INTRODUCTION
Many medical conditions, including all cases of cancer, must be diagnosed by removing a sample of tissue from the patient and sending it to a pathologist for examination. This procedure is called a biopsy, a Greek-derived word that may be loosely translated as "view of the living." Any organ in the body can be biopsied using a variety of techniques, some of which require major surgery (e.g., staging splenectomy for Hodgkin's disease), while others do not even require local anesthesia (e.g., fine needle aspiration biopsy of thyroid, breast, lung, liver, etc). After the biopsy specimen is obtained by the doctor, it is sent for examination to another doctor, the anatomical pathologist, who prepares a written report with information designed to help the primary doctor manage the patient's condition properly.
The pathologist is a physician specializing in rendering medical diagnoses by examination of tissues and fluids removed from the body. To be a pathologist, a medical graduate (M.D. or D.O.) undertakes a five-year residency training program, after which he or she is eligible to take the examination given by the American Board of Pathology. On successful completion of this exam, the pathologist is "Board-certified." Almost all American pathologists practicing in JCAHO-accredited hospitals and in reputable commercial labs are either Board-certified or Board-eligible (a term that designates those who have recently completed residency but have not yet passed the exam). There is no qualitative difference between M.D.-pathologists and D.O.- pathologists, as both study in the same residency programs and take the same Board examinations.
TYPES OF BIOPSIES
- Excisional biopsy.
A whole organ or a whole lump is removed (excised). These are less common now, since the development of fine needle aspiration (see below). Some types of tumors (such as lymphoma, a cancer of the lymphocyte blood cells) have to be examined whole to allow an accurate diagnosis, so enlarged lymph nodes are good candidates for excisional biopsies. Some surgeons prefer excisional biopsies of most breast lumps to ensure the greatest diagnostic accuracy. Some organs, such as the spleen, are dangerous to cut into without removing the whole organ, so excisional biopsies are preferred for these. - Incisional biopsy.
Only a portion of the lump is removed surgically. This type of biopsy is most commonly used for tumors of the soft tissues (muscle, fat, connective tissue) to distinguish benign conditions from malignant soft tissue tumors, called sarcomas. - Endoscopic biopsy.
This is probably the most commonly performed type of biopsy. It is done through a fiberoptic endoscope the doctor inserts into the gastrointestinal tract (alimentary tract endoscopy), urinary bladder (cystoscopy), abdominal cavity (laparoscopy), joint cavity (arthroscopy), mid-portion of the chest (mediastinoscopy), or trachea and bronchial system (laryngoscopy and bronchoscopy), either through a natural body orifice or a small surgical incision. The endoscopist can directly visualize an abnormal area on the lining of the organ in question and pinch off tiny bits of tissue with forceps attached to a long cable that runs inside the endoscope. - Colposcopic biopsy.
This is a gynecologic procedure that typically is used to evaluate a patient who has had an abnormal Pap smear. The colposcope is actually a close- focusing telescope that allows the physician to see in detail abnormal areas on the cervix of the uterus, so that a good representation of the abnormal area can be removed and sent to the pathologist. - Fine needle aspiration
(FNA) biopsy.This is an extremely simple technique that has been used in Sweden for decades but has only been developed widely in the US over the last ten years. A needle no wider than that typically used to give routine injections (about 22 gauge) is inserted into a lump (tumor), and a few tens to thousands of cells are drawn up (aspirated) into a syringe. These are smeared on a slide, stained, and examined under a microscope by the pathologist. A diagnosis can often be rendered in a few minutes. Tumors of deep, hard-to-get-to structures (pancreas, lung, and liver, for instance) are especially good candidates for FNA, as the only other way to sample them is with major surgery. Such FNA procedures are typically done by a radiologist under guidance by ultrasound or computed tomography (CT scan) and require no anesthesia, not even local anesthesia. Thyroid lumps are also excellent candidates for FNA. - Punch biopsy
This technique is typically used by dermatologists to sample skin rashes and small masses. After a local anesthetic is injected, a biopsy punch, which is basically a small (3 or 4 mm in diameter) version of a cookie cutter, is used to cut out a cylindrical piece of skin. The hole is typically closed with a suture and heals with minimal scarring. - Bone marrow biopsy
In cases of abnormal blood counts, such as unexplained anemia, high white cell count, and low platelet count, it is necessary to examine the cells of the bone marrow. In adults, the sample is usually taken from the pelvic bone, typically from the posterior superior iliac spine. This is the prominence of bone on either side of the pelvis underlying the "bikini dimples" on the lower back/upper buttocks. Hematologists do bone marrow biopsies all the time, but most internists and pathologists and many family practitioners are also trained to perform this procedure.
