The Utility of Diagnostic Imaging in Fish Bone Impaction

Objectives: The purpose of this pilot study was to obtain an Australian perspective on evaluating the utility of plain film radiography and computed tomography (CT) to rule out fish bone impaction in the upper aerodigestive tract in the emergency department (ED) setting. Methods: A retrospective multicentre cohort study was conducted. A total of 73 patients met the inclusion criteria. A subgroup of patients underwent CT. We studied the sensitivity and specificity of x-ray and CT along with other demographic variables to determine the likelihood of true fish bone impaction. Results: Out of the 73 patients, 28 patients had true bone impaction. The sensitivity for x-ray was 42.9% and specificity was 73.3%. The sensitivity of CT was 87.5% and specificity was 71.4%. We found a significant difference in the mean age of presentation for true bone and false bone impaction, P = 0.02. Conclusion: Due to the low sensitivity of x-ray we do not recommend the utilisation of plain film radiography to rule out bone impaction Advances in low dose radiation multidetector CT scanners may replace plain film radiography as a screening tool.


Introduction
Fish bone impaction in the upper aerodigestive tract represents a common emergency department (ED) presentation and one which frequently requires review by otolaryngology specialists. Such patients can present with variable symptomatology ranging from severe pain and odynophagia to being relatively asymptomatic. In a prospective study of fish bone impaction a "sharp pricking sensation on swallowing" had the best predictive value of any symptom (76%) [1]. Other symptoms included pain on swallowing, foreign body sensation, pain How to cite this paper: Kumar, S., Yu, C., Toppi, J., Ng, M., Hill, F. and Sist, N. The duration of symptom onset to presentation at ED also showed a correlation with the presence of fish bone on endoscopy with the yield of fish bone retrieval decreasing as the duration increased [1].
The yield of fish bone retrieval using endoscopy has been shown to decrease as the duration of presentation to ED increases [1]. In patients presenting within 12 hours of symptom onset, 60% of them were found to have fish bones, whereas patients presenting between 12 to 24 hours and 3 to 7 days yielded a bone 38% and 20% of the time respectively [1].
Several cadaveric studies have also been performed evaluating the efficacy of various imaging modalities in the detection of fish bones. A study by Lue et al.
involving the plain film analysis of 10 types of fish bone in a human cadaver suggested that the visualisation of fish bones was more dependent on their position rather than their degree of radio-opacity [2].
Typically, patients presenting with suspected fish bone impaction will receive plain film radiography with an otolaryngology consult for flexible nasoendoscopy to visualise the foreign body. Utilisation of plain film radiography is controversial due to its low sensitivity [1] [2] [3]. Studies have suggested that plain film radiography has a relatively low sensitivity (24% -54.8%) and high specificity (72% -100%) when it comes to the detection of fish bones [4] [5] [6] [7] [8].
The low sensitivity has been shown to be related to the comparatively low densities of certain fish bones and difficulties in evaluation related to the calcification of surrounding laryngeal structures [2] [3].
Despite this x-ray has been advocated for use in the initial evaluation of fish bone impaction because of the presumed perception that it is cost-effective and leads to a quicker diagnosis with minimal radiation exposure [4] [9].
In comparison, Computer Tomography (CT) has been shown to be highly accurate in identifying fish bones with sensitivity and specificity values approaching 100% [4].
A recent study by Devarajan et al. evaluating the utility of the plain-film screen for fish and chicken bone impaction considered its efficacy in terms of the cost incurred by the hospital, patients' length of stay and radiation exposure [4]. It found plain film radiography did not reduce the cost to the hospital or length of stay in false impactions compared to true impactions. The authors went on to suggest that low dose radiation multidetector CT evaluation could serve as an alternative screening tool [4] [10].
The most common sites for fish bone impaction are the palatine tonsils, tongue base, vallecula and piriform sinus [11]. Fish bones impacted in the palatine tonsils should be detectable by direct examination [11].
As there is limited data from an Australian population and conflicting opinions of the use of plain film radiography as screening tools, the primary aim of this study was to quantify the accuracy of x-ray and to test the perception that plain film radiography can be used to rule out fish bone impaction in the upper

