FOCA 2023 Lecture 9: Perineum Anatomy PDF

FOCA 2023 Perineum Dr. Mark Hankin Professor & Senior Anatomist [email protected] Radiopedia Disclosures & Conflicts of Interest Authorship Anatomy & Physiology Revealed v4 2019, McGraw-Hill Clinical Anatomy: A Case Study Approach 2013, McGraw-Hill Test Prep for the USMLE® – Clinical Anatomy Q&A 2019,...

FOCA 2023 Perineum Dr. Mark Hankin Professor & Senior Anatomist [email protected] Radiopedia Disclosures & Conflicts of Interest Authorship Anatomy & Physiology Revealed v4 2019, McGraw-Hill Clinical Anatomy: A Case Study Approach 2013, McGraw-Hill Test Prep for the USMLE® – Clinical Anatomy Q&A 2019, Thieme Medical Publishers If you have used any of these resources, I hope you found them helpful. 2 Context The goal in FOCA of the lectures and labs on pelvis and perineum is to present the basic anatomy derived from XX or XY genotypes. As you are aware, gender is fluid. However, in the next two lectures, I will be referring to “male” and “female” anatomy. For the sake of clarity, when I refer to female anatomy, I am referring to someone whose sex assigned at birth is female or cisgender female; likewise for male anatomy. The goal for this information is to provide a foundation for later learning that considers gender-affirming care, including gender reassignment surgery, in which surgeons can address authoritatively the anatomical gender-affirming changes done intraoperatively. 3 Conceptual Objectives 1. Describe the organization of the perineum in the female and male, including skeletal components and surface anatomy. 2. Explain the anatomy of the urogenital diaphragm and perineal “pouches”. 3. Describe the anatomy and neurovascular supply of the penis, scrotum, the clitoris, vulva and vagina. 4. Describe the inguinal canal, including its features and the structures that pass through it. Describe the key differences between direct and indirect inguinal hernias. 5. Describe the origin, course and distribution of the pudendal nerves and the sites of pudendal nerve block. 6. Describe the anatomy of the cavernous tissue in males and females, including innervation of and mechanisms involved in the erection of and in emission and ejaculation in the male. Perineum 5 puffsynth's Triangles of the Perineum The perineum is divided into two triangles by a transverse line between the ischial tuberosities 0 Anterior: Urogenital triangle External genitalia & termination of the urinary tract Posterior: Anal triangle Anal canal, anus & fat peror 6 Drake 3e 5.72A Female Perineum Urogenital triangle External genitalia (vulva) ⎻ Mons pubis ⎻ Labia majora & minora ⎻ Clitoris ⎻ Vestibule of the vagina ⎻ Greater vestibular glands ⎻ Openings of urethra & vagina Anal triangle Anus & anal canal Pudendal nerves and branches Fat 7 Drake 3e 5.72A Male Perineum Urogenital triangle Root of scrotum Bulb of penis, with overlying skin Anal triangle Anus & anal canal Pudendal nerves and branches Fat 8 Drake 3e 5.73A Anal Triangle 9 Ischio-anal Fossae Ischio-anal fossae Fat-filled regions on either side of anal canal & anus Nerves & vessels cross the fossa (from the pudendal canal) to supply the lower anal canal r to an i Obturator internus and its deep fascia (with pudendal canal) va Lateral wall Le skeletal ternus External anal sphincter Levator ani Obturator in Medial wall 08 Ischio-anal fossa U LeterInternet Pudendal canal on 10 Netter 6e 370 Neurovasculature of the Anal Triangle Inferior rectal nerve Branch of pudendal nerve off pudendal nerve It Inferior rectal blood vessels Branches/tributaries of internal pudendal vessels 11 ECA5e 3.68 External anal sphincter A A Inferior rectal nerve & artery 12 Urogenital Triangle 13 Subcutaneous Perineal Fascia Two layers – continuous with anterior abdominal wall Fatty layer ~ Camper’s fascia Membranous layer = Perineal/Colles fascia ~ Scarpa’s fascia Perineal membrane (deep fascia lies deep to subcutaneous tissue Scarpa’s fascia (membranous) Deep fascia Superficial fascia Campers fascia (fatty) Perineal membrane Scarpa’s fascia (membranous) Perineal fascia (Colles) Campers fascia (fatty) Perineal membrane Perineal (Colles) fascia Dartos fascia (on penis) Dartos fascia (on scrotum) Perineal Membrane Thick, fibrous fascia in the urogenital triangle Attached to the pubic arch and ischiopubic ramus Anchors the roots of