Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (164 page)

   Hepatomegaly refers to an enlarged liver with a vertical span >12 cm as percussed in the midclavicular line. Studies have suggested that by ultrasound, a midhepatic (sagittal) diameter >15.5 cm indicates hepatomegaly in 75% of the cases. By radioisotope scanning, a span of >15–17 cm in the midclavicular line indicates hepatomegaly.

   Hepatomegaly may occur in the absence of pathology (i.e., normal variant) or as a result of a depressed right hemidiaphragm, Riedel lobe, or subdiaphragmatic space occupying lesions.

   Differential Diagnosis and Workup (Figure
5-6
)

   The causes of hepatomegaly can be subdivided into processes involving the following:

   Hypertrophy or hyperplasia of cells intrinsic to the normal liver parenchyma

   Hepatomegaly secondary to infiltration of the liver by cells or organisms not normally present

   Vascular causes resulting in congestion of the liver

   Common causes: Fatty liver (nonalcoholic steatohepatitis) is a common cause of hepatomegaly. The most common cause of fatty liver in the United States is chronic alcoholism. Other causes of fatty liver include diabetes, obesity, hyperlipidemia (metabolic syndrome), protein malnutrition, and prolonged TPN.

   Other causes: In addition to infectious and drug-related causes, clinically important causes of hepatomegaly include hemochromatosis, α
₁
-antitrypsin deficiency, Wilson disease, autoimmune hepatitis, SLE, and RA.

   Cholangiohepatitis is a rare disorder in which intrahepatic and extrahepatic bile ducts become obstructed with bile stones, leading to secondary inflammation of the liver.

   Congestion from heart failure includes all causes of elevated right heart pressures (e.g., cor pulmonale, tricuspid regurgitation, constrictive pericarditis, ventricular dysfunction).

   Hepatocellular carcinoma represents approximately 2.5% of all carcinomas in the United States and approximately 30–50% of all carcinomas in Asians living in Asia, where chronic active hepatitis due to hepatitis B virus is common. Other risk factors include chronic hepatitis C or chronic liver disease of any type.