Case 372:   Abscess (pyogenic)

Diagnostic Category:

Clinical Presentation:

85 year-old man with fever. Sonographic search for source of fever.

US: Gas containing, multiloculated, mimicking neoplasm with CEUS

Imaging Findings:

Gray-scale ultrasound demonstrates fluid collection in segment 3, dominated by numerous small gas inclusions (echogenic foci with ring down artifacts). Color Doppler echoes are a result of gas artifacts, there is no increased vascularity. There are several other smaller loculations more superiorly located in segment 2.

Contrast enhanced ultrasound (CEUS) early arterial phase demonstrates a hypervascular capsule surrounding the collection in segment 3 with suggestion of a subtle hypoechoic rim peripherally, suggestive of perifocal edema.

Parenchyma anterior to the collection in segment 3 as well as more superiorly in segment 2 is less vascular than parenchyma more laterally in segment 4, typically due to phlegmon and numerous microabscesses, mimicking washout of a malignancy on later venous phase.

Note that appearance of abscesses and surrounding microabscesses may mimic malignant necrotic masses with infiltrative growth pattern particularly on late venous phase.

Parenchyma in segment 4 is hypervascular on arterial phase due to inflammation in adjacent segments 2 and 3.

Courtesy Dr. Gerd Stuckmann, Institute for Radiology and Nuclear Medicine, Kantonsspital Winterthur,  Switzerland.