ABR cheat sheet

BI-RADS: 0 incomplete (needs additional imaging); 1 negative; 2 benign; 3 probably benign (<2% malignancy, 6-month follow-up); 4 suspicious (4A 2-10%, 4B 10-50%, 4C 50-95%); 5 highly suggestive (>=95%); 6 biopsy-proven malignancy.

Mass margins ranked by suspicion: circumscribed < obscured < microlobulated < indistinct < spiculated; spiculated margins carry the highest suspicion.

Simple cyst on ultrasound: anechoic, circumscribed, imperceptible wall, posterior acoustic enhancement; no aspiration or follow-up needed.

Coarse popcorn calcification suggests an involuting fibroadenoma; amorphous, pleomorphic, or fine linear branching calcification raises concern for DCIS.

Extremely dense breast tissue lowers mammographic sensitivity and independently increases breast cancer risk; supplemental ultrasound or MRI may be added.

ACR recommends annual screening mammography beginning at age 40 for average-risk women.

Breast MRI has the highest sensitivity of any modality; accepted indications include BRCA mutation, extent-of-disease evaluation, and occult primary presenting with axillary metastases.

Architectural distortion without a visible mass is suspicious for malignancy and generally requires biopsy rather than short-interval follow-up.

Sentinel lymph node biopsy uses radiolabeled colloid and/or blue dye and is standard for clinically node-negative invasive breast cancer.

Late gadolinium enhancement confined to the subendocardium in a coronary territory indicates ischemic injury; mid-wall or epicardial enhancement suggests nonischemic cardiomyopathy.

Cardiac amyloidosis shows diffuse subendocardial LGE with abnormal myocardial nulling and elevated native T1; cardiac sarcoid shows focal FDG uptake with matched perfusion defects.

Stanford type A dissection involves the ascending aorta and is a surgical emergency; type B spares the ascending aorta and is usually managed medically.

Acute intramural hematoma appears as a crescentic high T1 signal on noncontrast MRI; acute hematoma measures roughly 40-60 HU on CT.

In acute pulmonary embolism, an RV/LV diameter ratio >1.0 with septal bowing indicates right ventricular strain.

Coronary CTA has a high negative predictive value in low-to-intermediate pretest probability; heavy calcification reduces specificity.

Abdominal aortic aneurysm repair is generally offered at diameter >=5.5 cm in men or growth >1 cm per year.

Simple pericardial fluid attenuates near 0-20 HU; higher attenuation suggests hemopericardium or exudate.

Agatston calcium scoring is performed without contrast; a score of 0 confers a very low risk of obstructive coronary disease.

LI-RADS LR-5 (definite HCC) requires arterial phase hyperenhancement with washout and/or enhancing capsule in a cirrhotic liver, allowing treatment without biopsy.

Hepatic hemangioma: peripheral nodular enhancement with centripetal fill-in and blood-pool signal on delayed phases.

Focal nodular hyperplasia: arterial hyperenhancement with a central scar that enhances on delayed imaging; no treatment is required.

Caliber thresholds: small bowel >3 cm, colon >6 cm, cecum >9 cm (cecal diameter near 9 cm signals impending perforation).

Acute appendicitis: appendix diameter >6 mm with periappendiceal fat stranding and wall enhancement.

Pneumatosis intestinalis with portomesenteric venous gas suggests transmural bowel ischemia and is more specific than gas alone.

Primary sclerosing cholangitis: multifocal strictures with beading of intrahepatic and extrahepatic bile ducts.

Crohn disease is transmural with skip lesions; ulcerative colitis is continuous, mucosal-based, and begins in the rectum.

Acute pancreatitis: CT is most accurate after 72 hours for detecting necrosis; the Atlanta classification separates interstitial edematous from necrotizing disease.

Bosniak classification: I simple benign cyst; II few thin septa; IIF needs follow-up; III requires surgery or biopsy; IV has enhancing solid components and is usually malignant.

Adrenal nodule <10 HU on unenhanced CT indicates a lipid-rich adenoma; absolute washout >60% at 15 minutes also supports adenoma.

Renal cell carcinoma: clear cell subtype is hypervascular with avid enhancement; papillary subtype is hypovascular and may mimic a cyst.

PI-RADS 4-5 lesions warrant targeted biopsy; PSA density and diffusion-weighted imaging strongly influence suspicion.

Testicular torsion: absent or decreased Doppler flow with the whirlpool sign of the cord; surgical detorsion is time-critical.

Mature cystic teratoma: fat density or fat signal with calcification or a Rokitansky nodule; bilateral in about 10-15% of cases.

Nephrogenic systemic fibrosis risk is greatest with group I linear gadolinium agents in patients with eGFR <30 mL/min per 1.73 m2.

