Nutcracker syndrome takes its name from the anatomy: the left renal vein (draining the left kidney) passes between the aorta and another artery, and in some people that gap closes like a nutcracker on the vein.
Its signature symptoms sit higher than other pelvic vein problems: left flank pain (the side, under the ribs — kidney territory), sometimes worse after exercise, and blood in the urine (visible or found on testing). Here's the connection that matters for pelvic pain: the left ovarian vein drains into the left renal vein — so when the renal vein is compressed, pressure backs down the ovarian vein into the pelvis, and that vein often becomes an escape route. This is why coiling the ovarian vein without checking for Nutcracker first can misfire.
Years of unexplained "kidney pain" with normal kidney scans, plus pelvic congestion symptoms, is the story that should put Nutcracker on the list — the KINUUM check screens for exactly this cluster.