CASE 8101 Published on 02.11.2010

Surgical drape as retained foreign body

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Alves N, Sousa M, Louro C.

Patient

27 years, female

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Clinical History

A 27 year old female, former intravenous substance user on methadone replacement therapy, who had underwent caesarean 5 months previous, presented with inflammatory signs over the suture and localized pain. These did not improve with medical therapy.
An ultrasound (US) of the abdominal wall was performed.

Imaging Findings

High frequency US of the abdominal wall reveals fluid surrounding a hyperechoic structure, 7mm deep in the abdominal wall. This appears to be a hollow, tubular thin solid structure (56mm long) eliciting inflammatory reaction.
US showed hyper-echoic structure suggestive of foreign body (FB). The hypothesis raised was that of a lost surgical drain (or part) within the abdominal wall. However, such a drain had not been employed. Surgical exploration revealed a coiled portion of thin transparent plastic sheet.

Discussion

In caesareans (and other surgeries) an incise drape is commonly used. It consists in a clear adhesive surgical drape of flexible film that provides a sterile surface to the wound edge. Incision of skin and more profound layers towards the uterus is preceded by cutting the incise drape.
On this case we hypothesize that a small portion of the cut plastic was lost during the intervention. Inside the abdominal wall the sheet coiled and presented on US as a thin tubular, arcuate hyperechoic image.

US technique involves high-frequency (7.5MHz or higher) linear-array transducer. US permits accurate location of the superficial FB, estimation of size, shape and orientation, as well as skin marking and guidance for excision [1-4]. It allows evaluation of surrounding tissues, assessment of fluid collections, injury to tendons, vascular or neurologic structures.
The degree of echogenicity of a given foreign body (FB) relates to the differences in acoustic impedance at the interface between the FB and surroundings [4]. FBs present as hyperechoic [4-6] at least initially, as wooden FBs can become less echogenic with time [7].

FBs present with different posterior artefacts, depending on the surface attributes. Flat, smooth surfaces with large radiuses cast dirty shadows, while irregular surfaces or those with small radiuses cast clean shadows [8].
The presence of hypoechoic rim surrounding the FB represents inflammatory reaction and can be found when the FB is present in the soft tissues for over 24 hours. This finding is reported to improve sensitivity and specificity of the US examination. [9-11]

US is the ideal modality to evaluate superficial FBs, being more effective than computed tomography (CT) [6,11,12]. Multiple studies have shown US to have high sensitivity and specificity (90.0% and 96.7% respectively on Jacobson’s series [11]).

US limitations include operator dependence (studies show low sensitivity and specificity for those “relatively inexperienced” [13,14]). Furthermore, effectiveness of US is only valid for superficial FBs, and these may not be accessible to US when deep to bone or gas [5,6]. US is prone to false positive findings, benefiting from correlation with conventional radiography (CR). US may underestimate FB size when imaged end on, parallel to the beam [15].

CR may detect up to 80% of FBs [16]. Some FBs are not radiopaque - particularly those of vegetable origin as wood splinters: up to 85% of these cannot be identified on radiographs [3,11]. Plastic FBs such as the one described are reported to be radiolucent [7].

CT is reported to be about 15 times more sensitive than CR [9], but less sensitive than US and MR. It requires ionizing radiation, is less available and more costly than US, and in some cases (such as paediatric) requires sedation.

MR does not require radiation but is more costly, less available and may not offer good differentiation between a FB with low signal intensity and surrounding tissue of inherent low signal (scar tissue, tendons, calcifications) [11,16].

Differential Diagnosis List

Foreign body (surgical material): incise drape.

Final Diagnosis

Foreign body (surgical material): incise drape.

References

[1] Callegari L, et al. (2009) Ultrasound-guided removal of foreign bodies: personal experience. Eur Radiol 19(5):1273-9 (PMID: 19153745)

[2] Creel SA, Girish G, Jamadar DA, Morag Y, Jacobson JA (2009) Sonographic surface localization of subcutaneous foreign bodies and masses. J Clin Ultrasound 37(3):158-60 (PMID: 19170122)

[3] Whittle C, et al. (2000) Detection and characterization by ultrasonography of soft tissue foreign bodies. Rev Med Chil 128(4):419-24 (PMID: 10962860)

[4] Boyse TD, et al. (2001) US of soft-tissue foreign bodies and associated complications with surgical correlation. Radiographics 21(5):1251-6 (PMID: 11553831)

[5] Bray PW, Mahoney JL, Campbell JP (1995) Sensitivity and specificity of ultrasound in the diagnosis of foreign bodies in the hand. J Hand Surg Am 20(4):661-6. (PMID: 7594298)

[6] Mizel MS, Steinmetz ND, Trepman E (1994) Detection of wooden foreign bodies in muscle tissue: experimental comparison of computed tomography, magnetic resonance imaging, and ultrasonography. Foot Ankle Int 15(8):437-43 (PMID: 7981816)

[7] Horton LK, Jacobson JA, Powell A, et al. (2001) Sonography and radiography of soft-tissue foreign bodies. AJR Am J Roentgenol 176:1155 (PMID: 11312171)

[8] Rubin JM, Adler RS, Bude RO, et al. (1991) Clean and dirty shadowing at US: a reappraisal. Radiology 181(1):231-6 (PMID: 1887037)

[9] Flom LL, Ellis GL (1992) Radiologic evaluation of foreign bodies. Emerg Med Clin North Am 10(1):163-77 (PMID: 1732094)

[10] Gilbert FJ, Campbell RS, Bayliss AP (1990) The role of ultrasound in the detection of non-radiopaque foreign bodies. Clin Radiol 41(2): 109-112 (PMID: 2407413)

[11] Jacobson JA, Powell A, Craig JG, Bouffard JA, van Holsbeeck MT. Wooden foreign bodies in soft tissue: detection at US. (1998) Wooden foreign bodies in soft tissue: detection at US. Radiology 206(1):45-8 (PMID: 9423650)

[12] Orlinsky M, Knittel P, Feit T, Chan L, Mandavia D (2000) The comparative accuracy of radiolucent foreign body detection using ultrasonography. Am J Emerg Med 18(4):401-3 (PMID: 10919527)

[13] Hill R, Conron R, Greissinger P, Heller M (1995) Ultrasound for the detection of foreign bodies in human tissue. Ann Emerg Med 29(3):353-6 (PMID: 9055774)

[14] Crystal CS, et al. (2009) Bedside ultrasound for the detection of soft tissue foreign bodies: a cadaveric study. J Emerg Med 36(4):377-80 (PMID: 18930374)

[15] Howard CB, Nyska M, Mellor I, Leiberman N, Mozes G (1992) Sonographic underestimation of the size of a foreign body. J Clin Ultrasound 20(6):412-4 (PMID: 1328316)

[16] Donaldson JS (1991) Radiographic imaging of foreign bodies in the hand. Hand Clin 7(1):125-34 (PMID: 2037630)

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