Grace Feng
Case: A 59-year-old male presented with a chief complaint of retained bullet in his abdomen. He reported a past medical history of multiple gunshot wounds in 2017 and had an exploratory laparotomy related to those injuries. He was uncertain why the bullet was not initially removed, but reported the wound site was stable until several days ago, when it began leaking serous fluid. He denied fevers, chills, and purulent discharge or pain at the wound site.
Vitals: BP 112/72 | HR 72 | Temp 98.4 ºF (36.9 ºC) | Resp 16 | SpO2 98% on RA
On physical examination of the abdomen, it was grossly soft, non-tender, and non-distended, with a well-healed exploratory laparotomy scar. There was a keloid scar approximately 4cm lateral to the left of the umbilicus measuring 2x3 cm with minimal serous drainage and a firm, subcutaneous mass palpable underneath.
Bedside ultrasound was performed to evaluate for foreign body, abscess, and/or cellulitis.
Figure 1: Longitudinal view of the abdomen using the curvilinear probe.
Figure 2: Longitudinal view of the abdomen using the curvilinear probe.
Discussion:
Retained foreign bodies (FBs) account for 7-15% of patient cases presenting with traumatic wounds and/or lacerations in the emergency department. These FBs are commonly made of glass, metal, and wood, and can serve as a nidus for infection or granulomatous tissue formation.1 Ultrasound is highly sensitive for the detection of FBs, especially superficially, and is also capable of detecting inflammatory and edematous changes in skin and soft tissue associated with cellulitis and abscesses.1,2 While all FBs are hyperechoic on ultrasound, metallic FBs may present with posterior reverberation or posterior acoustic shadowing, depending on its size and curvature.1,3 Inflammation surrounding the FB typically manifests as a hypoechoic halo, which can represent edema, abscess, fibrous tissue, or granulation tissue.1 Infectious processes can cause both edema and abscesses. The former is more characteristic of cellulitis, which typically manifests as hyperechoic areas of soft tissue interspersed with hypoechoic fluid, i.e. subcutaneous edema. This gives a “cobblestone” appearance on ultrasound. Similarly, on ultrasound, abscesses appear as a hypoechoic fluid collection and may have irregular borders, contain debris, and/or swirl with compression.2
In this case, the patient had a documented retained FB that became newly symptomatic. While the FB was palpable on physical exam, due to extensive scar tissue in the region, it was uncertain how deep the FB was and whether it had provoked an infection. In Figure 1, the FB can be seen just below the probe as a well-circumscribed mass with irregular internal components and significant posterior acoustic shadowing. The irregular internal components likely represent fibrotic tissue and the retained bullet. In Figure 2, the FB briefly appears similarly to an abscess, with a nearly anechoic region. However, the clear posterior acoustic shadowing with continued visualization of deeper visceral structures reassures that there is not fluid within the mass, which would lead to posterior acoustic enhancement. Based on these ultrasound findings, it was determined the patient’s retained FB was very superficial and had no evidence of provoking local or systemic infection. Following local anesthetic injection, a pair of forceps was used to expose and extract the foreign body, and the patient tolerated the procedure very well.
References:
1. Carneiro, B. C., Cruz, I. A., Chemin, R. N., Rizzetto, T. A., Guimarães, J. B., Silva, F. D., ... & Nico, M. A. (2020). Multimodality imaging of foreign bodies: new insights into old challenges. Radiographics, 40(7), 1965-1986.
2. Creditt, A.B., Joyce, M., Tozer, J. (2018). Skin and Soft Tissue Ultrasound. In: Clinical Ultrasound. Springer, Cham. https://doi.org/10.1007/978-3-319-68634-9_15
3. Rubin, J. M., Adler, R. S., Bude, R. O., Fowlkes, J. B., & Carson, P. L. (1991). Clean and dirty shadowing at US: a reappraisal. Radiology, 181(1), 231-236.