Hydronephrosis with a dilated ureter indicates obstruction at or below the ureterovesical junction; abrupt transition favors stone or stricture.

Bladder cancer with detrusor muscle invasion (stage T2) generally requires cystectomy; non-muscle-invasive disease is managed with transurethral resection.

TIPS creates a portosystemic shunt between a hepatic vein and portal vein branch; the target post-procedure portosystemic gradient is <12 mmHg.

Postembolization syndrome (pain, fever, nausea after embolization) is expected and managed supportively, but must be distinguished from abscess.

Uterine fibroid embolization requires bilateral uterine artery catheterization; ovarian reserve and fertility are usually preserved.

Percutaneous drainage is generally indicated for abscess collections larger than 3 cm; smaller collections may resolve with antibiotics alone.

TACE and Y-90 radioembolization are locoregional options for intermediate-stage HCC, used for bridging, downstaging, or palliation.

IVC filters are placed when anticoagulation is contraindicated or has failed; retrievable filters should be removed once protection is no longer needed.

Lower GI bleeding: CTA can localize hemorrhage at rates near 0.3-0.5 mL/min; empiric embolization is performed when angiography shows extravasation.

Access-site complications include pseudoaneurysm, arteriovenous fistula, and retroperitoneal hematoma; pseudoaneurysms may be treated with thrombin injection or covered stents.

Bone lesion by location: epiphysis (chondroblastoma, giant cell tumor); metaphysis (osteosarcoma, nonossifying fibroma); diaphysis (Ewing sarcoma, lymphoma).

Osteosarcoma: aggressive periosteal reaction with sunburst pattern and Codman triangle in the metaphysis of a young patient.

Chondrosarcoma: rings-and-arcs chondroid matrix calcification; peak incidence in adults over 40 years.

Giant cell tumor: eccentric lytic soap-bubble lesion extending to the subarticular surface in a skeletally mature patient aged 20-40.

Osteomyelitis: MRI is the earliest study, showing marrow T1 hypointensity and T2 hyperintensity with enhancement; radiographic changes lag 10-14 days.

DXA: T-score <= -2.5 at spine, total hip, or femoral neck defines osteoporosis; -1.0 to -2.5 defines osteopenia.

Meniscal tear: grade 3 intrasubstance signal contacting an articular surface; grade 1-2 signal is degenerative and usually asymptomatic.

Gout shows juxta-articular erosions with overhanging edges and preserved joint space; CPPD shows chondrocalcinosis.

Rotator cuff tear: the supraspinatus tendon is most commonly involved; a full-thickness tear shows a fluid-filled gap on MRI.

Acute infarct: restricted diffusion on DWI with corresponding ADC hypointensity within minutes; noncontrast CT is often normal early.

Hyperdense MCA sign indicates acute intraluminal thrombus; an ASPECTS score <=6 indicates a large established infarct core.

Hypertensive hemorrhage typical locations: basal ganglia, thalamus, pons, and cerebellum; acute blood is hyperdense on CT.

Epidural hematoma is biconvex and limited by cranial sutures (usually arterial); subdural hematoma is crescentic and crosses sutures (usually venous).

Multiple sclerosis: lesions disseminated in space and time in periventricular, juxtacortical, infratentorial, and spinal cord regions; Dawson fingers are perpendicular perivenular plaques.

Meningioma: extra-axial mass with a dural tail and homogeneous enhancement; MR spectroscopy of tumors shows elevated choline and reduced NAA.

In HIV, multiple ring-enhancing basal ganglia lesions favor toxoplasmosis; periventricular or ependymal spread favors primary CNS lymphoma.

Normal pressure hydrocephalus: ventriculomegaly out of proportion to sulcal enlargement with a callosal angle <90 degrees.

Pituitary macroadenoma exceeds 10 mm, expands the sella, and may invade the cavernous sinus (Knosp grading).

Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP); predictive values depend on disease prevalence in the tested population.

Positive likelihood ratio = sensitivity/(1 - specificity); values >10 substantially increase post-test probability.

ALARA: keep radiation dose as low as reasonably achievable while preserving diagnostic adequacy, using time, distance, shielding, and protocol optimization.

CT dose descriptors: CTDIvol reflects dose per slice; DLP equals CTDIvol times scan length; effective dose is expressed in mSv.

Structured reporting and appropriateness systems (BI-RADS, LI-RADS, PI-RADS, Lung-RADS, ACR Appropriateness Criteria) standardize practice and communication.

Gadolinium: avoid group I linear agents when eGFR <30 mL/min due to NSF risk; hold metformin if eGFR <30.

