Keywords
fishbone - foreign body - radiography - sensitivity - specificity
Introduction
Foreign body in upper aerodigestive tract is an important clinical problem. There
may be mild to serious complications such as tender or irritation of pharynx, infection,
abscess, esophageal perforation, mediastinitis, and death. Fishbone is one of the
most common foreign bodies in the upper aerodigestive tract.[1]
[2]
[3]
[4] The common site for a fishbone impact is the base of the tongue, palatine tonsils,
valleculae, and upper esophagus.[5] Although most cases can be diagnosed by physical examination, some difficult-to-diagnose
cases may need investigations including radiography, barium swallowing, computed tomography
(CT), and endoscopy. Plain radiography is the first investigation for diagnosis fishbone
foreign body due to non-invasive technique. In the past, plain radiography allowed
poor visualization of a fishbone foreign body in the soft tissue comparing with a
CT scan[4]
[6] or endoscopy. Recently, radiography has developed with novel techniques and advanced
digital technology. It yields better visualization and is more precise than conventional
plain radiography.[7] Using digital radiography as the diagnostic tool for detecting fishbone foreign
body in the throat may help to decrease unnecessary endoscopy and CT scan.
Several studies[3]
[4]
[8]
[9]
[10] reported varied radio-opacity of fishbones, which depend on numerous factors including
the size of the bone, calcium content, and the salinity of the water in which the
fish grow.[3]
[5] Although the radio-opacity of the fishbone is varied, it is not significantly different
between fish that is uncooked, roasted, or simmered in a stock.[4] Therefore, we designed the embedded uncooked fishbone in the throat of the fresh
human cadaver to assess the accuracy of digital radiography for diagnosing a fishbone
foreign body.
Methods
We included in our study 15 commonly eaten species of fish in Southeast Asia ([Fig. 1]). We designed the study into three phases to assess the value of radiography in
the diagnosis of fishbone foreign bodies in the throat. The study took place during
September 2012 to August 2013.
Fig. 1 Fifteen species of fishbone included: (1) Walking catfish; (2) Short-body mackerel;
(3) White snapper; (4) King mackerel; (5) Jullien's Golden-price carp; (6) Silver
barb; (7) Threadfin bream; (8) Striped snakehead; (9) Yellow stripe trevally; (10)
Black pomfret; (11) Snake skin gourami; (12) Nile tilapia (13); Striped catfish; (14)
Mullet; (15) Red tilapia.
In the first phase, we evaluated subject contrast of fishbones for each species with
the ratio between pixel value of fishbone (the value of X-ray can pass through the
object) and background pixel value (the value of X-ray can pass through the area around
the fishbone). Backgrounds in each area must be similar in pixel value, varying no
more than 10%. In this study, the background pixel value was different from 0.58%.
The mean of background pixel value was 3690.79 with a standard deviation of 21.32.
Additionally, two radiologists assessed the visibility and classified participants
into three groups: invisible group, unclear group, and obvious group. If the two radiologists'
interpretations were different, they had to reach a consensus.
In the second phase, we applied the lateral soft tissue neck digital radiograph to
evaluate the embedded fishbone foreign body of each species in the fresh human cadaver's
throats. We cut all of the fishbones to 2 cm in length and recorded the diameter of
bones by caliper (scale 0.1 mm). After placing each species of the fishbone on the
vallecula of the fresh human cadaver, we took lateral neck digital radiograph with
60 kvP, 100 mA, 5mAs by general radiography system: radnet 80/radnext 50 Hitachi and
digital radiography “Fuji film DR” FDR D-EVO (DR-ID600) ([Fig. 2]). In addition, we designed one radiograph without fishbone as a controlled trial.
The visibility of fishbone was interpreted in the same way as the first phase.
Fig. 2 The arrow indicates the embedded fishbone in fresh human cadaver's valleculae.
