Ultrasonographic delineation of a foreign body in the calf

Sir,

An 8-year-old boy came with a history of painful swelling of his left leg and discharging sinuses (at the medial and lateral aspect) for the last 4 months. There was history of fever. Detailed history revealed that about 6 months ago, he fell down from the roof of his house on a tree and sustained injury. He was treated locally and pieces of wood were removed from the wound and then sutured. The wound healed temporarily. After 2 months he developed swelling and draining sinuses in his left leg. At the time of admission, his laboratory results were normal except for low hemoglobin level. Plain radiography of the leg showed soft tissue thickening leg with obliteration of fat planes in the calf region. No foreign body could be identified. Using a high frequency linear probe, ultrasonography (USG) was done, which revealed a linear echogenic focus of 3.2 cm size and 4-5 mm thickness with posterior shadowing at the postero-medial aspect of his left leg intramuscularly, just subjacent to the medial external skin opening [Figure 1]. A thin hypoechoic tract was seen extending obliquely between the two external skin openings along the echogenic focus/foreign body. Soft tissue edema and inflammatory changes noted around the lesion. No pus was expressed out at the time of examination. Subsequently the patient was taken for exploration of the wound and a wooden piece was removed [Figure 2]. Patient was continued on antibiotics. On follow-up, the swelling has decreased and skin opening of the sinuses showed healing without any discharge.

Figure 1.

Ultrasonography (USG) in calf region shows linear echogenic focus of foreign body with surrounding hypoechoic edema

Figure 2.

Photograph of wooden foreign body after its removal

The imaging appearance of wooden foreign bodies is variable.[1,2,3] Plain radiographs did not reveal the foreign body due to its radiolucent nature. Wood was highly echogenic and revealed pronounced acoustic shadowing on sonography. In computed tomography (CT) retained wood appears as isodense or subtle hyperdense focus. With magnetic resonance imaging (MRI), wooden foreign bodies show variable signal intensity that was equal to or less than that of skeletal muscle on both T1- and T2-weighted images. Though MRI shows the surrounding inflammatory response better than CT, a painful swollen soft-tissue mass or pseudotumor may suggest the possibility of malignancy or infection, rather than indicating a retained foreign body.[4] A history of recurrent localized infections with or without sinus formation should prompt a search for an occult foreign body.[5] Remote trauma, however trivial, should lead to search for missed foreign body, particularly in children. Wood, with its porous consistency and organic nature, is an excellent medium for microorganisms, and the retained wooden foreign matter may result in cellulitis, abscess, and sinus or fistula formation. CT is reserved for deep foreign bodies or when foreign bodies are not seen on radiographs or USG but are still suspected or to confirm the plane of the foreign body detected on USG. Davae et al.,[6] used power Doppler to delineate soft tissue foreign bodies and found surrounding hypervascularity reflecting neovascularity of the reactive granuloma. USG can also aid in guiding the extraction or retrieval of the foreign body.