DISCUSSION
Image enhancement systems increase the contrast of the blood vessels for
improved visibility of the submucosal vasculatures. Using the NBI
enhancement system, the ELS classified the submucosal vascular patterns
in laryngeal lesions as longitudinal and perpendicular, with an
association of the perpendicular pattern with malignancy, and the
longitudinal pattern with benign conditions. In the present study, the
vascular patterns reproduced by Image1 S endoscopy in benign and
malignant lesions were highly consistent with those defined in the ELS
classification. The prediction of the pathological diagnosis strongly
correlated with the definitive pathological diagnosis of the lesions.
Moreover, the evaluations of the patterns were highly consistent among
the evaluators, irrespective of their work history, or their previous
experience with image enhancement systems. These consistencies stated
above, are directly related to improved visibility of the vasculatures
by contrast enhancement. Therefore, Image1 S is considered to be an
effective and practical technique for evaluation of the vascular
characteristics of laryngeal lesions to predict malignancy.
Stanikova et al. used both NBI and the Image1 S system to investigate
the relationship between the vascular patterns and the pathological
diagnosis of laryngeal lesions (7). They found the sensitivity and
specificity values for NBI endoscopy of 83% and 98% respectively,
whereas those values for Image1 S were 86% and 96%, respectively. In
diagnostic use, the high specificity of the test indicated a strong
association of benign lesions with the longitudinal pattern and a weak
association with the perpendicular pattern, suggesting an ability to
detect the patterns in benign lesions. However, in our study, Image 1
endoscopy showed a higher sensitivity (96%) and a lower specificity
(72%) values, compared to the previous study. In diagnostic use, the
high sensitivity of the test is related to the improved detection of
vascular patterns in dysplastic and malignant lesions, and it indicates
a strong association between the perpendicular pattern and malignant
lesions and a weak association between the longitudinal pattern and
malignancy. Thus, malignant and dysplastic lesions were predicted with
certainty with the Image1 S technique and, as a result, relatively few
cases of cancer were missed in the endoscopic examination. Our study was
conducted on a relatively small number of subjects; however, the sample
size was sufficient because malignant and premalignant subjects were
most prevalent in the whole sample. In addition, a highly sensitive test
with many true positives requires a minimum sample size for
statistically significant results. Image1 S endoscopy, therefore, proved
to be a sensitive and reliable screening test for the prediction of
malignancy in suspicious lesions presenting with a perpendicular
vascular pattern.
The false positive and false negative cases and the cases excluded from
the survey did not have any significant effect on the statistical
parameters, but they are clinically important when screening to predict
malignancy. The only false negative case was a low-grade dysplasia
associated with a longitudinal pattern; this case may reflect the small
extent of neo-angiogenesis in low grade dysplastic lesions (8). Among
the false positive cases, one case with benign granular cell tumor and
two cases with granulation tissue, were negatively associated with a
perpendicular vascularization pattern. A perpendicular pattern in benign
tumors has also been reported by Arens et al. for HPV-related papilloma.
That study used contact endoscopy with NBI system and emphasized the
differences in turning angle of the vessels within the vascular loop;
where wide long turns in the papilloma differed from short, acute turns
in terms of carcinogenesis (2). Distinction of these differences was not
possible in our endoscopic examination, but coupling the image1 S system
with contact endoscopy, which would result in a nearly 60-fold gain in
magnification, may help to clarify these distinctions. Two other false
positive cases with granulation tissue after laser surgery appeared to
be related to the wound healing processes, which can make vascular
evaluation difficult.
The cases excluded from the survey were those presenting with
leukoplakia and granulation tissue, and they featured with surface
characteristics that limited the visualization of the vasculatures. The
limitation in the leukoplakia case was the umbrella effect of keratosis
(9). Likewise, the vasculatures in the granulation tissue cases were
obscured due to the exudative material that covered the surface. For
these reasons, endoscopic image enhancement techniques may have a
limited value in keratotic and exudative lesions. Nevertheless, a high
rate of accuracy with many true positives and true negatives was
achieved in our study using Image1 S enhancement, apart from the few
exceptions mentioned above.
This study also evaluated the practical utility of the ELS concept of
vascular patterns, by conducting an electronic survey, on a group of
otolaryngologists with a varying degrees of work experience. This part
of the study had two major limitations: one was that digital images
provide less information than actual video-endoscopic examination, and
the other was the varying degree of knowledge among the evaluators
regarding the ELS classification is variable. Despite these limitations,
the survey results were consistent between the authors and the
participants regardless of previous work experience and quality of the
images, i.e., the vascular patterns were identified with high accuracy
by all the evaluators. This study confirms the feasibility of using the
ELS classification in routine endoscopic examination and for e-screening
and e-learning purposes.
In the survey, we also questioned whether the spectral light images are
preferred over the white light images for discrimination of the vascular
patterns. Technically, white light provides sharpness and local
brightness, whereas spectral modes provide the highest image contrast.
The spectral modes have been used previously in several situations,
including urinary bladder imaging, for improved visualization of the
parathyroid gland in endoscopic thyroidectomy, during endonasal sinus
surgery, and for treatment of oral cavity and oropharynx lesions in
combination with contact endoscopy (10-13). Based on the empirical
observations of the users in the present study, the spectral modes,
which produced high contrast images, were apparently preferred over
white light when examining laryngeal lesions.