In this case, we confirm the possibility of a CBD stone forming around a fish bone as a nidus. Moreover, in the absence of an observable fistula, the fish bone was assumed to have migrated into the CBD, although the route and mechanism of this migration remain to be clarified.
We summarize previously published cases on CBD foreign bodies in Japan. We identified 54 reports (of 63 cases) that identified the following causes: iatrogenic (42/63, 66.7%), oral ingestion (17/63, 27.0%), extracorporeal penetration (1/63, 1.6%), and parasites (3/63, 4.8%). In the world, foreign bodies introduced by ingestion have included toothpicks [1, 2], needles [3], fish bones [4, 5], chicken bones [6], and plant fibers [7, 8]. Due to the high fish consumption in Japan, a fish bone was the most identified foreign body in the CBD in 16 cases, including our case [4, 9,10,11,12,13,14,15,16,17,18,19], and plant fiber in one cases [20] (Table 1).
Choledochoduodenal fistulae and post-biliary jejunostomies have been reported as routes of foreign body migration into the CBD [1, 5]. Other possibilities include direct access by needle-shaped objects, such as a fish bone [1, 4, 7], transhepatic migration [21], and transpapillary regurgitation [2, 3, 8, 10, 22, 23]. There is also the possibility of excretion of foreign bodies from the liver into the bile duct, as shown in a case of a shrapnel splinter in the right thoracic cavity that migrated into the CBD through the diaphragm and liver [24]. Foreign bodies could also migrate into the CBD through the papilla, as shown by cases in which soft material impaction, such as plant stems or fibers and a chicken bone, in the duodenal papilla was the contributing source of the CBD foreign body [6, 8, 20].
In our case, after distal gastrectomy and Roux-en-Y reconstruction, severe adhesions were found between the residual stomach and liver, as well as around the duodenal stump and hepatoduodenal ligament, although there was no fistula or jejunostomy. Additionally, no previous duodenal papillae treatment had been performed. Thus, besides the transpapillary route, transient gastrohepatic, and duodenal biliary fistulae were considered as possible causes but with no conclusive evidence. During the clinical course, since the fish bone migrated into the bile duct, there were no specific abnormalities, such as pain or inflammation associated with perforation. As such, we considered transpapillary foreign body migration as the most likely route of migration, as previously described [25]. In six cases (37.5%) reported in Japan, migration through the duodenal papilla was considered [10, 15,16,17,18,19]. The introduction of an ingested foreign body into the bile duct via reflux should also be considered, regardless of duodenal papilla treatment [7, 10]. In cases of post-gastrectomy, abnormal motility of the sphincter of Oddi has been observed by severing the intrinsic neural connection from the stomach at the proximal duodenum. As evidenced by the paradoxical response to cholecystokinin, post-gastrectomy sequelae may stimulate the contraction of the sphincter of Oddi. But it has not been clarified how a motor disorder of the sphincter of Oddi is related to regurgitation [26]. A study investigating reflux of oral contrast agents into the bile ducts during magnetic resonance cholangiopancreatography identified prior intervention to the duodenal papilla, parapapillary diverticulum, and pneumobilia as risk factors for reflux, although gastrectomy was not associated with the development of reflux [27].
Once the physiological analysis is completed, it is followed by the anatomical analysis. As several of the ingested foreign bodies reported to date have a thin needle-like shape and are approximately a few centimeters long, we hypothesize that they may be easily caught in the duodenal folds by peristalsis when passing through the curvature of the duodenum. Given that the duodenum is fixed to the retroperitoneum, the shape of the duodenum is almost flat in the direction of the papillary side of the small curvature, opposite to the greater curvature. Therefore, a long and thin object, such as a fish bone, that moves along a diagonal line in the major axis of the duodenal may unexpectedly be caught in the duodenal papilla.
Several hypotheses have been put forth as to why a fish bone is not expulsed from the CBD. The tip of the fish bone may have become lodged in the wall of the bile duct, subsequently being pushed into the bile duct by peristalsis, even if exposed to the duodenal papilla. Bile stasis might also be an associated factor. However, clear research evidence regarding these routes is needed. There is also the possibility of reflux into the afferent loop due to distal intestine stenosis or obstruction; however, such symptoms were not observed in our patient. Migration of the foreign body from the afferent loop to the duodenum, insertion into the duodenal papilla, and its persistent location in the bile duct appear to be coincident.
In our case, a retrospective review of prior images identified that the process of CBD stone formation around the fish bone took approximately 2 years. The fish bone initially stagnated in the CBD, without stone formation, for the first year. Subsequently, a CBD stone gradually grew around the fish bone and finally became incarcerated for approximately 2 years, causing acute cholangitis. Prior studies have shown the potential for food-based foreign bodies in the CBD to act as a nidus for stone formation, making excretion difficult [1, 9]. In our case, the stone that formed around the fish bone was formed of ocher bilirubinate. Bilirubin becomes deconjugated by the bacterial infection associated with cholestasis, resulting in the aggregation of poorly soluble calcium salts that led to stone formation around the fish bone [23]. Stone formation associated with a bacterial infection in the CBD is suggestive of reflux from the duodenal papillae.
In various reports, CT imaging has been useful to identify aspirated fish bones [9, 12, 28]. In our case, the fish bone in the CBD was visible on coronal plane MPR CT images performed at the onset of the cholangitis. On images of the axial plane CT, only a dot-like high-density area was observable, even though it could not be confirmed as an abnormality as the patient did not develop any symptoms. In particular, it was difficult to detect the very small spotted high-density area on the axial plain, which was performed before the cholangitis as a periodical examination. Today, owing to improvements in CT processing speed and resolution, CT reconstructed imaging could be routinely performed in cases with biliary system abnormalities.
Although endoscopic treatment is currently a well-established procedure, the patient would more likely be treated initially by single- or double-balloon endoscopy [9, 12]. However, this would have been technically difficult to perform in our case due to the altered anatomy following the Roux-en-Y reconstruction. The success rate of reaching the duodenal papilla would still be low especially in the presence of a residual stomach, and shortly after the introduction of the new procedure at the institution. Therefore, we proceeded with open surgery as the more reliable treatment option during which severe adhesions were carefully dissected, although the procedure itself was the same as for normal bile duct stones and, therefore, there were no safety issues.
In our case, as a clinical experience, there was a progression from the invasion of the fish bone into the CBD to stone formation and the onset of cholangitis. However, though we speculate on a transpapillary pathway of migration of the fish bone into the CBD, there was no confirmatory evidence. There is a need to accumulate cases and experiences to improve our understanding of the process of foreign body invasion of the CBD.
