Pathology
Pathology items link mechanism to morphology: how cells respond to injury, how inflammation is classified, and how benign and malignant lesions are distinguished.
Core rules
- Reversible injury shows swelling and fatty change; irreversible injury shows membrane damage and mitochondrial failure.
- Necrosis types: coagulative (ischaemia, architecture preserved), caseous (tuberculosis), liquefactive (brain abscess), fat (pancreatitis), fibrinoid (vasculitis).
- Acute inflammation: neutrophils and oedema; chronic inflammation: lymphocytes, macrophages and fibrosis, with granulomas in TB, leprosy, sarcoidosis and Crohn disease.
- Malignancy features: pleomorphism, high nuclear-cytoplasmic ratio, mitoses, invasion and metastasis. Grading describes differentiation; staging describes spread and predicts prognosis better.
- Anaemia: use mean corpuscular volume to classify as microcytic, normocytic or macrocytic.
Worked example
A 45-year-old woman has fatigue, haemoglobin 8 g/dL and MCV 70 fL with a low ferritin. This is microcytic hypochromic anaemia, and the low ferritin confirms iron deficiency. In a man or a postmenopausal woman, look for gastrointestinal blood loss and investigate the gut, not only prescribe iron.
Traps
- Calling a high red cell count with low MCV iron deficiency when it suggests thalassaemia trait.
- Assuming every granuloma is tuberculosis.
- Confusing grading with staging.
- Ignoring a normal ferritin in inflammation, where it can be falsely raised.