Introduction to Pathology

Pathology is the study of disease. Many types of disease exist, and, in general, many conditions can be readily demonstrated by imaging studies. Additionally, image-guided interventional procedures and therapeutic protocols are often utilized in the management of disease. Therefore, it is critical for radiologic professionals to have a thorough understanding of basic pathologic processes. This foundation begins with a working knowledge of common pathologic terms, an understanding of impact of disease and prevention on U.S. health care expenditures, and the role of genetics in the development and individualized treatment of different pathologic processes. It is also important to understand the role of the Centers for Disease Control and Prevention (CDC) in terms of tracking, monitoring, and reporting trends in health and aging. This information is captured and reported by the National Center for Health Statistics (NCHS).

This chapter serves as a brief introduction to terms associated with pathology, recent health trends, and a review of cellular biology and genetics.

Pathologic Terms

Any abnormal disturbance of the function or structure of the human body as a result of some type of injury is called a disease. After injury, pathogenesis occurs. Pathogenesis refers to the sequence of events producing cellular changes that ultimately lead to observable changes known as manifestations. These manifestations may be displayed in a variety of fashions. A symptom refers to the patient’s perception of the disease. Symptoms are subjective, and only the patient can identify these manifestations. For example, a headache is considered a symptom. A sign is an objective manifestation that is detected by the physician during examination. Fever, swelling, and skin rash are all considered signs. A group of signs and symptoms that characterizes a specific abnormal disturbance is a syndrome. For example, respiratory distress syndrome is a common disorder in premature infants. However, some disease processes, especially in the early stages, do not produce symptoms and are termed asymptomatic.

Etiology is the study of the cause of a disease. Common agents that cause diseases include viruses, bacteria, trauma, heat, chemical agents, and poor nutrition. At the molecular level, a genetic abnormality of a single protein may also serve as the etiologic basis for some diseases. Proper infection control practices are important in a health care environment to prevent hospital-acquired nosocomial disease. Staphylococcal infection that follows hip replacement surgery is an example of a nosocomial disease, that is, one acquired from the environment. The cause of the disease, in this case, could be poor infection-control practices. Iatrogenic reactions are adverse responses to medical treatment itself (e.g., a collapsed lung that occurs in response to a complication that arises during arterial line placement). If no causative factor can be identified, a disease is termed idiopathic.

The length of time over which the disease is displayed may vary. Acute diseases usually have a quick onset and last for a short period, whereas chronic diseases may manifest more slowly and last for a very long time. An example of an acute disease is pneumonia, and multiple sclerosis is considered a chronic condition. An acute illness may be followed by lasting effects termed sequelae—for example, a stroke, or cerebrovascular accident, resulting in long-term neurologic deficits. Similarly, chronic illnesses often manifest in acute episodes, for example, an individual diagnosed with diabetes mellitus experiencing hypoglycemia or hyperglycemia.

Two additional terms refer to the identification and outcome of a disease. A diagnosis is the identification of a disease an individual is believed to have, and the predicted course and outcome of the disease is called a prognosis.

The structure of cells or tissue is termed morphology. Pathologic conditions may cause morphologic changes that alter normal body tissues in a variety of ways. Sometimes, the disease process is destructive, decreasing the normal density of a tissue. This occurs when tissue composition is altered by a decrease in the atomic number of the tissue or the compactness of the cells or by changes in tissue thickness, for example, atrophy from limited use. Such disease processes are radiographically classified as subtractive, lytic, or destructive and require a decrease in the exposure technique. Conversely, some pathologic conditions cause an increase in the normal density of a tissue, resulting in a higher atomic number or increased compactness of cells. These are classified as additive or sclerotic disease processes and require an increase in the exposure technique. It is important for the radiographer to know common pathologic conditions that require an alteration of the exposure technique so that high-quality radiographs can be obtained to assist in the diagnosis and treatment of the disease.

Government agencies compile statistics annually with regard to the incidence, or rate of occurrence, of disease. Epidemiology is the investigation of disease in large groups. Health care epidemiology is grounded in the belief that the distributions of health states (good health, disease, disability, and death) are not random within a population and are influenced by multiple factors, including biologic, social, and environmental factors. Health care epidemiologists conduct research primarily by working with medical statistics, data associations, and large cohort studies. The prevalence of a given disease refers to the number of cases found in a given population. The incidence of disease refers to the number of new cases found in a given period. Diseases of high prevalence in an area where a given causative organism is commonly found are said to be endemic to that area. For example, histoplasmosis is a fungal disease of the respiratory system endemic to the Ohio and Mississippi River valleys. It is not uncommon to see a relatively high prevalence of this disease in these areas. Its appearance in great numbers in the western United States, however, could represent an epidemic.

