Surgery of the Liver and Biliary Tract

Chapter 72 Surgery of the Liver and Biliary Tract



Stephen J. Birchard


Surgery of the liver and biliary tract is commonly performed in small animals and can be very challenging. Animals frequently are presented with surgical diseases of these organs, such as liver tumors and obstruction or infection of the biliary system. Some of the procedures described in this chapter require specialized training and facilities. Others, such as liver biopsy, partial hepatectomy, and simple exploration of the biliary tract, can be performed in a standard veterinary practice. Regardless of the procedure, preparation for the surgery by reviewing anatomy, pathophysiology, and specific techniques is very important for a successful outcome. Preparation of the patient prior to surgery also is extremely important because most of these diseases have serious metabolic effects.



SURGERY OF THE LIVER



Anatomy



Liver Lobes



• The liver is divided into six lobes: the right lateral, right medial, caudate, quadrate, left medial, and left lateral.

• The caudate lobe is divided into the caudate process and the papillary process.


Liver Attachments



• The major liver attachments to other organs and the body wall are the triangular, hepatogastric, and hepatoduodenal ligaments.

• The falciform ligament extends from the liver to the diaphragm and ventral abdominal wall. This mesenteric remnant can be quite large and fat-filled in obese animals. Consider removing this structure during liver surgery to gain better exposure of the cranial abdominal structures.

• The hepatorenal ligament is a thin fold of peritoneum that extends from the renal fossa of the caudate lobe to the ventral surface of the right kidney.


Blood Supply



Portal Vein



• The portal vein receives blood from the spleen, pancreas, and intestines.

• The major hepatic branches of the portal vein are the right lateral trunk, right medial branch, and left lateral trunk.

• The portal vein is the confluence of the cranial and caudal mesenteric veins and the splenic vein.

• The portal vein can be seen at the base of the mesoduodenum. It forms the ventral boundary of the epiploic foramen.

• The portal vein eventually empties into the liver and supplies approximately 80% of the blood flow of the liver. The remaining 20% comes from the hepatic arteries.

• In the fetus, the ductus venosus connects the portal vein to the caudal vena cava, allowing blood to bypass the liver. This vessel closes soon after birth in normal dogs. If it remains patent, it is called a patent ductus venosus and is one of the several types of portosystemic shunts.


Hepatic Arteries and Veins



• The hepatic artery is a branch of the celiac artery. Variable numbers of hepatic artery branches supply the liver lobes. The hepatic arteries are located in the vicinity of the hepatoduodenal ligament and are adjacent to the common bile duct. The cystic artery, which supplies the gallbladder, is a branch of the left branch of the hepatic artery.

• Six to eight large hepatic veins drain the liver lobes to the caudal vena cava.

• The hepatic veins enter the vena cava at the hilus of the liver and are obscured by the liver parenchyma.


Preoperative Considerations


Liver diseases cause a variety of significant hematologic and metabolic disorders in animals. Prior to surgery, perform appropriate diagnostics to confirm the disease and check for involvement of other organs. (See Chapter 71 for diagnosis of liver problems.)


Of particular concern to the surgeon are the following potential problems:


• Hypoproteinemia—Evaluate serum proteins and consider administration of plasma, colloids, or hyperalimentation if significantly low.

• Anemia—Evaluate the animal’s hemogram and establish a baseline packed cell volume so that changes can be kept in perspective. Blood loss before, during, and after liver surgery is common and should be monitored closely.

• Coagulopathy—Analyze the animal’s coagulation profile and correct abnormalities if possible (see Chapter 23). Fresh whole blood transfusion before or during surgery may be necessary.

• Diffuse disease—Hepatic neoplasia may result in metastatic lesions. Thoracic and abdominal radiography and abdominal ultrasonography are helpful in determining the extent of disease.

• Impaired liver function—Manage hepatic encephalopathy, if present, medically (see Chapter 71) to stabilize the animal prior to surgery.

• Hypoglycemia—Consider giving the animal intravenous (IV) fluids supplemented with glucose before and during surgery (e.g., 5% dextrose in lactated Ringer’s solution).



Key Point


Diffuse hepatic disease may cause serious metabolic problems that can be compounded by anesthesia and surgery. Analyze liver function tests, such as serum bile acid and blood ammonia concentrations (see Chapter 71), to determine the animal’s ability to undergo anesthesia and surgery.



• Liver trauma
• Thoroughly evaluate all animals with a history of trauma to rule out thoracic trauma such as pneumothorax, pulmonary contusions, and other cardiopulmonary problems (see Chapter 166). Evaluate for damage to other organs such as the urinary tract, gastrointestinal tract, and neurologic and skeletal systems.

• Animals with liver trauma usually have hemoperitoneum. Severe blood loss will cause clinical signs of shock and should be treated (see Chapter 156 for treatment of hypovolemic shock).



Key Point


Most animals with liver trauma can be treated conservatively (e.g., IV fluids, whole blood transfusion, or autotransfusion of abdominal blood if not contaminated with bacteria or neoplastic cells).



Liver Biopsy and Partial Hepatectomy—Surgical Procedure



Objectives



• Examine the entire liver and biliary system for grossly evident abnormalities.

