A Firm and Painful Plaque on the Thorax: The Role of Ultrasound in the Detection of Foreign Bodies

The presence of a subcutaneous foreign body may not be easily suspected after the initial history and exploration of the patient. The authors report a 54-year-old male who came to the Department of Dermatology, Hospital Universitario de Fuenlabrada, Madrid, Spain with a firm plaque, fixed to deep structures, which showed several draining orifices over the costal grid. After several tests, the authors performed an ultrasonography that revealed the presence of a fistula from a foreign body secondary to a previously untreated costal fracture that occurred several years before. The authors believe ultrasonography is a readily available and useful tool that may help dermatologists in daily clinical practice, with the advantage of being a noninvasive test.

Retained foreign bodies (FBs) are found in 7%-15% of wounds in the emergency department worldwide,¹ and up to 38% are missed on initial physician evaluation. General evaluation for a retained FB includes a detailed history and physical examination. Metal, glass, and wood are the most common FBs.¹ If a FB is suspected, the main image techniques that may help clinicians with the diagnosis are plain radiography, ultrasonography (US), and computerized tomography. Ultrasonography has a potential use in many areas of dermatology, and its role has also expanded.²

A 54-year-old man with a history of HIV and hepatitis B infection was referred to the Department of Dermatology, Hospital Universitario de Fuenlabrada, Madrid, Spain by his general practitioner with a painful lesion on his back that had appeared 5 years prior. He related occasional and recurrent suppurative episodes from this lesion, and the only remarkable fact on anamnesis was the patient, previous to the onset of the lesion, had suffered a costal fracture that had not been treated.

On examination, the authors observed a firm plaque on the right costal grid, which was fixed to deep structures and presented several draining orifices. This plaque was secondary to the callous of the previous costal fracture (Figure 1). The material drained from under these orifices was scarce. 

Initial differential diagnosis included tuberculosis, atypical mycobacteria, and chronic osteomyelitis. Therefore, a thorax X-ray and several cultures were done.

The X-ray showed flattening of the diaphragm, air trapping, and a previously untreated costal fracture on the right hemithorax. Neither revealed pleural effusion or pulmonary consolidation that suggested tuberculosis or atypical mycobacteria. Likewise, the cultures for bacteria, mycobacteria, and fungus were negative.

Subsequently, a fine-needle aspiration biopsy revealed polymorphous nuclear leukocytes and few macrophages. Ziehl-Neelsen, periodic acid-Schiff, and Grocott stains were negative.

At this stage, the authors were still unable to make a diagnosis, a high-frequency US (SonoScape S20 Exp/S20 Pro/s20/S15, Sonologic, Australia) was performed. As a result, the authors observed hypoechoic linear images that ran from the fractured rib to the dermis and the epidermis. These images suggested fistulae from the costal grid to the skin. On the dorsolumbar region, the authors saw a hyperechoic image surrounded by a hypoechoic area (Figure 2) that seemed to be the origin of the linear hypoechoic images to the skin. Consequently, a diagnosis was made of an osseous foreign body located on the right broad dorsal muscle surrounded by an area of abscess with fistula to the skin. 

The authors consulted with doctors of the Department of General Surgery who evaluated the patient; then the surgical repair of the costal fracture with the removal of the foreign body and fistulectomy were planned. 

The inclusion of a FB may be secondary to multiple mechanisms including ingestion, inhalation, aspiration, and trauma. Foreign bodies may be exogenous, as there are multiple examples in the scientific literature,^3,4 or endogenous⁵ as was this case. 

Although a lesion with a FB may heal without complications, in most cases, healing is delayed due to prolonged and excessive inflammation. Common sequelae are infection and the formation of granuloma.⁶ Infections related to the presence of a FB are characteristically chronic, delayed, recurrent, and resistant to antimicrobial therapy. Drainage from the site of a retained FB may prove to be sterile.⁷ Other complications are neuropraxia, nerve laceration, nail deformities, metacarpal fracture, epidermoid cysts, tetanus, gas gangrene, cellulitis, abscess, osteomyelitis, mycetoma, tenosynovitis, monoarticular arthritis, and lymphangitis.⁸ Sinus and fistulas are usually secondary to the presence of a FB, necrotic tissue in the affected area, or from certain types of microbial infection. These conditions may be asymptomatic, but most often they are prone to infection, which may manifest in recurrent or persistent discharge and pain if there is swelling. It might also cause formation of a chronic ulceration.⁹

Accurate imaging interpretation of a FB should include the location and composition of the FB and its relationship with the surrounding anatomical structures. The choice of the most appropriate imaging modality may depend on convenience, availability, operator experience, cost, and, most importantly, sensitivity.¹⁰

