THE FIELD OF DIAGNOSTIC ANATOMIC PATHOLOGY
Anatomic pathology is that field of study which describes gross and microscopic anatomic abnormalities in organisms, tissues, and cells, with the goal of diagnosing individual diseases. The field encompasses autopsy pathology, surgical pathology, and cytopathology.
WHAT WE DO
Autopsy pathologists make a set of gross and microscopic diagnoses on a dead patient, and then define the causal relationship between these different diagnoses. For example, if a patient dies in septic shock with renal failure, acute pyelonephritis, lung failure, and mental status changes, then the logical progression of these multiple diseases is “acute pyelonephritis, leading to septic shock and multiorgan (renal, pulmonary, and CNS) failure.” The logical ordering of diagnoses requires understanding of the body’s normal structure/function, knowledge of the antemortem events, and an ability to integrate these facts with morphologic observations made at the time of autopsy examination. When done correctly, it creates closure for both the family and the treating clinical team, because it coherently explains the disease processes leading to death. TV has made a detective of the autopsy pathologists involved in criminal cases; these forensic pathologists do double duty as physicians and expert witnesses when they get drawn into the legal drama of assignment of blame and guilt. Thanks to these portrayals, noncognoscenti in the lay public think that all pathologists are autopsy pathologists. Although the majority of pathologists have had training in the area of autopsy pathology, most of their anatomic pathology effort involves surgical pathology and cytopathology.WHAT WE DO
Surgical pathologists use the same understanding of the body’s normal structure/function, knowledge of concurrent clinical and laboratory abnormalities, and ability to integrate these facts with morphologic observations to make gross and microscopic diagnoses on living patients who undergo surgical biopsies or resections of abnormal individual organs. These diagnoses also inform the patient, family, and treating clinical team, and do so at a time when the patient can hopefully be treated to slow or eliminate the disease process.
TV pays no attention to surgical pathologists, even though most pathologists practice surgical pathology. Lawyers, on the other hand, pay close attention to surgical pathologists because of the potentially lucrative monetary awards tied to missed or delayed diagnoses. Surgical pathology is an umbrella field, with specialists for each of the organ systems. Some of these organ systems are sufficiently complex and subtle that they merit case diagnosis by subspecialty-boarded pathologists, for example, neuropathology, hematopathology, and dermatopathology. Hematopathology is a unique subgroup, in that it integrates data from a variety of other sources (flow cytometry, cytogenetics, and molecular pathology) with standard microscopic examination of lymph node, spleen, and marrow.
WHAT WE DO
Cytopathologists diagnose diseases based on scant samples that typically show only cellular features, that is, samples lacking elements of tissue architecture. These specimens include fine needle aspirates (FNAs), scrape smears (think PAP smears), paraffin-embedded cell blocks, and needle cores.
High-volume fluids, for example, large pleural effusions, can be pelleted by centrifugation, fixed in formalin, embedded in paraffin as cell blocks, then sectioned and stained as are surgical pathology paraffin blocks. Needle cores can be received along with FNA specimens, and do give architectural context to the abnormal cell population. TV pays no attention to cytopathologists, either, even though many pathologists practice cytopathology, but lawyers are interested for the same reasons as above.
To summarize, anatomic pathology is an umbrella set of diagnostic specialties that includes the following:
Autopsy pathology: The entire deceased person is available for diagnosis.
Surgical pathology: Limited specimens including biopsies and resections from living persons are available for diagnosis.
Cytopathology: Very limited specimens with limited or no architectural context from living persons are available for diagnosis.
CURRENT PRACTICE OF DIAGNOSTIC ANATOMIC PATHOLOGY
Diseases can be distinguished from each other based on differences at the molecular, cellular, tissue, fluid chemistry, and/or individual organism level. One-hundred fifty years of attention to the morphologic and clinical correlates of diseases has led to sets of clinical, radiographic, pathologic, and laboratory diagnostic criteria for the recognized diseases, as well as a reproducible nomenclature for rapid description of the changes associated with newly discovered diseases. The set of genotypic and phenotypic abnormalities in the patient is used to determine the diagnosis, which then infers a predictable natural history, and which can be used to optimize therapy by comparison of outcomes among similarly-afflicted individuals. The disease diagnosis becomes the management variable in clinical medicine, and management of the clinical manifestations of diseases is the basis for day-to-day activities in clinics and hospitals nationwide. The pathologist is responsible for integration of the data obtained at the clinical, radiographic, gross, microscopic, and molecular levels, and for issuing a clear and logical statement of diagnoses in a timely fashion.
