Congenital anomalies of the spleen from an embryological point of view.

The spleen is the major accumulation of lymphoid tissue in the human body, an organ which prenatally produces and postnatally controls blood cells. Normally, a developed spleen lies in the upper left quadrant in parallel with the long axis of the 10th rib. It is a mesodermal derivate which first appears as a condensation of mesenchymal cells inside the dorsal mesogastrium at the end of the fourth embryonic week. Some congenital anomalies of the spleen are common, such as splenic lobulation and accessory spleen, while other conditions are rare, such as wandering spleen and polysplenia. Splenogonadal fusion is also a rare developmental anomaly, resulting from abnormal fusion of the splenic and gonadal primordia during prenatal development. The purpose of this article is to describe the normal development of the human spleen, supplemented with our own photomicrographs and a review of congenital anomalies of the spleen with their possible embryonic basis.