An accessory spleen (AS) is a lobule of splenic tissue found in ectopic locations. Identification of AS is particularly important in patients with immune thrombocytopenia (ITP) requiring splenectomy as unrecognized AS can later cause refractory symptoms. The AS can also be a source of significant intraabdominal hemorrhage. The aim of this meta-analysis was to systematically analyze the data on the prevalence, number, location, and morphometry of AS.

An extensive search of the major electronic databases was conducted to identify all studies that reported relevant data on the AS. No date or language restrictions were applied. Data on the study type, the prevalence of AS, location, morphometry and number of AS per patient were extracted from the eligible studies and pooled into a meta-analysis.

A total of 81 studies (n = 22,487 subjects) were included into the quantitative analysis. The overall pooled prevalence of AS was 14.5% (95%CI: 12.4–16.7), while the pooled prevalence of AS in ITP patients was 16.7% (95%CI: 12.1–21.7). The majority of accessory spleens were located in the splenic hilum (62.1% [95%CI:51.5–76.3]). Moreover, 26% of ITP patients with an AS have more than one.

The findings of this study provide an evidence-based foundation of anatomical knowledge about the AS. Surgeons should take particular caution in identifying an AS, as unnoticed AS during splenectomy can lead to recurrence of hematological diseases or can be a potential source of bleeding in the future.