Pathology
What you must understand
Pathology questions usually test mechanisms of disease and the microscopic or gross pattern that follows. Build a mental map of the four core processes: cell injury and death (necrosis vs apoptosis), inflammation (acute vs chronic, granulomas), neoplasia (benign vs malignant, grading vs staging, oncogenes vs tumour suppressors), and haemodynamic disorders (thrombosis, embolism, infarction, oedema). Know the classic morphological patterns: coagulative, liquefactive, caseous and fat necrosis, and be able to match them to organs and causes. For neoplasia, remember that staging predicts prognosis better than grading, and that tumour suppressor genes (e.g., p53, RB) require loss of both alleles (two-hit hypothesis).
Traps that appear in questions
- Confusing metaplasia (reversible change of one mature cell type to another) with dysplasia (disordered growth, pre-malignant).
- Mixing up transudate vs exudate (protein and cell content, specific gravity).
- Attributing a granuloma to the wrong cause (e.g., forgetting that tuberculosis produces caseating granulomas while sarcoidosis produces non-caseating ones).
- Forgetting that apoptosis is energy-dependent and inflammation-free, unlike necrosis.
Worked example (rule of thumb)
A patient with sudden unilateral leg swelling after immobilisation: suspect deep vein thrombosis. The Virchow triad - stasis, endothelial injury, hypercoagulability - explains the mechanism. If the clot embolises to the lung, it produces a pulmonary embolism, classically with sudden dyspnoea and pleuritic pain. Rule of thumb: immobilisation = stasis = thrombosis.
Exam strategy
For each disease, state the mechanism, the organ pattern, and the complication. That three-part structure answers most pathology stems.