Contents

• Introduction
• Gallery of Surgical objects
• Radiography
• CT
• MRI
• References

Introduction

Retention of surgical objects in the abdomen or pelvis occurs with a frequency of 1 in 100 to 5,000 operations, and accounts for 50% of malpractice claims for retained foreign bodies [1, 2]. A retained surgical sponge or swab is also known as a gossypiboma, derived from gossypium (Latin; cotton) and boma (Swahili; place of concealment). Clinically, retained sponges may be asymptomatic or result in a granulomatous response with abscess development, intestinal obstruction, or fistula formation. Radiologically, gossypibomas may be confused with post-operative collections or tumors, particularly with the increasing surgical use of absorbable haemostatic sponges to control hemorrhage. In order to provide accurate interpretation, radiologists need to be familiar with the imaging findings of both inadvertent and intentional postoperative surgical objects.

Key Points

• Plain radiographs performed intraoperatively or in the early postoperative period are often of suboptimal quality, and need to be carefully scrutinized to detect retained objects. Digital manipulation of soft-copy images may be helpful.
• Awareness of the typical radiological appearances is critical to the diagnosis of retained surgical sponges or swabs. Inadvertently retained sponges are often clinically unsuspected and may be first recognized at imaging. A high index of suspicion is required, because a history of an incorrect sponge count is frequently lacking and because a radio-opaque marker is not always visible.
• CT or MRI may be helpful in problematic cases.
• Intentional placement of absorbable hemostatic sponges is an increasingly common surgical technique, and these sponges may mimic an abscess or collection on post-operative CT. 

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Commonly Retained Surgical Objects

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Radiography

Plain radiographs are the most commonly used method to detect retained sponges. The clinical history cannot be relied upon to indicate the correct diagnosis; a normal sponge counts does not exclude the possibility of a retained sponge. In one series, the sponge count was reported as correct in 22 of 29 (76%) patients with retained sponges in the abdomen [2]. Most sponges are detectable because they incorporate a radio-opaque marker. The body of the sponge itself may be faintly radio-dense on ex-vivo radiographs, but is unlikely to be seen in vivo. Intra-operative or portable early post-operative radiographs may be of suboptimal quality, and hot-lighting of hard copy radiographs or digital magnification and manipulation of soft copy images may facilitate detection. The adequacy of the field of view should also be evaluated, with particular attention to partially imaged sponges at the periphery of the image. It is important to note that not all sponges have visible radio-opaque markers. In one series, 3 of 29 retained radio-opaque sponges lacked a visible radio-opaque marker [2].

The value of soft copy image manipulation is illustrated in this radiograph performed because of an incorrect sponge count in a 24 year old woman undergoing caesarean section.

(a) The original image settings result in a generally under penetrated film, and a questionable density (arrow) is faintly identified over the left sacral ala.	(b) After digital manipulation of the window and level, the marker (arrow) of a 4 x 4 in sponge is identified.

The importance of scrutinizing the periphery of the image is illustrated in this radiograph performed postoperatively in a 62 year old woman who had undergone abdominal aortic aneurysm repair.

(a) The initial radiograph shows a partially imaged laparotomy sponge marker at the edge of the film.	(b) A second radiograph centered to include more of the left side of the abdomen demonstrates three additional sponge markers. The sponges were surgically removed.

Retained sponge in a 30 year old woman after right hemicolectomy and partial small bowel resection for Crohn¹s disease. A fistulagram was requested two weeks after surgery because of wound dehiscence and discharge.

(a) Injection of contrast into a small opening in the lower part of the wound demonstrates a fistula passing superiorly around the marker (arrow) of a retained 4 x 4 inch surgical sponge and ending in communication with the biliary tract, with contrast draining to the duodenum.	(b) Magnified view of the retained sponge shown in (a).

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CT

At CT, retained sponges are typically seen as a soft tissue density mass, and may show a "whorled" texture or a "spongiform" pattern with contained air bubbles [4]. Inspection of the scout radiograph may be helpful as beam hardening artifact on the axial images may make the characteristic appearances of the marker less obvious. A retained sponge should not be misinterpreted as a fluid collection, although adjacent abscess formation may be seen. The described CT appearances of absorbable haemostatic sponges, which may be made of gelatin (Gelfoam®; Surgifoam®) or oxidized cellulose (Surgicel®), are of mixed or low attenuation masses containing focal central collections of gas [5,6] although we have also observed peripheral gas collections. Abscess formation can coincidentally complicate a surgically packed operative site [6], and therefore the knowledge that absorbable haemostatic sponges have been used should not deter the radiologist from further investigation in the appropriate clinical setting. Differentiation of absorbable haemostatic sponges from other surgical sponges is facilitated by the usual presence of a radio-opaque marker in the latter.

CT appearances of a retained laparotomy sponge after radical prostatectomy.

(a) Scout radiograph demonstrates the marker of a retained sponge in the pelvis.	(b) CT image demonstrates the sponge anterior to the bladder. Beam hardening artifact is noted around the marker.

(a) Retained sponge in a 69 year old man 4 weeks after aorto-femoral bypass. Axial CT image confirms the presence of a retained sponge anterior to the transverse colon.	(b) Axial CT image at a level inferior to (a) shows a fluid collection. The sponge was removed surgically, and the adjacent collection was drained and found to be an abscess.

CT performed because of fever 3 months after bilateral salpingo-oophrectomy for tuboovarian abscess in a 43 year old woman. Axial CT image shows an ill-defined soft-tissue density mass (arrow) with a mottled lucent center in the left lower quadrant. Review of the operative note confirmed absorbable hemostatic sponge (Gelfoam® and Surgicel®) had been used to control bleeding in the left pelvis. The mass was considered to represent residual absorbable sponge, and gradually resolved on subsequent serial CT scans (not shown).

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MRI

At MRI, retained sponges are typically seen as a soft tissue density mass with a thick well-defined capsule and a "whorled" internal configuration on T2-weighted imaging [7]. The MRI appearances of retained absorbable haemostatic sponges have been described in a series of five patients [8], and consist of intermediate T1 and high T2 signal intensity. A complex mixed signal internal pattern similar to the "whorled" appearance of other retained surgical sponges may be seen on T2-weighted images, as may an increased signal peripheral zone on T1-weighted images.

MR imaging of a retaiend sponge in a 56 year old man complaining of frequency 5 months after radical retropubic prostatectomy.

Axial spin-echo T1 (500/15 ms) image following contrast demonstrates a well-defined thick walled structure anterior to the contrast filled bladder. 

Axial fast spin-echo T2 (4000/105 ms) weighted image demonstrates the whirled configuration of the sponge body. The sponge was surgically removed.  

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References

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