|Year : 2015 | Volume
| Issue : 5 | Page : 582-584
Role of high resolution ultrasound in evaluation of soft tissue foreign bodies
Amit T Kharat, Akshay Ajit Shah
Department of Radio-diagnosis, D. Y. Patil University, Dr. D.Y. Patil Medical College, Hospital and Research Centre, Pimpri, Pune, Maharashtra, India
|Date of Web Publication||10-Sep-2015|
Amit T Kharat
Department of Radio-diagnosis, D. Y. Patil University, Dr. D.Y. Patil Medical College, Hospital and Research Centre, Pimpri, Pune, Maharashtra - 411 018
Source of Support: Nil., Conflict of Interest: There are no conflicts of interest.
|How to cite this article:|
Kharat AT, Shah AA. Role of high resolution ultrasound in evaluation of soft tissue foreign bodies. Med J DY Patil Univ 2015;8:582-4
We read with immense interest, the case report titled "Foreign body in the knee with no history of trauma." The article is informative. However, we would like to highlight the role of high-resolution ultrasound (HRUS) in evaluating cases with soft tissue foreign bodies.
Foreign bodies are relatively uncommon, may be overlooked and can cause harm to the patient. Even the most careful individual will have suffered puncture wounds from splinters, needles, thorns, and glass.
Metallic materials are opaque on radiographs. However, it is imperative for referring physicians to understand that thorns, splinters, wooden fragments, and pieces of plastic are usually not sufficiently opaque to be visualized on radiographs.,,,, Contrary to above, a glass of any variety is radiopaque.,,
Unlike this study where the foreign body is metallic and seen on radiograph, the imaging of a nonopaque object can be difficult as their characteristics vary on different imaging modalities such as radiography, ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI).
Localization of radiopaque foreign bodies on plain radiographs is limited primarily by overlying bone, size, and density of the foreign bodies. Although radiographs outline the shape of the foreign body, they are not useful for three-dimensional localization and visualization of nearby neurovascular structures, tendons, and muscles. It is in such a scenario, HRUS scores.
Foreign organic matter, in penetrating injuries, may be poorly visualized on radiographs, especially if the object is saturated over a long period of time by blood and tissue fluid. In such conditions, HRUS offers hope for visualization of a suspected foreign object in the superficial tissues of the body.,,,,,, On HRUS, foreign objects frequently give a localized, reproducible hyperechoic signal.
On review of the literature on this subject, Crawford and Matheson, in 1989, studied a series of 39 patients with a clinical suspicion of retained foreign body within the hand with negative radiographs of the hand performed using soft tissue factors. The subjects were evaluated by HRUS scan. A follow-up at surgery revealed 20 patients to have radiolucent foreign bodies; these included 18 wood particles and 2 revealed thorns. HRUS scan correctly diagnosed 19 of the foreign bodies prior to surgery but failed to detect only one. The above study proved that the HRUS done using high-resolution scanning is very sensitive and quite accurate for the diagnosis of foreign bodies, which are difficult to assess by conventional radiographic methodology. HRUS also provides fairly accurate three-dimensional localization of the foreign body, which is of high significance to the operating surgeon.
Bray et al., in 1995, revealed the sensitivity and specificity of HRUS in imaging and diagnosis of foreign bodies in the region of hand in a controlled environment. Totally, 15 fresh but frozen cadaver hands were used for the experiment, and they were divided into 21 prior standardized locations for foreign body insertion. The foreign bodies used were of two sizes and three types of materials (wood, glass, and metal). The foreign bodies were targeted and inserted randomly within the 50% of the predesigned sites, while the empty sites were used as controls. Scanning was done by a single radiologist. The results revealed that out of the 166 foreign bodies inserted, around 156 were easily detected by US. Totally, 10 sites were falsely diagnosed as negative, with a sensitivity of 94%. Also, one false positive was also there, and 148 were true negatives. This brought the HRUS specificity to 99%. The study concluded that the high specificity of HRUS permits foreign body localization.
HRUS detects a variety of soft tissue foreign bodies, including wood splinters, glass, metal, and plastic. HRUS can be done using high-resolution transducers (7-11 MHz), particularly when the foreign body is superficially located. The degree of echogenicity of a foreign body is proportional to the differences in acoustic impedance at the interface of the foreign body and surrounding tissue. The exact location of a radiopaque foreign body, its relationship with surrounding structures, and associated soft tissue injuries are not apparent on plain radiographs and can be easily assessed with HRUS.
The artifact occurring deep to a foreign body depends primarily on its surface attributes rather than its composition. Smooth and flat surfaces produce a dirty shadow or reverberation artifact whereas irregular surfaces produce a clean shadow. Metal and glass often demonstrate reverberation due to their flat surfaces.
If a foreign body is present in the soft tissues longer than a day, a foreign body inflammatory reaction can create a hypoechoic rim around the echogenic foreign body. This hypoechoic rim improves the sensitivity and specificity of the HRUS examination.
HRUS permits examination of the surrounding muscles, tendons, ligaments, and neurovascular structures. Soft tissue infection is by far the most common complication of a penetrating foreign body, followed by nerve injury.
However, there are certain limitations of this technique, the most important being operator dependence. Familiarity with the HRUS appearances of soft tissue foreign bodies and a detailed evaluation of the region with a high frequency linear transducer (7-11 MHz) in both the longitudinal and transverse orientations are imperative for accurate assessment. The average examination time for HRUS evaluation of soft tissue foreign bodies has been reported to be approximately 10 min.
Air introduced into the tissue at the time of injury or surgical exploration can cause reverberation artifacts that may mimic the presence of a foreign body; it can make HRUS examination impossible. HRUS examination should be performed again in 48 h, which would allow time for air absorption.
To conclude, using HRUS may reduce the complications associated with the blind surgical exploration of soft tissue foreign body removal. Furthermore, no ionizing radiation is used.
For detection of superficial, radiopaque, and nonradiopaque foreign bodies, HRUS has been shown to be more effective than CT. CT has a higher cost, involves ionizing radiation, may have limited availability, and can involve anesthesia. MRI also has a higher cost and limited availability as compared to HRUS for evaluating nonmetallic foreign bodies. Evaluation of metallic foreign body is a contraindication for MRI. In addition, MRI often does not allow differentiation of foreign bodies from other structures that can also have low signal intensity such as scar tissue, tendons, and calcifications.
HRUS is a bedside, portable, and easily available imaging modality with high intra tissue contrast resolution without harmful ionizing radiation. HRUS is the modality of choice for the detection of radiolucent foreign bodies, which may be a challenge to image on other imaging modalities.,, HRUS, for radiopaque foreign bodies, can provide precise localization in relation to muscles, tendons, vessels, and nerves prior and during the surgery. For all types of foreign bodies, US can aid assessment of the surrounding soft tissues and demonstrate associated soft tissue complications.
In this case, HRUS would have complemented in pre- and intra-operative localization of the needle, relationship of the needle to the joint and surrounding neurovascular bundle, and to gauge the extent of damage to the surrounding soft tissues.
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