Systemic Pathology by Organ System
System-by-system anchors
Cardiac: atherosclerosis and hypertension dominate; myocardial infarction evolves from coagulative necrosis to granulation tissue to scar. Respiratory: obstructive (asthma, COPD, bronchiectasis) versus restrictive (fibrosis, pneumoconiosis); lung cancer - squamous cell central, adenocarcinoma peripheral, small cell neuroendocrine with paraneoplastic syndromes. GI: peptic ulcer (H. pylori), celiac disease (villous atrophy), IBD (Crohn transmural granulomas vs ulcerative colitis mucosal and continuous), colorectal adenoma-carcinoma sequence. Liver: steatosis, hepatitis, cirrhosis (regenerative nodules, fibrosis), hepatocellular carcinoma. Renal: nephrotic (podocyte injury, proteinuria) versus nephritic (glomerular inflammation, hematuria); clear cell, papillary, and chromophobe carcinoma. Endocrine: papillary thyroid (Orphan Annie nuclei, psammoma bodies), follicular, medullary (amyloid, calcitonin); diabetic microvascular and macrovascular complications. Gynecologic: endometrial hyperplasia versus carcinoma; ovarian serous, mucinous, germ cell, sex cord-stromal. Breast: fibroadenoma, ductal carcinoma in situ, invasive ductal and lobular. Neuro: glioblastoma (pseudopalisading necrosis), meningioma, metastases. Skin: melanoma Breslow thickness. Bone: osteosarcoma, Ewing, chondrosarcoma.
Traps
Questions exploit "most common" versus "most common cause of death," site-specific histology, and overlapping patterns (Crohn vs ulcerative colitis; benign versus malignant thyroid).
Rule of thumb: in the colon, right-sided cancers present with iron-deficiency anemia and a mass; left-sided cancers obstruct.
Worked example: a peripheral lung mass in a nonsmoker is more likely adenocarcinoma, but never exclude squamous cell carcinoma by location alone - histology and immunohistochemistry decide.