Informed consent requires the indication, risks, benefits, alternatives, and an opportunity for the patient to ask questions.

Satisfaction of search is a perceptual error in which finding one abnormality stops the search for additional findings.

Tc-99m MDP bone scan reflects osteoblastic activity; a superscan shows diffusely increased skeletal uptake with faint or absent renal activity.

High-probability V/Q scan: two or more mismatched segmental or subsegmental perfusion defects with normal ventilation.

HIDA scan: nonvisualization of the gallbladder beyond 4 hours (including after morphine augmentation) indicates acute cholecystitis.

FDG-PET: SUVmax is a semiquantitative measure of glucose metabolism used in staging lymphoma and lung cancer and in assessing treatment response.

Dual-phase sestamibi parathyroid imaging: both thyroid and parathyroid take up tracer early, but the adenoma retains activity as thyroid washes out.

I-131 is used to treat Graves disease and differentiated thyroid cancer; pregnancy and lactation are contraindications.

MAG3 renography with furosemide distinguishes obstructive from nonobstructive hydronephrosis by the drainage half-time.

Radiation exposure is reduced by time, distance, and shielding; dose rate decreases with the inverse square of distance.

Hypertrophic pyloric stenosis: nonbilious projectile vomiting at 3-6 weeks; pyloric muscle thickness >3 mm and canal length >14 mm.

Intussusception: ages 6 months to 3 years with colicky pain; target sign on ultrasound; ileocolic intussusception is reduced with air or contrast enema.

Malrotation with volvulus: bilious emesis in a neonate; upper GI series shows a corkscrew duodenum and is a surgical emergency.

Necrotizing enterocolitis: prematurity, feeding intolerance, pneumatosis intestinalis, and portal venous gas.

Nonaccidental trauma: metaphyseal corner (classic metaphyseal) fractures, posterior rib fractures, and fractures of differing ages.

Croup produces a steeple sign on frontal radiograph; epiglottitis produces a thumb sign with a thickened aryepiglottic fold.

Medulloblastoma: midline cerebellar mass with restricted diffusion; pilocytic astrocytoma: cyst with an enhancing mural nodule.

Developmental dysplasia of the hip: ultrasound screening before 6 months of age; alpha angle <60 degrees is abnormal.

Wilms tumor is an intrarenal mass that displaces and distorts the kidney; neuroblastoma is extrarenal and frequently calcifies.

USPSTF lung cancer screening: annual low-dose CT for adults aged 50-80 with >=20 pack-year history who currently smoke or quit within 15 years.

Lung-RADS: category 1-2 continues annual screening; category 4B (solid component >=8 mm) prompts immediate diagnostic workup.

Sarcoidosis: bilateral symmetric hilar and right paratracheal adenopathy (Garland triad) with perilymphatic nodules.

Usual interstitial pneumonia: peripheral, basal, subpleural honeycombing with traction bronchiectasis, characteristic of idiopathic pulmonary fibrosis.

Pulmonary embolism: Hampton hump (peripheral wedge-shaped opacity) and Westermark sign (focal oligemia) are late and infrequent plain film signs.

The silhouette sign localizes an opacity to a structure sharing a radiographic border with the lung (e.g., lingula obscures the left heart border).

Upper-lobe cavitary lesions suggest tuberculosis, squamous cell carcinoma, or granulomatosis with polyangiitis; dependent cavitation suggests aspiration.

Pneumothorax on a supine radiograph: deep sulcus sign; tension pneumothorax shows mediastinal shift away from the affected side.

Gallstone: echogenic focus with posterior acoustic shadowing; a simple cyst shows posterior acoustic enhancement.

Acute cholecystitis: wall thickness >3 mm, pericholecystic fluid, sonographic Murphy sign, and a distended gallbladder with sludge or stones.

Deep vein thrombosis: failure of the vein to compress with transducer pressure, with echogenic thrombus and diminished phasic flow.

Testicular torsion: absent or diminished Doppler flow with a whirlpool sign of the spermatic cord; salvage declines markedly after about 6 hours.

FAST exam windows: subxiphoid pericardial, right upper quadrant (Morison pouch), left upper quadrant (splenorenal), and suprapubic views for free fluid.

Thyroid nodules: TIRADS assigns risk using composition, echogenicity, shape (taller-than-wide), margins, and echogenic foci such as microcalcifications.

First trimester: crown-rump length dates pregnancy; nuchal translucency is measured at 11-14 weeks for aneuploidy screening.

Ectopic pregnancy: empty uterus with an adnexal mass or free fluid; a gestational sac containing a yolk sac outside the uterus is diagnostic.

Resistive index = (peak systolic - end diastolic)/peak systolic velocity; elevated RI indicates increased distal vascular resistance.