By Edward O. Uthman, MD. Diplomat, American Board of Pathology
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 biopsy
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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