Over the past century, life expectancy in the United States has continued to increase. The majority of children born at the beginning of the twenty-first century are expected to live well into their eighth decade (Fig. 1-1). Over the past 100 years, the principal causes of death have shifted from acute infections to chronic diseases. These changes have occurred as a result of biomedical and pharmaceutical advances, public health initiatives, and social changes over the past century (Fig. 1-2). But experts disagree about the trend of increased life expectancy continuing into the twenty-first century. Some believe that increased knowledge of disease etiology and continued development of medical technology in combination with screening, early intervention, and treatment of disease could have positive results. However, many experts express concern about the quality of life of older adults. In other words, the possibility of older adults spending their added years in declining health and lingering illness, instead of being active and productive, is a concern.

The mortality rate is the average number of deaths caused by a particular disease in a population. Death certificates are collected by each state, forwarded to the NCHS, and subsequently processed and published as information on mortality statistics and trends. The NCHS and the U.S. Department of Health and Human Services (USDHHS) monitor and report mortality rates in terms of leading causes of death according to gender, race, age, and specific causes of death such as heart disease or malignant neoplasia. Trends in these mortality patterns are identified by age, gender, and ethnic origin and tracked to help identify necessary interventions. For instance, the age-adjusted death rate for heart diseases has steadily decreased for both women and men in the United States. This trend demonstrates a 30% to 40% decline over the past 20 years resulting, in part, from health education and changes in lifestyle behaviors. Because mortality information is gathered from death certificates, changes in the descriptions and coding of “cause of death” and the amount of information forwarded to the NCHS may alter these statistics. For instance, changes in the way deaths were recorded and ranked in terms of the leading causes of death occurred between 1998 and 1999. Since 1999, mortality data and cause-of-death statistics have been gathered and classified according to the Tenth Revision, International Classification of Diseases (ICD-10), and in 2007 additional ICD-10 codes were added to clarify the underlying causes of death.

Chronic diseases continue to be the leading causes of death in the United States for adults age 45 years and older. Heart diseases and malignant neoplasia remained the top two causes of deaths in 2007 for both males and females, responsible collectively for 48.6% of all deaths. The third, fourth, and fifth top causes of death in 2007 were stroke, chronic lower respiratory diseases, and accidents, respectively. Alzheimer disease continues to increase and was ranked as the sixth leading cause of death in 2007. Emphasis has been placed on reducing the deaths associated with these chronic diseases, and slight decline was noted through 2007. The decrease in deaths due to heart disease may be clearly attributed to advances in the prevention and treatment of cardiac disease. An increased understanding of the genetics of cancer is certainly responsible for better screening and individualized treatment for many types of neoplastic disease. Advances in diagnostic and therapeutic radiologic procedures have also played a role in the reduction of deaths associated with these chronic diseases.

As the mortality rate for heart disease and cancer have declined, increases have been noted in Alzheimer disease and diabetes mellitus. Among children and young adults (age 1–44 years), injury remains the leading cause of death.

Mortality rates from any specific cause may fluctuate from year to year, so trends are monitored over a 3-year period. These data are used to evaluate the health status of U.S. citizens and identify segments of the population at greatest risk from specific diseases and injuries. Current data are available on the NCHS Web site and may be accessed at www.cdc.gov/.

The incidence of sickness sufficient to interfere with an individual’s normal daily routine is referred to as the morbidity rate. The CDC is also responsible for trending morbidity rates in the United States. States must submit death certificates to the NCHS, making it fairly easy to obtain accurate data about the mortality rate of a specific population. It is more difficult to obtain accurate data about the morbidity rate. This information comes primarily from physicians and other health care workers reporting morbidity statistics and information to the various governmental and private agencies.

Health Care Resources

Health care delivery in the United States has two fundamental and diverse functions, with one area focused on healthy lifestyle for prevention and the second area focusing on restoration of health after a disease has occurred. Improvements in health care interventions such as technology, electronic communications, and pharmaceuticals have greatly contributed to a shift from inpatient services to outpatient services (Fig. 1-3). Ambulatory care centers range from hospital outpatient and emergency departments to physicians’ offices. In response to this shift, emphasis has been placed on increasing the number of physician generalists, including family practitioners, internal medicine physicians, and pediatricians. Inpatient admissions and hospital length of stay have remained fairly consistent over the past 10 years; however, emergency department visits have continued to steadily increase since the late 1990s, with many emergency departments reporting admissions exceeding their capacity (Fig. 1-4).

FIGURE 1-3 Number of outpatient hospital visits per 1000 persons during 1988 to 2008.

The rate of growth in U.S. health expenditures is staggering. In 2010, U.S. health spending accounted for 17.3% of the gross domestic product, a larger share than in any other major industrialized country, with U.S. health care expenditures totaling $2.6 trillion (Table 1-1). The average annual health spending increase from 2010 through 2020 is projected to outpace average annual growth in the overall economy by 4.7%. The major sources of funding for health care include Medicare, funded by the federal government for older adults and disabled individuals; Medicaid, funded by federal and state governments for the poor; and privately funded health care plans. However, the Centers for Medicare and Medicaid Services (CMS) project that private insurance and out-of-pocket spending on health care will almost double to a rate of 4.8% in 2013. Estimates from the CDC National Health Interview Survey for 2010 indicated that approximately 16% of the U.S. population was uninsured at the time of the interview (Fig. 1-5

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