the external genitalia 15 Drake 3e 5.35A Perineal Membrane Perineal membrane anchors roots (erectile tissue) of external genitalia Ischiopubic ramus Erectile tissue has sponge-like vascular spaces that engorge with blood Female Crura of clitoris Bulb of the vestibule Greater vestibular glands (Bartholin’s) Male Crura & bulb (root) of penis Bulbo-urethral glands (Cowper’s) Crus (L. leg, limb); pl. Crura 16 Drake 3e 5.70 Skeletal Muscles Cover Erectile Tissue Skeletal muscles cover the roots of the external genitalia Bulbospongiosus muscle Female: Covers bulb of vaginal vestibule & greater vestibular glands (Bartholin’s) Male: Covers bulb of penis Ischiocavernosus muscle Female: Covers crus of clitoris Male: Covers crus of penis 17 Drake 3e 5.71 Perineal Membrane & Muscles Crus of clitoris Bulbospongiosus m., covering bulb of vestibule Ischiocavernosus m., covering crus of clitoris Crus of clitoris (ischiocavernosus removed) Bulbospongiosus removed; bulb of vestibule revealed Perineal membrane Inferior views of female perineum 18 Perineal Body Bulbospongiosus Bulb of vestibule Midline, fibromuscular tissue at junction of the urogenital & anal triangles Attachment for muscles: Bulbospongiosus Transverse perineal Greater vestibular (Bartholin’s) gland Transverse perineal mm Levator ani Levator ani External anal sphincter Perineal body External anal sphincter Note: the “perineal body” is sometimes referred to clinically as the “perineum” Netter 6e 356 Perineal Membrane & Pouches Pelvic cavity Superior Perineal membrane separates superficial & deep perineal pouches Inferior fascia of pelvic diaphragm Deep perineal pouch Perineal membrane Superficial perineal pouch Perineal fascia Perineal skin Inferior Perineal membrane iiiiii uterus UB Deep pouch Superficial pouch Deep pouch Perineal (Colles) fascia Perineal membrane Superficial pouch Perineal (Colles) fascia Perineal Pouches (Compartments) Superficial perineal pouch Potential space between membranous layer of subcutaneous tissue (Colles’ fascia) & perineal membrane Contains roots & bulbs of clitoris/penis, glands, distal urethra & neurovasculature Perineal membrane Crus of clitoris & ischiocavernosus m. Urethra Urethral sphincter Ischiopubic ramus Bulb of vestibule & bulbospongiosus m. Deep perineal pouch Superior to perineal membrane & inferior to pelvic diaphragm Contains proximal urethra, external urethral sphincter, glands & neurovasculature Deep Pelvic diaphragm Deep perineal pouch Perineal membrane Superficial perineal pouch Superficial Subcutaneous (Colles’) fascia Urethra Perineal membrane Crus of penis & ischiocavernosus m. Bulb of penis & bulbospongiosus m. Urethral sphincter Ischiopubic ramus External Genitalia – Female Female External Genitalia Mons pubis Fatty elevation over pubic region Acquires coarse hair at puberty propitiation public Labia majora (S. Labium majus) Skins folds with areolar tissue & fat (end of round ligament of uterus) Labia minora (S. Labium minus) interfold Small skin folds, medial to labia majora Anteriorly, they form the prepuce (covering or “foreskin”) of the clitoris Considerable variation (size & shape) 23 COA7e 3.67A Female External Genitalia Vaginal vestibule Volva Ameanslips Space between labia minora Contains external urethral orifice (anterior) & introitus (posterior) Hymen of the vaginal orifice Thin mucous membrane that initially covers introitus (considerable variation); remnants are called hymenal caruncles Hymenal rupture has been equated with the first sexual penetration. It is now appreciated, however, that rupture is a poor predictor of previous sexual experience, and there can be many causes for the initial rupture. 24 COA7e 3.67C Vulvar Glands Vestibular bulb Greater vestibular glands (Bartholin’s) Either side of vestibule (in superficial pouch) Greater vestibular glands Secrete mucus into vaginal vestibule Origin of most vulvar adenocarcinomas Male homolog: bulbo-urethral (Cowper’s) gland Lesser vestibular/Para-urethral glands (Skene's) Open into vestibule, between the urethra & introitus (vaginal opening) Secrete mucus into vaginal vestibule Male homolog: prostate 25 Netter6e 354 & 356 Female External Genitalia Clitoral prepuce & frenulum of clitoris are midline structures formed as extensions of the labia minora Prepuce (clitoral hood) Prepuce Labium majus Glans