Case 370:   Abscess (amebic)

Diagnostic Category:

Clinical Presentation:

39 year old man returning from a 3 year bike trip around the world (34.000km) and presenting with fevers (39.3°C), arthralgias, and chest and right abdominal pain. GOT (ALT) 130, GPT (AST) 156, AP 147 (<130nl), CRP >200, HB 13.9 (14.4 – 17.5g/dl), WBC 14.400 (neutrophils: 11.990, lymphocytes 950).

US: Five days after starting metronidazole - "double-rim" and "straight-border-sign" with CEUS

Imaging Findings:

Gray-scale ultrasound demonstrates a well-defined hypoechoic mass in segment 7 without posterior acoustic enhancement or Doppler flow.

Continuous rim enhancement represents the abscess capsule, which is surrounded by a thin rim of hypovascular edema ("double-rim sign"), typical for abscess, best seen on both arterial images.

Hepatic parenchyma in segments 7 and 8 is very hypervascular and similar to renal enhancement on arterial phases due to inflammation. Compare normal weak hepatic enhancement of uninvolved segments 5 and 6 on the top right corner of the arterial phase images, forming the "straight border sign", which demarcates the border between two vascular territories.

Reactive hyperperfusion due to inflammation may be limited to the involved segment only, to two segments supplied by the same arterial branch (as in this case) or could include the entire lobe.

This ultrasound exam was performed 5 days after empiric initiation of treatment with metronidazole to support treatment descision. Amebic abscess was confirmed after ultrasound guided fine needle aspiration.

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