Clinically, diseases present to front-line physicians as patients with sets of signs and symptoms. Symptoms are the patient’s complaints of perceived abnormalities. Signs are detected by examination of the patient. The clinical team, including the pathologist, “works up” the patient based on the possible causes of the signs and symptoms (the “differential diagnosis”). Depending on the differential diagnosis, the workup typically involves history taking, physical examination, radiographic examination, fluid tests (blood, urine, sputum, stool), and possibly tissue biopsy.
Radiographically, abnormalities in abundance, density, or chemical microenvironment of tissues allow distinction from surrounding normal tissues. Traditionally (since Roentgen’s discoveries in the late 19th century), imaging technology was based on differential absorption of electromagnetic waves by tissues that led to summation differences in exposure of silver salt photographic films and, now, digital detectors. Tomographic approaches such as CT (described in 1972) and NMR/MRI (described in 1973) complement summation radiology, allowing finely detailed visualization of internal anatomy in any plane of section. In this modern era, ultrasound allows visualization of tissue with acoustic density differences, for example, a developing fetus or gallbladder stones. Most recently, physiology of neoplasms can be screened with positron emission tomography PET (described in 1977) for decay of short half-life isotopes such as fluorodeoxyglucose. Neoplasms with high metabolism can be distinguished physiologically from adjacent low-metabolism tissues, and can be localized with respect to normal tissues by pairing PET with standard CT. The result is an astonishingly useful means of identifying and localizing new space-occupying masses, assigning a risk for malignant behavior and, if malignant, screening for metastases in distant sites. This technique is revolutionizing the preoperative decision-making of clinical teams, and improves the likelihood that patients undergo resections of new mass lesions only when at risk of morbidity from malignant behavior or interference with normal function.
Pathologically, disease is diagnosed by identifying gross and microscopic abnormalities, then determining whether these morphologic findings match the set of diagnostic criteria previously described for each disease. Multivolume texts are devoted to the epidemiology, clinical presentation, and gross/microscopic diagnostic criteria used for diagnosis, prognosis, and prediction of response to therapy. Pathologists diagnose disease by generating a differential diagnosis, then finding the best fit for the clinical presentation, the radiographic appearance, and the pathologic (both clinical laboratory and morphologic) findings. Logically, this “Venn diagram” of the clinical, radiologic, and pathologic differential diagnoses should overlap. Unexpected features expand the differential diagnosis, and may raise the possibility of previously undescribed diseases. For example, Legionnaire’s disease, human immunodeficiency virus (HIV), Hantavirus pneumonia, and severe acute respiratory syndrome (SARS) are examples of newly described diagnoses in the last 40 years.
The mental construct of etiology (cause), pathogenesis (progression), natural history (clinical outcome), and response to therapy is the standard approach for pathologists thinking about a disease. The prognosis reflects the integration of the expected natural history and the expected response to therapy. A disease may have one or more etiologies (initial causes, e.g., agents, toxins, mutagens, drugs, allergens, trauma, or genetic mutations). A disease is expected to follow a particular series of events in its development (pathogenesis), and to follow a particular clinical course (natural history). Disease can result in a temporary or lasting change in normal function, including patient death. Multiple diseases of different etiologies can affect a single organ, for example, infectious and neoplastic diseases involving the lung. Different diseases can derive from a single etiology, for example, emphysema, chronic bronchitis, and small cell lung carcinoma in long-term smokers. The same disease (e.g., emphysema of the lung) can derive from different etiologies (e.g., emphysema from either alpha-1-antitrypsin deficiency or cigarette smoke).