Veins in the perineum generally accompany the arteries and join the internal pudendal veins that connect with the internal iliac vein in the pelvis (Fig. 5.78). The exception is the deep dorsal vein of the penis or clitoris that drains mainly the glans and the corpora cavernosa. The deep dorsal vein courses along the midline between the dorsal arteries on each side of the body of the penis or clitoris, passes though the gap between the inferior pubic ligament and the deep perineal pouch, and connects with the plexus of veins surrounding the prostate in men or bladder in women.
External pudendal veins, which drain anterior parts of the labia majora or the scrotum and overlap with the area of drainage of the internal pudendal veins, connect with the femoral vein in the thigh. Superficial dorsal veins of the penis or clitoris that drain skin are tributaries of the external pudendal veins.
Lymphatic vessels from deep parts of the perineum accompany the internal pudendal blood vessels and drain mainly into internal iliac nodes in the pelvis.
Lymphatic channels from superficial tissues of the penis or the clitoris accompany the superficial external pudendal blood vessels and drain mainly into superficial inguinal nodes, as do lymphatic channels from the scrotum or labia majora (Fig. 5.79). The glans penis, glans clitoris, labia minora, and terminal inferior end of the vagina drain into deep inguinal nodes and external iliac nodes.
Lymphatics from the testes drain via channels that ascend in the spermatic cord, pass through the inguinal canal, and course up the posterior abdominal wall to connect directly with lateral aortic or lumbar nodes and pre-aortic nodes around the aorta, at approximately vertebral levels LI and LII. Therefore disease from the testes tracks superiorly to nodes high in the posterior abdominal wall and not to inguinal or iliac nodes.
Surface anatomy of the pelvis and perineum
Palpable bony features of the pelvis are used as landmarks for: locating soft tissue structures, visualizing the orientation of the pelvic inlet, and defining the margins of the perineum.
The ability to recognize the normal appearance of structures in the perineum is an essential part of a physical examination.
In women, the cervix can be visualized directly by opening the vaginal canal using a speculum.
In men, the size and texture of the prostate in the pelvic cavity can be assessed by digital palpation through the anal aperture.
Orientation of the pelvis and perineum in the anatomical position
In the anatomical position, the anterior superior iliac spines and the anterior superior edge of the pubic symphysis lie in the same vertical plane. The pelvic inlet faces anterosuperiorly. The urogenital triangle of the perineum is oriented in an almost horizontal plane and faces inferiorly, whereas the anal triangle is more vertical and faces posteriorly (Figs. 5.80 and 5.81).
How to define the margins of the perineum
The pubic symphysis, ischial tuberosities, and tip of the sacrum are palpable on patients and can be used to define the boundaries of the perineum. This is best done with patients lying on their backs with their thighs flexed and abducted in the lithotomy position (Fig. 5.82).
The ischial tuberosities are palpable on each side as large bony masses near the crease of skin (gluteal fold) between the thigh and gluteal region. They mark the lateral corners of the diamond-shaped perineum.
The tip of the coccyx is palpable in the midline posterior to the anal aperture and marks the most posterior limit of the perineum.
The anterior limit of the perineum is the pubic symphysis. In women, this is palpable in the midline deep to the mons pubis. In men, the pubic symphysis is palpable immediately superior to where the body of the penis joins the lower abdominal wall.