A pathologist is a medical doctor who specializes in diagnosing disease by examining tissues, organs, and bodily fluids. When a patient has a health issue involving the intestines, such as persistent pain or abnormal growth, samples are taken, and the pathologist determines the underlying cause. Analysis of intestinal tissue is the definitive method for identifying conditions ranging from inflammatory disorders to cancer. This diagnosis directly influences the treatment plan chosen by the patient’s clinical team. The process begins when a biopsy or surgical specimen arrives in the laboratory.
Preparing the Intestinal Tissue for Analysis
The process begins immediately after the intestinal sample reaches the pathology laboratory. The first step is fixation, which involves placing the tissue into a chemical solution, typically buffered formalin. Fixation stops cellular decay and preserves the cellular and architectural details for later microscopic study. Proper fixation ensures the cellular structures remain intact for accurate diagnosis.
Following fixation, the tissue undergoes “grossing,” where a pathologist or assistant physically examines the specimen. The tissue is carefully measured, weighed, and described in detail, noting features like color, texture, and visible lesions or tumors. For larger surgical specimens, the pathologist selects specific, representative areas to be sampled. This includes areas of disease, surrounding healthy tissue, and surgical margins in cancer cases.
These selected tissue pieces are placed into cassettes for tissue processing. The cassettes run through chemical baths that remove water and replace it with melted paraffin wax. This wax embedding provides a solid structure so the soft tissue can be cut into extremely thin slices using a microtome. These thin tissue sections are then floated onto glass slides, ready for staining and microscopic analysis.
The Diagnostic Process Under the Microscope
Most intestinal samples are stained using the standard Hematoxylin and Eosin (H&E) technique. Hematoxylin stains cell nuclei deep blue or purple, and eosin stains the cytoplasm and extracellular matrix pink or red. The H&E-stained slide provides a high-contrast view of the tissue’s architecture, allowing assessment of cellular shape, organization, and structural abnormalities.
The pathologist examines these slides to identify changes in the normal lining (mucosa) and underlying layers. They look for distortion of intestinal villi or crypts, abnormal inflammation patterns, or disorganized cell growth indicating a tumor. The pattern of these changes allows for the initial differentiation between various diseases.
When H&E findings are inconclusive, the pathologist uses specialized techniques like immunohistochemistry (IHC). IHC uses chemically tagged antibodies to bind to specific proteins (antigens) within the tissue. This molecular labeling makes particular cellular components or markers visible under the microscope. IHC is helpful for determining the exact type and origin of a cancer or identifying a specific infectious agent, guiding treatment decisions.
Molecular testing examines the tissue’s DNA and RNA using techniques like next-generation sequencing. This allows the pathologist to detect specific genetic mutations, chromosomal alterations, or gene expression patterns. In intestinal cancers, molecular testing can reveal mutations that make a tumor susceptible to certain drugs, leading to highly personalized treatment strategies.
Major Diseases Identified in Intestinal Samples
The most frequently sought finding is neoplasia, the abnormal growth of cells leading to tumors or masses. Pathologists differentiate between benign tumors, such as common polyps, and malignant tumors (cancer), like adenocarcinoma. For malignant tumors, the pathologist determines the specific type, its grade (aggressiveness), and the stage (spread within the intestinal wall and to surgical margins).
Inflammatory Bowel Disease (IBD)
Inflammatory conditions include Inflammatory Bowel Disease (IBD), such as Crohn’s disease and ulcerative colitis. The pathologist looks for characteristic patterns of inflammation and architectural changes. Crohn’s disease often shows deep, transmural inflammation affecting all layers of the intestinal wall. Ulcerative colitis is typically limited to the superficial lining of the large intestine.
Infectious Processes
Infectious processes are also a significant part of intestinal pathology. Microscopic examination identifies the causative agent or the specific tissue damage it causes. Pathologists can detect viral infections, such as cytomegalovirus (CMV), or parasitic organisms like Giardia. Identifying the specific pathogen guides the physician in choosing the correct antimicrobial or antiviral treatment.
Other Conditions
Pathologists also identify conditions like celiac disease, an autoimmune disorder that damages the small intestine. Microscopic findings for celiac disease include a flattening of the small intestinal villi and an increase in lymphocytes within the lining. The ability to precisely identify the differences between these conditions is indispensable in gastrointestinal health.
Communicating Findings and Patient Care
The culmination of the pathologist’s work is the pathology report, the formal document containing all findings from the gross examination and microscopic analysis. This report includes a description of the tissue, techniques used, and the definitive diagnosis. For cancer cases, the report must include detailed information on the tumor type, grade, and, critically, the status of the surgical margins, which indicates if the tumor was completely removed.
The pathologist functions as a consultant, communicating these detailed findings to the treating physician, such as the gastroenterologist or surgeon. The report serves as the foundation for all subsequent patient management and treatment decisions, including the need for surgery, chemotherapy, or immunosuppressive therapy. For unexpected or highly significant findings, the pathologist may communicate results verbally to the clinical team to ensure rapid action. This collaboration ensures the patient receives appropriate and timely care based on the precise diagnosis.