clitoris Labium minus Frenulum of clitoris Fold of skin that covers clitoris Frenulum (fourchette) Small fold posterior to clitoris Frenulum of labia minora (fourchette) 26 Clitoris: A Modern View Erectile tissue Crura of clitoris Attached to ischiopubic rami Form the body of clitoris Corpora cavernosa Body of clitoris - corpora cavernosa Extensions of crura into the body Non-erectile tissue Glans clitoris Formed by thin tissue extensions of the bulb of the vestibule (pars intermedia & commissure) Suspensory ligament Condensation of deep fascia – forms a sling around clitoris at junction of root and body Suspensory lig. Body of clitoris Commissure & pars intermedia Glans clitoris Crura of clitoris Vestibular bulb (of clitoris) Vaginal orifice Greater vestibular gland Coverings of the Clitoris Deep-to-superficial Tunica albuginea Thick, white-ish (L. albugo = white), fibrous capsule around each erectile body Deep (clitoral) fascia (Buck’s) Dorsal nerve of clitoris Subcutaneous tissue Prepuce (skin) Dorsal artery & vein (deep) of clitoris Deep (clitoral) fascia (Buck’s) Thick fascia external to tunica albuginea Covers dorsal arteries, deep dorsal vein, and dorsal nerves Subcutaneous tissue (superficial fascia) Sensory branches of dorsal nerve (from the pudendal) 28 ECA5e 3.49 External Genitalia – Male 29 Male External Genitalia – Penis Dorsal In anatomical position, the penis is erect In the flaccid penis, the dorsal surface faces anteriorly Prepuce (foreskin, circumcised) Root, body & glans of penis External urethral orifice (meatus) Prepuce (foreskin) Uncircumcised Circumcised Appearance determined by circumcision 30 Grant’s Atlas 13e 3.47B Penis has Three Erectile Bodies Root of penis Suspensory ligament Deep fascia forms a sling around penis at junction of root & body Crus of penis (paired) Attached to ischiopubic ramus & perineal membrane Bulb of penis (unpaired) Attached to perineal membrane Body (shaft) of penis Corpora cavernosum (paired) Fused in midline, except posteriorly where they continue as crura Corpus spongiosum (unpaired) Separate from corpora cavernosa Contains spongy (penile) urethra Ends as glans of penis 31 Gilroy Thieme Atlas of Anatomy 3e 21.28A Coverings of the Penis Superficial-to-deep Superficial fascia (deep to skin) Sensory branches of dorsal n. (from pudendal) Superficial dorsal veins (may be visible through skin) Deep (penile) fascia (Buck’s) Buck’s fascia Thick fascia external to tunica albuginea Covers dorsal artery, vein & nerve Tunica albuginea (L. albugo = white) Thick, white-ish fibrous capsule around each erectile body 32 ECA5e 3.49 Inguinal Region, Inguinal Canal, Spermatic Cord & Hernias 33 Inguinal Canal Structures that pass through the canal: Both sexes Ilio-inguinal nerve (passes thru only part of the canal & emerges from superficial ring) Female Remnant of round ligament of the uterus Male Spermatic cord (muscular layers, vas deferens, gonadal vessels & nerves) Spermatic cord Round ligament of the uterus Labium majus Spermatic Cord Contains structures that pass to/from testis & scrotum Three fascial layers External – Cremasteric – Internal Contents Vas (ductus) deferens Testicular artery Pampiniform venous plexus (testicular vein) Sympathetic nerve fibers Genital branch of genitofemoral n. Lymphatic vessels Remnant of processus vaginalis 35 Gilroy 3e 13.14 Scrotum an Extension of Abdominal Wall Fasciae of scrotum & spermatic cord derive from extensions of anterolateral abdominal wall * Tra ns Int abd ob Ext o l bl XXX Recommended video by Dr. Peter Ward: Descent of Testes & Layers of Spermatic Cord (https://www.youtube.com/watch?v=qjpzfFsnr10) * 5. Transversus abdominis m. does NOT contribute to spermatic fascia Not for testing…but you should know the concept 36 Dartos & Cremaster Muscles Both muscles elevate the testes Dartos muscle (smooth m) Dartos fascia (penis) Superficial inguinal ring Muscle in scrotal wall that inserts into dermis Nerves: Ilio-inguinal (L1) & posterior scrotal (S3) ⎼ Sympathetics (to dartos) ⎼ Sensory (somatic afferent) to scrotal skin Cremaster muscle (skeletal m) Muscle around spermatic cord External spermatic fascia Cremaster (spermatic cord) Dartos fascia (scrotum) Nerve: Genitofemoral (L1-L2) 37 Netter 6e 365 Cremasteric Reflex Reflex is elicited by lightly stroking the superior and medial thigh