Misinterpretation of Silver Coated Wounds Dressing as Gastrograffin Bowel Leak: Case Report

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Suspecting this opacity may be secondary to the Silver coated dressing, the managing physician removed most layers of the Atrauman® Ag dressing, leaving in only one sheet of the dressing and the CT was repeated. Surprisingly the previously noted opacity disappeared completely despite the retained thin film as demonstrated in Figure 2.

Figure 2. Silver Coated dressing was taken out from the anterior abdominal wall wound

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Case 2: A 23 year old male motor vehicle accident victim sustained splenic injury and perianal laceration. The perianal wound was packed with ACTICOAT (Smith & Nephew) silver dressing. The Abdominal & Pelvis CT scan reported a contrast leak (Figure 3a).The dressing was removed in order to delineate a true gastrograffin contrast leak from an artifact.

Figure 3. a: Silver coated dressing in the perirectal cavity with gastrograffin in rectum; b: Silver coated dressing taken out and packed with Gauze; still Gastrograffin is seen in rectum

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The third case is that of a patient who developed a severe wound infection post laparotomy with small bowel resection for bowel injury in a motor vehicle accident. The wound was managed with AQUACEL® Ag silver dressing (Conva Tec). A CT scan was done to rule out an intra-abdominal abscess. Again, we observed the silver dressing resulting in an opacity at the wound bed as seen in Figure 4. In this case Oral Contrast media was diluted but the dressing gave a Hounsfield Number close to gastrograffin contrast.

Figure 4. Anterior abdominal wound is packed with silver coated dressing. Clearly there is air around the dressing which may lead to misinterpretation

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2. Discussion

As a topical antimicrobial agent, silver has been used for hundreds of years in wound care. Silver has been employed in the prevention & management of wound infection in multiple forms & configurations; its solid elemental form (e.g. silver wire placed in wounds), as silver salt solutions used to cleanse wounds (e.g. silver nitrate solution) ^[1], and more recently as creams or ointments containing a silver–antibiotic compound (silver sulfadiazine cream) ^[2].

In recent years, a wide range of wound dressings containing elemental silver or a silver-releasing compound have been developed ^[3]. These dressings have overcome some of the problems associated with the first silver preparations. Namely, they are easier to apply, may provide sustained availability of silver, need less frequent dressing changes, in addition to providing additional benefits such as management of excessive exudate, maintenance of a moist wound environment and facilitation of autolytic debridement ^[4].

The first CT-images were produced in 1971 at Atkinson Morley’s Hospital in London. Sir Godfrey Hounsfield was awarded the Nobel Prize in Physiology/Medicine along with Allan McLeod Cormack in 1979 for their work with CT scans ^[5].

Man is based on water and surrounded by air. This was the background for creating the linear Hounsfield scale where water represents a value of 0 and air represents a value of -1000. The complete formula was given as:

Typical values for different elements and tissues range from -1000 to more than +1000, i.e. from air to bone respectively. Of importance is that fat is -100, muscles and blood have a value of approximately +40. This makes it possible to evaluate things that do not have a specific structure – a spherical mass may be composed of fat or other elements, benign vs. malignant. Fluid-containing cavities (cysts) may contain fluids that appear watery or have an attenuation corresponding to blood. The differentiation between these various elements is of significant importance to the managing physician ^[6].

The CT images are most commonly calculated on a 512 512 pixel matrix, although 256 x 256 and 1024 x 1024 matrices may also be used. The density of tissues is either measured by CT number or Hounsfield Unit as shown in table1. The Hounsfield number is a normalized value of the calculated x-ray absorption coefficient of a pixel in a computed tomogram. A normalized index of x-ray attenuation based on a scale of -1000 (air) to +1000 (bone), with water being 0; is employed in interpretation of CT imaging ^[7].

Table 1. The HU of common substances

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