In the third phase, the aim was to study the accuracy of the radiography to diagnose
the fishbone foreign body in any site of the throat including tonsil, base of tongue,
vallecula, and upper esophagus. Regarding varying ossification of the laryngeal cartilage,
we used only one fresh human cadaver; however, we were concerned with multiple embedding
of all of fishbones in one cadaver that could affect the radiologists' interpretations
due to the phenomenon of air in soft tissue as an artifact around the fishbone. Therefore,
we selected one fishbone in each of the three visibility group and cut to 2 cm in
length and in a similar diameter. Each species of fishbones was embedded into the
tonsil, base of tongue, vallecula, and upper esophagus. We applied lateral neck digital
radiograph. We created controlled radiograph without fishbone for the three visibility
groups. The same two radiologists interpreted the radiographs, who noted whether the
fishbone was present or absent in the cadaver's throat and described the site of where
the fishbone presented. The local ethics committee approved this study (HE551282).
Results
[Table 1] shows the subject contrasts of fifteen species of fishbone. Regarding visibility,
all species of fishbone were obvious in the first phase; whereas, visibility of fishbone
in the second phase (embedded fishbone in the cadaver' throat) was varied. The radiologists
interpreted the obvious visible group as 46.67%, the unclear group was 20%, and the
invisible group was 33.33% ([Table 1]). We analyzed the correlations of visibility factors including subject contrast
and diameter of fishbone with the Spearman's rank Correlation Coefficient which showed
non-significant correlation (p = 0.09 and p = 0.24, respectively). Furthermore, the analysis of variance between visibility in
each group and subject contrast was also not statistically significant (p = 0.25) ([Table 2]). In the third phase, we selected the King Mackerel, Striped Snakehead, and Silver
Barb as the agents of the three visibility groups: the invisible, unclear, and obvious
groups, respectively. Overall, the radiologists correctly interpreted ten of fifteen
radiographs (66.67%, 95%CI: 38.38–88.17). Regarding the precision of digital radiograph,
the fishbone foreign body at the base of tongue resulted in the highest accuracy;
whereas, the tonsil was of difficult interpretation with the poorest diagnostic value
([Table 3]).
Table 1
Subject contrast and visibility of fifteen species of fishbone
|
Species of fishbone
|
Phase 1
|
Phase 2
|
|
Diameter
of FB (mm)
|
Mean of pixel value
|
Subject contrast
|
Visibility
|
Visibility
|
|
FB (US)
|
BG (US)
|
|
Black Pomfret
(P.niger)
|
0.9
|
3653.86
|
3705.85
|
0.99
|
2
|
2
|
|
Yellowstripe Trevally
(S. leptolepis)
|
0.9
|
3646.50
|
3704.77
|
0.98
|
2
|
1
|
|
Short-bodied Mackerel
(R. brachysoma)
|
1.3
|
3641.68
|
3694.38
|
0.99
|
2
|
0
|
|
King Mackerel
(S. commerson)
|
1.8
|
3636.22
|
3711.80
|
0.98
|
2
|
0*
|
|
Jullien's Golden-Price Carp
(P. jullieni)
|
1.5
|
3624.26
|
3713.50
|
0.98
|
2
|
2
|
|
Walking catfish
(Clarias spp.)
|
0.8
|
3600.91
|
3679.74
|
0.98
|
2
|
1
|
|
Snake Skin Gourami
(T. pectoralis)
|
0.8
|
3589.61
|
3643.21
|
0.99
|
2
|
0
|
|
Mullet
(Mugilidae)
|
1
|
3580.75
|
3681.44
|
0.97
|
2
|
0
|
|
Threadfin Bream
(Nemipterus spp.)
|
1.3
|
3568.00
|
3681.78
|
0.97
|
2
|
2
|
|
Nile Tilapia
(O. niloticus)
|
1
|
3565.09
|
3664.08
|
0.97
|
2
|
0
|
|
Striped Catfish
(P. sutchi)
|
1
|
3554.20
|
3678.40
|
0.97
|
2
|
2
|
|
Silver Barb
(B. goinonotus)
|
1.5
|
3543.37
|
3677.45
|
0.96
|
2
|
2*
|
|
Red Tilapia
(O. niloticus)
|
1.9
|
3521.59
|
3691.50
|
0.95
|
2
|
2
|
|
Striped snakehead
(C. striata)
|
1.5
|
3517.81
|
3716.51
|
0.95
|
2
|
1*
|
|
White Snapper
(L. calcarifer)
|
1.2
|
3490.95
|
3717.40
|
0.94
|
2
|
2
|
Abbreviation: BG, background; FB, fishbone.
