Histopathology
Histopathology is the branch of pathology that involves the microscopic examination of tissues to diagnose diseases. It's considered the "gold standard" for diagnosing many diseases, especially cancer, because it allows pathologists to assess the overall tissue architecture, the relationship between cells, and the cellular morphology within its natural context.
What it analyzes:
Tissue biopsies
Small pieces of tissue removed from a lesion or organ (e.g., skin biopsy, liver biopsy, colon biopsy).
Surgical resections
Larger pieces of tissue or entire organs removed during surgery (e.g., mastectomy specimen, colectomy specimen).
Autopsy tissues
Tissues collected post-mortem to determine cause of death or study disease progression.
The Process
Gross Examination
The pathologist first visually examines the tissue specimen, describes its features, and selects specific areas for microscopic examination.
Tissue Processing
The selected tissue is chemically fixed (to preserve it), dehydrated, cleared, and embedded in paraffin wax to create a solid block.
Sectioning
Thin slices (sections) of the paraffin-embedded tissue are cut using a microtome.
Staining
The sections are placed on glass slides and stained, most commonly with Hematoxylin and Eosin (H&E), which highlights cellular structures. Special stains or Immunohistochemistry (IHC) may also be used to detect specific proteins or features.
Microscopic Examination
A pathologist examines the stained slides under a microscope to identify abnormalities in cell shape, size, organization, and tissue architecture, leading to a diagnosis.
Definitive Cancer Diagnosis
Crucial for confirming the presence of cancer, determining its specific type, grade (how aggressive it looks), and stage (how far it has spread), which are all vital for treatment planning.
Diagnosis of Inflammatory Diseases
Identifying specific patterns of inflammation in conditions like inflammatory bowel disease, autoimmune disorders, or infections.
Identification of Infections
Detecting pathogens (e.g., bacteria, fungi, viruses) within tissues.
Assessment of Organ Diseases
Diagnosing conditions affecting organs like the kidney, liver, or lung based on structural changes.
Guiding Treatment
Provides critical information that dictates surgical approaches, chemotherapy, radiation therapy, and targeted therapies.
Cytopathology
Cytopathology is the branch of pathology that involves the microscopic examination of individual cells or small clusters of cells obtained from various body sites. It is often a less invasive and quicker diagnostic method compared to histopathology, frequently used for screening or preliminary diagnosis.
Exfoliative Cytology
Cells that are shed or scraped from body surfaces (e.g., Pap test for cervical cancer screening, sputum for lung cancer, urine for bladder cancer).
What it analyzes
Fine Needle Aspiration (FNA) Cytology:
Cells collected by inserting a thin needle into a lump or mass (e.g., thyroid nodules, breast lumps, lymph nodes) and aspirating cells.
Fluid Cytology
Cells collected from various body fluids (e.g., pleural fluid from the lungs, peritoneal fluid from the abdomen, cerebrospinal fluid (CSF)).
Brushings/Washings
Cells collected by brushing or washing internal surfaces (e.g., bronchial brushings, gastric washings).
Clinical Importance
Cancer Screening
Most famously, the Pap test for cervical cancer. It allows for early detection of precancerous changes.
Preliminary Diagnosis of Lumps/Masses
FNA cytology can quickly determine if a lump is benign (non-cancerous), malignant (cancerous), or inflammatory, guiding whether a more invasive biopsy is needed.
Detection of Malignancy in Fluids
Identifying cancer cells in effusions (fluid collections) can help stage cancer or diagnose recurrence.
Diagnosis of Infections cryto
Identifying infectious agents (e.g., fungi, parasites, certain bacteria) or viral changes in cells.
Less Invasive
Often preferred as a first-line diagnostic tool due to its minimally invasive nature, lower cost, and quicker turnaround time.
Relationship and Complementarity
Complementary Tools
Histopathology and Cytopathology are often used together. Cytopathology might provide an initial indication or screen, and if abnormalities are found, a definitive histopathological biopsy is often performed.
Tissue Context vs. Cellular Detail
Histopathology provides the crucial tissue architecture, showing how abnormal cells relate to surrounding normal tissue. Cytopathology excels at showing detailed cellular morphology, but without the architectural context.
Diagnostic Pathway
A common pathway is: Cytology (screening/preliminary diagnosis) → Histopathology (definitive diagnosis/characterization) → Molecular/Genetic testing (for targeted therapy).