Pelvic Anatomy and Uterine Variants

Quick Answer: Know uterine position, cycle-dependent endometrium, and Müllerian anomalies (arcuate vs septate vs bicornuate). Septate = normal outer contour + internal septum. Bicornuate = deep fundal cleft + widened intercornual distance >4 cm. Ovaries: follicles, corpus luteum.

Pelvic Orientation and Technique

Transvaginal imaging with empty bladder optimizes endometrial and ovarian detail. Sagittal uterus: endometrium central, cervix inferior, fundus superior. Transverse sweeps locate ovaries in the anterior cul-de-sac lateral to uterus—position varies with adhesions, retroversion, or prior surgery.

Postmenopausal: atrophic small uterus, thin endometrium, ovaries often not visualized—acceptable when no adnexal concern.

Uterine Position

Registry trap: retroverted uterus labeled pathologic without other findings.

Müllerian Anomaly Classification (High-Yield)

Worked Scenario: Septate vs Bicornuate

External fundus contour smooth with echogenic septum extending toward cervix: septate uterus. Deep fundal cleft with widened intercornual distance: bicornuate. Septate has normal outer contour—this distinction is the most tested Müllerian fact on registry.

3D coronal uterus after saline or in mid-secretory phase improves classification—2D alone may undercall septum length.

Cervix and Incidental Findings

Nabothian cysts: benign mucus retention in cervix. Gartner duct cysts: anterolateral vaginal wall, separate from cervix. Bartholin gland cyst: superficial labial location—not adnexal.

Ovarian Cyclic Anatomy

Corpus luteum is physiologic—distinguish from ectopic ring (intrauterine pregnancy should be sought; corpus luteum is within ovary).

Adnexal Landmarks and Mobility

Broad ligament and infundibulopelvic ligament guide expected ovary position. Fixed ovary with tenderness suggests adhesions (PID, endometriosis)—document for surgeon.

Pelvic Kidney

Renal cortex and hilum in pelvis may mimic mass—recognize reniform architecture before labeling adnexal neoplasm.

IUD and Endometrium

Levonorgestrel IUD creates echogenic device with posterior shadowing; endometrium may appear irregular but thin—document position on sagittal and transverse views.

Postpartum Uterus

Enlarged uterus with echogenic endometrial stripe days after delivery may be normal involution vs RPOC—correlate with bleeding, Doppler, and clinical exam.

Exam Traps

• Arcuate over-called septate (measure indentation depth and external contour)
• Bicornuate missed when coronal fundus not imaged
• Corpus luteum called ectopic gestational sac
• Pedunculated fibroid mistaken for ovary without identifying uterine stalk

GYN anatomy items test spatial reasoning—fundal contour and cavity division determine Müllerian classification answers.

Transabdominal vs Transvaginal Indications

Transabdominal (TA) imaging requires full bladder to elevate uterus and provides overview of large masses and fundal fibroids. Transvaginal (TV) with empty bladder optimizes endometrial detail, early pregnancy, and adnexal evaluation. Registry items test when TV is mandatory (suspected ectopic, endometrial pathology, cervical length).

Endometrial Cycle Changes (Premenopausal)

Premenopausal endometrial thickness interpretation requires cycle day context—no universal abnormal cutoff like postmenopausal bleeding protocol.

Cervical Anatomy and Length

Cervical length measured transvaginally from internal os to external os in straight line—not curved along canal. Short cervix (<25 mm before 24 weeks) increases preterm delivery risk in high-risk screening. Funneling of internal os with membranes may accompany shortening. Nabothian cysts in cervix are benign incidental findings.

Vaginal and Adnexal Landmarks

Gartner duct cysts arise in anterolateral vaginal wall. Bartholin cysts are superficial labial. Urethral diverticulum may mimic cystic mass anterior to vagina. Correct anatomic assignment prevents misdirected surgery on registry clinical correlation items.

Arcuate vs Septate: Measurement Discipline

Arcuate uterus shows smooth fundal indentation <1 cm into endometrial cavity with normal external contour. Septate uterus has normal external fundus but echogenic septum dividing cavity—septum may extend to cervix. 3D coronal reconstruction after saline or in secretory phase measures septum width for surgical planning (metroplasty candidacy).

Unicornuate and Didelphys

Unicornuate uterus shows single horn with rudimentary non-communicating horn possible—may contain endometrium and cause pain. Uterus didelphys shows two separate horns and often two cervices—pregnancy may occur in one horn. Document cervical duplication on transverse sweep.

Ovarian Mobility and Adhesions

Normal ovary moves with probe pressure. Fixed ovary with tenderness suggests adhesions from PID or endometriosis—document for surgeon. Ovarian transposition (surgical relocation) may appear in oncology history—ovary may sit unusually high in pelvis.

3D Coronal Uterus

3D coronal plane improves septate vs bicornuate classification—measure septum length and intercornual distance >4 cm for bicornuate. Septate uterus has normal external fundus with internal septum.

Corpus Luteum vs Ectopic

Corpus luteum lies within ovary with peripheral vascularity; ectopic ring sign is extrauterine with positive hCG. Always correlate with intrauterine pregnancy when present.