• Obtain tissues for biopsy or completely remove the lesion by partial hepatectomy.

• Minimize intraoperative blood loss.


Equipment



• Standard general surgery pack and suture

• Balfour and malleable retractors

• Tru-Cut biopsy needle, Anchor Soft Tissue Biopsy Device (Anchor Products Co., Addison, IL), or skin punch biopsy instrument

• Tissue stapling device (e.g., Autosuture TA, U.S. Surgical, Norwalk, CT) (optional)

• Gelfoam


Technique



1. Place the animal in dorsal recumbency and prepare the entire ventral abdomen and caudal one-third of the sternum for aseptic surgery.

2. Perform a standard ventral midline abdominal approach. If additional exposure is necessary, also perform a left or right paracostal abdominal incision or a caudal median sternotomy.

3. Use laparotomy sponges to protect the abdominal wall and place Balfour retractors to expose the liver and associated viscera.

4. Identify areas of liver to be removed or biopsied. If necessary, mobilize involved liver lobes by incising the triangular ligaments. Greater exposure of the liver can be achieved by placing a laparotomy sponge between it and the diaphragm.

5. Liver biopsy can be achieved by a variety of techniques:
a. Obtain tissue samples from the periphery of the lobe, using the “guillotine” technique.

b. Use absorbable suture to surround a small segment of liver and tie the suture tight to cut through the parenchyma and strangulate the blood vessels and bile ducts (Fig. 72-1). Alternatively, place the suture in a horizontal mattress pattern.

c. Excise the tissue distal to the ligature, using a scalpel or Metzenbaum scissors. Check for bleeding and, if necessary, place a small piece of Gelfoam over the cut surface for hemostasis.

d. Alternatively, use a Tru-Cut needle or skin biopsy punch to obtain small pieces of liver tissue. These are especially helpful if the lesion is centrally located in the liver lobe rather than peripherally. Be sure to include some normal tissue in the biopsy specimen.

6. Remove large lesions by partial hepatectomy (Fig. 72-2):
a. Divide the liver parenchyma proximal to the lesion, using large crushing clamps or finger fractionation (gently squeezing the liver parenchyma between fingers to isolate vessels). Ligate the ducts and vessels with absorbable sutures (e.g., 3-0 or 4-0 chromic catgut).

b. Alternatively, use surgical staples (e.g., U.S. Surgical Autosuture TA) to crush the tissue and ligate the vessels in one step.

c. Complete removal of an entire liver lobe requires carefully placed ligatures to attenuate the large arteries and veins at the liver hilus. Oversew or transfix the vessels to prevent ligature slippage. Place large clamps on the vessels prior to resection of the lobe to prevent cranial retraction of the vessel (Fig. 72-3).

image

Figure 72-1 Guillotine method for intraoperative liver biopsy. Place a loop of absorbable suture around the tip of a liver lobe and tie tightly to cut through the liver parenchyma, ligating the vessels. Cut the suture ends and then cut the vessels to allow removal of the biopsy specimen.


image

Figure 72-2 Partial hepatectomy. Lesions at the periphery of the liver lobe can be removed by placing crushing clamps across the lobe, proximal to the lesion, and then cutting distal to the clamps. Use absorbable sutures to ligate vessels proximal to the clamps. Tie these ligatures tightly as in the guillotine method for liver biopsy (see Fig. 72-1).


image

Figure 72-3 Double ligation (A) and transection (B) in total liver lobectomy.



Postoperative Care and Complications



• Monitor for postoperative hemorrhage (oozing of blood from the incision, distention of the peritoneal cavity, pale mucous membranes). Administer blood transfusion if the hematocrit drops below 20%.

• Give supportive therapy with IV fluids and glucose until oral intake of food and water resumes.

• Monitor for evidence of pancreatitis (vomiting, abdominal pain, increased serum amylase and lipase). Delay resuming oral intake and keep on IV fluid therapy until this resolves.

• After massive liver resection, monitor liver function by evaluating bilirubin and serum bile acid concentrations. Liver function reportedly becomes abnormal after resection of 60% or more of the liver.


SURGERY FOR PORTOSYSTEMIC SHUNTS


Portosystemic shunts are abnormal vascular communications between the portal vein and a systemic vein. Diagnosis and medical treatment of this condition are discussed in Chapter 71. Animals with portosystemic shunts can initially improve with medical management. However, the definitive and most effective therapy for long-term resolution of clinical signs is surgical attenuation of the shunt vessel. With recent advances in the intraoperative and postoperative management of these animals, morbidity and mortality rates associated with surgery have decreased to very acceptable levels.



Anatomy


Portosystemic shunts are divided anatomically into extrahepatic and intrahepatic (Fig. 72-4). Definition of shunt anatomy preoperatively is important because intrahepatic shunts are much more difficult to correct surgically than are extrahepatic shunts. Also, familiarity with the anatomy helps decrease surgical time and patient morbidity.


image

Figure 72-4 Schematic representation of an extrahepatic portacaval shunt and an intrahepatic portacaval shunt.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Surgery of the Liver and Biliary Tract

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