Diagnostic Ultrasound - Abdomen and Pelvis

Vagina
Anatomy: Pelvis
TERMINOLOGY
Abbreviations
• Ultrasound (US), vaginal artery (VA), uterine artery (UA)
GROSS ANATOMY
Overview
• Muscular tube formed by smooth muscle and elastic
connective fibers
• Serves as excretory duct for uterus, female organ for
copulation, and part of birth canal
• Extends up and back from vestibule of external genitalia to
surround cervix of uterus
• Has anterior and posterior walls, normally in apposition,
with longer posterior wall
• Superiorly, cervix projects downward and backward into
vagina and divides vagina into shallow anterior, deep
posterior, and lateral fornices
• Upper half of vagina lies above pelvic floor, lower half lies
within perineum
• Lined with stratified squamous epithelium
• Inner mucosal surface of wall form rugae when collapsed
• Thin mucosal fold called hymen surrounds entrance to
vaginal orifice
• Outer surface (adventitial coat) is thin fibrous layer
continuous with surrounding endopelvic fascia
• Vasculature
○ Arterial supply
– VA: Can branch directly from internal iliac artery
(anterior trunk) or sometimes from inferior vesical
artery or UA
– Vaginal branches of UA
– Branches of VA and UA anastomose to form 2 median
longitudinal vessels: Azygos arteries, one in front and
one behind vagina
○ Venous drainage
– Form venous plexus around vagina
– Eventually drains to internal iliac veins
• Variations with age
○ Menarche: 7-10 cm long
○ Postmenopausal: Shrinks in length and diameter;
fornices virtually disappear
Anatomic Relationships
• Anterior
○ Superior: Bladder base
○ Inferior: Urethra
• Posterior
○ Upper 1/3: Rectouterine pouch of Douglas
○ Middle 1/3: Ampulla of rectum
○ Lower 1/3: Perineal body
• Lateral
○ Upper 1/3: Ureters
○ Middle 1/3: Levator ani and pelvic fascia
○ Lower 1/3: Bulb of vestibule, urogenital diaphragm, and
bulbospongiosus muscles
• Ligamentous supports
○ Upper 1/3: Levator ani muscles, transverse cervical
(cardinal), pubocervical, and sacrocervical ligaments
○ Middle 1/3: Urogenital diaphragm
○ Lower 1/3: Perineal body
IMAGING ANATOMY
Ultrasound
• Transabdominal US with distended bladder is standard
imaging technique
○ Caudal angulation on both longitudinal and transverse
scans
○ Commonly found at/near sagittal midline of pelvis
○ Length and wall thickness vary in response to bladder
and rectal filling
○ Combined thickness of anterior and posterior vaginal
walls should not exceed 1 cm for transabdominal scan
with distended bladder
○ Characteristic appearance of 3 parallel lines
– Highly echogenic mucosa centrally, may be difficult to
visualize if stretched by distended bladder
– Moderately hypoechoic muscular walls
• Transperineal US with nondistended bladder for
assessment of uterine prolapse or for difficult cases
○ Vagina, especially vaginal canal, is less well-defined
EMBRYOLOGY
Embryologic Events
• Uterus and upper vagina are formed from paired müllerian
(paramesonephric) ducts
• Paired ducts meet in midline and fuse, forming
uterovaginal canal
• Lower vagina is formed from urogenital sinus
CLINICAL IMPLICATIONS
Uterine Prolapse
• Ligamentous support of pelvic organs may be damaged or
become lax, leading to uterine prolapse or prolapse of
vaginal walls
• Cystocele: Sagging of bladder with bulging of anterior
vaginal wall
• Rectocele: Sagging of ampulla of rectum with bulging of
posterior vaginal wall
• Best to be investigated by transperineal US supplemented
with 3D
Müllerian Duct Anomalies
• Failure of müllerian duct development ± fusion
• Vagina most commonly affected in uterus didelphys (class
III anomaly); vaginal septum seen in ~ 75% of cases
Pelvic Abscess
• Common site: Rectouterine pouch of Douglas
• Feasible for transvaginal US-guided drainage of pelvic
abscess without doing major operation
Persistent Sexual Arousal Syndrome
• Persistent sexual arousal during sleep in postmenopausal
women
• VA blood flow as one diagnostic aid
• VA normally shows high-resistance flow
• During sexual arousal, increased blood flow to VA with lowresistance
spectral waveform
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