Diagnostic Imaging & Radiology Flashcards

A 45-year-old woman undergoes MRI of the liver using hepatobiliary contrast agent (gadoxetate disodium). On the 20-minute hepatobiliary phase image, a lesion shows absent uptake compared to surrounding liver parenchyma. Which of the following diagnoses is MOST consistent with this finding?

Answer: Hepatocellular carcinoma (HCC)

Gadoxetate disodium (Primovist/Eovist) is taken up by functioning hepatocytes via OATP1B1/1B3 transporters. HCC cells typically downregulate these transporters, resulting in absent or reduced uptake on the hepatobiliary phase — appearing hypointense. FNH retains functioning hepatocytes and classically shows iso- or hyperintense signal on the hepatobiliary phase. Hemangiomas lack hepatocytes entirely but also appear hypointense; however, their characteristic enhancement pattern on dynamic phases (peripheral nodular enhancement with centripetal fill-in) distinguishes them. Regenerative nodules in cirrhosis generally retain OATP expression. The combination of arterial hyperenhancement and hepatobiliary phase washout/hypointensity is a major LI-RADS criterion for HCC.

On a chest CT performed without contrast, a pulmonary nodule measures 6 mm in diameter and has an attenuation value of -120 HU. Which Fleischner Society recommendation is MOST appropriate for an average-risk patient?

Answer: No further follow-up required for this incidental finding

An attenuation value of -120 HU indicates fat density, classifying this nodule as a hamartoma or lipoid lesion — almost certainly benign. The Fleischner Society guidelines specifically exclude pure fat-containing nodules and calcified nodules from surveillance recommendations because they carry negligible malignancy risk. For a 6 mm solid nodule in an average-risk patient, follow-up CT at 6–12 months would typically be recommended, but the fat content changes the management entirely: no follow-up is needed. PET-CT and biopsy would be inappropriate and unnecessarily invasive.

During fluoroscopy-guided percutaneous transhepatic cholangiography (PTC), the interventional radiologist notes that contrast injected into a dilated biliary system tracks into a hepatic vein rather than the biliary tree. What is the MOST likely complication that has occurred?

Answer: Biliovenous fistula formation

When contrast injected during PTC tracks into a hepatic vein, a biliovenous (or bilio-hepatic venous) fistula has been created — an inadvertent communication between the biliary system and the hepatic venous system. This occurs when the needle punctures a hepatic vein along the access tract. It is typically managed conservatively with an indwelling biliary drain, as the fistula often closes once biliary decompression reduces biliary pressure. Portal vein injury would show portal venous flow patterns; arteriovenous malformations are pre-existing; hepatic artery pseudoaneurysm would present with arterial pulsatile flow on fluoroscopy and typically causes hemobilia.

A 62-year-old man with known multiple myeloma undergoes whole-body low-dose CT as part of staging. Compared to conventional skeletal survey (plain radiographs), which statement BEST describes the role of low-dose CT?

Answer: Low-dose CT detects lytic lesions earlier and is now preferred over skeletal survey per IMWG guidelines

The International Myeloma Working Group (IMWG) updated guidelines recommend whole-body low-dose CT (WBLDCT) as the new standard for myeloma bone disease assessment, replacing the conventional skeletal survey. WBLDCT detects lytic lesions requiring only 10–30% trabecular bone loss (compared to 30–50% for plain radiographs), significantly improving sensitivity. While MRI is superior for marrow infiltration assessment (particularly spine and pelvis), WBLDCT provides a rapid whole-body evaluation with better sensitivity than skeletal survey for cortical and trabecular lesions. PET-CT/FDG-PET is complementary and superior for extramedullary disease. The radiation dose of WBLDCT is similar to or lower than a full skeletal survey series.

A radiologist reviewing a fetal MRI at 28 weeks gestation identifies a posterior fossa cyst communicating with the fourth ventricle, complete vermian agenesis, and marked elevation of the tentorium cerebelli and torcular Herophili. What is the MOST accurate diagnosis?

Answer: Dandy-Walker malformation (DWM)

The triad of (1) posterior fossa cyst communicating with the fourth ventricle, (2) complete or partial vermian agenesis/hypoplasia, and (3) elevated tentorium and torcular Herophili (torcular-lambdoid inversion) is pathognomonic for Dandy-Walker malformation. Mega cisterna magna has a normal vermis and no communication with the fourth ventricle. Blake's pouch cyst shows vermian hypoplasia but the vermis is typically rotated superiorly rather than absent, and the tentorium is less dramatically elevated; it communicates with the fourth ventricle but represents a different embryological defect. Joubert syndrome is characterized by the 'molar tooth sign' on axial MRI (elongated superior cerebellar peduncles and a deep interpeduncular fossa) with vermian hypoplasia but does NOT have a posterior fossa cyst communicating with the fourth ventricle.

A nuclear medicine physician reviews a myocardial perfusion SPECT study and notes a fixed defect in the inferolateral wall that is present on both stress and rest images. The patient has no prior history of myocardial infarction. Which artifact or technical factor should be considered FIRST before concluding this represents scar tissue?

Answer: Lateral wall attenuation artifact from the lateral chest wall in female patients

In female patients, breast tissue attenuation is the most common cause of fixed anterior and anterolateral perfusion defects on SPECT MPI. However, the inferolateral wall is most commonly affected by left hemidiaphragm attenuation in male patients and can also be seen in females. The question specifies 'inferolateral' and 'no prior MI' — diaphragmatic attenuation typically affects the inferior wall in supine imaging. The lateral chest wall (breast tissue in women) creates a fixed defect in the lateral and anterolateral walls, while the inferolateral pattern can be caused by the lateral aspect of the diaphragm. Attenuation correction (CT-based or germanium-line source) and prone imaging are used to differentiate artifact from true infarction. Patient motion causes misregistration and smearing artifacts, not fixed photopenic defects. Compton scatter from liver typically causes inferior wall hot spots, not defects.