Pathology: injury, inflammation and tumour logic
Pathology in this exam is asked as mechanism first, morphology second, clinical consequence third. General pathology supplies the vocabulary: cell injury and adaptation, acute and chronic inflammation, healing, haemodynamics, and neoplasia. Systemic pathology supplies the cases, and the better questions force you to link a named risk factor to a named histological pattern.
Core rules
- Reversible injury shows cellular swelling and fatty change; irreversible injury shows membrane rupture, mitochondrial permeability transition and nuclear changes (pyknosis, karyorrhexis, karyolysis).
- Acute inflammation is neutrophil-predominant and mediated by vasoactive amines and arachidonic acid products; chronic inflammation is macrophage and lymphocyte predominant with fibrosis.
- Transudate versus exudate: exudate has high protein and high specific gravity, reflecting increased vascular permeability.
- Oncogenes are activated by gain of function (RAS, MYC, HER2); tumour suppressors are lost by loss of function (TP53, RB, APC).
- Grading describes differentiation; staging describes spread and carries the stronger prognosis.
Worked example
A 62-year-old presents with progressive dysphagia for solids then liquids and weight loss. The clinical sequence points to a mechanical oesophageal obstruction. In the upper and middle oesophagus the expected tumour is squamous cell carcinoma, linked to smoking, alcohol and hot beverages. In the lower oesophagus, adenocarcinoma arising in Barrett metaplasia is commoner and follows chronic reflux. The question then hinges on location and risk factors, not on the word dysphagia. Cachexia and local invasion (recurrent laryngeal nerve, trachea) explain hoarseness or cough.
Traps that cost marks
- Confusing a tumour marker with a diagnostic test; markers are for monitoring, not screening.
- Metastasis to bone may be osteolytic or osteoblastic depending on primary, so 'bone lesion = lytic' is unsafe.
- Apoptosis is energy-dependent and does not incite inflammation; necrosis does.
- Caseating versus non-caseating granulomas is a discriminator worth memorising as a pair, not in isolation.