Spontaneous ruptures of the spleen are divided into two distinct groups: those occurring in an organ which is in any way altered from the normal, and those in which the spleen appears to be normal on macroscopic and microscopic examination.
Among the more common causes of rupture in the former group may be listed, in the order of frequency, according to Berger's1 statistics, malaria, trauma, pregnancy (usually in cases in which the spleen was already diseased), typhoid, leukemia, syphilis, alcoholic cirrhosis, tuberculosis, hemophilia, capsular varices, typhus, anemia, eclampsia, relapsing fever, infarct, abscess and aneurysm. Among these Besnier2 includes also epilepsy and purpura.
The causes of rupture in apparently normal spleens are not understood, and judging from the literature opinions are scarce. This, I believe, is due to the fact that such cases are rare and the material available for study is still more rare.
Up to the present
Dardinski VJ. SPONTANEOUS RUPTURE OF AN APPARENTLY NORMAL SPLEEN. JAMA. 1932;99(10):831-832. doi:10.1001/jama.1932.27410620001009a