Normal response is immediate contraction of cremaster muscle, which elevates ipsilateral testis Clinical Application http://www.clinicalexams.co.uk Involves sensory and motor fibers from two different nerves Afferent: Sensory fibers of the ilioinguinal nerve from inner thigh are stimulated by stroking Efferent: These activate motor fibers of the genital branch of genitofemoral nerve, which causes cremaster muscle to contract & elevate the testis Cesmebasi et al. 2014 4 https://doi.org/10.1002/ca.22481 Testes, Epididymis & Vas (Ductus) Deferens Epididymis & vas deferens form pathway for sperm, from testis to ejaculatory duct 1. Testis 2. Rete testis 3. Efferent ductules 4. Epididymis (head–body–tail) 5. Ductus deferens 6. Ejaculatory duct (in prostate) 39 Inguinal Hernias INDIRECT INGUINAL HERNIA DIRECT INGUINAL HERNIA (Hesselbach’s) Direct inguinal hernias Pass do not pass through deep ring, but enter the inguinal canal and may pass through superficial ring Indirect inguinal hernias Pass through deep inguinal ring and inguinal canal, and may pass through superficial ring Hernia sac from either type can enter the scrotum Direct hernias will be adjacent to spermatic cord Indirect hernias will be within spermatic cord Inguinal Hernias & Physical Examination Superficial inguinal ring is palpable just lateral to the pubic tubercle Clinical Application Examiner’s finger follows spermatic cord superiorly to superficial ring When patient is asked to cough, the presence of a herniated mass may be detected as an “impulse” on the finger Clinical reality: It may be difficult to distinguish a direct from an indirect hernia by physical examination. Often, this distinction is made during surgical repair. 41 Vasculature of the Perineum 42 Pudendal Artery Supplies the Perineum Main branchers of the internal pudendal (from internal iliac) Inferior rectal Clitoris Perineal body Perineal - Ends as posterior labial/scrotal Anus Artery of clitoris/penis - Dorsal clitoral/penile - Deep (cavernous) clitoral/penile 43 Vasculature to Perineum from Pudental Posterior labial artery Dorsal artery of the clitoris Posterior scrotal aa. Deep (cavernous) artery of the clitoris Clitoral a. Perineal a. Internal pudendal a. Inferior rectal a. Perineal a. Internal pudendal a. Inferior rectal a. 44 Pudendal Veins Drain the Perineum Corpora cavernosa & glans of clitoris/penis → Deep dorsal (cavernous) clitoral/penile vein* → Prostatic (uterovaginal) venous plexus → Internal pudendal vein * Deep dorsal vein (clitoris or penile) leaves the perineum through a gap in the perineal membrane, just inferior to the pubic arch Innervation of the Perineum 46 Pudendal Nerve (S2-S4) After passing through greater & lesser sciatic foramina Inferior rectal nerves and then… Enters pudendal (Alcock’s) canal (a passageway within obturator fascia) It enters the perineum to form: 1. Perineal nerve (& branches) 2. Posterior labial/scrotal 3. Dorsal nerve of clitoris/penis 47 Pudendal Nerve Supplies the Perineum Three branches to know: 1. Inferior rectal n. Crosses ischio-anal fossa to supply inferior anal canal (sensory) & external anal sphincter 2. Perineal (superficial & deep) Sensory to vaginal vestibule vaginal orifice & posterior labia Motor to ischiocavernosus & bulbospongiosus mm. Dorsal n. of clitoris Posterior labial nn. Dorsal n. of clitoris Perineal n. Inferior rectal n. 3. Dorsal nerve of clitoris Sensory to skin and glans 48 Pudendal Nerve Supplies the Perineum Posterior scrotal nn. Three branches to know: 1. Inferior rectal Crosses ischio-anal fossa to supply inferior anal canal (sensory) & external anal sphincter Dorsal n. of penis 2. Perineal (superficial & deep) Motor to ischiocavernosus & bulbospongiosus mm. Sensory to posterior scrotum Perineal n. 3. Dorsal nerve of penis Pudendal n. Sensory to skin and glans Inferior rectal n. 49 Innervation of Labia & Scrotum Ilio-inguinal n. (ant. scrotal n.) Genitofemoral n. (genital br.) Three nerves provide sensory innervation for the labia majora & scrotum Anterior Ilio-inguinal n. (ant. labial n.) Genitofemoral n. (genital br.) Pudendal n. (post. scrotal nn.) Ilio-inguinal n. (L1) Anterior labial/scrotal n. Lateral Genitofemoral n. (L1-L2) Genital br. Posterior Pudendal n. (perineal nn.) Pudendal n. (post. labial n.) Pudendal n. (S2-S4) Posterior labial/scrotal br. Inf. rectal