Systems and methods are disclosed for diagnosing and treatment planning for vascular steal syndromes and retrograde flow. One method includes receiving a reference blood flow direction at a location in a reference vasculature; determining a patient-related blood flow direction at a location in a patient's vasculature corresponding to the location in the reference vasculature; determining a difference in direction, between the reference blood flow direction of the reference vasculature and the patient-related blood flow direction of the patient's vasculature; and generating a representation of the location in the patient's vasculature associated with the difference in direction between the reference blood flow direction and the patient-related blood flow direction, or generating a treatment recommendation for the patient's vasculature based on the difference in direction between the reference blood flow direction and the patient-related blood flow direction.