Deformation of kidneys following obstruction of left ureter.
The atrophy of the left kidney would only have been caused if the obstruction of the ureter was a chronic condition. An acute obstruction would have most likely caused a condition called “hydronephrosis” - the swelling of a kidney due to backup of urine.
Long-term swelling can cause permanent kidney damage (such as atrophy), but if it only affects one kidney, the body can generally function without severe complications.
A Text-Book of Pathology. W. G. MacCallum, 1916.