Splanchnic artery aneurysms, particularly those involving the left gastric artery, are infrequent occurrences and often lack noticeable symptoms, but their rupture involves a significant risk of mortality. We present a case involving an unruptured left gastric artery aneurysm (LGAA) that extended into the right hemithorax. This case report outlines the categorization, clinical manifestations, and diagnostic challenges associated with such aneurysms. Our findings could offer valuable insights for clinicians and radiologists when adopting a systematic approach for the early detection and management of LGAA.