In the spectral Doppler of the superior mesenteric artery, flow reversal would most likely be indicated by which finding?

• A. Reversed diastolic flow
• B. Decreased peak systolic velocity
• C. Collateralization
• D. Absence of diastolic flow

Answer: (C)

Flow reversal in the superior mesenteric artery on spectral Doppler is shown by diastolic flow that becomes retrograde. Normally the SMA has forward diastolic flow because the gut bed is a low-resistance pathway, especially after a meal. When there is significant proximal stenosis or occlusion, distal pressure falls and resistance rises, causing diastolic flow to diminish and can reverse. This diastolic reversal is the sign you’d look for to indicate flow reversal.

Decreased peak systolic velocity just means the systolic velocity is lower, which reflects reduced flow but not actual retrograde flow. Absence of diastolic flow indicates a loss of forward diastolic component, but not necessarily reversal. Collateralization signals the development of alternative pathways to bypass chronic occlusion, which is a compensatory change rather than a direct Doppler sign of flow reversing in the SMA itself.