The pharynx is a muscular tube extending from the base of the skull to the level of the cricoid cartilage. It plays a crucial role in life processes such as breathing, swallowing, and speech. The pharynx is surrounded by a multi-layered wall composed of mucosa, pharyngobasilar fascia, the muscle layer with upper and lower constrictors, and buccopharyngeal fascia [4]. The pharynx is funnel-shaped, flat at the front and back, wide in the upper area, and narrow in the lower region. Since fish bones are slender and sharp, they can easily enter the hypopharynx or esophagus together with the food mass while eating [5]. Once sharp fish bones become embedded into the base of the tongue, the piriform fossa, the posterior hypopharyngeal wall, and other nearby areas, they are able to penetrate the upper digestive tract and enter the peripharyngeal space if left treated [4]. After entering the peripharyngeal space, the fish bones can move into various spaces in the neck due to swallowing, esophageal peristalsis, vascular pulsation, or neck muscle activity, thereby forming cervical migratory foreign bodies [6]. Migratory fish bones are heterologous, which predisposes them to abscess formation. Severe cases can cause serious complications or mortality due to injury to neurovascular structures [6,7,8]. This is worthy of serious attention by clinicians, especially for otolaryngologists who work in areas with high seafood consumption.

The key to successful removal of a foreign body in the neck is to clearly identify the location of the foreign body before and during the operation. Laryngoscopy, lateral neck X-ray, and neck CT scans are commonly used for diagnosing migratory foreign bodies in the neck [9, 10]. In a few studies, B-ultrasound has been used to guide foreign body removal [11, 12]. Neck CT imaging is better at detecting recently embedded short fish bones, and for large and hard bones. However, it is not effective in detecting small fish bones embedded for a long time. After obtaining a detailed history, patients who presented in our department with a high suspicion of migratory foreign bodies underwent a combination of laryngoscopy, neck B-ultrasound, and neck CT three-dimensional reconstruction [13]. For migratory fish bones in the oropharynx (such as the retropharyngeal space), the bulging, red, or swollen posterior pharyngeal wall is easily detected by laryngoscopy. However, the positive rate for laryngoscopy is low because there are no obvious abnormalities in the migrated foreign bodies. Neck B-ultrasound is easy to perform, inexpensive, avoids radiation exposure, is appropriate for both radiolucent and radiopaque foreign bodies, and allows foreign bodies in the neck to be located precisely. It can also determine the distance between the foreign body and the skin surface, as well as its relationship with adjacent blood vessels. The present study demonstrates that B-ultrasound is highly effective at diagnosing cervical migrating fish bones. However, its diagnostic capability around the throat and trachea is limited due to the presence of air-filled spaces such as the trachea and esophagus. Thin-slice CT scans and three-dimensional reconstruction provide a comprehensive view of foreign bodies in the neck from various angles. Moreover, they can accurately depict their shape, size, position, and relationship to neighboring structures. This method is also able to assess the nature of the foreign body and the presence of vascular damage. A review of the literature indicates that CT scans exhibit high specificity but low sensitivity for the diagnosis of migrating fish bones [3, 11, 14, 15]. The current study found that the success rate of CT scans (18/30) was not as high as that of B-ultrasound, in line with the findings of Chen et al. [2] Likely reasons for the lower detection rate of CT scans include: (1) most elongated fish bones are not visible on X-rays, making CT detection challenging; (2) the delay between fish bone ingestion and the onset of symptoms allows time for inflammation, partial absorption, organization, and decalcification of the fish bones, thus reducing the success rate of CT scans in the neck; and (3) the thickness of CT slices is often greater than the diameter of the fish bone, leading to possible misdiagnosis even with three-dimensional CT reconstruction [3]. Therefore, B-ultrasound and CT scans each have advantages for diagnosing migratory fish bones in the neck. B-ultrasound is more sensitive for foreign bodies located at the front and sides of the neck, whereas cervical CT scans are better for detecting fish bones in the retropharyngeal space [3]. Combining B-ultrasound with CT scans significantly increases the diagnostic accuracy for migratory fish bones in the neck and reduces the risk of a missed diagnosis [2]. Based on our clinical experience, we therefore propose a diagnostic and treatment strategy for cervical migratory fish bones that emphasizes the critical role of B-ultrasound, in contrast to previously reported strategies in the literature [10, 14, 16].

The fish bone is a heterologous foreign body in the neck that may induce local inflammation upon entering soft tissues, leading to infections in soft tissue spaces and potentially severe complications. Hence, timely removal of the foreign body after a definitive diagnosis is imperative. In the present study, the time elapsed from the moment of foreign body ingestion to the onset of neck symptoms ranged from 26 to 151 days, with an average of 61.7 ± 35.2 days. This concurs with the findings of other researchers [2, 17].

Removal of the foreign body was conducted using external cervical approaches and transoral endoscopic surgery. The external cervical incision approach targets lateral, anterior, and submandibular foreign bodies, with preoperative B-ultrasound marking the surface projection. During the procedure, the surrounding vital nerves and vessels were carefully protected while searching for foreign bodies in the inflamed area. If a local foreign body granuloma had formed, this was completely excised and the tissue examined for fish bones. In the 6 cases where the fish bone was located in the retropharyngeal space, these were removed via transoral endoscopic surgery guided by high-definition endoscopy. Based on the location of the foreign body, its proximity to surrounding tissues (epiglottis and tonsil), and the observation of local swelling on the posterior pharyngeal wall under high-definition endoscopy, a vertical incision was made on the mucosa of the posterior pharyngeal wall. Complete hemostasis ensured a clear surgical field, allowing the foreign body to be meticulously separated with laryngeal forceps under high-definition endoscopy and then removed. The use of high-definition endoscopy resulted in less trauma and avoided neck scarring, thereby adhering to the principles of minimally invasive surgery and aesthetic considerations [18]. During the procedure, it was important to compare the length of the foreign body to the preoperative assessment, to verify the completeness of the foreign body, and to check for new sections at its ends. If discrepancies in length or new sections were noted, a thorough inspection of the area around the foreign body was conducted until all foreign bodies were identified and removed.

Intraoperative B-ultrasound may be utilized for dynamic exploration if it proves challenging to locate the foreign body during surgery. The relationship between the foreign body and the hyoid bone, neck sheath, thyroid cartilage, and other fixed anatomical structures should be explored during the operation. The vascular clamp tip can be positioned to locate the foreign body according to the adjacent relationship [2, 7]. Hence, in 9 patients we successfully identified the direction and position of fish bones and removed these with the help of intraoperative B-ultrasound.