n. (pudendal br.) 50 Dermatomes of the Perineum Dermatomes provided primarily by S3-S5 nerves (mostly pudendal) Anterior parts of perineum innervated by L1 nerves associated with anterior abdominal wall (mostly ilio-inguinal) Anocutaneous (anal) reflex (anal “wink”) occurs when tactile or noxious stimulus in peri-anal region causes brief contraction of external anal sphincter Afferent & efferent limbs of reflex provided by inferior rectal nerve (br. of pudendal) Afferent: supplies perianal skin & mucosa of the lower anal canal Efferent: supplies external anal sphincter Drake 3e 5.14 Local Anesthesia for Childbirth Most of perineum Pudendal block (S2-S4) relieves perineal pain from most of perineum Clinical Application Anesthetic bathes nerve where it crosses the sacrospinous ligament, near the ischial spine Anterior perineum Ilio-inguinal (L1) block abolishes pain from anterior perineum 52 Neuraxial Anesthesia for Childbirth Lumbar epidural & spinal blocks both introduce anesthetic at L3-L4 vertebral levels Clinical Application Epidural Anesthetic infused into epidural space → affects nearby nerve roots Spinal (subarachnoid) Anesthetic infused (“one-shot”) into subarachnoid space → affects nearby nerve roots and spinal cord 53 Anatomy of the Sexual Response 54 Cavernous & Pudendal Nerves Cavernous nerves innervate corpora cavernosa of clitoris or penis, and corpus spongiosum of penis Parasympathetics from S2-S4 via prostatic plexus (female: vesical plexus) Sympathetics from T1-L2(L3) via prostatic plexus (female: vesical plexus) Pelvic splanchnics Erection: parasympathetic Erectile bodies engorge & become turgid Emission: sympathetic Ejaculate moves into prostatic urethra Pelvic splanchnics Vesical plexus Pelvic plexus Ejaculation: parasympathetic & somatic Forceful expulsion of semen from urethra Rectal plexus Cavernous nerves Prostatic plexus Clitoris or penis Gray’s 41e 76.26 Erection Parasympathetics in cavernous nerves regulate erection of penis or clitoris Buck’s fascia Buck’s fascia Cavernous nerves inhibit (relax) smooth muscle in coiled helicine arteries, which straighten and allow blood to flow into and engorge venous cavernous spaces in corpora cavernosa Result: outflow veins compressed against Buck’s fascia & venous outflow blocked - Male corpus spongiosum also engorges but not as much (don’t want to block ejaculation) – its internal pressure is ⅓ – ½ of corpora cavernosa - Female vestibular bulb also becomes swollen (tumescent) Motor fibers in pudendal nerve stimulate bulbospongiosus muscles, further compressing deep penile veins & impeding venous outflow (role 56 of ischiocavernosus not clear) Emission and Ejaculation Emission: sympathetic fibers Male: emission is when seminal fluid enters the prostatic urethra Sympathetic fibers (L1-L2) stimulate peristalsis of vas deferens, seminal glands & prostate, which leads to emission. Sympathetics also close internal urethral sphincter to prevent retrograde ejaculation into the bladder Female: emission considered (by some) to be represented by expulsion of a small quantity of whitish fluid from para-urethral (Skene’s) glandsz Ejaculation: somatic & parasympathetic fibers Male ejaculation: seminal fluid, with secretions from bulbo-urethral (Cowper‘s) glands, is expelled from distal end of penile urethra Pudendal nerve stimulates bulbospongiousus contraction to propel seminal fluid in urethra Parasympathetics inhibit (relax) external urethral sphincter & stimulate para-urethral smooth muscle contraction Female ejaculation also occurs, either during sexual arousal or organs. Not well understood, but may contain acid phosphatase (helps sperm motility) & fructose (energy source for sperm). The source may be the paraurethral glands (Skene‘s glands). 57 END 58 Ovaries & Testes Ovaries & testes are retroperitoneal and descend to pelvis or scrotum 8 wk 7 wk Labia majora & scrotum are homologues Ovaries come to be located along lateral pelvic wall - Female: gubernaculum persists as the round ligament (& ovarian lig.), which passes thru inguinal canal & attaches to labium majus Testis passes thru inguinal canal & into an outpouching of peritoneal cavity (processus vaginalis) that leads to developing scrotum - Processus vaginalis obliterated - Male: gubernaculum persists as the scrotal ligament 15 wk 7 mo 9 mo Mature