Dr. Low is an Associate Professor and Dr. Killius is a Fellow in the Abdominal Image Division of the Department of Radiology, Duke University Medical Center, Durham, NC.

The majority of alimentary or abdominal foreign bodies occur due to accidental ingestion. Most (80% to 90%) will pass uneventfully, but others may cause obstruction or perforation depending on their morphology and size. ^1,2 Less commonly, foreign bodies may be introduced through other routes or percutaneously. Finally, it is important to recognize iatrogenic foreign bodies that may be introduced either deliberately or by mishap during surgical, diagnostic, or therapeutic procedures.

The objectives of radiography should be to recognize the appearance of opaque and lucent foreign bodies, as well as diagnose complications of their presence. There are also a few therapeutic options available to the radiologist to assist patients with these foreign bodies.

Ingested foreign bodies

An appropriate history is usually available, which will give a key to the type of foreign body expected, as well as to the expected site of obstruction or other symptoms. Bolus impaction in adults is usually caused by animal or fish bones or by unchewed boluses of meat ³ (figure 1). Occasionally, however, such history is not available (especially in children, mentally incompetent, or uncooperative patients) and 20% of patients may be asymptomatic ^4,5 (figure 2). Indeed, when one foreign body is known to have been ingested, consideration should be given to the possibility of a second. ^2,6 Children usually impact with ingested and sometimes unwitnessed coins, toys, or other foreign objects. ³

A foreign body may become impacted in the pharynx, which in turn may cause choking or gagging because it is large or associated laryngeal spasm. ⁴ Conversely, a foreign body impacted in the esophagus may be regurgitated back into the pharynx with similar risk of airway compromise. ^2,6 A crash cart for cardiopulmonary resuscitation must be immediately available during assessment of these patients.

Approximately 70% to 80% of ingested impacted foreign bodies will lodge in the pharynx or cervical esophagus. ^4,6-8 This is particularly likely to occur with sharp objects such as fish bones ³ (figure 3A). When this is the suspected location of impaction, the most useful initial study is a lateral soft-tissue view of the neck. ³ It should be centered below the angle of the mandible with the patient seated up-right, neck extended, shoulders low and posterior. The patient phonating "Eeee" may prove useful to distend the pharynx and improve visibility. ⁸ Regardless of optimal technique, it may be difficult to differentiate small bone fragments from laryngeal cartilage calcifications. A reference guide to the range of such calcifications is of value in exploring this problem. ⁹

In the esophagus, favored sites of hold-up include the level of the aortic arch, the left main bronchus, and the gastroesophageal junction, especially when there is a pre-existing stricture ^3,4 (figure 3B). A barium swallow may be required to find these obstructed foreign bodies and is also warranted for follow-up after the acute impaction is resolved to detect an underlying stricture that is usually present. ^2,3 A foreign body impacted in the pharynx or esophagus is unlikely to pass spontaneously, and warrants immediate removal. ^2,4 Once in the abdomen, the foreign body may stop at the gastric pylorus (usually if it is thicker than 2.0 cm and longer than 5.0 cm), fail to traverse the duodenal sweep (usually if it is long, >10 cm), or obstruct at the ileocecal valve. ² Again, a pre-existing stricture may make passage of the body difficult (figure 4).

The nature of the offending foreign body is important to its detection and management. Metal or bony material are easily seen. Similarly, lead-containing glass or crystal may be visible. Plastic or wood is almost always a challenge unless there is some adherent lead paint. Fish bones are usually a problem, as they are often sharp and cause considerable irritation, and are variably opaque. Other sharp and pointed objects (e.g., other meat bones, toothpicks, razors, and pins) are at risk of perforating the gut ^1,10 (figure 5). Sometimes, the penetrating object may seal the perforation and prevent leakage of bowel content until it is removed. ⁸ Ideally, such objects should be removed while still in the stomach. ²

Metallic ingested foreign bodies require special consideration in their management. The acid of the stomach may react chemically with the metal and result in mucosal inflammation, ulceration, and perforation. Similarly, gastric acid may break the seal of an ingested battery, leading to corrosive toxicity. This is of particular concern with miniature alkaline batteries. These batteries are in common use in electronic devices and toys and are small and easily swallowed. ^6,11 Break down of the swallowed battery allows discharge of its contents. They may contain strong concentration (40% to 45%) sodium or potassium hydroxide, which has been reported to be responsible for perforation by alkali necrosis of the esophagus, stomach, and small bowel Meckel's diverticulum with serious or fatal consequence. ^6,11-13 The chemical toxicity of heavy metals that may be contained within some of these batteries is also of concern. Silver, manganese, cadmium, nickel, zinc, and lithium are all used in their composition. Mercury is another consideration as it may be absorbed into the circulation ^6,14 (figure 6). The amount of mercury (usually in the form of elemental mercury or as mercuric oxide) within a battery ranges from 0.09 to 21 g. The lethal dose of the toxic form of mercury (as chloride or oxide) for humans is not known exactly, but is estimated to be 1.0 to 4.0 g. ^2,12

