General and Systemic Pathology for the Radiologist
Why pathology matters to a radiologist
Radiology questions on this exam rarely ask you to diagnose histology in isolation. They test whether you can connect an imaging pattern to an underlying pathological process, predict behaviour, and anticipate complications. Build your knowledge around four axes: cell injury and death, inflammation and repair, neoplasia, and haemodynamic and metabolic disturbance.
Core concepts to master
Understand the difference between necrosis and apoptosis: coagulative necrosis preserves tissue architecture (classically infarcts of solid organs), caseous necrosis is structureless and granulomatous, and liquefactive necrosis dominates brain infarcts and abscesses. Know that granulomas are collections of activated macrophages, and that their imaging correlate is often a nodule, cavity, or calcification. For neoplasia, separate benign from malignant by differentiation, local invasion, and metastasis; recognise that tumour grade reflects differentiation and stage reflects spread, and that only stage reliably predicts survival. Learn the pathways of metastatic spread (haematogenous, lymphatic, transcoelomic, perineural) because they explain distribution patterns such as pulmonary, hepatic, and peritoneal deposits.
Traps in questions
Common pitfalls include equating size with malignancy, assuming all calcification means benign disease, forgetting that inflammation can mimic tumour on imaging, and confusing paraneoplastic syndromes with metastatic disease. Another trap is attributing a lesion's appearance to histology when the question is really about chronicity: acute inflammation causes oedema and enhancement, chronic inflammation causes fibrosis and atrophy.
Worked rule of thumb
If a question describes a mass with central low attenuation, a thick irregular enhancing rim, and surrounding oedema, think necrosis with active inflammation or tumour rather than a simple cyst. A thin imperceptible wall favours benign cyst; a thick nodular wall favours malignancy or abscess. Use wall morphology, not size, as your discriminator.
Systemic Pathology by Organ System: Applying It to Imaging
Organ-based reasoning
Systemic pathology questions reward a structured organ-by-organ approach. For each system, know the common neoplastic and non-neoplastic processes, their typical imaging appearances, and their complications.
Cardiovascular and respiratory. Understand atherosclerosis as intimal lipid deposition with inflammation and fibrosis, and its consequences: ischaemia, aneurysm, and thrombosis. In the lung, separate obstructive disease (emphysema, chronic bronchitis) from restrictive disease (fibrosis), and recognise that fibrosis produces reticulation, traction bronchiectasis, and honeycombing, whereas emphysema produces hyperlucency and vascular pruning.
Gastrointestinal and hepatobiliary. Know that adenoma-carcinoma sequences underlie colorectal cancer, that cirrhosis is bridging fibrosis with regenerative nodules, and that portal hypertension drives varices and ascites. Pancreatic adenocarcinoma is desmoplastic and hypovascular, which is why it appears hypoenhancing.
Genitourinary, endocrine, and musculoskeletal. Recognise that renal cell carcinoma is typically hypervascular, that thyroid nodules require cytology because imaging cannot exclude malignancy, and that bone metastases are osteolytic (breast, lung, kidney, thyroid) or osteoblastic (prostate, breast).
Traps
Do not assume a benign imaging appearance excludes malignancy; do not confuse a paraneoplastic syndrome with metastatic spread; and remember that infection, infarction, and tumour can all produce cavitation.
Worked example
A hypoenhancing pancreatic head mass with ductal dilatation and painless jaundice should prompt the diagnosis of pancreatic adenocarcinoma causing biliary obstruction, not chronic pancreatitis, because the desmoplastic stroma produces delayed, poor enhancement and the double-duct sign reflects obstruction at the ampulla.