Can u see a enlarged spleen lying on your back?

Usually not. Enlarged spleens peek out from below the rib arch on the left, but won't protrude upward. Even if the abdomen is sunken in and fully relaxed, most people have enough fat and/or ab muscle to prevent it from being visible even when it is easily felt. A very large spleen (gaucher's, schistosomiasis, malaria) might be seen as an asymmetry in the upper left quadrant.