Look at the regulations regarding the health of students -- I doubt that they apply a more stringent health standard than to PRs, where one is not supposed to be an undue burden. What has caused your enlarged spleen? Malaria? Thalassemia? Neither of these are likely to be prohibitive.
Also, and I mention this only for reference, it is unlikely that a medical examination will identify the enlarged spleen itself (unless it is physically palpable). If you don't mention it, it probably won't come up though this would be a lie of omission. However, if it is caused by a blood condition, that might be identified.