter may change with the cardiac and respiratory cycles, as does the caudal vena cava.14 Portosystemic shunts usually have low flow resistance, so portal flow velocity may be increased.14
The right lateral intercostal view is also useful in detection of intrahepatic portosystemic shunts.3 On ultrasound, an intrahepatic shunt appears as a large, tortuous vessel coursing from the portal vein to a hepatic vein or the caudal vena cava [Figure 10].3 Right divisional and central divisional intrahepatic shunts are best viewed from the right lateral intercostal view.6
Portal vein thrombosis, although rare, can be diagnosed using the right lateral intercostal scan plane [Figure 11].23 In four dogs with portal vein thrombosis, ultrasonographic findings included a hyperechoic structure in the vessel lumen, increased portal flow, some blood flow around the thrombus, or no flow on color Doppler.23 Other findings included splenomegaly, thrombosis, and peritoneal fluid.23 Portal vein thrombosis can lead to portal hypertension. A tumor near the portal vein can cause thrombosis by direct vascular invasion or by distorting the vessel wall.23
Diseases of the biliary system are often incompletely evaluated via the subcostal approach, and the right lateral intercostal approach may be useful.2 One indication for this approach is suspected biliary tract obstruction, especially when assessment of the common bile duct is desired [Figures 12A, 12B].2 With biliary obstruction, the common bile duct becomes enlarged within 24 to 48 hours. Intrahepatic bile duct dilatation occurred within 5 to 7 days after complete obstruction in an experimental model.2 The intrahepatic bile ducts are more tortuous and demonstrate irregular branching compared to hepatic blood vessels.2
The right intercostal approach is useful to identify pancreatitis [Figures 13A, 13B]. The intercostal approach avoids pain induced by pressure on the ventral abdomen from the transducer. The most consistent landmarks for the right pancreatic lobe are the duodenum and the right kidney. The right lobe of the pancreas is found dorsal or medial to the duodenum and ventral to the right kidney. With inflammation, vascular landmarks are often not visible.16 The normal pancreas is usually slightly hyperechoic to the liver. With inflammation, the pancreas becomes hypoechoic and enlarged.16 The duodenum may be dilated, fluid- or gasfilled, have thickened walls, and lack peristalsis.16 In some cases, the duodenum can be displaced ventrally and laterally by the enlarged pancreas.16 Other ultrasonographic findings associated with pancreatitis include peritoneal effusion, hyperechoic mesentery, and biliary obstruction.8,17 With inflammation, the pancreas may be shifted dorsolateral to the duodenum.17 Pancreatic neoplasia and cystic lesions of the right lobe and body may also be evaluated using the right intercostal approach.
Diseases of the right kidney may be more thoroughly evaluated via the right intercostal view than the standard subcostal approach. The intercostal view also allows comparison of the echogenicities of the liver and renal cortex [Figures 14A, 14B, 15, 16]. In a normal dog, the renal cortex may be hypo-, iso-, or hyperechoic compared to the adjacent liver.18 Renal cortical echogenicity may be increased relative to the liver with nephrotoxicosis or nephrocalcinosis. The right intercostal view may be especially helpful in cases of chronic renal disease in which the kidneys are decreased in size, or in focal renal diseases (e.g., mass lesions, infarcts, cysts).
Ultrasonography is a useful tool in the evaluation of adrenal diseases that lead to diffuse enlargement (e.g., pituitary- dependent hyperadrenocorticism, adrenal nodules and masses). The right lateral intercostal view is valuable in the assessment of caudal vena cava infiltration or compression by adrenal mass lesions. The hepatic, pancreaticoduodenal, and gastric lymph nodes can be assessed via the intercostal window [Figures 17A, 17B]. Normal lymph nodes may not be seen because their echogenicities are similar to surrounding fat and muscle. Inflammation and neoplasia cause lymph nodes to enlarge and become hypoechoic, making them more detectable.20,24
Percutaneous, ultrasound-guided, fine-needle aspirate and biopsy are two commonly performed procedures.25,26 Lesions of the right cranial abdomen might not be accessible from a standard ventral subcostal approach, but they may be accessible via the right intercostal approach. A liver sample for biopsy can be obtained from approximately the 10th to 12th intercostal spaces.27 Use of ultrasound during renal biopsies helps obtain diagnostic samples and avoids the renal artery and vein.25 To obtain a biopsy of the right kidney, the kidney is found at the 11th or 12th intercostal space just ventral to the epaxial muscles.27
Conclusion
A ventral subcostal approach is often inadequate for a complete ultrasonographic examination. The right lateral intercostal scan plane allows for a thorough evaluation of the liver, porta hepatis, pancreas, duodenum, right kidney, right adrenal gland, and cranial abdominal lymph nodes. This approach is most useful in large and deep-chested dogs, dogs with gas in the gastrointestinal tract, and in cases of microhepatia, peritoneal effusion, and abdominal pain.
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Citation: Journal of the American Animal Hospital Association 43, 4; 10.5326/0430179
Right lateral intercostal ultrasonographic view of the porta hepatis of a normal 3-year-old, spayed female golden retriever. The aorta is seen as the most dorsal vascular structure. The caudal vena cava (CVC) is ventral and to the right of the aorta. The portal vein (PV) is ventral and to the right of the caudal vena cava. D=dorsal, V=ventral, R=right, L=left.
Ultrasound image of the porta hepatis of a 6- year-old, spayed female miniature schnauzer obtained via the right lateral intercostal window. The common bile duct (BD) is ventral and to the right of the portal vein (PV). The hepatic artery (HA) is a smaller vessel found dorsal and to the left of the portal vein. One of the hepatic veins (HV) is visible dorsal to the portal vein. D=dorsal, V=ventral, R=right, L=left.
