Pelvic Venous Flow Disorder

Venous Anatomy of the Pelvis

The venous drainage from the pelvis, as in the other areas of the body, is compartmentalized. There are the musculoskeletal compartment, consisting of the external iliac venous systems interconnected with the gluteal and pelvic floor muscles, and the visceral compartment, consisting mainly of the reproductive organs, the bladder, and the rectum.

Despite the general separation of these venous drainage pathways, there are areas of interconnections. The venous return from the perineum and vulva drains into both the greater saphenous vein in the area of the saphenofemoral junction and into the internal pudendal vein, which traverses the pelvic floor and merges with the inferior rectal vein carrying blood into the internal iliac vein. Reflux within this network can direct pelvic venous outflow into the greater saphenous vein.

The inferior gluteal vein is formed from the coalescence of small veins in the superior posterior thigh that are part of an anastomotic network with the lateral circumflex femoral vein, a tributary of the deep femoral vein. Thus, the inferior gluteal vein represents a connection between the deep femoral vein and the pelvic venous drainage system. This pathway may be a cause of recurrent varicose veins of the posterior lateral thigh.

The obturator vein collects blood from the superior, posterior, and medial thigh through connections with the medial circumflex femoral vein and carries it into the pelvis through the obturator foramen, establishing another communication between the pelvis and the lower extremity. There may also be a pubic vein, which represents a direct connection between the obturator vein and the external iliac vein. These pathways might also allow reflux of pelvic venous blood into the lower extremity.

The left ovarian vein is formed from the coalescence of veins of the pampiniform plexus within the mesosalpinx. This larger single vein travels superiorly out of the pelvis and joins the left renal vein. There is generally a single valve within the left ovarian vein located just proximal to its junction with the renal vein, which prevents reflux of blood from the left renal vein into the ovarian vein and the pelvis. The anatomy of the right ovarian vein is similar except that it directly enters the inferior vena cava below the level of the right renal vein.

The uterus, capable of dramatically increasing its blood flow during pregnancy, has two venous outflow pathways. The myometrium has numerous veins that form a broad plexus on the outer surface of the organ. These smaller veins coalesce to form bilateral uterine veins that travel through the broad ligaments to join the internal iliac veins. Superiorly, the venous plexus on the surface of the uterus also forms tributaries that merge with the ovarian venous plexus within the mesosalpinx. Valves are uncommonly found within these venous outflow tracts, allowing uterine blood to drain either through the uterine or ovarian veins.

The rectal venous plexus communicates directly with the internal iliac vein through the internal pudendal vein and with the uterine, vaginal, and bladder venous outflow tracts anteriorly through collaterals, unifying this visceral compartment.

These venous pathways provide not only direct flow patterns for venous drainage of the structures of the pelvis but also collateral pathways for drainage of the legs. Few valves are present within the major veins of the pelvis. Although the absence of valves within these major veins might allow some lateral movement of blood, general principles of venous drainage apply: The direction of venous outflow from the lower extremities and pelvis should be cephalad, blood should flow from smaller veins to larger veins, and venous drainage on each side of the pelvis should be equal and adequate and there should be little blood forced across the midline to drain through the contralateral venous system. The hallmarks of pelvic venous flow disorder are the movement of venous blood from larger veins into smaller veins, the presence of serpentine varicose veins within the pelvis, and venous flow crossing the midline and returning through the contralateral venous system. These abnormalities are often the cause of chronic pelvic pain, recurrent thigh varicose veins, or left leg edema.

Pathophysiology

Although there are likely many as yet undefined causes of pelvic venous flow disorder, there are two known etiologies: loss of ovarian vein valvular function and overload of the internal iliac venous system. Either of these causes can lead to abnormal pelvic venous flow patterns, pelvic varicose veins, or reflux into the lower extremity venous system and lower extremity varicose veins.

The presence of isolated retrograde flow in the ovarian vein is not sufficient for the diagnosis of pelvic venous flow disorder or pelvic congestion syndrome. Pelvic congestion syndrome is identified by reflux in the ovarian vein that flows into ipsilateral varicose veins and then continues to flow across the pelvis to drain through the contralateral pelvic venous system. Retrograde flow through the left ovarian vein can be caused by primary valvular incompetency, pregnancy, or nutcracker syndrome, which cause valvular dysfunction, venodilation, and retrograde flow into the pelvis. The driving pressures from the left renal vein enhance reflux through the ovarian vein, into the pampiniform plexus, and then into the presacral or uterine venous collaterals to drain via the contralateral internal iliac vein or into the superficial or deep systems of the lower extremity ( Figure 1 ).

Similarly, May–Thurner syndrome can force significant amounts of venous blood from the left lower extremity into the ipsilateral internal iliac vein, overloading this venous pathway. The result is that venous blood from the left lower extremity descends through the left internal iliac vein, crosses the pelvis through transpelvic collaterals, and exits through the right internal iliac vein ( Figure 2 ). When these pathways are well developed, there is often minimal edema of the left leg but increasing episodes of pelvic discomfort. In a review of 50 computed tomography (CT) scans obtained in the emergency department to evaluate abdominal or pelvic pain without left leg pain, 66% were noted to have moderate or severe left common iliac vein compression.