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Essay: Diagnostic accuracy of conventional ultrasound in differentiating between benign and malignant thyroid nodules

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  • Published: 15 October 2019*
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Title
An evaluation of the diagnostic accuracy of conventional ultrasound (US) in differentiating between benign and malignant thyroid nodules in adult patients, using fine needle aspiration cytology (FNAC) as reference standard: a protocol for a structured literature review.
Aim
Examine the accuracy of conventional ultrasound in differentiating between benign and malignant thyroid nodules using the gold standard (FNAB/CYTOLOGY) as reference standard.
Objectives
1- To evaluate the influence of the underlying thyroid appearance on the diagnosis of thyroid malignancies using US.
2- To evaluate whether the ultrasonographic features of thyroid nodules are associated with histological malignancy.
3- To determine the limitations of conventional ultrasound in differentiating between thyroid nodules.
4- To determine conventional ultrasound markers in the detection of malignant thyroid nodules.
Literature search process
Literature searches are most commonly undertaken using computers and electronic databases. Computer databases offer access to vast quantities of information, which can be retrieved easily and quickly. This ease of access and retrieval makes an electronic search far more efficient than a manual one (Younger, 2004). The electronic databases that have been used in this review are CINAHL, MEDLINE, AMED, PubMed (PMC) and GCU library. Furthermore, Google Scholar was searched in order to minimise the risk of missing any studies. In addition, the reference lists of the included studies and relevant reviews were searched to identify any additional studies.
Keyword searches are the most common method of identifying literature (Ely and Scott, 2007). With regard to search terms, the terms related to the index test (   ultrasound OR ultrasonography   ), the reference standard (   fine needle OR cytopathology OR FNAC   ) and the target condition (   thyroid nodule OR thyroid neoplasm   ) were used to search the predefined databases. According to Cronin et al. (2008), it is a good idea to consider alternative keywords with similar meanings that might elicit further information. So, some of keywords and terms were also used as medical subject heading terms (MESH) which can help to utilise synonyms for keywords in order to provide wider access to appropriate articles in order to increase specificity as well as accessibility (Gault et al., 2002). However, the next step is combining keywords. To help with these combinations, many databases use commands called Boolean operators. The most common Boolean operators are AND   , OR   , and NOT (Ely and Scott, 2007). These keywords were entered through the GCU library database for publications dating from 2007 to 2017 to find sources relevant to the study. The search will not be restricted to a certain sample size. It will, however, be restricted to English language studies and original articles, excluding reviews or reports.
Successful search strategies are usually highly structured and built around a population, intervention, comparison, and outcome (PICO) framework. PICO frameworks help the searcher search terms by their thematic groups. They are very effective for identifying medical literature. This is due to the fact that the medical model of research can typically be defined by these characters (Sayers, 2007). The first search found a total of 176,806 hits. This search engine, however, contains filters that can be applied to refine the search and reduce the number of hits to something manageable. Therefore, the first filter applied was the combination of AND with the main keywords of the research question: thyroid nodule   , ultrasonography   , and fine needle   . This reduced the search result to 45. The second filter applied was the publication date (from 2007 to 2017) to ensure the information was up-to-date. This reduced the search result to just 25 hits. The next step was to read the abstract of each article to determine whether the study related to the main aim of the search question. Any article with a possible connection to the question was imported to RefWorks for further review to decide whether it qualified as an appropriate part of the literature review.
Search result
Three primary studies of the diagnostic accuracy of ultrasound in differentiating between benign and malignant thyroid nodules were selected from the final search results. One primary study was aimed at calculating the diagnostic accuracy of ultrasound in the detection of carcinoma in thyroid nodules taking fine needle aspiration cytology as the reference standard (Alam et al., 2014). Another study evaluated whether the ultrasonographic features of thyroid nodules were associated with histological malignancy. It also sought to identify useful criteria for clinical decision making (Cappelli et al., 2007). The last study chosen determined the value of the cytological classification system and ultrasound (US) in predicting malignancy in indeterminate thyroid nodules (Maia et al., 2011).
Critical methodological appraisal
Study design
The critiqued study was published in 2014 by Alam et al. In addition, the study used a prospective design approach to calculate diagnostic accuracy of ultrasound in detection of carcinoma in thyroid nodules taking fine needle aspiration cytology as the reference standard.
Sampling
The sample comprised 76 (76%) females from a total of 107. The male to female ratio was 1:3, the mean age was 41.77  SD 12.31 years, and the age range was 17   72 years. Patients from either gender presenting palpable thyroid nodules (diagnosed by primary physician on clinical examination) were referred to the radiology department of Aga Khan University Hospital (AKUH), Karachi, for thyroid ultrasound followed by fine needle aspiration cytology of their thyroid nodules, between December 2010 and December 2012.
Methods and analyses
In this study, all of the ultrasounds of thyroid glands were performed by a single radiologist on a Nemio XG ultrasound machine equipped with 3.5-5MHz curvilinear and 7.5-15 MHz linear probes. Data was entered and analysed in SPSS 20.0. In this study, the overall sensitivity of thyroid US for detecting a malignant nodule was reported to be 82%. This study, however, had several limitations that may have affected the final outcome. The first limitation was that a single radiologist performed all the ultrasounds. If more than one radiologist was involved, it would have been possible to calculate the inter-observer variability. Secondly, the small number of malignant nodules was another limitation.
In conclusion, US displays a high diagnostic accuracy in detecting malignancy in thyroid nodules on the basis of features like echogenicity, margins, micro calcifications, and shape. Radiologists must be familiar with such signs on ultrasounds, which provide assistance in distinguishing benign from malignant thyroid nodules, thus avoiding unnecessary FNAC.

References

Alam, T., Khattak, Y.J., Beg, M., Raouf, A., Azeemuddin, M. and Khan, A.A. (2014) Diagnostic accuracy of ultrasonography in differentiating benign and malignant thyroid nodules using fine needle aspiration cytology as the reference standard   , Asian Pacific Journal of Cancer Prevention: APJCP, 15(22), pp. 10039   10043.
Cappelli, C., Castellano, M., Pirola, I., Cumetti, D., Agosti, B., Gandossi, E. and Agabiti Rosei, E. (2007) The predictive value of ultrasound findings in the management of thyroid nodules   , QJM, 100(1) pp. 29   35.
Cronin, P., Ryan, F. and Coughlan, M. (2008) Undertaking a literature review: a step-by-step approach   , British Journal of Nursing, 17(1), pp. 38   43.
Ely, C., Scott, I. (2007) Essential study skills for nursing. Edinburgh: Elsevier.
Gault, L.V., Shultz, M. and Davies, K.J. (2002) Variations in medical subject headings (MeSH) mapping: from the natural language of patron terms to the controlled vocabulary of mapped lists   , Journal of the Medical Library Association, 90(2), pp. 173   180.
Maia, F.F.R., Matos, P.S., Pavin, E.J., Vassallo, J. and Zantut-Wittmann, D. (2011) Value of ultrasound and cytological classification system to predict the malignancy of thyroid nodules with indeterminate cytology   , Endocrine Pathology, 22(2), pp. 66   73.
Sayers, A. (2007) Tips and tricks in performing a systematic review: reference management and identifying search terms and keywords   , British Journal of General Practice, 57(545), p. 999.
Younger, P. (2004) Using the internet to conduct a literature search   , Nursing Standard, 19(6), pp. 45   51.

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