Pathology 6-Introduction to Pathology

Anatomic Pathology

*Anatomic Pathology* is a division of pathology concerned with the diagnosis of disease based on the examination of tissues, organs, or whole bodies (autopsy). -Forms of examination include gross, microscopic, chemical, immunologic, and molecular. -It is subdivided into *surgical*, *cytologic*, and *autopsy pathology* (including forensic pathology).

Excisional Biopsy

*Definition*: A procedure is called an excisional biopsy when an *entire* mass or suspicious area is removed, eg. removal of the whole spleen in Hodgkin's disease.

Incisional Biopsy

*Definition*: A procedure is called an incisional biopsy when only a *portion* of a lesion is removed with scalpel with preservation of the histological architecture of the tissue's cells.

Autopsy

*Definition*: Examination of the organs of a dead body according to anatomic and pathologic criteria. -Synonyms: necropsy, postmortem examination -Etymology: -Autopsy: Gr: see myself. -Necropsy: Gr: see the dead.

Cytopathology/Cytology

*Definition*: The branch of pathology that studies and diagnoses disease on the cellular level. -From the greek for cyto- (cell) and logia (study).

Biopsy

*Definition*: The removal of a sample of tissue from the body of the living patient for examination. -Greek, for "bio" + "psy" (view of the living) -The tissue specimen is sent to the pathology laboratory for gross and microscopic examination in order to determine the existence or cause of disease. -Any organ of the body can be biopsied using a variety of techniques.

Morphologic Changes

*Morphology* refers to *structural alterations* in cells or tissues that are either characteristic of the disease or diagnostic of the etiology. -E.g., unregulated cell growth in cancer can lead to a physical mass with specific characteristics.

Pathogenesis

*Pathogenesis* is the sequence of events in the response of the cells or tissues to the etiologic agent(s) - from the initial stimulus to the ultimate expression of the disease. -E.g. in cancer, a genetic change (etiology) can lead to unregulated cell proliferation (pathogenesis).

Summary

*Pathology* is the study of disease. -There are four aspects of a disease process: 1. Etiology 2. Pathogenesis 3. Structural (morphologic) changes 4. Functional (clinical) consequences -The pathology profession is broken down into two divisions: *Anatomic and Clinical Pathology* 1. Anatomic pathology is involved in the diagnosis of disease by the examination of cells (cytology), tissues (biopsy), organs (surgical specimen), or whole bodies (autopsy). 2. Clinical pathology is a division of pathology concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, and tissues using the tools of chemistry, hematology, microbiology, immunology, and molecular pathology.

Clinical Pathology

-A division of pathology concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, and tissues using the tools of *chemistry, hematology, microbiology, immunology, and molecular pathology*. -Examples of tests ordered through the clinical lab include a complete blood count (CBC), chemistry panels, and cultures for microbiology. -The blood bank is also located in the clinical lab. -Crossmatching of blood products, and blood product distribution occur here.

Endoscopic Biopsy

-An *endoscope* is an instrument for examining visually the interior of a bodily canal or a hollow organ such as the colon, stomach, bronchial tree or bladder. -Examples include bronchoscopy, colonoscopy, sigmoidoscopy, and esophogealgastroduodenoscopy (EGD). -The physician can inspect the entire lining of the organ in question, can visualize an abnormal area, and pinch off bits of tissue with forceps attached to a long cable that runs inside the endoscope.

Spontaneous Exfoliation

-An example of spontaneous exfoliation is when cells of the pleural cavity or peritoneal cavity are shed into the pleural fluid. -This fluid can be collected via, eg, thoracentesis (pleural tap) for examination.

Tissue Processing: Fixation

-Cassettes are placed into a fixative. -Formalin (a 10% solution of formaldehyde) is probably the best and most used fixative. -The purpose of fixation is to preserve tissue permanently in a life-like state. -Formalin forms cross-links between lysine residues in the proteins. -This cross-linkage does not harm the structure of proteins greatly, so that antigenicity is not lost.

Tissue Processing: Staining

-Cells and their organelles are quite transparent under the microscope. -Pathologists have developed many staining methods that help them see cytological details of the cell. -*Hematoxylin and eosin (H&E)* is a traditional staining method for routine procedure in histopathology laboratory. -Results of H&E staining: nuclei are stained blue and cytoplasm is stained pink red. -The stained section on the slide must be covered with a thin piece of plastic or glass to protect the tissue from being scratched.

Autopsy Procedures

-Initially, the external aspects of the body is examined for pathologic changes. -After opening the body cavities, organs are dissected and isolated. -Each organ is then weighed, sliced and examined by the prosector. -Organs are sampled for microscopic examination (as well as possible clinical chemistry analysis or microbiological culture). -Sections of the organ are cut, placed in cassettes, and put in a container of formalin.* -Finally, the organs are returned to the body cavities and reconstruction of the body produces an acceptable cosmetic result so that relatives may view the body after autopsy.

Tissue Processing: Embedding

-Once the tissue has been fixed it must be infiltrated with a firm medium to allow for cutting into thin sections. -The usual way this is done is with paraffin. -The technique of getting fixed tissues in paraffin is called embedding.

Punch Biopsy

-Punch biopsy is used by dermatologists to sample skin rashes or tumors. -Biopsy punch is basically a small (3 mm in diameter) version of a cookie cutter, which is used to cut out a cylindrical piece of skin.

