Introduction to Pathology

What is Pathology?

• The study of diseases and the changes they cause.
• Incorporates both basic sciences and clinical practice.
• Focuses on structural and functional changes in cells, tissues, and organs.
• Attempts to explain why symptoms of disease occur.

Fundamental Items of Pathologic Study

• Definition: Each disease has a specific definition.
  • Example: an abscess is a localized suppurative inflammation.
• Etiology (Causes):
  • Predisposing factors: Bring the body under the influence of a direct cause.
    • Example: Skin abrasion can allow entry of organisms causing abscess formation.
  • Direct causes:
    • Exogenous: From outside the body. Bacteria, viruses, and parasites.
    • Endogenous: Originates from the body itself. Autoimmune diseases.
• Pathogenesis of a disease:
  • The mechanism by which a disease develops.
• Lesion:
  • Observable changes in structure and function of tissues and organs.
  • Examined both grossly (naked eye) and microscopically (microscope).
  • Gross description includes changes in size, shape, color, cut surface, and consistency of the organ.
• Fate or outcome of the disease:
  • Regression: The disease improves.
  • Progression with complications: The disease worsens and leads to additional problems.
  • Prognosis: Prediction of how the patient’s disease will progress.

Components of Pathological Picture

• Signs: Objective symptoms observed by doctors.
  • Examples: Ascites (fluid buildup in the abdomen), cachexia (weight loss), cough, dysphagia (difficulty swallowing), organ enlargement (hepatomegaly, splenomegaly).
• Symptoms: Subjective signs reported by patients.
  • Examples: Chest pain, loss of appetite, weakness, numbness, headache, toothache, etc.

Types of Pathological Specimens

• Biopsy: Specimen taken from a living patient in the operating room.
• Diagnostic cytology: Examination of body fluids for cells.
  • Examples: Effusions, sputum, urine, cerebrospinal fluid (CSF).
• Autopsy: Specimen removed from a dead body in the postmortem room.

Cytological Diagnosis (Cytopathology)

• Diagnosis based on isolated cells in body fluids.
• Samples can be acquired through:
  • Exfoliated cells: Shed cells from tumors found in sputum, urine, CSF, pleural effusion, etc.
  • Wash: Flushing fluids through organs to collect cells.
  • Brushing or scraping: Obtaining cells from lesions visualized by endoscopy (bronchoscopy, gastroscopy, colonoscopy).
  • Fine needle aspiration smear: Sampling cells with a needle guided by imaging, for diagnosis of thyroid, liver, pancreas, breast, and lymph node cancers.

Histopathological Diagnosis

• Definitive method: Diagnoses based on the examination of tissues removed by surgeons.

Types of Biopsy Specimens

• Excisional biopsy: Removal of the entire lesion.
  • Examples: Radical mastectomy, nephrectomy, total cystectomy.
• Tru-cut needle biopsy: Taking a tissue sample using a needle.
• Incisional biopsy: Taking a piece of the lesion.
• Punch biopsy: Taking a small sample using a tool, usually for oral, nasal, or rectal tumors.
• Endometrial curetting (D&C biopsy): Obtaining a sample from the lining of the uterus.
• TUR specimens: Removal of tissue from the bladder or prostate using a resectoscope (cystoscopy).
• Endoscopic biopsy: Obtaining a sample from the larynx, esophagus, stomach, and colon during upper and lower endoscopy.

Techniques Used in Pathology

• Frozen section: Rapid preparation of fresh tissue to distinguish between benign and malignant tumors and determine margins.
• Paraffin sections: The primary method for pathological diagnosis, prepared from tissue and stained with hematoxylin and eosin.
• Immunoperoxidase technique (Immunohistochemistry):
  • Used to detect specific proteins, enzymes, and hormones in tumor cells, often representing tumor markers that identify the presence of a tumor.
• Serum Tumor Markers:
  • Tumor-derived or associated molecules detectable in blood or other bodily fluids.
  • Used for diagnosis and monitoring treatment effectiveness.
  • Examples: Carcinoembryonic antigen (CEA) in gastrointestinal and breast carcinoma, alpha-fetoprotein in hepatic carcinomas, prostatic acid phosphatase in prostatic carcinoma.
• Electron microscopy:
  • Examining ultra thin sections of tissue for diagnosing complex diseases and cancers.
• Molecular diagnosis:
  • PCR (polymerase chain reaction): For diagnosing leukemias.
  • Flow cytometry: Measures the DNA content of tumor cells.

How Pathological Specimen is Prepared and Examined

• Fixation:
  • Prevents tissue decay and autolysis.
  • Stabilizes it for histological examination.
  • Usually performed with formaldehyde (formalin) (10% solution) or alcohol for cytological smears.

Objectives of Pathology Study (Why)

• To describe disease processes and correlate clinical manifestations with pathological changes in diseased organs.
• To predict the course and outcome (fate and prognosis) of various diseases.
• To emphasize the role of histopathology and diagnostic cytology in the diagnosis and treatment of diseases.
• To develop accurate diagnoses.