Plain radiography should be the initial imaging technique used to identify a FB.⁸ It is the easiest to interpret, the least expensive, and the most readily available for viewing radiopaque foreign bodies.⁷ Glass and wood can be radiolucent and difficult to see on radiograph images. Glass accounts for up to 50% of missed FBs using physical examination, and radiographs have been found to be only 7.4% sensitive at identifying FBs made of wood.¹

Even when the FB cannot be seen there are often indirect radiographic signs of a retained FB that should be sought, such as lytic bone lesions, periosteal reaction of bone, pseudotumors, and deep swelling of soft tissue.⁸ A radiolucent filling defect occurs when the object is less dense than soft tissue.⁷ A comparison of inspiratory and expiratory views facilitates the detection of air trapping.¹¹

Ultrasonography should be the next modality of choice when a FB is suspected and not found under X-ray.  The accuracy, sensitivity, and positive predictive value of US in detecting radiolucent soft-tissue FBs was analyzed in a study to be 90.2%, 97.9%, and 92%, respectively.¹²

While US is potentially useful for any type of FB, it is most effective in cases of detection of radiolucent FBs such as wood, plastic, thorns, and cactus spines. In addition, the sensitivity of US improves with the size of the FB.¹ 

Low-frequency and high-frequency US are used for different purposes. Low-frequency US is used for visualizing larger, deeper structures such as internal organs. The superficial anatomy of skin structures and neoplasms are not visible when using low-frequency US; therefore, high-frequency US is generally employed for dermatologic purposes.² Practical application of this modality has identified foreign objects as small as 0.5 mm and as deep as 4 cm.¹³

Most FBs in soft tissues, independent of the nature of the FB, are hyperechoic, and the induced inflammatory changes appear as a surrounding hypoechoic mass, as illustrated in this case study. This could be more easily detected in a homogeneous hypoechoic area such as subcutaneous fat, muscles, or inflammatory tissue.⁸ Metal and glass may cause a “comet tail” artefact, while gravel demonstrates strong posterior acoustic shadowing. Power Doppler may be used to identify acute inflammatory changes and neogranulation around FBs, but it may not prove positive for up to 2 days after intrusion.¹³

Other advantages of US are that it can help determine the size and shape of a FB and so may aid to locate it and its relation with other anatomic structures such as bone, tendons, blood vessels, or joints. Localizing some FBs can be easier with multiple views, metallic markers, or needles inserted close to the FB.¹⁴ Furthermore, US allows the possibility of a realtime guided removal of the FB under sterile conditions. Due to its safety and inferior rate of complications, US may replace surgical exploration.¹² Ultrasonography-guided removal of FB can prevent extensive dissection in comparison to blind surgical exploration. Moreover, focused surgery allows for a reduced incision size with less postoperative pain.¹⁵

The main disadvantages of US are that FBs positioned behind gas or bone cannot be seen.⁸ Other pitfalls are that small FBs may reflect faint echoes that cannot be reliably distinguished from surrounding tissue. Long and thin objects that are clearly visible in one position disappear when the angle of the transducer is changed. The tendons in the hand may be mistaken for linear FBs or with hypoechoic inflammatory tissue, depending on the axis of visualization. Old scar tissue, small bones and calcifications, fresh bleeding, and sutures can produce false-positive findings under US.⁷

Computed tomography is not always readily available, though it can help if the detection of the FB has not been achieved with other imaging tests⁸ or when there is a risk of infection or joint injury.¹⁴ The principal disadvantages are its cost and greater radiation dose in comparison with radiography. In addition, some degree of patient cooperation is needed; therefore, it may be difficult to perform on young children.⁷

Fistulization secondary to an unhealed bone fracture has been seldom described. After an exhaustive literature review, the authors have found the report of an Asiatic 26-year-old female patient who had suffered a pelvic fracture at the age of 10 and had a complete vaginal obstruction with heterotopic ossification; the patient menstruated through a fistula in the distal vaginal vault.⁵ In the current case, the US gave the authors fast and valuable information that allowed them to make a correct diagnosis, thus avoiding further invasive tests or unnecessary treatments. 

Ultrasonography may be a reasonable alternative in cases where preoperative tests are needed and it may aid clinicians to locate the FB during surgical removal. The authors believe US is a useful tool in the daily clinical practice, though training is necessary and learning curves expected to interpret the images properly.

From the Department of Dermatology, Hospital Universitario de Fuenlabrada, Madrid, Spain

Address correspondence to:
Anastasia A. Garrido-Ríos, MD
Department of Dermatology
Hospital Universitario de Fuenlabrada
Camino del Molino, 2
28942 Fuenlabrada
Madrid, Spain
anastasia.garrido@salud.madrid.org

Disclosure: The authors disclose no financial or other conflicts of interest.