Introduction to Pathology

Study Notes

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.

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.

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.

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.

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

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.

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.

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

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.