2 | MATERIALS AND METHODS
2.1 | Search strategy
Study search and data collection was performed from June to September
2021. Major online medical databases such as PubMed, Embase, Scopus, Web
of Science and Google Scholar were searched to gather all studies in
which the variations, maximal diameter and ostial area of the PVs were
investigated. The following search terms were used utilizing the Boolean
technique: (pulmonary veins anatomy OR pulmonary veins anatomy variation
OR accessory pulmonary veins OR anomalous pulmonary venous return OR
pulmonary veins origin) AND (pulmonary veins ostial area) AND (pulmonary
veins diameter OR pulmonary veins width). Neither date, language,
article type nor text availability conditions were applied. An
additional search through the references of the identified studies was
conducted at the end of the search stage to ensure the accuracy of the
process. During the study, the Preferred Reporting Items for Systematic
Reviews and Meta-Analyses (PRISMA) guidelines were followed.
Additionally, The Critical Appraisal Tool for Anatomical Meta-analysis
(CATAM) was used to provide the highest quality findings .
2.2 | Eligibility assessment
The database search and the manual search identified a total of 9119
studies which were initially evaluated by two independent reviewers.
After removing the duplicates and irrelevant records, a total of 1573
articles were qualified for a full-text evaluation. To minimize the
potential bias and to maintain an accurate statistical methodology,
articles such as case reports, case series, conference reports, reviews,
letters to the editors and studies that provided incomplete or
irrelevant data were excluded. Inclusion criteria involved original
studies with extractable numerical data regarding variations, maximal
diameter and ostial area of the PVs. As a result, 73 studies were
included for variations analysis, 86 for diameter analysis and 18 for
ostial area analysis. The AQUA Tool which was specifically designed for
anatomical meta-analyses was used to minimize the potential bias of
included studies . The flowchart outlining the study inclusion process
is shown in Figure 1.
2.3 | Data extraction
Data from studies that met inclusion criteria were extracted by two
independent reviewers. Qualitative data, such as year of publication,
country and continent of origin, methodology of data collection,
information about the diseases in the studied groups were gathered.
Quantitative data, such as sample size, numerical data regarding
prevalence among variations of the PVs, mean maximal diameter of every
PV with its standard deviation or interquartile range and mean ostial
area of every PV with its standard deviation or interquartile range were
also extracted. Studies containing mean results, but without standard
deviation or interquartile range or unclear or unspecified variations
were excluded. Any discrepancies between studies identified by the two
reviewers were resolved by contacting the authors of the original
studies wherever possible or by consensus with a third reviewer.
2.4 | Statistical analysis
To perform the meta-analyses, STATISTICA version 13.1 software (StatSoft
Inc., Tulsa, OK, USA), MetaXL version 5.3 software (EpiGear
International Pty Ltd, Wilston, Queensland, Australia) and Comprehensive
Meta-analysis version 3.0 software (Biostat Inc., Englewood, NJ, USA)
were used. A random-effects model was used in all analyses. Chi-squared
test and I-squared statistic were employed to assess the heterogeneity
among the studies . A p-value and confidence intervals were used to
determine statistical significance between studies. A p-value lower than
0.05 was considered statistically significant. In case of overlapping
confidence intervals, differences were considered statistically
insignificant. I-squared statistics were interpreted as follows: values
of 0-40% were considered as “might not be important”, values of
30-60% were considered as “might indicate moderate heterogeneity”,
values of 50-90% were considered as “may indicate substantial
heterogeneity” and values of 75-100% were considered as “may indicate
substantial heterogeneity”.