Coins have traditionally been considered relatively inert in their chemistry. A dime (17 mm) or a penny (18 mm) will usually pass through the intestinal tract if there is no hold up in the pharynx or esophagus. ² In 1982, the copper penny (95% copper, 5% zinc) was replaced by the zinc penny (2.4% copper, 97.6% zinc). The zinc results in chemical reactivity including the development of gastric erosions. ^2,15

Swallowed, concealed illicit drugs (e.g., crack in vials, cocaine in condoms) can produce a very confusing picture, especially in the absence of a useful history from the patient. These drug couriers, known as "mules" or "body packers," use the gastrointestinal tract to smuggle their cargo undetected by the custom authorities. Imaging may be called upon to examine these suspects without physical intrusion. Occasionally, a courier may be imaged without suspicion because of a medical presentation (such as may occur if a package is disrupted resulting in drug intoxication, or if the packages result in a bowel obstruction). On plain films, bundles of cocaine are visible in up to 90% of cases and appear as multiple uniformly round or oval densities (figure 7). The density of the packet will vary with the wrapping material used (dense aluminum foil versus lucent wax) and the processing of the surrounding balloons or condoms (there may be a tiny amount of air trapped between the layers, producing a lucent rim). In cases of doubt, ultrasonography and computed tomography would be appropriate to further define the suspect material. ^2,16-19

A few therapeutic options are available for the radiologist to assist in the management of some of these patients. A bolus impacted at the gastroesophageal junction may pass spontaneously during a barium swallow, aided by IV glucagon to relieve sphincter spasm, and effervescent agents. ^2,3,20 A Foley balloon catheter may be introduced and passed with fluoroscopic guidance past the offending bolus. The balloon can then be distended and the foreign body can be extracted from the esophagus as the catheter is withdrawn. ^2,4,21 Occasionally, a magnet-tipped probe can be passed fluoroscop-ically into the esophagus or stomach to retrieve a metal foreign body. ²² Considerable care must be taken with impactions of >24-hour duration because of the potential for esophageal perforation from pressure necrosis. ³

A few pathological conditions may produce a radiographic appearance mistaken for foreign bodies. The presence of intestinal infestation by Ascaris lumbricoides may produce a radiographic appearance mistaken for foreign bodies (fragments of catheter or other tubing). These parasites appear as long, thin, tubular filling defects in the bowel (figure 8). They might be particularly confusing when seen on CT, as the worm will only be seen in small sections on multiple images. ²³ Sonography of ascariasis has also been described; this modality is useful in its ability to visualize the curling movements of the worms, establishing the diagnosis with certainty. ²⁴ Luminal filling defects may also be seen with bezoars (figure 4C), gallstone ileus (figure 9), and polypoid tumors.

Parenterally inserted objects

Objects may reach the abdominal cavity or alimentary tract through the anus, urogenital canal (figure 10), or percutaneously, either deliberately or accidentally. ⁷ An obvious history is usually forthcoming, which will aid in the identification of the presence or absence of the suspected foreign body. Occasionally, such information is withheld (figure 11), either due to patient embarrassment or to avoid criminal prosecution.

Iatrogenic foreign bodies

Deliberately retained surgical clips are well recognized. Inadvertently retained material include laparotomy pads, sponges, Penrose drains, needles, hemostats, and forceps ⁷ (figure 12). Nonopaque surgical material, such as sponges, always include radiopaque markers in their manufacture ²⁵ (figure 13). Occasionally, these are left intentionally to maintain hemostasis, especially if postoperative oozing is anticipated. They should be removed either before the closure of the operation or at re-exploration soon after. ²⁵ A retained surgical sponge may result in development of an inflammatory mass, a gossypiboma. ²⁶

Increasing use of enteric and vascular catheters and other devices will require recognition to identify the correct location or misplacement. The most serious potential misadventure of a feeding catheter or nasogastric tube is placement in the tracheobronchial tree, which can lead to life-threatening pneumothorax, especially when the tube is removed. ^27,28 The malposition of the tube may also go unrecognized as the device may only be visible on the periphery of the field of view of an abdominal radiograph (figure 14).

The historical use of Thorotrast as an intravascular contrast medium­­with resultant permanent retention of the dense material within the reticuloendothelial system of the liver, spleen, and lymph nodes­­may result in a bizarre appearance of the abdominal radiograph to the unwary ^29,30 (figure 15). Intravenous injection with mercury has been reported and will produce a similarly strange appearance with droplets of the liquid metal visible in the liver, kidneys, lungs, and gut. ³¹ Thorotrast was also used to opacify hollow organs with resultant permanent retention of the material under the epithelial surface, such as renal opacification after retrograde pyelography. ³² AR

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