Pelvic anatomy
region including the fallopian tube and ovary.
region of the pelvis located above the pelvic brim.
the one fimbriae attached to the ovary.
a bony ridge on the inner surface of the ilium and pubic bones that divides the true and false pelvis.
extension of a double layer of peritoneum between visceral organs.
the surface region in both males and females between the pubic symphysis and the coccyx; area below the pelvic floor.
time before the onset of menstrual cycles.
refers to the process of physical changes by which a child’s body becomes an adult body capable of reproduction.
Pelvic anatomy (fig. 19-1)
• Pelvis begins at the iliac crests and ends at the symphysis pubis.
• Divided into the true and false pelvis by the iliopectineal line.
True pelvis
• Also known as pelvic cavity.
• Located inferior to the pelvic brim.
• Muscles and ligaments form a pelvic floor.
• Anterior boundary—symphysis pubis.
• Posterior boundary—sacrum and coccyx.
• Posterolateral wall—piriformis and coccygeus muscles.
• Anterolateral wall—hip bone and obturator internus muscles.
• Lateral boundaries—fused ilium and ischium.
• Pelvic floor—levator ani and coccygeus muscles.
• Contains—female reproductive system, urinary bladder, distal ureters, and bowel.
False pelvis
• Located superior to the pelvic brim.
• Anterior boundary—abdominal wall.
• Posterior boundary—flanged portions of the iliac bones and base of the sacrum.
• Lateral boundaries—abdominal wall.
| PELVIC MUSCLE | DESCRIPTION | LOCATION | SONOGRAPHIC APPEARANCE |
| Levator ani | Most caudal structures within the pelvic cavityMedial to the obturator internus musclesPosterior to the vagina and cervix | Low-level, mildly curved linear echoes posterior to the vaginaHypoechoic compared to the normal uterus | |
| Iliopsoas muscles | Formed by the psoas major and iliacus musclesLateral landmark of the true pelvis | Course anterior and lateral through the false pelvisDescend until attaching to the lesser trochanter of the femur | Low-level gray echoes with a distinct central hyperechoic focus |
| Piriformis muscles | Arise from the sacrumForm part of the pelvic floorCourse through the greater sciatic notch | Posterior to the uterus, ovaries, vagina, and rectumAnterior to the sacrumCourse diagonally to the obturator internus muscle | Low-level linear echoesHypoechoic compared to the normal uterus |
| Psoas major | Arises from the lumbar spineDescends into the false pelvis | Course laterally and anteriorly into the false pelvisExits posterior to the inguinal ligament | Low-level echogenicityRound in shape in the transverse plane |
| Obturator internus muscles | Lateral margins of the true pelvisSurround the obturator foramen | Posterior and medial to the iliopsoas musclesLevel of the vaginaLateral to the ovaries | Low-level linear echoes abutting the lateral walls of the urinary bladder |
Pelvic ligaments
• Not routinely visualized by ultrasound.
• With intraperitoneal fluid collections, ligaments will appear moderately thin and hyperechoic.
| PELVIC LIGAMENT | DESCRIPTION |
| Broad | Winglike double fold of peritoneumDrapes over the fallopian tubes, uterus, ovaries, and blood vesselsExtends from the lateral walls of the uterus to the sidewalls of the pelvisProvides a small amount of support for the uterusCreates the retrouterine and vesicouterine pouchesDivided into the mesometrium, mesosalpinx, and mesovarium segments |
| Cardinal | Continuation of the broad ligamentExtends across the pelvic floorAttaches at the isthmus portion of the uterusFirmly supports the cervix |
| Ovarian | Extends from the cornua of the uterus to the medial aspect of the ovary |
| Round | Arises in the uterine cornua, anterior to the fallopian tubesExtends from the uterine fundus to the pelvic sidewallsHelps to maintain anteflexion of the uterine body and fundusExcessive stretching can permit retroflexion of the uterine body and fundusContracts during labor |
| Suspensory | Also known as infundibulopelvic ligamentExtends from the lateral portion of the ovary to the pelvic sidewall |
| Uterosacral | Extends from the upper cervix to the lateral margins of the sacrumFirmly supports the cervix |
| VESSEL | LOCATION | INFORMATION |
| Arcuate vessels | Prominent vascular structures in the outer one third of the myometrium | Branch of the uterine arteryRadial arteries arise from the arcuate arteriesSpiral arteries of the endometrium arise from the radial arteriesRadial arteries branch into straight arteries to support the inner myometrium and endometriumLarger-caliber vessels are typically arcuate veins |
| Internal iliac arteries | Posterior to the uterus and ovariesFollows a posterior course and enters the true pelvis near the sacral prominence | Aka: hypogastric arteriesSupply the bladder, uterus, vagina, and rectumGive rise to the uterine arteries |
| Ovarian arteries | Arise from the lateral margins of the abdominal aorta, slightly inferior to the renal arteriesCourse medial within the suspensory ligaments | Primary blood supply to the ovariesConnect with the uterine arteries |
| Ovarian veins | Course within the suspensory ligaments | Right ovarian vein empties directly into the inferior vena cavaLeft ovarian vein empties into the left renal vein |
| Uterine arteries | Medial in the levator ani musclesAscend in a tortuous course lateral to the uterus within the broad ligament | Supply the cervix, vagina, uterus, ovaries, and fallopian tubesCourse lateral and terminate at the confluence with the ovarian artery |
Pelvic spaces
• Not uncommon to visualize a small amount of free fluid in the retrouterine pouch.
