Apparent bilateral aldosterone suppression during adrenal venous sampling associated with preferential drainage into the left inferior phrenic vein.

SUMMARY: A 54-year-old woman with primary aldosteronism caused by left adrenal adenoma underwent adrenal venous sampling (AVS) for subtype classification and unexpectedly exhibited bilateral aldosterone suppression (BAS) despite adequate selectivity. BAS on AVS is a recognized diagnostic pitfall that can obscure surgically curable unilateral diseases, particularly left-sided cases. In this case, venous anatomy was carefully reassessed considering the inconclusive AVS findings. Although adrenal arteriography is infrequently used in the diagnostic workup of primary aldosteronism, it was incorporated as an adjunct to assess venous anatomy. No additional drainage route was identified on the obtained angiographic images, and the cranial and medial superficial location of the tumor in close proximity to the left inferior phrenic vein raised the suspicion of preferential drainage into this vessel. Although the complete tumor-drainage pathway was not directly visualized, targeted venous sampling based on this anatomical hypothesis enabled accurate lateralization of a unilateral disease. This case underscores interpreting BAS within the context of venous anatomy, particularly on the left side, rather than as definitive evidence of bilateral primary aldosteronism.