Pathology: Cell Injury, Inflammation, Neoplasia and Haemodynamics
Pathology: what is tested
Pathology tests mechanisms of cell injury, inflammation, neoplasia and haemodynamic disease, plus the interpretation of macroscopic and microscopic findings. The exam rewards linking a morphological pattern to a mechanism and a clinical consequence.
Core rules
- Reversible injury shows swelling and fatty change; irreversible injury shows membrane rupture, mitochondrial damage and nuclear dissolution. Necrosis is accidental and inflammatory; apoptosis is programmed and non-inflammatory.
- Acute inflammation: vasodilatation, increased permeability, neutrophil emigration, then macrophages. Granulomas are collections of activated macrophages, seen in tuberculosis and sarcoidosis.
- Neoplasia: benign tumours are well circumscribed and non-invasive; malignant tumours invade and metastasise. Grading describes differentiation; staging describes anatomical spread and is the stronger prognostic factor.
- Virchow's triad for thrombosis: endothelial injury, altered blood flow and hypercoagulability. Infarction occurs when perfusion falls below tissue demand.
Worked example. A 62-year-old has iron-deficiency anaemia and a caecal mass. Biopsy shows adenocarcinoma invading through the muscularis propria with one regional lymph node metastasis and no distant spread. Reasoning: this is T3N1M0, stage III (IIIB) colorectal cancer. Staging, not grading, determines prognosis and the need for adjuvant chemotherapy; the right-sided location explains anaemia rather than obstruction.
Traps that cost marks
- Mixing grading and staging in colorectal cancer.
- Calling carcinoma in situ invasive when the basement membrane is intact.
- Forgetting that caseous necrosis is typical of tuberculosis.
- Describing apoptosis as inflammatory.