Method
A retrospective multicentre cohort study of patients presenting to Eastern Health Emergency Departments was conducted between January 2010 to December 2015. All patients presenting to one of either Box Hill Hospital, Maroondah Hospital or the Angliss Hospital with a possible fish impaction between the study period were included in the final analysis. Patients who did not undergo a radiological investigation and subsequent gold standard investigation were excluded from the study.
In this study, the gold standard of diagnosis was defined as direct visualisation via endoscopy (flexible nasoendoscopy or laryngoscopy). The imaging modalities were interpreted by a consultant radiologist.
Electronic and paper records from the emergency departments and hospital wards were accessed to obtain data including sex, race, age, symptomology, x-ray performed, CT performed, onset of symptomology and time to presentation to ED, representations, Ear Nose and Throat (ENT) consultation, form of endoscopy and location of true bone impaction was also recorded.
The outcome of each of the imaging modalities was determined whether it was a true positive true negative. The sensitivities, specificities, positive predictive values (PPV) and negative predictive values (NPV) were calculated. Descriptive statistics were used to summarise the characteristics of the included patients. Frequencies and percentages were used for categorical variables. Chi Square tests were used to compare categorical variables. Mann-Whitney U tests (two groups) were used to compare the means of continuous variables where data were not normally distributed. Tables and graphs were generated using Microsoft Excel to assist in interpretation of results. Statistical analysis was carried out using Graphpad Software [12]. P-values of less than 0.05 (5%) were chosen as the level of significance.

Results
A total of 73 patients were included in the final analysis from the period of 2010 and 2015 with suspected fish bone impaction. Table 1 summarises the demographic and clinical data that were obtained during this study. A total of 28 patients (38.4%) had true bone impaction. The majority of presentations were female in gender (75%). There was no significant difference in terms of gender or race and bone impaction rates (P-value = 0.6 and 1.0, respectively) ( Table 1).
The mean age of presentations for true bone impaction was 56.5 and for false bone impaction 46.3 ( Table 1). The difference was significant (P-value = 0.02).
The mean duration of presentation post ingestion of a foreign body was 16 hours with true bone impaction, and 24 hours for false bone impaction, this difference Open Journal of Radiology was not significant (P-value = 0.11) ( Table 1). Table 2 summarises sensitivity and specificity data for plain film radiography.
Of the 24 x-rays that were reported as positive for bone impaction, 12 were deemed as true impaction. The sensitivity for x-ray was 43% and specificity was 73% with a positive predictive value of 50% and negative predictive value of 67.4%.
A total of 13 patients also received a CT, of these a total of 7 were reported as positive for bone impaction with 6 being deemed as true impaction. The sensitivity of CT was 85.7%, specificity 83.3%, positive predictive value 85.7% and negative predictive value 83.3%. Table 3 summaries the frequency of symptomatology experienced by patients.
Foreign body sensation and odynophagia were the most common symptoms observed, with a frequency of 48.4% and 33.0% respectively.      [13]. Therefore, we cannot rule out fish bone impaction with x-ray alone. Open Journal of Radiology A total of 51% of the patients who presented to Box Hill ED were of Asian descent. This is likely due to Box Hill town centre being in close proximity to Box Hill Hospital. Box Hill town centre has a large Asian population and contains predominantly Asians restaurants, which often incorporate small fish bones [4].

Statement of Principal Findings
We found no statistical significant difference (P = 0.8) between Asians and Non-Asians for true and false bone impaction rates [4].
We found a significant difference (P = 0.03) between the mean average age of true (55.0 years old) and false bone impaction (47.1 years old). Older age was more likely to be associated with true bone impaction. Devarajan  However, there is also evidence to suggest plain film radiography has poor sensitivity irrespective to inter-species variation in bone radiopacity [2] [3].

Conclusions
Although x-ray has a low radiation dose (0.2 mSv) [20] and cost in comparison to CT scanning [4], due to the low sensitivity of x-ray we do not recommend the utilisation of plain film radiography to rule out bone impaction in the upper aerodigestive tract.
The results from our pilot study have demonstrated discrepancies in literature, with regards to symptomology, mean duration prior to presentation to ED (hours) and average age and true bone impaction. Due to these results and the limited Australian data available, we propose a multicentre prospective study to further evaluate the efficacy of plain film x-ray in ruling out bone impaction in an Australian population. Further studies utilizing low dose CT evaluation also need to be conducted. Until then we recommend an ENT consult with flexible nasoendos copy which has previously proven to be a safe effective and economic algorithm in the management of patients with suspected bone impaction [1].

Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the authorship, research and publication of this article.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethics
Ethics approval was obtained from the Office of Research and Ethics, Eastern Health. Reference number: LR08/2016.

Supplementary Material
The data was obtained through Symphony software, and electronic medical records through Eastern Health, Box Hill, Victoria.