Abscess Evaluation and Drainage
Chuan-Jay Jeffrey Chen
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1. A 24-year-old man with a history of intravenous heroin use presents with erythema and swelling of the left second finger over the proximal interphalangeal (PIP) joint. His finger is held in flexion due to the swelling, limiting the images able to be obtained using ultrasound gel and the linear probe. What is the next best step to assess the swelling?
A. Order a computed tomography (CT) scan of the hand
B. Consult the hand surgery service
C. Submerge the hand in a water bath
D. Use warmed ultrasound gel
1. Correct Answer: C. Submerge the hand in a water bath
Rationale: Using ultrasound to assess abscesses, lacerations, or other pathology within the hand or foot can be difficult due to significant pain, anatomic restrictions, or other factors that limit the ability of the probe to make contact with the skin. Water baths can significantly decrease discomfort without compromising imaging quality. Warmed ultrasound gel would increase contact with the skin. While CT imaging or a hand surgery consult may also reveal an abscess, they take significantly more time and resources than using a simple water bath.
1. Blaivas M, Lyon M, Brannam L, Duggal S, Sierzenski P. Water bath evaluation technique for emergency ultrasound of painful superficial structures. Am J Emerg Med. 2004;22(7):589-593.
2. LeDonne S, Sengupta D. US probe: Ultrasound water bath for distal extremity evaluation. www.emdocs.net/us-probe-ultrasound-water-bath-for-distal-extremity-evaluation/
3. Shih J. Ultrasound for the win! 53M with right index finger swelling. www.aliem.com/2017/07/ultrasound-win-53m-right-index-finger-swelling/
2. Which of the following features of Figure 79.1 best suggests the diagnosis of abscess?
A. “Dirty” shadowing
B. “Clean” shadowing
D. Posterior acoustic enhancement
2. Correct Answer: D. Posterior acoustic enhancement
Rationale: Because abscesses are fluid-filled spaces, ultrasound waves are less attenuated and hence tissues deep to the abscess appear hyperechogenic (posterior acoustic enhancement). “Dirty” shadowing suggests air or gas, which scatters ultrasound waves. “Clean” shadowing suggests a solid object that does not permit ultrasound waves to pass through, such as bone or gallstones. Cobblestoning suggests cellulitis without abscess.
1. O’Rourke K, Kibbee N, Stubbs A. Ultrasound for the evaluation of skin and soft tissue infections. Mo Med. 2015;112(3):202-205.
3. A 3-year-old girl presents with significant redness and swelling over her forearm. On physical examination, you perceive a 2 cm area of fluctuance. You obtain the point-of-care ultrasound image shown in Figure 79.2 over the area of fluctuance.
How deep should you make your incision?
A. No incision
B. 0.5 cm
C. 1.2 cm
D. >2 cm
3. Correct Answer: A. No incision
Rationale: The image demonstrates cobblestoning without any signs of abscess. At ˜0.5 cm, the epidermis/dermis layer gives way to subcutaneous tissue, which in this case is filled with subcutaneous edema. Beyond 1.2 cm lies muscle. While Figure 79.2 is a single still image, there are no clear fluid collections, areas with septae or sediment, defined areas with significant posterior acoustic enhancement, or other signs of abscess. Therefore, no incision is indicated.
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