With the patient lying on his/her stomach, the skin over the biopsy site is deadened with a local anesthetic. The needle is then inserted deeper to deaden the surface membrane covering the bone (the periosteum). A larger rigid needle with a very sharp point is then introduced into the marrow space. A syringe is attached to the needle and suction is applied. The marrow cells are then drawn into the syringe. This suction step is occasionally uncomfortable, since it is impossible to deaden the inside of the bone. The contents of the syringe, which to the naked eye looks like blood with tiny chunks of fat floating around in it, is dropped onto a glass slide and smeared out. After staining, the cells are visible to the examining pathologist or hematologist.
This part of procedure, the aspiration, is usually followed by the core biopsy, in which a slightly larger needle is used to extract core of bone. The calcium is removed from the bone to make it soft, the tissue is processed (see "Specimen Processing," below) and tissue sections are made. Even though the core biopsy procedure involves a bigger needle, it is usually less painful than the aspiration.
SPECIMEN PROCESSING
After the specimen is removed from the patient, it is processed in one or both of two major ways:
- Histologic Sections: This involves preparation of stained, thin (less than 5 micrometers, or 0.005 millimeters) slices mounted on a glass slide, under a very thin pane of glass called a coverslip. There are two major techniques for preparation of histologic sections:
- Permanent Sections: This technique gives the best quality of specimen for examination, at the expense of time. The fresh specimen is immersed in a fluid called a fixative for several hours (the necessary time dependent on the size of the specimen). The fixative, typically formalin (a 10% solution of formaldehyde gas in buffered water), causes the proteins in the cells to denature and become hard and "fixed." Adequate fixation is probably the most important technical aspect of biopsy processing.
The fixed specimen is then placed in a machine that automatically goes through an elaborate overnight cycle that removes all the water from the specimen and replaces it with paraffin wax. The next morning, a technical professional, called a histologic technician, or "histotech," removes the paraffin- impregnated specimen and "embeds" it in a larger bloc of molten paraffin. This is allowed to solidify by chilling and is set in a cutting machine, called a microtome. The histotech uses the microtome to cut thin sections of the paraffin block containing the biopsy specimen. These delicate sections are floated out on a water bath and picked up on a glass slide.
Then the paraffin is dissolved from the tissue on the slide. With a series of solvents, water is restored to the sections, and they are stained in a mixture of dyes. The most common dyes used are hematoxylin a natural product of the heartwood of the logwood tree, Haematoxylon campechianum, which is native to Central America, and eosin, an artifcial aniline dye. The stain combination, casually referred to by pathologists as "H and E" yields pink, orange, and blue sections that make it easier for us to distinguish different parts of cells. Typically, the nucleus of cells stains dark blue, while the cytoplasm stains pink or orange. - Frozen Sections: This technique allows one to examine histologic sections within a few minutes of removing the specimen from the patient, but the price paid is that the quality of the sections is not nearly as good as those of the permanent section. Still, a skilled pathologist and a knowledgeable surgeon can work together to use the frozen section's rapid availability to the patient's great benefit.
- Permanent Sections: This technique gives the best quality of specimen for examination, at the expense of time. The fresh specimen is immersed in a fluid called a fixative for several hours (the necessary time dependent on the size of the specimen). The fixative, typically formalin (a 10% solution of formaldehyde gas in buffered water), causes the proteins in the cells to denature and become hard and "fixed." Adequate fixation is probably the most important technical aspect of biopsy processing.
- Smears: The specimen is a liquid, or small solid chunks suspended in liquid. This material is smeared on a microscope slide and is either allowed to dry in air or is "fixed" by spraying or immersion in a liquid. The fixed smears are then stained, coverslipped, and examined under the microscope.
Like the frozen section, smear preparations can be examined within a few minutes of the time the biopsy was obtained. This is especially useful in FNA procedures (see above), in which a radiologist is using ultrasound or CT scan to find the area to be biopsied. He or she can make one "pass" with the needle and immediately give the specimen to the pathologist, who can within a few minutes determine if a diagnostic specimen was obtained. The procedure can be terminated at that point, sparing the patient the discomfort and inconvenience of repeated sticks.
More info including definitions of different types of things that pathologists look for in specimens at
http://www.cancerguide.org/pathology.html
-Satwik
