Station 4 – Vulva and Perineum

Station Moderator: Dr. Gareth Yokochi

1.1   Pre-test

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1.2   Objectives

1. Identify the common landmarks of the perineum in order to describe the external genitalia exam
2. Describe the course of the pudendal nerve and identify the landmarks when performing a pudendal nerve block
3. Describe the anatomic structures and muscles of the vulva involved in a 4^th degree perineal laceration
4. Identify the vaginal fornices and its importance in vaginal surgery.

1.3  Relevant Anatomy

• Perineum
• Vulva- labia majora, labia minora, mons pubis, clitoris, vestibule, Skene’s gland, Bartholin’s gland
• Muscles of the vulva- superficial transverse perineus, bulbospongiosus (aka, bulbocavernosus), ischiocavernosus muscles
• Pudendal nerve
• Vagina- posterior fornix
• Superficial and Deep Pouches

1.4 Case 4

Ms. Vulvineum is a 31 yo G1P0 at 38w0d by LMP consistent with 8 week ultrasound here for active labor. She wants to have natural childbirth without an epidural. She dilates to complete and starts to push, but the fetal heart rate tracing has recurrent deep variable decelerations. Operative delivery is recommended given the fetal heart tracing and the patient is agreeable. The patient receives a pudendal nerve block for anesthesia and a forceps-assisted vaginal delivery is performed with delivery of the baby and a 4^th degree perineal laceration.

Discussion:

• Identify and name the boundaries of the perineum.
  • thighs laterally,
  • pubic symphysis superiorly
  • coccyx inferiorly

1.4.1  Structures of the vulva:

• Labia majora

Discussion:

• • Labia major has underlying adipose tissue
  • Fuses anteriorly with mons pubis and posteriorly with perineum
  • Skin has hair follicles, sebaceous and sweat gland

• Labia minora

Discussion:

• • Labia minora does not have adipose tissue
  • Skin has sebaceous and sweat glands, no hair follicles

• Mons pubis
• Clitoris

Discussion:

• • Clitoris located anterior to the labia minora
  • Homologue of the penis

• Vestibule

Discussion:

• • Area between labia minora bounded by the clitoris anteriorly and perineum posteriorly
  • Urethra and vagina open into the vestibule

• Skene’s & Bartholin’s glands

Discussion:

• • Drain into the vestibule
  • Associated with vaginal lubrication
  • Cysts or abscesses can develop in these glands

1.4.2  Associated nerves

Question: What does the pudendal nerve innervate in this region?

• Vulva
• Anterior to the urethra, the vulva is innervated by the ilioinguinal and genitofemoral nerves.

Question: What is the course of the pudendal nerve?

• Originates from the sacral plexus (S2-S4)
• Passes between the piriformis and ischiococcygeus muscles
• Leaves pelvis through the greater sciatic foramen
• Crosses the sacrospinous ligament (close to the insertion to the ischial spine)
• Re-enters pelvis through the lesser sciatic foramen.

Question:  Where do you inject the lidocaine when performing a pudendal nerve block?

• Identify the ischial spine and inject 1 cm posterior and medial to ischial spine

Question: How do you check if the pudendal nerve block was effective?

• Absence of the anal wink

1.4.3  Muscles associated with the vulva

Identify the muscles of the vulva

• Superficial transverse perineal
• Bulbocavernosus
• Ischiocavernosus

These muscles overlie associated erectile tissues with similar names.

• Corpus cavernosum and crura
• Corpus spongiosum and bulb of vestibule

Describe the structures involved in first to fourth degree perineal lacerations

• First degree perineal laceration- vaginal mucosa and perineal skin
• Second degree perineal laceration- Vaginal mucosa + Perineal body
• Third degree perineal laceration- 2^nd degree + anal sphincter
• Fourth degree perineal laceration- 3^rd degree + rectal mucosa

1.4.4  Vagina

Discussion:

• Lower 1/3 of vagina crosses over the urogenital diaphragm and is surrounded by the bulbocavernosus muscles
• Vagina is lined by stratified squamous epithelium and 3 layers of smooth muscle
• Mesonephric duct remnants can be seen as Gartner duct cysts in the subepithelial layer

1.4.5 Vaginal Fornices

• Located around the cervix
  • anterior
  • posterior
  • 2 lateral fornices

Discussion:

• Posterior fornix close to pelvic peritoneum and pouch of Douglas allowing easy access to peritoneal cavity (culdocentesis, entry for TVH).

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