Pathology and Basic Sciences Relevant to Radiology
Pathology and basic sciences underpin every imaging sign. This domain tests mechanisms: why an abscess has a rim, why an infarct is wedge-shaped, how tumours spread, and what staging and grading actually mean.
Mechanisms that generate imaging patterns
- Acute inflammation causes vasodilation and capillary leakage, producing oedema and rim enhancement.
- Infarction produces a non-enhancing wedge with surrounding oedema; haemorrhage alters signal on MRI.
- Neoplasia progresses through dysplasia and carcinoma in situ to invasion; tumour angiogenesis gives heterogeneous enhancement.
- Dystrophic calcification occurs in dead tissue; metastatic calcification occurs with abnormal calcium-phosphate balance.
Staging, grading and markers
- TNM describes anatomical extent: T tumour size and local invasion, N regional nodes, M distant metastases.
- Grade describes differentiation and is a histological, not radiological, judgement.
- Immunohistochemistry patterns help: CK7/CK20, TTF-1 for lung and thyroid, ER/PR/HER2 in breast.
Worked example
A 4-cm lung mass with ipsilateral hilar nodes and no distant disease is T2a N1 M0, stage IIB in the 8th edition. Imaging tells you T, N and M but not grade; describing it as high-grade from CT alone is wrong.
Traps
- Calling every enhancing lesion malignant; enhancement reflects vascularity, not histology.
- Mixing up staging and grading in reports.
- Forgetting pseudoprogression after treatment, where apparent growth reflects inflammation rather than tumour.