AOBR Radiology cheat sheet

Adenoma vs hyperplasia on adrenal CT: adenomas are lipid-rich with unenhanced attenuation <10 HU; absolute washout >60% and relative washout >40% at 15 min favor adenoma.

Bosniak classification: category I and II cysts are benign (simple, thin-walled, hairline septa, calcification); IIF requires follow-up; III and IV are surgical.

Pulmonary nodule: solid nodules ≥8 mm warrant PET/CT or biopsy when risk is intermediate-high; subsolid nodules are followed with longer intervals because of indolent growth.

Fleischner-style size rules: solid nodules <6 mm in low-risk patients generally need no routine follow-up; ≥8 mm solid nodules require further evaluation.

Fat-containing renal mass: angiomyolipoma shows macroscopic fat (<-20 HU); a fat-containing mass with calcification or bone raises concern for RCC with osseous metaplasia.

Bowel obstruction on CT: transition point with dilated proximal and collapsed distal bowel; closed-loop obstruction shows a U- or C-shaped fluid-filled loop with mesenteric whirl.

Thyroid nodule ultrasound: suspicious features are hypoechogenicity, irregular margins, microcalcifications, taller-than-wide shape, and extrathyroidal extension; each increases malignancy risk.

Cystic pancreatic lesion: main-duct IPMN involves the main pancreatic duct ≥5 mm and carries high malignant potential; branch-duct IPMN is followed by size criteria.

Hepatic hemangioma: peripheral nodular enhancement with centripetal fill-in on delayed phases; MRI shows lightbulb T2 hyperintensity.

Transjugular intrahepatic portosystemic shunt (TIPS): indicated for refractory variceal bleeding or refractory ascites; contraindicated in severe encephalopathy, right heart failure, and pulmonary hypertension.

HCC treatment: Barcelona Clinic Liver Cancer (BCLC) staging guides therapy; ablation for early small tumors, transarterial chemoembolization (TACE) for intermediate multifocal disease.

Uterine fibroid embolization (UFE): particles are injected into both uterine arteries; ovarian artery supply and collateral flow must be assessed; pregnancy and active infection are contraindications.

Percutaneous drainage: abscesses >3 cm are typically drained with catheter; smaller collections may respond to antibiotics alone.

Central venous access: the right internal jugular vein is preferred for large-bore catheters because it provides a straight course to the SVC and lower pneumothorax risk than subclavian.

Sclerotherapy of varices: sodium tetradecyl sulfate or polidocanol are common agents; foam preparation increases surface contact and reduces required volume.

Embolization materials: coils for focal arterial occlusion; particles for capillary-level embolization; glue and Onyx for high-flow or nidus lesions.

Complications of TACE: postembolization syndrome (fever, pain, nausea) is expected; hepatic abscess risk rises with biliary-enteric anastomosis or sphincterotomy.

Acute ischemic stroke: noncontrast CT excludes hemorrhage; ASPECTS score quantifies early ischemic change; large-vessel occlusion requires CT angiography and may qualify for thrombectomy.

Hemorrhagic transformation: petechial hemorrhage (HI1/HI2) versus parenchymal hematoma (PH1/PH2); PH2 with mass effect worsens prognosis.

Subarachnoid hemorrhage: hyperdense basal cisterns on noncontrast CT; if CT is negative and suspicion high, lumbar puncture shows xanthochromia.

Multiple sclerosis: dissemination in space and time; periventricular, juxtacortical, infratentorial, and spinal cord lesions; Dawson's fingers on sagittal FLAIR.

Brain abscess: ring-enhancing lesion with restricted diffusion (dark ADC) centrally, distinguishing it from most necrotic tumors.

Cerebral venous sinus thrombosis: empty delta sign on contrast CT; hyperdense sinus on noncontrast CT; MR venography confirms.

Spinal cord compression: cord edema and T2 hyperintensity; emergent MRI and steroids; epidural abscess shows peripheral enhancement.

Glioblastoma: irregular thick ring enhancement, central necrosis, and surrounding edema; IDH-wildtype and MGMT promoter status guide therapy.

Hypertrophic pyloric stenosis: ultrasound shows pyloric muscle thickness >3 mm and channel length >15 mm; occurs at 3-6 weeks of age with nonbilious projectile vomiting.

Intussusception: target sign on ultrasound; ileocolic most common; air or contrast enema is both diagnostic and therapeutic when no perforation or peritonitis.

Malrotation with midgut volvulus: upper GI series shows corkscrew duodenum; surgical emergency; bilious vomiting in a neonate is a red flag.

Necrotizing enterocolitis: pneumatosis intestinalis, portal venous gas, and pneumoperitoneum; occurs in premature infants; perforation requires surgery.

Developmental dysplasia of the hip: ultrasound before ossification; alpha angle <60 degrees or femoral head coverage <50% is abnormal; Pavlik harness for early cases.

Pediatric bone lesions: osteosarcoma shows sunburst periosteal reaction and Codman triangle; Ewing sarcoma is diaphyseal with onion-skin periosteal reaction.

Wilms tumor vs neuroblastoma: Wilms arises from kidney and displaces it; neuroblastoma is adrenal, calcifies, and crosses the midline.

Pediatric radiation dose: use weight-based protocols and limit CT; ultrasound and MRI are preferred when feasible to reduce lifetime dose.

Alpha/beta model: BED = nd(1 + d/(alpha/beta)); tumor alpha/beta ~10 Gy, late normal tissue ~3 Gy; larger fraction size increases late toxicity.

Tumor control probability rises with dose; normal tissue complication probability rises with dose and volume; treatment planning balances the two.

Head and neck cancer: concurrent chemoradiation improves survival; dose ~70 Gy for gross disease, 60-66 Gy for high-risk postoperative beds.

Prostate cancer: dose escalation improves biochemical control; hypofractionation uses fewer, larger fractions with similar late toxicity when planned carefully.

Breast conservation: whole-breast radiation after lumpectomy reduces local recurrence; accelerated partial breast irradiation is an option for selected early-stage patients.

Lung SBRT: stereotactic body radiation for early-stage NSCLC; high BED per fraction; central tumors carry higher toxicity risk than peripheral tumors.

Spinal cord tolerance: conventional fractionation limits cord dose to about 45-50 Gy; exceed only with strong justification and careful planning.

Radiation pneumonitis: typically 1-6 months after thoracic radiation; risk rises with mean lung dose and V20; steroids for symptomatic cases.