Wooden foreign body in the dorsum of the hand

Clinical History

The detection of wooden foreign bodies is not straightforward. This case presents a wooden foreign body in the back of the hand. First, a standard plain radiography was obtained. Further exploration involved an ultrasound and MRI of the hand. The differences between the imaging techniques are discussed.

Imaging Findings

A 64-year-old man received a blow with a branch of a tree on his right hand. Radiographs at that moment showed no fracture or foreign body. During the next 5 months, there was a progressive swelling of the back of the hand. Since the patient did not remember foreign body penetration and since there were no signs of rubor, calor or dolor associated with the swelling, an extensive preoperative imaging was performed to exclude other than inflammatory processes.

Plain radiographs (Fig.1) show a periosteal reaction with central lucency at the radial side of the diaphyse of the fourth metacarpal bone. The dorsal soft-tissue swelling of the hand is well appreciated on the lateral view (Fig.2).

Ultrasound shows a heterogeneous hypoechoic soft-tissue mass superficially to the diaphyses of the third and fourth metacarpals (Fig.3). This mass is hyperemic on Power-Doppler ultrasound. The extensor tendons are located in the periphery of the mass. A linear hyperechoic structure is delineated within the soft-tissue mass and penetrating between metacarpal IV and the capitate bone in an anteroposterior direction (Fig.4).

MRI of the right hand confirms these findings. An unsharp delineated mass is located subcutaneously in the back of the hand. The mass is centered on the diaphyse of the fourth metacarpal. It is heterogeneous and hypointense on the T1-weighted images and hyperintense on the T2-weighted images (Fig. 5-6). In this soft-tissue mass a hypointense linear structure, a foreign body, is delineated. After intravenous injection of contrast medium, an intense and diffuse enhancement of the soft-tissue mass is seen (Fig.7-10).

Discussion

The detection of wooden foreign bodies is not straightforward. Patients often present some time (months to years) after the initial injury. A history of penetrating injury is not always present or patients may have forgotten the penetrating trauma, as is in our case. The correct diagnosis and location is important since wooden foreign bodies may act a nidus for infection. Cellulite, abscess, fistula formation, synovitis and osteomyelitis are possible complications.

Often, a standard radiograph is firstly obtained, but is usually unremarkable as it fails to reveal a radiolucent foreign body [1,2]. However, secondary effects, such as osteolytic or osteoblastic changes in the adjacent bones, can be visualized [3].

Ultrasound is able to show the wooden foreign body as linear hyperechoic structure, with an acoustic shadowing, depending on the density of the wood. Ultrasound has been well studied in the evaluation of retained foreign bodies and has proved to be both specific as sensitive [4]. It is superior to CT and MRI for the detection of small wooden foreign bodies.

Wooden foreign bodies are hypointense on T1- and T2-weighted sequences. MRI shows the surrounding inflammatory tissue that is hypointense on T1-weighted images and hyperintense on T2-weighted images. It has been reported that wood in soft-tissue may absorb the surrounding hematoma and exudate, prolonging T1 and T2 relaxation times [5]. Enhancement of the inflammatory tissue is seen after contrast medium intravenous injection. The identification of a wooden foreign body can be difficult, especially when the foreign body is small and there is no associated abscess or fluid collection. A signal void with surrounding nonspecific granulation tissue may be the only finding.

CT depicts the wooden foreign body as an area of high attenuation compared with the surrounding skeletal muscle and fat. A bone window is best for optimal visualisation of the foreign body. Compared to MRI, it is more difficult to delineate the inflammatory tissue.

Foreign bodies can be divided in two main groups: radiopaque and non-radiopaque foreign bodies. Radiopaque foreign bodies, such as glass, metal or stone, are visible on plain radiographs. However, ultrasound may offer additional information for more accurate localization. Ultrasound can also evaluate soft-tissue or neurovascular complications. Non-radiopaque foreign bodies, such as wood or plastic, are not directly visible on plain radiographs, but secondary effects, such as osteolytic or osteoblastic changes in adjacent bones, may be visible. Ultrasound can detect and localize the non-radiopaque foreign body. MRI and CT are often performed to evaluate symptoms such as nonspecific swelling and pain. CT has a higher cost and involves ionizing radiation. MRI has also a higher cost and has a more limited availability.

The best imaging strategy for detection and evaluation of foreign bodies is to start with a combination of plain radiography and ultrasound, which may reveal the foreign body in most cases. Only when these exams are negative, a contrast-enhanced MRI is recommented.

Differential Diagnosis List

Final Diagnosis

Wooden foreign body in the back of the hand

URL:	https://eurorad.org/case/8616
DOI:	10.1594/EURORAD/CASE.8616
ISSN:	1563-4086