MRCOG Part 1 - Anatomy: High-Yield Chapter

Sources: Campbell-Walsh-Wein Urology, Berek & Novak's Gynecology, Color Atlas of Human Anatomy Vol 2, Gray's Anatomy for Students

1. Bony Pelvis

• Divided by the pelvic brim (linea terminalis) - a line from the sacral promontory to the superior margin of the pubic symphysis
• True pelvis = below the brim; False pelvis = above the brim
• Four bones: 2 innominate bones (ilium + ischium + pubis each) + sacrum + coccyx

2. Fascia and Ligaments of the Pelvis

Pelvic Fascia

• Three strata: inner (rectus fascia, Denonvilliers fascia), intermediate (parametrium, paracolpium), outer (transversalis fascia, obturator fascia)
• Arcus Tendineus Fascia Pelvis (ATFP) = "white line" - runs from pubic bone to ischial spine; lateral attachment of pubocervical fascia
• Parametrium = fascia attached to uterus
• Paracolpium = fascia surrounding vagina

Uterine Ligaments (very high yield)

3. The Ureter - Most Tested Surgical Relationship

1. At the pelvic brim - ovarian vessels cross OVER the ureter as it enters the pelvis
2. In the broad ligament - ureter runs lateral to the uterosacral ligament
3. At the ischial spine level - ureter passes UNDER the uterine artery ("water under the bridge") - lies 2-3 cm lateral to the cervix
4. At the bladder entry - ureter crosses anterior upper vagina as it enters the bladder

Mnemonic: "Bridge over water" = uterine artery (bridge) over ureter (water)

• 75% of iatrogenic ureteric injuries are from gynecological procedures
• Laparoscopic hysterectomy = highest risk; vaginal hysterectomy = lowest risk
• 91% of injuries occur at the pelvic ureter level
• Source: Berek & Novak's Gynecology

4. Blood Supply

Arterial Supply

• Right ovarian vein → directly into inferior vena cava (below right renal vein)
• Left ovarian vein → into left renal vein
• (Same pattern as testicular veins - explains why left-sided varicocele is more common)

Venous Drainage

5. Lymphatic Drainage (commonly tested in oncology context)

6. Innervation of the Pelvis

Somatic Innervation

• Sacral plexus = ventral rami of L4-L5 and S1-S4, on the piriformis muscle
• Exits pelvis through greater sciatic foramen; can be injured in sacrospinous ligament fixation

• Arises from S2-S4 just above the sacrotuberous ligament
• Exits through greater sciatic foramen, wraps around the ischial spine/sacrospinous ligament, re-enters through lesser sciatic foramen
• Travels in Alcock's canal (pudendal canal) on the medial wall of the ischiorectal fossa
• Branches: inferior rectal nerve → dorsal nerve of clitoris → perineal nerve
• Entrapment risk: sutures during sacrospinous fixation must be placed medial to ischial spine (at least 1.5 cm)

• Obturator nerve (L2-L4) - passes through obturator canal; supplies medial thigh; at risk in lymphadenectomy
• Femoral nerve (L2-L4) - lateral to psoas; can be compressed by retractor blades
• Ilioinguinal/iliohypogastric nerves - at risk in Pfannenstiel incision

Autonomic Innervation

• Sympathetic: T10-L2 (hypogastric nerves → inferior hypogastric plexus)
• Parasympathetic: S2-S4 (pelvic splanchnic nerves / nervi erigentes)
• Inferior hypogastric plexus (pelvic plexus) = lies lateral to the cervix and rectum; forms Frankenhäuser's ganglion (uterovaginal plexus) lateral to cervix
• Injury during hysterectomy → bladder dysfunction, sexual dysfunction

7. Pelvic Floor and Perineum

Pelvic Diaphragm (Levator Ani Complex)

• Pubococcygeus (pubovaginalis + puborectalis + pubococcygeus proper) - originates from ATFP and pubic bone
• Iliococcygeus - originates from ATFP and ischial spine
• Coccygeus (ischiococcygeus) - sacrospinous ligament forms its fibrous skeleton

Perineum

• Urogenital triangle (anterior): contains external genitalia and urogenital diaphragm
• Anal triangle (posterior): contains anus and ischiorectal fossae

• Retropubic (Retzius) space - between pubis and bladder
• Vesicovaginal space
• Rectovaginal space
• Pararectal space
• Paravesical space

8. Uterus - Structure and Relations

• Anteverted (forward tilt at cervicouterine junction) and anteflexed (body bent forward on cervix) - normal position
• Layers: perimetrium (peritoneum) → myometrium → endometrium
• Separated from bladder anteriorly by the vesicouterine pouch
• Separated from rectum posteriorly by the rectouterine pouch (pouch of Douglas)
• Anterior wall of vagina = 7.5 cm; posterior wall = 9 cm (cervix is higher on posterior wall)

9. Ovary - Key Anatomy

• Lies in the ovarian fossa on the lateral pelvic wall (posterior to broad ligament)
• Boundaries of ovarian fossa: obliterated umbilical artery (anterior), ureter and internal iliac artery (posterior)
• Attached by: mesovarium (to broad ligament), ovarian ligament (to uterus), infundibulopelvic ligament (to pelvic wall - contains ovarian vessels)
• Blood supply: ovarian artery from aorta; venous drainage as described above
• Lymphatics: para-aortic nodes (same as kidney level)
• Innervation: ovarian plexus (with ovarian artery) and inferior mesenteric plexus

10. Quick-Fire High-Yield Facts for SBAs

1. "Water under the bridge" = ureter under uterine artery, 2-3 cm lateral to cervix
2. Right ovarian vein → IVC; left ovarian vein → left renal vein
3. Pudendal nerve = S2-3-4; enters/exits via greater and lesser sciatic foramina; runs in Alcock's canal
4. Cardinal ligament = main support of cervix; uterosacral = secondary support
5. Ovarian lymphatics drain to para-aortic nodes (not iliac) - same level as kidneys
6. Vulvar lymphatics drain to inguinal nodes first
7. Broad ligament = NOT a true ligament; peritoneal fold containing the uterine tube, ovary, and vessels
8. Round ligament maintains anteversion; ends in labia majora; passes through inguinal canal
9. Levator ani (pubococcygeus + iliococcygeus) = main pelvic floor muscle; innervated by S3-S4
10. Frankenhäuser's ganglion = uterovaginal autonomic plexus, lateral to cervix; damaged in radical hysterectomy → bladder atony
11. Pouch of Douglas = deepest part of peritoneal cavity in females; between uterus and rectum; aspirated via culdocentesis
12. Obturator nerve (L2-4) - at risk in pelvic lymphadenectomy; supplies medial compartment of thigh
13. Infundibulopelvic ligament = contains ovarian vessels; always identify ureter before clamping
14. Parametrium = uterine fascia; paracolpium = vaginal fascia
15. Perineal body = central tendon between vagina and anus; damaged in third/fourth degree perineal tears

MRCOG Exam Tips

• Questions on the ureter are extremely common - know all four danger zones
• Lymphatic drainage is heavily tested, especially ovarian and cervical nodes
• Pudendal nerve course appears frequently in perineal and surgical questions
• Bony pelvis types (gynecoid, android, anthropoid, platypelloid) appear in obstetric questions
• Frankenhäuser's ganglion is a favorite for autonomic anatomy questions
• Always connect anatomy to applied clinical scenarios (e.g., why ureteric injury in hysterectomy, why left varicocele more common)