Diagnostic Imaging & Radiology Flashcards

A 45-year-old patient undergoes MRI of the liver. On T1-weighted images, a lesion appears hyperintense before contrast administration and loses signal intensity on out-of-phase (opposed-phase) imaging compared to in-phase imaging. What does this finding most specifically indicate?

Answer: Intracellular lipid (fat) within the lesion

Signal dropout on opposed-phase (out-of-phase) T1 imaging compared to in-phase imaging is the hallmark of intracellular lipid (microscopic fat). This occurs due to chemical shift artifact — when fat and water protons coexist within the same voxel, they cancel each other on opposed-phase images. Hemorrhage and proteinaceous fluid can both appear T1 hyperintense but do NOT show signal dropout on opposed-phase imaging because they lack intracellular fat. Calcifications are typically hypointense on all MRI sequences.

During fluoroscopy-guided barium swallow, a patient demonstrates a posterior indentation on the esophagus at the level of the aortic arch with normal swallowing function. CT confirms a vascular anomaly. Which embryological remnant is most likely responsible?

Answer: Aberrant right subclavian artery (arteria lusoria)

An aberrant right subclavian artery (arteria lusoria) arises as the last branch of a left-sided aortic arch, coursing posterior to the esophagus to reach the right upper extremity. This creates a characteristic posterior indentation on the esophagus on barium swallow. It is the most common aortic arch anomaly (~0.5% of population) and is usually asymptomatic ('dysphagia lusoria' when symptomatic). A double aortic arch creates both anterior and posterior impressions. Right-sided arch with mirror-image branching rarely causes dysphagia and is strongly associated with congenital heart disease.

A radiologist reviewing a chest CT in a 60-year-old smoker notes a 8 mm solid pulmonary nodule in the right upper lobe. According to Fleischner Society 2017 guidelines for high-risk patients, what is the recommended follow-up strategy?

Answer: CT at 6–12 months; if stable, CT at 18–24 months

Per Fleischner Society 2017 guidelines, for high-risk patients with a solid nodule 6–8 mm, the recommendation is CT at 6–12 months, then if stable, CT at 18–24 months. The 3-month interval is typically reserved for nodules with suspicious morphology or very high clinical suspicion. No follow-up (option A) applies to nodules <6 mm in high-risk or <6 mm in average-risk patients. Option C (3 months then 18–24 months) is incorrect — the initial follow-up window for this size in high-risk is 6–12 months.

On a non-contrast CT of the head, a 70-year-old patient with acute neurological deficits shows a hyperdense lesion in the left sylvian fissure region. MRI DWI sequence shows no restricted diffusion. What is the most likely diagnosis?

Answer: Subarachnoid hemorrhage

Hyperdensity in the sylvian fissure on non-contrast CT is characteristic of subarachnoid hemorrhage (SAH), as blood tracks along the cisterns and sulci. The absence of restricted diffusion on DWI effectively excludes acute ischemic stroke, which would show marked DWI restriction in the MCA territory. Subdural hematomas appear as crescentic collections along the inner calvaria, not in cisterns. Cerebral venous sinus thrombosis can be hyperdense but appears in dural sinuses, not the sylvian fissure, and may show DWI changes in venous infarction.

A nuclear medicine scan using Tc-99m sestamibi is performed for myocardial perfusion imaging. Images show a fixed defect in the inferior wall that is present on both stress and rest images with no reversibility. Which interpretation and clinical correlation is MOST accurate?

Answer: Myocardial scar — non-viable infarcted tissue

A fixed defect (present on both stress and rest) with no reversibility on Tc-99m sestamibi imaging represents non-viable myocardial scar (prior infarction). Hibernating myocardium, by definition, shows a fixed or reduced perfusion at rest but demonstrates viability on FDG-PET (viable but chronically hypoperfused). Stunned myocardium would have normal resting perfusion post-stress with recovery over time. Diaphragmatic attenuation artifact classically affects the inferior wall but is distinguished from true fixed defects by prone imaging — however the question specifies this is present on rest images, and clinical context of fixed non-reversible defect points to scar over artifact as the primary interpretation.

A radiologist reviews a mammogram showing a mass with spiculated margins, architectural distortion, and associated fine pleomorphic calcifications. The ACR BI-RADS category assigned is 5. Which statement about the subsequent management is MOST accurate under standard clinical guidelines?

Answer: Tissue biopsy is recommended with malignancy probability >95%

ACR BI-RADS category 5 indicates findings that are 'highly suggestive of malignancy' with a positive predictive value >95%. The recommended action is tissue diagnosis (biopsy) — NOT watchful waiting or short-interval follow-up (which applies to BI-RADS 3). MRI may be used as an adjunct for extent of disease but is not a prerequisite before biopsy. Core needle biopsy is preferred over fine needle aspiration (FNA) for solid spiculated masses because it provides histological architecture and receptor status — FNA only yields cytology. Short-interval follow-up (option A) is for BI-RADS 3 lesions (<2% malignancy risk).