Diagnostic Ultrasound - Abdomen and Pelvis

Uterus
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Anatomy: Pelvis
GROSS ANATOMY
Overview
• Anatomical divisions
○ Body (corpus): Upper 2/3 of uterus
– Fundus: Uterine segment superior to ostia of fallopian
tubes
○ Cervix: Lower 1/3 of uterus
– Isthmus: Junction of body and cervix
• Parametrium: Outer layer, part of visceral peritoneum
• Myometrium: Middle layer
○ Smooth muscle; forms main bulk of uterus
○ Composed of 3 zones: Inner, middle, outer (outlined by
arcuate arteries)
• Endometrium: Inner layer
○ Stratum functionalis (inner): Thicker, varies with cyclical
changes
○ Stratum basalis (outer): Thin, does not change
Anatomic Relationships
• Extraperitoneal location in midline true pelvis
• Uterine position
○ Flexion is axis of uterine body relative to cervix
○ Version is axis of cervix relative to vagina
○ Anteversion with anteflexion is most common
• Peritoneum extends over bladder dome anteriorly and
rectum posteriorly
○ Vesicouterine pouch: Anterior recess between uterus
and bladder
○ Rectouterine pouch of Douglas: Posterior recess
between vaginal fornix and rectum; most dependent
portion of peritoneum in female pelvis
• Supporting broad ligaments
○ Paired, formed by double layer of peritoneum
○ Contain fallopian tubes superiorly, and round ligaments,
ovaries, ovarian ligaments, and blood vessels inferiorly
• Fallopian tubes connect uterus to peritoneal cavity
○ 4 segments: Interstitial, isthmus, ampulla, infundibulum
• Arterial: Dual blood supply
○ Uterine artery (UA) arises from internal iliac artery (IIA),
anastomoses with ovarian artery
○ Arcuate arteries arise from UAs; seen in outer 1/3 of
myometrium
○ Radial arteries arise from arcuate arteries and penetrate
vertically into myometrium
○ Basal and spiral arteries arise from radial arteries to
supply stratum basalis and stratum functionalis,
respectively
• Venous drainage mirrors arteries
○ Parametrial venous network prior to drainage into
uterine or ovarian veins
Endometrial Variations With Menstrual Cycle
• Proliferative phase (follicular phase of ovary)
○ End of menstrual phase to ovulation (~ 14 days)
○ Estrogen induces proliferation of functionalis layer
• Secretory phase (luteal phase of ovary)
○ Ovulation to beginning of menstrual phase
○ Progesterone induces secretion of glycogen, mucus, and
other substances
• Menstrual phase
○ Sloughing of functionalis layer
Uterine Variations With Age
• Neonatal: Prominent size secondary to effects of residual
maternal hormone stimulation
• Infantile: Corpus < cervix (1:2)
• Prepubertal: Corpus = cervix (1:1)
• Reproductive: Corpus > cervix (2:1)
○ 7.5-9.0 cm (length)
○ 4.5-6.0 cm (breadth)
○ 2.5-4.0 cm (thickness)
• Postmenopausal: Overall reduction in size, similar to
prepubertal uterus
IMAGING ANATOMY
Myometrium
• Inner layer (junctional zone): Thin and hypoechoic, < 12 mm
• Middle layer: Thick, homogeneously echogenic
• Outer layer: Thin, hypoechoic layer peripheral to arcuate
vessels
Endometrium
• Proliferative phase
○ Early: Thin single echogenic line
○ Progressive hypoechoic thickening (4-8 mm), classic
trilaminar appearance
• Secretory phase
○ Increased echogenicity and thickening up to 16 mm
• Menstrual phase
○ Early: Cystic areas within echogenic endometrium
indicating endometrial breakdown
○ Progressive heterogeneity with mixed cystic (blood) and
hyperechoic (clot or sloughed endometrium) regions
ANATOMY IMAGING ISSUES
Imaging Recommendations
• Sonohysterography (SHG) to evaluate endometrial
pathology
• 3D ultrasound to evaluate müllerian duct anomalies
EMBRYOLOGY
Embryologic Events
• Organogenesis phase: Uterus formed from paired
paramesonephric (müllerian) ducts
• Fusion phase: Paired ducts fuse in midline to form uterus
and upper vagina
○ Unfused portions remain as fallopian tubes
• Resorption phase: Resorption of uterine septum
Practical Implications
• Müllerian duct anomalies occur during 1 of 3 phases of
formation
○ Organogenesis: Uterine agenesis, hypoplasia,
unicornuate
○ Fusion: Didelphys, bicornuate
○ Resorption: Septate, arcuate