Tissue Processing: Dehydration

-Samples are transferred through baths of progressively more concentrated ethanol. -This is followed by a hydro-phobic clearing agent (e.g. xylene) to remove the alcohol. -This is the most time consuming step in tissue processing, taking at least 6-8 hours.

What is Pathology?

-The word *pathology* is derived from ancient greek meaning the *study (logos)* of *suffering (pathos)*. -*Definition*: The medical science, and specialty practice, concerned with all aspects of disease, but with special reference to the essential nature, causes, and development of abnormal conditions, as well as the structural and functional changes that result from disease processes.

Tissue Processing

-Tissue samples taken during the autopsy, biopsy, or surgical resection must be processed in the pathology laboratory to produce microscopic slides. -The pathologist (or an assistant) examines the gross appearance of the autopsy or surgical specimen, and places all or parts of the tissue sample into a plastic cassette.

Tissue Processing: Sectioning

-Tissues embedded with paraffin can be sectioned at 4 micrometers intervals. -The *microtome* is an instrument that cuts the embedded tissue specimen. -The microtome is basically a knife with a mechanism for advancing the paraffin block across the knife. -Once sections are cut they are floated on a warm water bath, then they are placed on a glass microscopic slide.

Fine Needle Aspiration

-When a sample of tissue or fluid is removed with a needle in such a way that cells are removed without preserving the histological architecture of the tissue cells. -In this technique, a thin, hollow needle is inserted into the mass to extract cells that, after being stained, will be examined under a microscope.

Two Main Categories of Autopsies

1. *Clinical autopsies* -When a patient dies in the hospital, an autopsy may be ordered by family members. -These autopsies answer specific questions and identify diseases or problems related to a patient's death that may have been unresolved during the patient's hospital stay. *Forensic (medicolegal) autopsies* -Forensic autopsies are performed in cases with *potential legal ramifications* to determine the cause of death and/or collect evidence that may be used in the prosecution of those alleged to be responsible for the death.

Subdivisions of the Practice of Pathology

1. Anatomic Pathology 2. Clinical Pathology

Types of Biopsy

1. Excisional biopsy 2. Incisional biopsy 3. Endoscopic biopsy 4. Punch biopsy 5. Shave biopsy

Resection Specimen

A resection specimen is the removal of tissues en masse. -This usually occurs after a previous biopsy has been taken and a pathologic diagnosis for this tissue has been rendered. -Eg. a colectomy may be performed after a biopsy of a lesion reveals cancer. -In addition to the therapeutic value of these procedures, the resultant specimen may be evaluated for prognostic criteria, eg. staging.

Techniques of Cell Collection

Cells are collected after they have been either spontaneously shed by the body (*spontaneous exfoliation*), manually scraped/brushed off of a surface in the body (*mechanical exfoliation*), or aspirated with a needle (*fine needle aspiration*).

Mechanical Exfoliation

Examples of mechanical exfoliation include Pap smears, where cells are scraped from the cervix with a cervical spatula.

Surgical Pathology Methods

Frozen Section -The surgeon sends the tissue in question in a fresh state to the lab. -The pathologist takes a small portion of the tumor tissue, places it in a special embedding medium, and proceeds to rapidly freeze the tissue in a cryostat machine that maintains a constant freezing temperature (-25°C, -13°F). -The tissue is then sectioned in the cryostat with a special microtome (the cryostat is essentially a microtome inside a freezer). -The frozen section is stained and interpreted by the pathologist at the time of surgery, while the patient is under general anesthesia. -The pathologist is able to make a pathological diagnosis within 20 minutes after getting the specimen, however, the technical quality of the sections is much lower than in routine tissue processing and staining.

Shave Biopsy

Shave biopsy is a biopsy technique performed with a surgical/razor blade and used for lesions that are elevated above the skin level or confined to the epidermis and upper dermis.

Surgical Pathology

Surgical pathology involves the analysis of biopsies, and resection specimen.

Aspects of Pathology

The four aspects of a disease process that form the core of pathology: 1. The cause (*etiology*) 2. The mechanisms of development (*pathogenesis*). 3. The structural alterations induced in the cells and organs of the body (*morphologic changes*). 4. The functional consequences of the morphologic changes (*clinical significance*).

Clinical Significance

The nature of the morphologic changes and their distribution in different organs or tissues influence normal function and determines the *clinical features* (signs and symptoms), course, and prognosis of the disease. -E.g. in cancer, a mass in the colon can lead to obstruction, with associated symptoms. -Also, depending on various characteristics, the cancer will be associated with a given prognosis.

The Study of Pathology

The study of Pathology can be divided into: *General Pathology* -The basic reactions of cells and tissues to abnormal stimuli that underlie all diseases. *Systemic Pathology* -Examines the specific responses of specialized organs and tissues to various stimuli, e.g. the pathology of the respiratory system, the pathology of gastrointestinal system, etc..

Etiology of Disease

There are two major classes of *etiologic factors*: 1. *Intrinsic (Genetic) factors* 2. *Acquired factors*, e.g. infectious, nutritional, chemical, physical -These classes may interact with one another in causing the disease.

Clinical Pathologists

Work in close collaboration with medical technologists, hospital administrators, and referring physicians to ensure the quality performance of the clinical lab