Transverse ultrasound image near the porta hepatis of an 8-year-old, male castrated beagle. The right limb of the pancreas (Panc) is dorsal and medial to the duodenum (Duo) and ventral to the portal vein (PV). A small hepatic lymph node (solid arrow) is seen adjacent to the duodenum. There is an indistinct hypoechoic nodule (dashed arrow) to the right of the caudal vena cava (CVC). D=dorsal, V=ventral, R=right, L=left.
Right lateral intercostal transverse view obtained caudal to the porta hepatis of a 4-year-old, spayed female, mixed-breed dog. The right adrenal gland (arrow) is located between the caudal vena cava (CVC) and the cranial pole of the right kidney (RK). D=dorsal, V=ventral, R=right, L=left.
Transverse ultrasound image at the level of the porta hepatis of a 7-year-old, castrated male rottweiler. A hepatic lymph node (LN) is seen ventral to the portal vein (P). C=caudal vena cava, D=dorsal, V=ventral, R=right, L=left.
Long-axis view of the liver and right kidney (RK) of a 9-year-old, castrated male, mixed-breed dog with hepatic cirrhosis. The liver is small with irregular margins. Free peritoneal effusion (FF) is also present. Cr=cranial, Cd=caudal, R=right, L=left.
Right lateral dorsal plane image of a 7-year-old, spayed female Alaskan malamute with a mass (dashed outline) in the right cranial aspect of the liver. This mass was not visible from the subcostal approach. R=right, L=left, Cr=cranial, Cd=caudal, GB=gall bladder, PV=portal vein, CVC=caudal vena cava.
Right lateral transverse view of a 10-year-old, intact female Shetland sheepdog with a single hyperechoic nodule (arrow) in the right aspect of the liver. This nodule was not visible from the subcostal approach. R=right, L=left, D=dorsal, V=ventral.
(A) Transverse ultrasonographic view of the porta hepatis of a 9-month-old, intact male Yorkshire terrier with a single portocaval shunt. The shunt vessel (arrow) connects the portal vein (PV) and caudal vena cava (CVC). (B) An example of a 7-month-old, intact female Maltese with a portocaval shunt. The tortuous shunt vessel (arrow) is seen entering the CVC. D=dorsal, V=ventral, R=right, Ao=aorta, HA=hepatic artery.
Transverse right intercostal view of a 9-monthold, intact male Labrador retriever with an intrahepatic portosystemic shunt. A large, tortuous shunt vessel is seen within the hepatic parenchyma, and it terminates within the caudal vena cava (CVC). Because of the tortuosity of the vessel, the entire shunt could not be seen in one image. Shunt=shunt vessel, PV=portal vein, R=right, L=left, D=dorsal, V=ventral.
Transverse right lateral intercostal view of an 11-year-old, spayed female, mixed-breed dog with a portal vein thrombus. The thrombus (arrow) is seen as an echogenic structure in the lumen of the portal vein. D=dorsal, V=ventral, R=right, L=left.
(A) Dorsal plane image at the porta hepatis of a 10-year-old, spayed female cocker spaniel with obstruction of the common bile duct (CBD). The common bile duct is easily seen and is the same size as the portal vein (PV). (B) Transverse right lateral intercostal view at the portal hilus of a 9-year-old, intact male boxer with common bile duct obstruction. The common bile duct is found ventral to the portal vein; it is dilated (9 mm) and its wall is subjectively thickened. Cr=cranial, Cd=caudal, D=dorsal, V=ventral, R=right, L=left.
(A) Transverse intercostal view of a 5- year-old, spayed female Irish setter with pancreatitis. The pancreas (arrow) is dorsomedial to the duodenum (duod). The pancreas is hypoechoic and surrounded by hyperechoic mesentery. (B) Dorsal intercostal view of a 7-yearold, spayed female, mixed-breed dog with pancreatitis. The hypoechoic pancreas (arrow) is medial to the duodenum. Cr=cranial, Cd=caudal, D=dorsal, V=ventral, R=right, L=left.
(A) Dorsal right intercostal view of a 3- year-old, intact male German shepherd dog with ethylene glycol toxicosis. The abnormally hyperechoic right renal cortex is seen in contact with the renal fossa of the caudate lobe of the liver. (B) Transverse intercostal image of the same dog. The hyperechoic renal cortex of the cranial pole of the right kidney (RK) is seen against the liver. Cr=cranial, Cd=caudal, R=right, L=left, D=dorsal, V=ventral.
Transverse intercostal view of a 12-year-old, spayed female poodle with hyperplasia of the right adrenal gland (arrow). The gland is found between the cranial pole of the right (RT) kidney and caudal vena cava (CVC). Ao=aorta, D=dorsal, V=ventral, R=right, L=left.
Dorsal view of the caudal vena cava (CVC) of an 8-year-old boxer with a tumor of the right adrenal gland. The tumor or thrombus (arrow) is a round, echogenic structure in the lumen of the caudal vena cava. Cr=cranial, Cd=caudal, R=right, L=left.
(A) Transverse intercostal view of a 9- year-old, castrated male Doberman pinscher with hepatic lymphadenopathy. Lymph nodes (LN) are present ventral and to the left of the portal vein (PV). The numbers 1 and 2 represent measurement calipers. (B) Dorsal view of the same dog. Note the enlarged, hepatic lymph node to the left of the portal vein. CVC=caudal vena cava, D=dorsal, V=ventral, Cr=cranial, Cd=caudal, R=right, L=left.
