Diagnostic Imaging Interpretation Flashcards

A 58-year-old patient presents with chronic low back pain. MRI of the lumbar spine reveals a disc herniation at L4-L5 with a Modic Type II endplate change. Which pathophysiological process does this finding represent?

Answer: Fatty marrow conversion within the vertebral endplate following chronic disc degeneration

Modic Type II changes represent fatty marrow conversion (yellow marrow replacement) within the vertebral endplates. They appear hyperintense on T1 and iso- to slightly hyperintense on T2 sequences. This contrasts with Type I (inflammatory edema: hypointense T1, hyperintense T2) and Type III (sclerosis: hypointense on both). Type II is associated with chronic degenerative disc disease and a relatively stable, non-acute process.

On a chest radiograph, you note a density at the right hilum that appears to 'disappear' into the mediastinum when traced superiorly. This hilum overlay sign being negative (i.e., the mass is NOT separable from the hilum) most strongly suggests the density is located in which anatomical region?

Answer: Within the hilum itself, arising from hilar vasculature or lymph nodes

The hilum overlay sign helps localize masses relative to the hilum. When a mass is in the anterior or posterior mediastinum, the hilar vessels remain visible through or separate from the mass (positive overlay sign). When the mass itself is hilar in origin — arising from lymph nodes or pulmonary vessels — the hilar vessels are obliterated and the mass cannot be separated from the hilum (negative overlay sign), confirming true hilar location.

A patient undergoes a nuclear medicine bone scan and demonstrates a 'superscan' pattern. Which of the following conditions is LEAST likely to produce this finding?

Answer: Multiple myeloma with purely lytic lesions and no osteoblastic response

A superscan on bone scintigraphy shows diffusely increased skeletal uptake with absent or markedly reduced renal and soft-tissue activity, creating an apparently 'normal' but abnormally intense image. It occurs when osteoblastic activity is globally elevated — as in widespread osteoblastic metastases (e.g., prostate cancer), metabolic bone disease (renal osteodystrophy, hyperparathyroidism), or diffuse Paget disease. Multiple myeloma classically produces purely lytic lesions that stimulate no osteoblastic response; consequently, bone scan is often falsely negative and a superscan pattern would not be expected.

On CT angiography of the chest, a pulmonary embolism is identified in the right lower lobe artery. Concurrently, you notice the interventricular septum is bowed toward the left ventricle and the right ventricle diameter exceeds the left. Which additional finding would MOST specifically indicate right ventricular pressure overload rather than simply volume overload?

Answer: Flattening of the interventricular septum during systole rather than diastole

Septal flattening during systole (the D-sign on short-axis views) is the hallmark of right ventricular pressure overload, because the RV must generate elevated pressures throughout systole to overcome pulmonary vascular resistance, pushing the septum leftward during the systolic phase. Volume overload causes septal bowing primarily during diastole (when RV is filling). Reflux into the IVC and hepatic veins indicates severe tricuspid regurgitation or RV failure rather than pure pressure overload. Main PA dilation and RV:LV ratio >1 are supportive but less specific for differentiating pressure vs. volume overload.

An MRI brain with gadolinium shows a ring-enhancing lesion at the gray-white matter junction in an immunocompetent 45-year-old with new-onset seizures. Diffusion-weighted imaging (DWI) demonstrates restricted diffusion within the ring. Which diagnosis does this DWI pattern MOST favor compared to a lesion with facilitated diffusion in the center?

Answer: Pyogenic brain abscess with pus in the core

Restricted diffusion (high signal on DWI, low ADC) within the center of a ring-enhancing lesion is the imaging hallmark of a pyogenic brain abscess. The thick pus contains densely packed bacteria, inflammatory cells, and necrotic debris that restrict water molecule movement. High-grade gliomas and metastases typically show facilitated diffusion (high ADC) in their necrotic cores because liquefactive necrosis allows free water movement. This DWI pattern is a critical discriminator that can prevent unnecessary biopsy of an infectious lesion in an otherwise immunocompetent host.

A fluoroscopic upper GI study with water-soluble contrast demonstrates extravasation at the gastroesophageal junction in a patient who had forceful vomiting. The leak is small and contained within the mediastinum. Compared to a free pleural leak, which of the following management principles applies MOST directly to this specific scenario?

Answer: Selected patients with contained mediastinal perforation may be managed conservatively with nil-per-os, antibiotics, and parenteral nutrition under close monitoring

Boerhaave syndrome (spontaneous esophageal perforation) classically carries high mortality, but the clinical approach is nuanced. Contained mediastinal perforations — with no free pleural or peritoneal spillage, minimal symptoms, and no sepsis — identified early can be managed conservatively in select patients: nothing by mouth, broad-spectrum antibiotics, proton pump inhibition, and total parenteral nutrition with serial imaging. Free thoracic leaks or perforations with sepsis require urgent surgical or endoscopic intervention. Barium is contraindicated in suspected perforation due to barium mediastinitis; water-soluble contrast is used first (as stated in the scenario). Nasogastric tube placement into the perforation would worsen the injury.