The anatomical space called the ischioanal fossa (synonym: the ischiorectal fossa) is the space inferior and lateral to the levator ani, lateral to the anal canal, medial to the internal obturator muscle, and superior to the urogenital diaphragm (syn: the superficial pelvic floor).
The ischioanal fossa mainly contains fat but also the pudendal canal (synonym: the Alcock’s canal) on the lateral wall of the ischioanal fossa. The pudendal canal contains the pudendal nerve and the internal pudendal blood vessels.
The picture shows the boundaries of the ischioanal fossa: The superficial pelvic floor inferiorly, the levator ani superiorly and medially, the anal canal medially and the internal obturator muscle laterally. The internal obturator muscle is only shown on the left side of the image.
The pudendal nerve exits the pelvis through the greater sciatic foramen, curls around the sacrospinous ligament and enters the ischioanal fossa through the lesser sciatic foramen.
The lesser sciatic foramen is formed by the sacrospinous ligament and the sacrotuberous ligament.
The pudendal nerve (red arrow) enters the ischioanal fossa via the lesser sciatic foramen formed by the sacrospinous ligament (green asterix) and the sacrotuberous ligament (magenta asterix). The sacrospinous ligament inserts on the ischial spine (green arrow). The internal pudendal artery is depicted with cyan arrow.
The pudendal nerve origins from the spinal nerves S2-S4 and whirls around the ischial spine.
The pudendal nerve depicted above the levator ani. The cyan arrow points at the pudendal nerve where it whirls around the ischial spine. Coccygeus muscle (yellow asterix), puborectal muscle (red asterix), pubococcygeal muscle (white asterix), iliococcygeal muscle (green asterix), internal obturator muscle (blue asterix).
The three muscles of the deep pelvic floor is formed as a hammock that supports the visceral content of the pelvis.
The levator ani (synonym: the deep pelvic floor) is formed as a hammock that origins from the ischial spine (green arrow), the fascia of the internal obturator muscle (green asterix) and the posterior aspect of the pubis. The internal obturator muscle is shown on the left side of the image.
The deep pelvic floor consists of the levator ani muscles which has two major components: The pubovisceral and the iliocyccygeal muscles.
The two pubovisceral muscles are the pubococcygeus and the puborectalis muscles.
The puborectalis muscle origins from the posterior surface of the pubic bone and inserts around the rectum. It supports the contraction of the anal sphincter.
The pubocyccygeus muscle origins from the posterior surface of the superior pubic ramus and inserts on the coccyx.
The iliococcygeal muscle origins from the ischial spine and the obturator internal muscle fascia.
The levator ani muscles are all innervated by direct branches of the ventral primary rami of the spinal nerves S2-S4.
The pubococcygeus muscle (cyan asterix) separates the puborectalis muscle (yellow asterix) and the iliococcygeal muscle (green asterix).
The muscles of the deep pelvic floor are known as the levator ani muscles. The deep pelvic floor has two components: The pubovisceral and the iliococygeal muscles. The pubovisceral muscles are the pubococcygeus and the puborectalis muscles.
The levator ani muscles are: The iliococcygeal muscle (green asterix), the pubococcygeus muscle (cyan asterix) and the puborectalis muscle (yellow asterix).
The pelvic floor can be separated into the superficial and the deep pelvic floors.
The superficial pelvic floor (synonym: the urogenital diaphragm) consists of the bulbospongiosus, ischiocavernosus, and the deep and superficial transverse perineal muscles.
The bulbospongiosus muscles (shown on the picture on page 2), the ischiocavernosus muscles and the deep and superficial transverse perineal muscles are all innervated by the deep branch of the perineal nerve from the pudendal nerve.
The bulbospongiosus muscles have been removed exposing the deep transverse perineal muscles. The ischiocavernosus and superficial transverse perineal muscles are depicted orange on the left side of the image and the deep transverse perineal muscle is orange on the right side of the image.
The superficial pelvic floor is innervated by the three pudendal nerve branches: The dorsal nerve of the penis or clitoris, the perineal nerve (synonym: the posterior scrotal nerve (or posterior labial nerve), and the inferior rectal nerve (synonym: inferior haemorhoidal nerve).
The dorsal nerve of the penis (or clitoris) is the terminal and the deepest branch of the pudendal nerve. It innervates the skin of the shaft of the penis in males and the clitoris in females.
The perineal nerve is the other terminal branch of the pudendal nerve. In males it innervates the posterior part of the skin of the scrotum. In females it innervates the posterior part of the labia and the vaginal vestibule.
The inferior rectal nerve is a branch from the perineal nerve (or directly from the pudendal nerve). It innervates the anal canal, the external anal sphincter muscle, the muscles of the superficial pelvic floor, and the puborectalis part of the levator ani muscle.
The pudendal nerve (cyan arrow) innervates the superficial pelvic floor via its three branches: the dorsal nerve of the penis or clitoris (blue arrow), the perineal nerve (magenta arrow), and the inferior rectal nerve (green arrow).
The perineal area can be divided into two triangles: the anterior (synonym: urogenital) triangle and the posterior (synonym: anal) triangle. The base of both triangles is the superficial transverse muscles. The lateral borders of the anterior triangle are the ischiocavernosus muscles. The lateral borders of the posterior triangle is the sacrotuberous ligament. The anterior triangle contains the root of the scrotum and penis in males and the vulva in females and it extends from the transverse perineal muscle to the pubic symphysis. The posterior triangle contains the anal canal and its external orifice – the anus – and it extends from the transverse perineal muscle to the coccygeal bone.
The borders of the anterior perineal triangle are the ischiocavernosus and the superficial transverse muscles – which are depicted in orange. The borders of the posterior perineal triangle are the superficial transverse muscles and the sacrotuberosus ligaments (blue color).
The transperineal ultrasound guided pudendal nerve block is indicated for postoperative analgesia after pelvic floor surgery including rectal extirpation.
The described technique is invented by Dr. Teresa Parras from St. Georges Hospital, London, UK, who has contributed the sonoanatomy pictures of the module.
The pudendal nerve exits the pelvis through the greater sciatic foramen whirls around the ischial spine and enters the ischioanal fossa through the lesser sciatic foramen.
