Does the Uterine Injection Site Matter for the Pelvic Sentinel Lymph Node Mapping? A Systematic Review and Meta-Analysis

: Background and Objectives: To summarize the evidence on in vivo uterine pelvic lymphatic drainage. Materials and Methods: A literature search was performed in multiple electronic databases from inception to December 2024. We included all the studies that compared two different uterine injection sites in the mapping of pelvic sentinel lymph nodes by injecting two different tracers into two distinct injection sites. The primary outcomes included the concordance and discordance rates in the mapped pelvic sentinel lymph nodes between the pairs of injection sites. The secondary outcomes were the detection rates per injection site and tracer. Four reviewers independently reviewed the records for inclusion, assessed the risk of bias, and extracted the data. Pooled concordance, discordance, and detection rates with 95% confidence intervals (CIs) were estimated using the random effects model. Heterogeneity was quantified using the I2 tests. Results: Out of 2512 records, we included 4 studies (172 patients and 344 hemipelves). Three studies injected the cervix with the technetium-99m and the uterine corpus with methylene blue; one study injected the cervix with indocyanine green and the utero-ovarian ligament with methylene blue. Both tracers/injection sites successfully identified a sentinel lymph node in 132 hemipelves (132/344; 38.4%), identifying the same sentinel lymph node in 116 cases (116/132; 87.9%). The pooled concordance rate per hemipelvis was 91.8% (95% CI 0.665-1.000; I2 = 92%; chi2p-value < 0.01). Two different sentinel lymph nodes were identified in the remaining 16 hemipelves, with a pooled hemipelvis discordance rate of 8.2% (95% CI 0.000-0.335; I2 = 92%; chi2p-value < 0.01). The cervix and technetium-99m were the injection site and tracer with the highest pooled detection rate. Conclusions: Different uterine injection sites appear to share a common pelvic lymphatic pathway and sentinel lymph node in most cases, consistent with the current practice in endometrial cancer. Future research will confirm whether cervical injections might be proposed for pelvic sentinel lymph node mapping in all gynecological cancers.