A biopsy is a medical procedure involving the removal of a small tissue sample for microscopic examination. This process, known as histology, allows healthcare providers to investigate the cause of symptoms or confirm various health conditions. It serves as a diagnostic tool, providing detailed insights into the cellular structure and composition of the tissue. By analyzing these samples, medical professionals can identify abnormalities and establish a precise diagnosis to guide subsequent medical care.
Methods of Tissue Collection
Tissue samples for histological examination are obtained through various techniques, each suited to different body areas or suspected conditions. An excisional biopsy involves surgically removing the entire suspicious lesion along with a margin of surrounding healthy tissue. This approach is often preferred when a lesion is small enough to be completely removed, such as for certain skin growths or small tumors.
An incisional biopsy removes only a portion of a larger lesion or tumor. This method is used when the lesion is too extensive for complete removal or if its location makes full excision difficult or cosmetically undesirable. Both excisional and incisional biopsies often require local anesthesia, and stitches may be needed to close the wound.
Needle biopsies use a hollow needle to collect tissue or fluid from internal organs, muscles, or bones. A fine needle aspiration (FNA) uses a very thin needle, sometimes guided by imaging, to extract cells or fluid, often from lumps that can be felt through the skin or from deep-seated organs. A core needle biopsy, in contrast, uses a larger needle with a sharper edge to obtain a small cylindrical piece of tissue, preserving more of the tissue’s architecture than an FNA.
Punch biopsies are primarily used for skin conditions, employing a circular blade to remove a full-thickness skin specimen. Shave biopsies, also for skin, scrape off the top layers using a surgical blade or razor. These are less invasive and often do not require stitches.
Endoscopic biopsies involve inserting a thin, flexible tube with a camera, called an endoscope, into a body cavity or organ. Small tools passed through the endoscope collect tissue samples from areas like the bladder, lungs, or colon.
From Sample to Slide: The Histology Process
Once a tissue sample is collected, it embarks on a journey through the histology laboratory to be prepared for microscopic analysis. The initial and important step is fixation, where the tissue is immediately placed into a preservative solution, most commonly 10% buffered formalin. Fixation stabilizes the tissue by preventing degradation and maintaining cellular structures.
Following fixation, the sample undergoes gross examination by a pathologist or a trained assistant. This involves a macroscopic assessment where the specimen is visually inspected, measured, and described for size, shape, and any visible abnormalities. Portions of the specimen are then selected and trimmed to fit into small, labeled cassettes for further processing.
The cassettes containing the tissue pieces then proceed to tissue processing, which prepares the sample for embedding. This multi-step process involves dehydration, where water is removed from the tissue by passing it through increasing concentrations of alcohol. Subsequently, clearing agents, such as xylene, replace the alcohol, making the tissue transparent and ready for wax infiltration.
After clearing, the tissue is infiltrated with molten paraffin wax. This wax-filled tissue is then placed into a mold with fresh molten wax, oriented, and allowed to cool and solidify into a solid block. This paraffin block provides support for cutting thin sections.
The solidified paraffin block is then mounted on a microtome, an instrument used to cut thin slices. These sections are then floated onto warm water, picked up onto glass slides, and allowed to dry. The wax is subsequently removed from the sections on the slides.
Finally, the tissue sections on the slides undergo staining to make their cellular components visible under a microscope. The most common staining method is hematoxylin and eosin (H&E) staining; hematoxylin stains cell nuclei blue, while eosin stains cytoplasm and extracellular matrix pink. For more specific diagnoses, special stains or immunohistochemistry techniques may highlight particular cell types, proteins, or microorganisms.
Understanding Your Biopsy Results
Once the tissue slides are prepared and stained, they are ready for microscopic examination by a pathologist. The pathologist examines the stained tissue sections under a microscope, looking for any abnormal cells, unusual tissue architecture, or other disease indicators. The pathologist’s expertise allows for the identification and classification of various conditions, including infections, inflammation, or cancerous growths.
The pathologist then compiles a pathology report, which serves as a medical document outlining their findings. This report includes patient identifiers, specimen collection details, and a macroscopic description of the sample. It also contains a microscopic description of the tissue, noting cellular characteristics and any abnormalities observed.
The report concludes with a final diagnosis. For cancer diagnoses, the report may include details like the type of cancer, its grade (how abnormal the cells look), and whether the margins (edges of the removed tissue) are clear of disease. This information is important for guiding treatment decisions.
After the report is finalized, it is sent to the referring physician, who communicates the results to the patient. It is important for patients to discuss their pathology report with their doctor, as the terminology can be technical and complex. Understanding the report’s details, with professional guidance, helps patients comprehend their diagnosis and the recommended next steps for their care.