Relationship of the recurrent laryngeal nerve to the inferior thyroid artery: A comparison of findings from two systematic reviews.

Systematic reviews (SRs) of anatomical studies may include a meta-analysis (MA) that provides weighted averages as pooled estimates of prevalence. The relationship of the recurrent laryngeal nerve (RLN) to the inferior thyroid artery (ITA) or its branches has been assessed in two published SRs, one without MA of 32 studies (SR1) and the other with MA of 79 studies (SR2). Both SRs reported differences in RLN-ITA patterns (in three categories) by side of the body, but the anterior pattern was less frequent in SR1 vs. SR2. The aim of this review was to explain the differences. The unweighted data from SR1 were found to be more affected (vs. SR2) by a single study with the largest number of RLNs and a low proportion anterior. In a MA using data from SR1, the pooled prevalence estimate for the anterior pattern was substantial (35%) on the right side (vs. 15% on the left) and close to the findings published in SR2. These consistent findings should be relevant to surgeons in attempting to avoid iatrogenic injury to RLNs. Comparison of methods and results from two or more SRs on the same anatomical relationships may be useful in evidence-based anatomy. Clin. Anat. 30:318-321, 2017.