There are standard procedures and methods that are used with nearly all types of biopsy samples. These procedures are the usual ways that a sample is prepared for use by the doctor. Other procedures, which are described later, may also be done on certain types of samples (such as lymph nodes and bone marrow).
Routine biopsy processing for histology
After the doctor removes the biopsy specimen, it is placed in a container with formalin (a mixture of water and formaldehyde) or some other fluid to preserve it. The container is labeled with the patient's name and other identifying information (hospital number and birth date, for example), site of biopsy (exactly where on the body it was taken from), and then sent to the pathology lab with a paper called a pathology requisition form. This form also identifies who submitted the biopsy, the date the biopsy was taken, information about the patient's symptoms, other abnormal test results, and what type of disease the doctor expects the biopsy may show.
Next, the pathologist or an assistant looks at the specimen without a microscope. In medicine, gross means seen without a microscope. This is what the pathologist observes by simply looking at, measuring, or feeling the tissue. Looking at the whole sample before it is processed further is called the gross examination and includes the tissue sample's size, color, consistency, and other characteristics. The lab staff may even take a picture of the sample as part of the record. The gross examination is important since the pathologist often sees features that suggest cancer. It also helps the pathologist decide which parts of a large biopsy are the most critical to study under a microscope.
For small biopsies, for example, like a punch biopsy or a core needle biopsy, the entire specimen is usually looked at under a microscope. The tissue to be looked at under the microscope is placed into small containers called cassettes. The cassettes hold the tissue securely while it is processed, and help keep small samples from getting lost. After processing, which may take a few hours but is usually done overnight, the tissue sample is placed into a mold with hot paraffin wax. The wax cools to form a solid block that protects the tissue. This paraffin wax block with the embedded tissue is placed on an instrument called a microtome, which cuts very thin slices of the tissue. These thin slices of the specimen are placed on glass slides, and dipped into a series of stains or dyes to change the color of the tissue. The color makes cells more distinctive when viewed under a microscope. For most biopsy specimens, routine processing as described above is all that is needed. At this point (usually the day after the biopsy was done), the pathologist looks at the tissue under a microscope. Looking at the solid specimens in this way is called histology, which is the study of the structures of cells and tissues.
Intra-operative consultation (frozen section)
Sometimes a surgeon needs information about a tissue sample during surgery to decide about immediate surgical treatment. If the surgeon cannot wait the day or more that it will take for routine processing and histology, he or she will request an intra-operative (during surgery) pathology consultation. This consultation is often called a frozen section exam.
How is it done?
When a frozen section exam is done, fresh tissue is sent from the operating room right to the pathologist. Because the patient is often under general anesthesia (kept asleep with drugs) it is important that the tissue be looked at quickly. It usually takes 10 to 20 minutes. The fresh tissue is grossly examined by the pathologist to decide which part of the tissue sample should be looked at under the microscope. Instead of processing the tissue in wax blocks, the tissue is quickly frozen in a special solution that forms what looks like an ice cube around the tissue sample. It is then thinly sectioned (sliced) on a machine called a refrigerated microtome, quickly stained (dipped in a series of dyes), and looked at under the microscope. Although the frozen sections usually do not show features of the tissue as clearly as sections of tissue embedded in wax, they are usually good enough to help the surgeon make decisions about the operation.
When is it done?
To find out if a tumor is cancer: Sometimes the type of operation needed depends on whether the tumor is cancer. For instance, just removing the tumor may be enough to treat a benign (not cancer) tumor, but a more extensive operation (removing more tissue and/or lymph nodes) may be needed if the tumor is cancer. In a case like this, the surgeon may send the tumor for a frozen section exam. This often can give enough information to help the surgeon decide what type of operation, if any, is best for the patient. Sometimes, though, the intra-operative consultation does not give a definite answer and the piece of tissue will need to go through routine or even special processing to get a clear answer. When this happens the surgeon usually stops the operation and closes the surgical incision. When the results are available in a few days, another operation may be needed.
To make sure all of the cancer is removed: Surgical treatment of cancer is often a difficult balance between removing enough tissue to feel that the cancer has been completely removed and leaving enough normal tissue to avoid or minimize damage. If the surgeon is concerned a cancer has not been removed completely, a slice from the edge of the tissue that was removed is sent for a frozen section diagnosis. If there is no cancer in that edge (called a margin), more surgery usually is not needed. But if cancer cells are found, it is assumed that some cancer cells are still present in the tissue left in the patient. If this happens, the surgeon will usually remove more tissue to try to get all the cancer cells and reduce the chance of cancer growing back. If it is not possible to remove more tissue, there may be other options, such as radiation to kill the remaining cancer cells.
Mohs surgery (microscopically controlled surgery)
This procedure is used to treat certain kinds of skin cancer. In Mohs surgery, the surgeon removes a thin layer of the skin that the tumor may have invaded and then checks the sample under a microscope. If cancer cells are seen, deeper layers are removed and checked until the skin samples are found to be free of cancer cells. This process is slow, but it means that more normal skin near the tumor can be saved. This is a highly specialized technique that should only be used by doctors who have been trained in this specific type of surgery and in recognizing skin cancer under a microscope.
Cytology specimen processing
How cytology specimens are processed depends greatly on the type of specimen. Some specimens are smeared directly on glass microscope slides by the doctor who gets the sample. The slides, which are called smears, are then sent to the cytology lab where they are dipped into a series of stains (colored dyes), much like those used for biopsy samples. Other specimens, such as body fluids, cannot easily be placed on a glass microscope slide because they are too dilute (there are too few cells in a large volume of fluid). Cytology labs have ways to concentrate these cells on a glass slide before staining. After processing and staining, the samples are examined under a microscope. The abnormal cells are found and marked with a special pen. A pathologist will then examine the marked cells and decide on a diagnosis.
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