Accessory Organs

The liver, gallbladder, and pancreas are in intimate contact with the duodenum (the first part of the small intestine). These organs provide substances that aid in the digestive process.

The liver is one of the heaviest organs in the body. One of the functions of the liver is to maintain a normal concentration of blood glucose, which is necessary to carbohydrate metabolism. It also plays a part in lipid metabolism by synthesizing fats that are stored in adipose tissue in the body. The liver also converts some amino acids into other types of amino acids.

One of the primary functions of the liver is to produce bile. This substance aids in the digestion of fats and is secreted into the duodenum via the bile duct. It is produced in the hepatic cells and secreted into the bile canals in the liver. The bile canals empty into the right and left hepatic ducts, which become the common hepatic duct. The common hepatic duct and the cystic duct join to form the common bile duct, which leads to the duodenum. The bile is secreted in response to the presence of proteins and fats in the small intestine.

Although the liver appears to be a single large structure, it has been described by Claude Couinaud, a French surgeon, as being segmental with each of the segments having its own outflow, inflow, and biliary drainage.¹ He described eight areas according to a concept of plates and vasculobiliary sheaths (Fig. 19-2). The performance of the diagnostic and interventional procedures performed is dependent upon an accurate knowledge of the relationships between the intrahepatic ducts. A standard anatomic description is present in approximately 60% of individuals, and the physician must determine the exact nature of the patient’s anatomy in order to perform a successful procedure.

Normally bile collects in the common bile duct until needed. Excess bile backs up the duct and enters the gallbladder, where it is stored and concentrated. In cases of blockage/obstruction of the ducts, bile accumulates in the liver, causing the bile salts and pigments to enter the bloodstream. This increase of bilirubin in the blood causes a condition referred to as jaundice. The body tissues become yellow as a result of the buildup of the pigments. One common reason for the blockage can be a large amount of fluid being absorbed from the bile or precipitation of the cholesterol in the bile. In both of these cases the result is the production of gallstones (biliary calculi), which can lodge in the ducts and create the blockage. Jaundice can be caused by other pathologic factors such as hepatitis, cirrhosis, trauma, biliary surgery, biliary cancer, tumors, and choledochal cysts. Box 19-3 summarizes the common interventions used to treat certain pathologic conditions affecting the biliary tract.

Urinary System

The urinary system is an integral part of the excretory mechanism. It consists of a pair of kidneys that help to maintain the proper chemical makeup of the blood, regulate the pH, and produce a hormone that stimulates red blood cell production in the bone marrow. They also maintain body fluid levels and produce renin, which helps to regulate the blood pressure.

Renin is an enzyme released by the kidneys into the renal veins to regulate the blood pressure, fluid balance, and the body’s sodium/potassium equilibrium. This substance activates the renin-angiotensin system, which is a vasoconstrictor that also stimulates aldosterone production from the adrenal glands. Aldosterone regulates the sodium and potassium levels in the blood. These elements will affect the blood pressure. Renin also helps to maintain the electrolyte balance in the body. These minerals are necessary for fluid balance and the maintenance of cardiac function, muscle contraction, and brain activity.

Renin levels are usually checked by means of a blood test. This is known as a plasma renin activity (PRA) test and is usually done fasting. All medications must be discontinued for a period of 2 to 4 weeks. The normal values vary with age and body position. Renin collection can be accomplished by means of sampling directly from the renal vein. Usually, samples from both kidneys are taken and compared to determine which kidney is affected. Abnormal findings from the PRA test can indicate several pathologic conditions. Box 19-4 lists some of the conditions that can be diagnosed.

The urinary system also includes a pair of ureters, the urinary bladder, and the urethra. The physiology related to the kidney function should be well known and will not be discussed here.

The kidneys are located against the dorsal body wall in the retroperitoneum at about the level of T11–T12 to L2–L3. The right kidney lies about 1 to 2 cm lower than the left owing to its position in relation to the liver. It is important to remember that because of their relationship with the pleura a danger of pneumothorax exists when percutaneous interventions are performed. The kidneys are surrounded by fat, which helps in maintaining their customary position. Each kidney has an upper pole, a lower pole, and an indentation on its medial aspect called the hilum. The blood and lymphatic vessels, nerves, and the ureter enter the kidney at the hilum.

Internally the kidney is divided into three sections: the cortex, medulla, and a flat cavity called the renal pelvis. It should be noted that there is a relationship between the location of the blood vessels and the renal pelvis. The renal vein is situated anteriorly followed by the renal artery and then the renal pelvis. Therefore, the renal pelvis presents itself when the patient is in the prone position. The renal pelvis narrows to leave the kidney as the ureter. This structure transports the urine to the urinary bladder.

The ureters descend behind the parietal peritoneum, running a parallel course with the vertebral column. As they approach the common iliac artery they run slightly medially and then posterolaterally, where they enter the pelvic cavity. The ureters then turn medially to enter the bladder. Each ureter narrows naturally in three places along its route: the junction between the ureter and the renal pelvis, at the level of the common iliac artery, and at the junction of the ureter with the bladder.

The urinary bladder is a muscular organ that serves to temporarily store urine. It lies primarily behind the symphysis pubis when empty. As it fills it expands superiorly. As it expands it displaces the bowel out of the pelvic cavity. The structure that carries the urine outside the body is the urethra. The urethra differs in length in the two sexes. The male urethra is approximately 20 cm (8 in) long while the female urethra is about 4 cm (1 1/2 in) in length. Two valves, the internal and external urethral sphincters, control the release of the urine.

Table 19-1 summarizes some of the currently applied nonvascular interventions for pathology of the urinary system.

Guidance Methods

To successfully localize the lesion, the procedure must be guided. This guidance is accomplished with ultrasonography, CT, conventional fluoroscopy, or magnetic resonance imaging. These modalities are used alone or in combination to provide the maximum diagnostic information about the components of the lesion and its location. Each of the modalities has advantages and disadvantages. The choice of method depends on the physician’s preference, equipment availability, and hospital protocol. Box 19-5 provides a summary of the types of modalities and some of the anatomic areas where they have been used.

Most needle biopsies require ultrasound or CT to guide the biopsy needles precisely. These techniques pinpoint the lesion’s location and allow a high degree of accuracy in sampling. The two guidance methods achieve the same results, but there are some basic differences between them. The use of ultrasound to guide the needle is both more cost-effective and safer for the patient than CT. Ultrasonographic equipment is considerably more economical to purchase and install. This method eliminates the need for exposure to radiation during the localization phase of the procedure. Equipment design also permits faster lesion location and puncture. Specialized puncturing transducers are available that accurately guide the puncture needle. In addition, the use of real-time ultrasonographic equipment permits visual guidance of the needle.

Although the use of ultrasound appears to be the best method of needle guidance, there are situations in which the use of ultrasonography is contraindicated or impossible. Indications for using CT for guided needle biopsy include the following:

1. Extremely obese patients

2. Presence of overlying gas

3. Presence of overlying bone

4. Skin pathology that precludes transducer contact

5. Pathology that contraindicates skin compression

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