Foreign bodies occur regularly in small animals and are very important and interesting. Foreign bodies may be ingested, inserted into a body cavity, or deposited into the body by a traumatic or iatrogenic injury. Most ingested foreign bodies pass through the gastrointestinal tract without a problem, but may cause a partial or complete obstruction of the small intestines. In the stomach, foreign body may also cause an obstruction, but also irritation of the gastric wall making the animal feel uncomfortable or nauseous. Most foreign bodies inserted into a body cavity cause only minor mucosal injury. However, ingested or inserted foreign bodies may cause bowel obstruction or perforation; foreign bodies may also lead to severe hemorrhage, abscess formation, or septicemia. Grass awns, wood pieces, such as sticks, small twigs or thorns, glass, and bullet wounds are common causes of traumatic foreign bodies in small animals. Metallic objects, except aluminum, are opaque, and most bones and glass foreign bodies are opaque on radiographs. Most plastic and wooden foreign bodies (sticks, BBQ sticks, thorns, splinters) and most fish bones are not opaque on radiographs.

Penetrating object injuries are a common problem in small animals, and retained foreign bodies in soft tissues complicate many such injuries. Because a retained foreign body may cause severe infection or inflammatory reaction, detection and removal of foreign bodies are necessary. Punctured wounds and soft-tissue lacerations are inspected, palpated, and explored to rule out the presence of a foreign body, and radiographic evaluations are routinely obtained to confirm radio-opaque foreign bodies such as glass, metal, and stone within the soft tissue. However, often foreign bodies are overlooked or not traceable at initial examination. A radiolucent foreign body, such as wood, frequently remains undetected. In such situations, other imaging modalities are needed for diagnosis. Sonography plays an important role in the evaluation of these patients. In humans, US has a reported sensitivity of 95% for detection of foreign bodies. Also computed tomography (CT) and magnetic resonance imaging (MRI) are valuable in detecting foreign bodies and to give a pre-surgical evaluation as how extended the soft-tissue changes are caused by the foreign body.

The correct selection of a diagnostic imaging modality along with knowledge of indirect radiologic findings can help determine the presence and location of a foreign body. Plain radiographs should be the initial screening modality for a suspected foreign body. Whereas most metal and glass foreign bodies are detectable on radiographs, many foreign bodies, including wood, are not. When a suspected superficial foreign body is not delineated on radiographs, ultrasonography should be the next modality of choice. CT and MRI should be reserved for deep foreign bodies or when foreign bodies are not seen on radiographs or ultrasonography but are suspected. Detection of radiolucent soft-tissue foreign bodies is a challenging problem, which is especially further complicated when retained foreign body is highly suggested by clinicians but radiography is negative. So, blind exploration is sometimes hazardous for patients.

In US, non-opaque foreign bodies are visualized as hyperechoic foci (often linear) with accompanying acoustic shadows. This shadow may be either complete or partial depending on the angle of insonation and the composition of the foreign body. A hypoechoic halo surrounding the foreign body is sometimes seen, which represents edema, abscess or granulation tissue.

In this lecture, the effectiveness of mainly US for detection of radiolucent foreign bodies will be presented, also demonstrating the clinical experiences using US in the management of patients with a suspected retained foreign body. Foreign bodies can penetrate different body parts and cavities via different routes. Foreign bodies may be inhaled, penetrate the skin or be swallowed (either in the gastrointestinal or respiratory tract).

When foreign body aspiration is suspected in a patient, screening radiographic studies employed include a dorsoventral and lateral radiograph of the cervical trachea and thorax. Obtaining 2 views of the foreign body helps in determining its location and excludes the presence of superimposed multiple foreign bodies. The potential is high for morbidity and mortality resulting from an aspirated foreign body; hence, if foreign body aspiration is suspected, it is important to find the foreign body to be able to remove it adequately. Radiopaque foreign bodies are easy to diagnose by using radiographs. With radiolucent foreign bodies, secondary radiographic signs, such as obstructive emphysema, atelectasis, pneumonia, and a mediastinal shift, help in diagnosing foreign body aspiration. Plain radiographic results cannot exclude foreign body aspiration. If the clinical suspicion is high for foreign body aspiration, endoscopy should be performed for definitive diagnosis and treatment. Images in patients with chronic bronchial foreign bodies may show atelectasis, with a mediastinal shift toward the foreign body and/or recurrent pneumonias in the affected lung segment. Also thickening of the pleura. Pleural effusion and/or periosteal new bone formation along the ribs may be seen, secondary to foreign body in the thoracic cavity. As a result of its greater contrast resolution, computed tomography (CT) scanning has been used to demonstrate airway foreign bodies that are radiolucent on plain radiograph. In addition to providing plain radiographic findings, such as hyperlucency, atelectasis, and lobar consolidation, CT scans can depict the foreign body within the lumen of the tracheobronchial tree and the 3-dimensional position of the foreign body within the thorax. If CT scans demonstrate signs of foreign body aspiration, the patient should undergo endoscopy for definitive diagnosis and treatment. Any process that causes obstruction or narrowing of the airway lumen can produce signs similar to those of foreign body aspiration. Examples include neoplastic disease, granulomatous disease, bronchial stenosis, and a mucus plug.

Penetrated foreign bodies, such as grass awns or splinters, often occur without clinical signs till the foreign body caused inflammation, abscess formation, pain or even more serious problems, such as pleuritis with or without pneumonia, peritonitis, or arthritis.

Swallowed foreign bodies often occur in young animals: puppies or kittens playing with toys or gobbling up bones or food still wrapped in plastic for instance. When these foreign bodies do not pass the gastrointestinal tract, they may cause a complete or partial ileus. A lateral and ventrodorsal radiographic examination may be performed as the first screening. Secondary signs to an obstruction caused by foreign bodies will be loss of detail, dilated small intestinal loops, and an empty colon. If a perforation has occurred, also free gas in the peritoneal cavity may be appreciated. Additional US may confirm the presence of a non-radiopaque foreign body, free gas, and ascites. Radiographs and US should be used as complementary techniques.