Morphological variations of the human spleen: no evidence for a multifocal or lobulated developmental origin

Objectives: Adult spleens show extensive morpholog-ical variation, with a reported prevalence of 40-98% clefts (also called notches or fissures) on the splenic surface and 10-30% accessory spleens at autopsy. It is hypothesised that both anatomical variants result from a complete or partial failure of multiple splenic primordia to fuse to the main body. According to this hypothesis, fusion of the spleen primordia is completed after birth and spleen morphological variations are often explained as stagnation of spleen development at the foetal stage. We tested this hypothesis by studying early spleen development in embryos, and compared foetal and adult spleen morphology.Methods and materials: We assessed 22 embryonic, 17 foetal and 90 adult spleens on the presence of clefts using histology, micro -CT and conventional post-mortem CT-scans, respectively.Results: The spleen primordium was observed as a single mesenchymal condensation in all embryonic specimens. The number of clefts varied from 0 to 6 in foetuses, compared to 0-5 in adults. We found no corre-lation between foetal age and number of clefts (R2 = 0.004). The independent samples Kolmogorov-Smirnov test showed no significant difference in the total number of clefts between adult and foetal spleens (p = 0.068).Conclusion: We found no morphological evidence for a multifocal origin or a lobulated developmental stage of the human spleen. Advances in knowledge: Our findings show that splenic morphology is highly variable, independent of devel-opmental stage and age. We suggest to abandon the term "persistent foetal lobulation" and to regard splenic clefts, regardless of their number or location, as normal variants.