An 58 year old intravenous drug user presents several days after attempting to inject in to the back of his hand. There is a fluctuant red hot swelling over the dorsum of the hand and wrist and you are asked whether this is a tendon sheath collection.
Describe and interpret these scans
Image 1: Dorsum of left wrist longitudinal section.
Image 2: Dorsum of left wrist transverse section.
There is a large superficial abscess lying above the tendons and tendon sheath that contains gas. Beginning superficially the subcutaneous fat is echogenic and inflamed. In the most superficial aspects of the collection are small very bright foci typical of gas. Deeper the heterogeneous predominantly hypoechoic abscess is seen. Deep to the main collection is a thin layer of subcutaneous fat separating it from the tendon sheaths and tendons themselves. Deeper still the cortex of underlying carpal bones are seen.
Wrist abscess containing gas
The patient was given broad spectrum antibiotics before going to the operating theatre for washout and exploration.
Gas in soft tissue infections raises the spectre of gas forming organisms with the requirement for urgent extensive debridement of necrotic tissue along with appropriate antibiotic therapy.
Abscesses associated with intravenous drug use are often polymicrobial with anaerobic organisms as well as aerobic gram-positive cocci. Users often inject small amounts of air which can appear dramatic on ultrasound – so the gas is not always from gas forming organisms. A high index of suspicion, urgent exploration, drainage and if necessary debridement, along with antibiotic cover is essential.