An FB may not be seen for a variety of reasons. This is in contrast to metallic objects and chicken bones that are invariably seen on plain radiographs. When looking for FBs below the diaphragm, plain radiographs are generally not of sufficient diagnostic value to be used routinely as they do not show the culprit FB in most cases. Rare cases of a hepatic abscess with an embedded FB secondary to a duodenal perforation and a duodenocaval fistula have also been reported. Rarely, the FB may perforate the duodenum, a Meckel diverticulum or the appendix. Acute angulations, change in direction and transition from a mobile to an immobile segment of bowel are thought to predispose to perforation by an ingested FB. Within the bowel, the most common sites of perforation are the ileum, the ileocecal junction and the rectosigmoid colon. Such patients usually present with features of peritoneal irritation, abdominal pain, bowel obstruction and/or sepsis, and the first clinical impression is often of appendicitis or diverticulitis. In addition, the onset of symptoms may be preceded by a time lag of months or even years, further complicating the problem. Accidentally ingested FBs may not be remembered by patients. Perforations distal to the esophagus occur in <1% of the cases and are more challenging to diagnose, both clinically and radiologically. However, plain radiography has been shown to have a sensitivity of only 32% for FB detection in the upper aerodigestive tract and esophagus. Other suspicious findings on a lateral radiograph include widening of the prevertebral soft tissue and the presence of retropharyngeal air. An FB impacted within the cervical esophagus on the other hand is more likely to be seen.

However, in certain cases, the FB may not be seen, especially if it is impacted at the level of the tonsils or at the base of the tongue. It may show the FB as a linear calcific structure, in which case no further imaging is usually required. When the FB is in the upper aerodigestive tract, a plain radiograph is usually the initial and most commonly ordered radiological investigation. A few small surrounding lymph nodes are also seen (black arrows in B). There is associated surrounding soft tissue inflammatory thickening (black asterisk). Noncontrast coronal reformations (A,B) through the neck show a curvilinear FB extending from the region of the left tonsillar fossa into the parapharyngeal space (white arrows). Rare complications like internal carotid artery puncture, internal jugular vein thrombophlebitis, brachial plexus injury and lodgment within the thyroid gland have all been reported. In certain cases, the FB may penetrate the mucosal lining and extend into the deep spaces of the neck, with resultant abscess formation. Because it is usually an acute event and presents with a short history, it is easily recognized and treated by the otolaryngologist. The most common site of impaction is usually at the level of the tonsils, although the impacted bone may be found at the base of the tongue, the vallecula or the pyriform fossa. Within the GI tract, entrapment in the upper aerodigestive tract is the most common complication following ingestion of an FB. It may rarely enter the airways and lodge itself within the trachea or major bronchi. Once swallowed, an FB may lodge itself in the upper aerodigestive tract, esophagus, stomach, small bowel or colon.

Fish bones