• Masses within the space of Retzius will displace the urinary bladder posteriorly.
• Masses within the vesicouterine pouch will displace the urinary bladder anteriorly.
• Ectopic pregnancy or hemorrhagic ovarian cyst (hemoperitoneum) accumulates in these spaces.
| PELVIC SPACE | LOCATION |
| Retrouterine PouchPosterior cul de sacPouch of Douglas | Anterior to the rectumPosterior to the uterusMost inferior point in the pelvic cavityMost common site for fluid to accumulate |
| Space of RetziusRetropubic spacePrevesical space | Anterior to the urinary bladderPosterior to the symphysis pubis |
| Vesicouterine PouchAnterior cul de sac | Anterior to the uterusPosterior to the urinary bladder |
Female reproductive system (fig. 19-2)
Vagina
• Collapsed muscular tube located posterior to the urinary bladder and urethra and anterior to the rectum and anus.
• Extends from the vulva to the cervix.
• Sides of the vagina are enclosed between the levator ani muscles.
• Half of the vagina lies above and the other half below the pelvic brim.
• Supplied by the vaginal and uterine arteries and empties into the internal iliac veins.
Uterus
• Hollow, pear-shaped retroperitoneal organ.
• Derived from the fused caudal portion of the paired, hollow müllerian ducts.
• Muscular organ covered by peritoneum, except below the anterior cervical os.
• Supported by the levator ani muscles, cardinal ligaments, and uterosacral ligaments.
• Uterine growth begins at approximately 7 to 8 years of age, accelerates during puberty, and continues to grow until approximately 20 years of age.
Tissue layers of the uterus
Endometrium
| REGION | DESCRIPTION |
| Body | Aka: corpusLargest portion of the uterusThick muscular segment of the uterusLocated posterior to the vesicouterine pouchLocated anterior to the retrouterine pouchLocated medial to the broad ligaments and uterine vessels |
| Cervix | Inferior portion of the uterusProjects into the vaginal canalMore fibrous and less flexibleAnchored at the angle of the bladder by the parametriumLocated between the vagina and the uterine isthmusPeritoneal reflection is not demonstrated anterior to the cervixApproximately 2.5 cm in length |
| Cornua | Lateral funnel-shaped horns of the uterusLocated between the uterine fundus and the interstitial portion of the fallopian tube |
| Endometrial cavity | Consists of a superficial functional layer and a deep basal layerFunctional layer sheds with mensesBasal layer regenerates new endometriumThickness is dependent on hormone levels |
| Fundus | Dome-shaped widest, most superior portion of the uterusLocated superior to the insertion of the fallopian tubesPosition may vary with bladder filling |
| Isthmus | “Narrow waist” of the uterusLocated between the cervix and body of the uterusTermed lower uterine segment during pregnancy |
Measuring the endometrium (fig. 19-4)
• Anterior–posterior thickness is measured in the sagittal plane.
• Measured from echogenic interface to echogenic interface (functional layer).
• Thin hypoechoic area (basal layer) is not included in the measurement.
• Fluid within the endometrial cavity is not included in the measurement.
| MENSTRUAL STATUS | LENGTH (cm) | HEIGHT (cm) | WIDTH (cm) | CERVIX/CORPUS RATIO |
| Premenarche | 2.0-4.0 | 0.5-1.0 | 1.0-2.0 | 2:1 |
| Menarche | 6.0-8.5 nulliparous8.0-10.5 parous | 3.0-5.0 nulliparous3.0-5.0 parous | 3.0-5.0 nulliparous5.0-6.0 parous | 1:2 |
| Postmenopausal | 3.5-7.5 | 2.0-3.0 | 4.0-6.0 | 1:1 |
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| POSITION | DESCRIPTION |
| Anteflexion | Uterine fundus bends on the cervix |
| Anteversion | Uterus bends slightly forwardCervix forms an angle ≤90° with the vaginal canalMost common uterine position |
| Dextroflexion | Uterine body is displaced or flexed to the right of the cervixTransverse imaging plane is best to evaluate whether uterus is dextroflexed |
| Levoflexion | Uterine body is displaced or flexed to the left of the cervixTransverse imaging plane is best to evaluate whether uterus is levoflexed |
| Retroflexion |