Ridley's The Vulva

Branches of the internal iliac and femoral arteries and veins supply and drain the perineum, and the details are shown in Table 2.2.

The internal pudendal artery , a branch of the internal iliac artery, leaves the pelvis through the greater sciatic notch below the piriformis muscle. Lying on the tip of the ischial spine, it turns forwards through the lesser sciatic foramen to enter the anal triangle posteriorly. Within this triangle it runs forwards on the side wall of the ischiorectal fossa enclosed by the fascia of the pudendal canal. During its course through the ischiorectal fossa, it gives off the inferior rectal artery, which arches over the fascial roof of the fossa to reach and supply the anococcygeal raphe, anal canal, and perineal body. After entering the urogenital triangle, the internal pudendal artery gives off the perineal branch to the perineal body and the posterior structures in the superficial perineal pouch. It enters the deep perineal pouch and supplies the erectile tissue lying in the vestibule, by perforating branches into the superficial perineal pouch, and the clitoris, by way of its deep and superficial terminal branches through the apex of the urogenital diaphragm.

The femoral artery gives off the superficial and deep external pudendal arteries in the femoral triangle. The superficial external pudendal artery pierces the deep fascia of the thigh anteriorly, to overlie the round ligament of the uterus. It runs medially to supply the mons pubis and labia. The deep external pudendal artery pierces the deep fascia of the thigh medially to enter the labia of the vulva. The terminal branches of the internal and external pudendal arteries anastomose with one another in the superficial perineal pouch.

The venous drainage follows the same pathways and eventually reaches the femoral and internal iliac veins. The internal iliac veins drain a rich venous plexus in the pelvic floor, which contributes to draining all the pelvic viscera. The venous drainage of the terminal gastrointestinal tract is therefore partially to the pelvic plexus but principally to the portal system via the superior rectal and thence the inferior mesenteric vein. The pelvic venous plexus therefore provides a portal systemic anastomosis, and portal hypertension can predispose to distension and even thrombosis of the pelvic, rectal, vaginal, and vulval veins.

The dermal microvasculature consists of a deep arterial plexus, the fascial network. The vessels from this region extend upwards to the border of the subcutaneous fat and then form a cutaneous network. This gives off branches to the appendages and ascending arterioles to a subpapillary plexus, which in turn forms capillary loops in the papillary layer between the dermoepidermal ridges. Blood is drained from these capillaries by venules which drain down to intermediate plexuses.

The lymphatic system transports fluids such as leaked protein from the extravascular compartment of the dermis. Small capillaries arise in the extracellular tissue spaces and form larger channels, which drain to the regional lymph nodes, and then via intermediate nodes before eventually returning to the thoracic duct. Any midline structure has bilateral lymphatic drainage. Therefore, the lymphatic drainage of either labium majus or minus is to both the ipsilateral and contralateral superficial lymph nodes [27].

The superficial regional lymph nodes of the perineum are found in two groups at the base of the femoral triangle. They communicate freely with one another and drain the whole of the perineum, including the lower thirds of the urethra, vagina, and anal canal.

These subsequently drain to deep nodes in the pelvis and ultimately to para‐aortic nodes on the posterior abdominal wall.

A variable number of lymph nodes lie transversely in the superficial fascia of the thigh, immediately below the medial two‐thirds of the inguinal ligament. The superficial femoral or subinguinal lymph nodes lie on both the medial and lateral aspects of the long saphenous vein. There are between 3 and 20 of these, and the lateral nodes send efferent lymphatics to the external iliac deep lymph nodes.

The external iliac lymph nodes are described in relationship to the external iliac vessels. They communicate freely with one another and with the obturator node, a large constant node, near the obturator nerve. It lies below the external iliac vessels on the side wall of the pelvis.

The medial group of three to six nodes lies on the medial side of the origin of the external iliac vein. Up to three of these nodes may be found in the femoral triangle medial to the femoral vein, where they are referred to as the deep femoral nodes. If all three are present, the lower one is situated just below the junction of the great saphenous and femoral veins. The medial node in the femoral canal and the uppermost node is known as the node of Cloquet or Rosenmuller. However, this is not always present [28].

The anterior group is variable and when present comprises no more than three nodes lying in the sulcus between the external iliac artery and vein.

The lateral group of two to five nodes lies on the lateral side of the external iliac artery.

The efferent lymphatics from the external iliac group drain to the common iliac nodes situated on the lateral side of the common iliac artery. Many small nodes lie close to each pelvic organ, and these drain into the numerous nodes embedded in the extraperitoneal tissue on the walls of the pelvis.

The interconnecting lymphatic spaces arise from the terminal bulbs lying in the papillary dermis. These form the lymphatic network, which ultimately drains into the lymph nodes. The vessels have a wide lumen and are lined with a single layer of endothelial cells.

The perineum has both somatic and autonomic innervation, and in each there are sensory and motor components.

As the perineum arises from the most caudal part of the developing embryo, the somatic innervation is from the most caudal segments, S1–S4. There is also some input from the upper lumbar segments L1‐2 in the nerve supply of the anterior perineal area.

This is entirely from the most caudal elements of both the sympathetic and parasympathetic systems.

Sympathetic innervationThe sympathetic pathways are restricted to the region between the first thoracic and second lumbar levels of the spinal cord. The sympathetic innervation of the perineum is located therefore at L1 and L2. It reaches the perineum via postganglionic fibres, arising from the first two lumbar and all four sacral ganglia of the sympathetic trunks. These fibres are distributed with the corresponding segmental nerves. In addition, other sympathetic fibres from L1 and L2 leave the sympathetic trunk as the hypogastric nerves (lumbar splanchnic presacral nerves) and descend into the pelvis to be associated with autonomic pelvic plexuses, which are distributed with the blood vessels.

Parasympathetic innervation

The parasympathetic pathways consist of cranial and caudal portions. The cranial portion is associated with four of the cranial nerves, whereas the caudal portion is associated with the second and third, or third and fourth, sacral segments of the spinal cord as the pelvic splanchnic nerves. These nerves together with the hypogastric sympathetic nerves form the autonomic pelvic plexuses.