Female Pelvis Anatomy

The Pelvic Skeleton

• 4 bones

  • 2 Innominate bones (coxal)

  • Sacrum - Posterior wall

  • Coccyx - Posterior wall

True (Lesser / Minor) Pelvis

• Area below pelvic brim

• Contains uterus and ovaries

False (Greater / Major) Pelvis

• Above the pelvic brim

• Contains mostly bowel

True and False Pelvis

True and false pelvis divided by imaginary line called the iliopectinal line that runs from the sacral promontory to the symphysis pubis

Obturator Internus Muscle (Internal Obturator Muscle)

• Covers the Innominate Bones

• Appear lateral to the ovaries - may mimic appearance of ovaries

• parallel and adjacent to the lateral pelvic wall

• easily missed with high gain

• True pelvis

Piriformis Muscle

• Posterior wall of true pelvis

• Travels from sacrum to greater trochanter of femur

• triangular shaped muscle

• usually obscured by overlying bowel gas in the sigmoid colon

• Most likely muscle to mistake for ovary

Levator Ani Muscles

• Make up the innermost layer of muscles to form the floor

• make up middle and anterior floor

• Lateral borders of the levator ani muscles cover the obturator internus muscle

• Resists intraabdominal pressure (from coughing and straining)

• holds pelvic organs in place

Levator ani muscles are composed of:

• Iliococcygeus

• Pubococcygeus

• Puborectalis

The Pelvic Muscles

• Filled bladder acts as a window to visualize three major muscle groups

  • Obturator Internus

  • Pelvic Floor Muscles

  • Iliopsoas Muscle

• Muscles may be mistaken for ovaries, fluid collection, or masses

  • a symmetric bilateral arrangement indicates they are muscles

Levator Ani U/S appearance:

• Best seen in transverse w/ caudal angulation at the most superior aspect of the bladder

• Hypoechoic, hammock-shaped area that is medial, caudal, and posterior to the obturator internus

Iliopsoas Muscle

• In false pelvis → never truly enters true pelvis, but courses along the border

• discretely marginated and hypoechoic

• both long and transverse images obtained through bladder midline with lateral angulation

• Too deep to see TV

The Perineum

• Area below the pelvic floor

• Diamond shaped and consists of skin and muscle

The Perineum is divided into 2 sections:

• Anterior Urogenital Triangle

  • Contains orifice for urethra and vagina

• Posterior Anal Triangle

  • Contains anus

The Urinary Bladder

• Smooth, hollow, thick-walled, musculo-membranous highly distendable collapsible muscular sac

• reservoir for urine

• retroperitoneal

• located along the pelvic floor - posterior to the symphysis pubis

  • between symphysis pubis and vagina

• lined with mucous membrane

• rugae in the wall - allow the bladder to expand

Bladder wall layers:

• Mucous membrane (transitional epithelium)

  • allows bladder to expand

• Submucosa (connective tissue)

• Muscle layer (Detrusor)

• Adventitia (Fibrous)

The Vagina

• Lies between the bladder and rectum

• muscular tube composed mostly of smooth muscle

• measures approximately 7-10 cm in length

Vaginal Anatomy:

• half of vagina lies in the perineum while lower half lies above pelvic floor

• fornix is found near cervix

  • anterior, lateral, and posterior fornices

• urethra located in anterior vaginal wall

Uterus

• Mobile, hollow, muscular, pear-shaped structure partially covered by peritoneum

• Located between bladder and rectum in the true pelvis

• Average nulliparous uterus measures about 7-8 cm long x 5.5 cm wide x 3 cm thick

  • multiparity may increase size by 1-2 cm in all dimensions

Four parts of uterus:

• fundus

• body

• isthmus

• cervix

Fundus

• uppermost part of uterus

• dome shaped region narrows at outer and lateral margins to form the cornua

• fallopian tubes arise laterally from cornua

Body (Corpus) of Uterus:

• Largest region

• houses the uterine cavity (endometrium)

• allows for dynamic changes during normal menstrual cycle and pregnancy

Isthmus of Uterus:

• Marks transition from corpus (body) to cervix

• known as uterine “waist”

• most flexible part of uterus

• called lower uterine segment during pregnancy

Cervix of Uterus:

• Neck of the Uterus

• 2-3 cm long in non-pregnant uterus

• Should be 3-4 cm long in pregnant women

• Endocervical canal

• Internal os: Communicates w/ uterus

• External os: Communicates w/ vagina

Uterine Layers:

1. Serosa (Perimetrium)

2. Myometrium

3. Mucosa (Endometrium)

Serosa (Perimetrium)

• Outermost layer of uterus

• thin

• not routinely visible. on TA U/S

• Better visualized TV

Myometrium

• thick middle layer of uterus

• smooth muscle surrounded by connective tissue

• forms bulk of uterus

Mucosa (endometrium)

• mucosal lining of uterine cavity

• varies in thickness throughout menstrual cycle

• continuous with lining of vagina

Uterus U/S appearance:

• Myometrium should be homogenous

• Smooth walled borders

• Arcuate vessels seen in periphery of uterus

Normal pre-puberty uterus measurements:

2.5-3.5 cm long x 1-2 cm AP thickness

Normal nulliparous uterus measurements:

7-8 × 5.5 × 3 cm

Normal multiparous uterus measurements:

8-9 x 5-6 × 5 cm

Normal post-menopausal uterus measurements:

3.5-6.5 × 1-2 × 2 cm

Broad Ligament

• Not a true ligament → double fold of peritoneum

• largest of all pelvic ligaments

• fat, vessels, and nerves in between the two layers

• minimally suspends the uterus

• Supports the ovaries due to the fact that they adhere to the posterior side of the ligament

Round Ligament

• Fibromuscular cords that hold uterine fundus in a forward position

• Extend from the cornua

• Provides anterior support

• Keep uterus in anteverted position

Cardinal ligaments AKA:

Transverse cervical ligaments

Cardinal ligaments

• Wide bands of ill-defined fibromuscular tissue

• Connect the cervix to the pelvic side wall and sacrum

• Maintain location of the cervix in the midline of the body

Uterosacral Ligament

• Connects the cervix to rectum and sacrum

• Provides posterior support

• Maintains midline placement of cervix

• Helps maintain anteverted position of the uterus

Ovarian Ligament AKA:

Utero-ovarian ligament

Ovarian Ligament

• Extends from each ovary to the lateral sides of uterus

• Fibromuscular cords within the broad ligament

Suspensory Ligament AKA:

Infundibulopelvic ligament

Suspensory Ligament (Infundibulopelvic ligament)

• Fold of peritoneum

• Connects ovary to pelvic wall

  • Extends up and over the iliac vessels

Anterior Cul-de-sac AKA:

Vesico-Uterine Pouch

Anterior Cul-de-sac (Vesico-Uterine Pouch)

Lies between the anterior wall of uterus and the bladder

Posterior Cul-de-sac AKA:

• Recto-Uterine Pouch

• Pouch of Douglas

Posterior Cul-De-sac

• Most posterior and dependent portion of the pelvic cavity

• First place to visualize fluid in the pelvis

Space of Reitzius AKA:

Prevesical / Retropubic space

Space of Reitzius

• Space between bladder and pubis

• Contains mostly fat

Anteverted uterine position:

• Most common

• Forward tilt of uterus maintaining 90° between cervix and vagina

Anteflexed uterine position:

• A forward bend of the uterine body on the cervix

• occurs at the isthmus

Retroverted uterine position:

• A tipping backward of the uterus without a bend between the cervix and body

• Approx. 10% of population

Retroflexed uterine position:

Bending backward of the uterine body on the cervix resulting in a sharp angle where it bends

The Fallopian Tubes AKA:

• Oviducts

• Salpinges (Salpinx)

Fallopian Tubes (Oviducts)

• Extend from the uterine fundus (cornua) toward the ovaries

• About 7-14 cm in length

  • Internal (lumen) dimensions:

    • Intramural - 1 mm

    • Ampulla - 6 mm

• Contained in a specific fold of the broad ligament called the mesosalpinx

3 layers of fallopian tube wall:

• Outer - serosa

• Middle - muscular

• Inner - mucosa

The fallopian tubes are divides into 4 regions:

• Interstitial (Intramural)

• Isthmus

• Ampulla

• Infundibulum

The Ovaries

• Paired, solid, almond-shaped glands that secrete hormones

• Not covered by peritoneum

Ovary measurements:

• Adult ovary = 2.5-5 × 1.5-3 × 0.6-2.2 cm (avg. 3 × 2 × 2 cm)

• Post-menopausal ovary - 2 × 1 × 1 cm

• Should calculate ovarian volume → L x W x H / 2 = cm³

  • Average volume during reproductive years is 6-9 cm³

Layers of the ovaries:

• Outer layer composed of germonal epithelium

• Thin fibrous layer - tunica albuginea

• Cortex - contains primordial follicles

• Medulla (Zona vasculosa of Waldeyer) - forms from embryonic mesenchyme and contains blood vessels, lymphatic vessels, and nerves

The ovaries location:

When the urinary bladder is empty, the ovaries are located in the ovarian fossa just beneath the pelvic brim adjacent to the iliac vessels and ureters

Ovaries U/S appearance:

• “swiss cheese” appearance

• low-level amplitude with follicles

• may be difficult to identify

  • reduce gain

  • TV > TA

  • Look anterior and medial to the iliac vessels

  • may have to press bowel out of the way

Pelvic Vasculature

• Common Iliac A’s bifurcate to internal and external iliac A’s

• External Iliac A’s and V’s supply and return blood to and from legs

• Internal arteries feed the pelvis and divides into anterior and posterior trunks

• Ovaries are anterior to Internal Iliac Artery

  • IIV’s are posterior to the arteries

Pelvic Arterial Flow Order:

Aorta → Common Iliac A → Internal Iliac A → Uterine A → Arcuate A’s → Radial A’s → Straight A’s → Spiral A’s

Pelvic Venous Flow Order:

Spiral V’s → Straight V’s → Radial V’s → Arcuate V’s → Uterine V’s → Internal Iliac V → Common Iliac V → IVC

Ovarian Vasculature Pathway:

Aorta → R/L Ovarian A → Ovary → R/R Ovarian V → IVC