* Fishbones represent each group of visibility (0 = invisibility group, 1 = unclear
visibility group, 2 = obvious visibility group).
Table 2
Correlation of the visibility factors
|
Spearman's rank Correlation Coefficient
|
p Value
|
|
Visibility versus Subject contrast
|
0.09
|
|
Visibility versus Diameter of fishbones
|
0.24
|
|
Analysis of variance
|
--
|
|
Visibility in each group versus Subject contrast
|
0.25
|
Table 3
Diagnostic value of radiographs for diagnosis fishbone foreign body in different site
of throat
|
Site
|
Sensitivity (95% CI)
|
Specificity (95% CI)
|
|
Base of tongue
|
1.00(0.44–1.00)
|
0.92(0.65–0.99)
|
|
Valleculae
|
0.67(0.21–0.94)
|
1.00(0.76–1.00)
|
|
Upper esophagus
|
0.67(0.21–0.94)
|
0.83(0.55–0.95)
|
|
Tonsil
|
0.00(0.00–0.56)
|
1.00(0.76–1.00)
|
Discussion
In the past, plain radiograph was used to detect the fishbone as a foreign body in
the throat, but the quality of visualization was poor. Since then, new advanced digital
technology has been developed that improves visualization. The accuracy of the radiograph
was reported but it was of varying value; therefore, we designed the study into three
phases to investigate diagnostic value. In the first phase, we placed the fishbone
on the homogenous background. All of them can be identified with high subject contrast
of 0.94–0.99. Although the fishbone has high radio-opacity, it was difficult to identify
when embedded in the throat in the second phase. We observed that the two radiologists'
visibility decreased in the second phase. The fishbones were classified into three
groups: obvious, unclear, and invisible group. Most of them fell into the obvious
group (46.67%), whereas the unclear and invisible group represented 20% and 33.33%,
respectively. The decreased visibility may be a consequence of many factors, including
site and air around of the embedded fishbone,[9] diameter[4] and direction of fishbone,[11] and human laryngeal ossification.[9] For identifying the correlation of visibility factors ([Table 2]), we designed the fishbone in the same length and placed it on a fresh human cadaver's
valleculae. We aimed to eliminate the confounding factors including site, direction,
and laryngeal ossification. The result showed the correlations of visibility factor
including subject contrast and diameter of fishbone that were not statistically significant
(p > 0.05). However, the limitation of this study is using only one cadaver due to concerns
with varying laryngeal ossification.
Regarding the site of the embedded fishbone in the throat, the base of the tongue
produced the highest accuracy, whereas, the tonsil was of difficult interpretation
with the poorest diagnostic value. These results may be a result of the angle of mandible,
obscuring the tonsil and causing greater difficulty in its interpretation than other
sites. However, embedding the fishbone in the cadaver in the third phase may present
the air around fishbone; therefore, we embedded the fishbone less than 8 times for
reducing this confounding factor.
Overall, our study yielded 66.67% accuracy (95%CI: 38.38–88.17), which is similar
to previous studies. Therefore, the radiograph is one of the non-invasive investigations
that help to diagnose fishbone foreign bodies in the throat, especially at the base
of tongue, valleculae, and upper esophagus. It does, however, have poor accuracy for
fishbones embedded at the tonsil, although a foreign body in this area is easily detected
with careful physical examination.
Conclusions
All species of fishbone have high radio-opacity but each one has different visibility
when embedded in the throat due to the existence of many confounding factors. However,
digital radiography provides high accuracy and great benefit in the diagnosis of fishbone
foreign bodies at the base of the tongue, vallecular, and upper esophagus.
