There are numerous locations where ingested foreign bodies can cause obstructions. Within the oesophagus, there are three common locations where obstructions may occur: at the level of the superior oesophageal sphincter, at the level of the aortic arch, and at the level of the inferior oesophageal sphincter [23, 24]. The removal of foreign bodies in the oesophagus is considered mandatory, including impacted food. Other anatomical locations where foreign bodies can cause obstructions include the pyloric sphincter and ileocaecal valve (especially large objects), as well as the rectosigmoid colon and anus. An object with a diameter larger than 25 mm is unlikely to pass through the pylorus [25]. Objects that are longer than 6 cm have a difficult time to pass through the duodenum and are also unlikely to pass through the ileocaecal valve [26]. Further areas prone to obstruction are locations with acquired or congenital strictures, such as anastomosis following atresia surgery. If a radiograph is performed, it needs to include the entire gastrointestinal tract, i.e. neck, chest and abdomen. One can determine if a flat circular foreign body, such as a coin or button battery, is situated in the oesophagus or trachea depending on its appearance. A circular foreign body appears round in the anterior–posterior view if situated in the oesophagus, and narrow if located in the trachea, as the posterior wall lacks cartilage rings and thus is not rigid. The image is reversed in a lateral view. Additionally, one ought to detect the trachea on the lateral view to ascertain if the foreign body resides within the trachea or posterior to it. The management of an ingested foreign body depends not solely on its location, but also on the type of foreign body ingested (Table 1). A clinician ought always to consider potential poisoning from ingested substances, whether deliberate or accidental. Radiographic follow-up can detect if an injury has occurred and early indications of it being retained [27]. If there is suspicion of perforation, then CT should be considered. Furthermore, ultrasound may be considered to evaluate the progression of a foreign body in the abdomen or if it has caused secondary effects or complications.

Coins are one of the most commonly ingested foreign objects, and patients typically present with dysphagia. Coins can cause mechanical obstruction, but are considered relatively safe as they lack sharp edges. One consideration is whether the metal composition of the coin could potentially have a toxic effect. The US penny has a high zinc content (97.5% zinc, 2.5% copper) and the Euro 10c, 20c and 50c coins consist of 89% copper [30, 31]. All metal coins risk reacting with the gastric acid in the stomach. The free metal ions can then have local or systemic effects on an individual. It has been reported that coins in hydrochloric acid lose between 0.43–11.3% of their weight over the course of a week [32]. The dissolved ions can then be absorbed or react further with the hydrochloric acid and become a salt. Zinc can react with gastric acid and result in zinc chloride. Zinc chloride causes vomiting, gastritis and, secondarily to this, gastro-oesophageal burns and haemorrhage that can ultimately result in scarring. Gastric acid can enable the body to absorb copper, which can cause acute liver failure. Treatment of ingested coins generally depends on their location and the symptoms. Urgent removal of any foreign body is indicated if the obstruction causes an inability to manage oral secretions. A coin that fails to pass the pylorus after 48 h may indicate the need for endoscopic removal, but this can vary depending on local practice [24]. The main role of the radiologist is to identify whether the foreign body is a coin, where it is located, and if it causes any obstruction.

Ingested batteries require more direct management, particularly button batteries, which can sometimes be mistaken for coins (Fig. 5). A coin appears solid on a radiograph, whereas a button battery has a metal casing that gives it a double-ring appearance. An irregular contour of the double ring is an indication that the encasing is no longer intact, and potential leakage of battery acid should be considered. Batteries cause an external current that hydrolyses fluids in tissues and creates hydroxide ions (OH-) at the negative pole of the battery. The battery itself causes physical pressure, and its contents, especially battery acid, can cause coagulation necrosis [33]. The harmful effect on the soft tissues is most prominent in the oesophagus, and any detected batteries in the oesophagus should be extracted as soon as possible [34]. Battery leakage has been documented as early as 2 h after being in a solution with the same pH as gastric acid [35]. It is therefore crucial for the radiologist to detect the presence and location of a battery, especially in the oesophagus, so it can be extracted before permanent damage occurs (Fig. 6).

Lung radiographs, anteroposterior (AP) views of foreign bodies in the mediastinum. a A coin which appears as a solid structure in a 3-year-old boy. b A button battery with a visible double ring (arrow) which is pathognomonic, in a 2-year-old girl

A 2-year-old girl presenting with haematemesis. a An anteroposterior radiograph displays a button battery within the stomach. b Magnified view of (a) shows small erosions (solid white arrows). c Axial view computed tomography (CT) with contrast, in soft tissue window, shows a pseudoaneurysm from the aortic arch, adjacent to the oesophagus (open white arrow). d Axial view CT with contrast, in soft tissue window, shows fluid accumulation between the oesophagus and the pseudoaneurysm, which was confirmed to be necrosis caused by the button battery (asterisk)

Ingestion of magnetic objects is common and can have potentially dire consequences. Magnets can be found in toys for children under the age of four, in building blocks, in wooden games, and in more traditional toy cars or trains. Magnets can be of various shapes and sizes with a metallic opacity on a radiograph. Magnets in different bowel loops can become attracted to one another through the bowel wall. Clinical information about the suspected foreign body is critical to making a correct diagnosis, but if there are two or more metallic objects adjacent to one another, it should raise concern for multiple ingested magnets (Fig. 7).

Anteroposterior (a), lateral (b) and left lateral decubitus (c) abdominal radiographs of a 1-year-old boy who presented at the emergency department with vomiting and a clinical suspicion of ileus or gastroenteritis. The radiographs reveal a radiopaque pearl bracelet in the bowel. The boy’s guardian denied known ingestion of foreign bodies

A magnetic object does not need any intervention if it is a single magnet without the presence of other metallic objects. However, if more than two magnets (or a magnet + magnetic object) are ingested, urgent intervention is indicated if they can be reached by endoscopy or if there are signs of perforation of the bowel caused by pressure from the magnets (Fig. 8). Bowel necrosis caused by magnets can result in entero-enteric fistula [36].

Magnification of the right decubitus view radiograph (1-year-old boy) shows a small quantity of free air between the liver and the diaphragm (arrow). Surgery verified perforation of four small bowel loops and 25 small magnetic balls

A magnet looks like any metallic object and can therefore be difficult to identify without information about the suspected type of foreign body. The radiologist should always raise concerns if two or more magnets or metallic objects are seen in close relation to one another.

Sharp objects can occasionally be ingested by children and older persons with self-destructive conduct. Ingested sharp objects, from razor blades to pins and fish bones, can cause perforation of the hollow viscera. A potential complication of sharp objects is that they may migrate out of the airways or gastrointestinal tract and cause local complications ranging from subcutaneous abscess of the neck or mesenteric fat to being present in the liver [37,38,39]. The location of the sharp object and any signs of perforation and migration determine the necessary management. The majority of ingested foreign bodies (80–90%) pass through the gastrointestinal tract spontaneously, and only 1% necessitate surgery [40]. Endoscopy is the preferred method if the object is located oral to the pylorus.