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Ovarian Ultrasound: Anatomy, Cycle, Doppler, and Pathology — Comprehensive Notes

Ovaries: Anatomy, Ultrasound, Hormones, Cycles, and Pathology – Comprehensive Notes

  • Overview and position

    • Normal female has two almond-shaped ovaries.
    • Typically located on the lateral sides of the uterus; position can vary (some near cervix, some next to uterus, some farther away).
    • Ovaries are mobile if ligaments are longer.
    • Landmarks to locate ovaries: internal iliac vessels (lateral) and uterus (medial).
    • Anatomical relationships to remember:
    • Ovaries are generally posterior-lateral and medial to the iliac vessels.
    • Ovaries are anterior to the internal iliac vessels and suspended posteriorly by the broad ligament.
    • Laterality question practice: how to identify right vs left ovary in relation to vessels.
    • Uterine position can affect ovarian location:
    • Retroverted/retroflexed uterus shifts ovaries laterally toward fundus or beyond.
    • Post-hysterectomy: ovaries tend to be more midline and centrally located because the uterine landmark (uterus) is no longer there; ovarian ligament may be absent.
    • In imaging, absence of a uterus as a landmark can make locating ovaries difficult; transvaginal approach may be needed.

  • Vascular supply and drainage

    • Arterial supply: gonadal artery (generic term for the artery; called ovarian in females, testicular in males) arising from the lateral aspects of the aorta.
    • Venous drainage: right ovarian vein drains into the IVC; left ovarian vein drains into the left renal vein.
    • Embryology note: gonadal vessels originate from the aorta and ascend/descend with gonads; this explains asymmetry of drainage.

  • Ovarian microanatomy

    • Outer layer: tunica albuginea (fibrous capsule).
    • Cortex: outer layer containing follicles (where follicles reside).
    • Medulla: central area containing vessels and connective tissue; medulla may be more echogenic on ultrasound.
    • Follicles originate in the cortex; theca and granulosa cells participate in follicle development and hormone production.
    • Tumor origins based on tissue layers:
    • Epithelial tumors originate from the tunica albuginea/epithelial covering.
    • Stromal tumors arise from connective tissue in the medulla/cortex region.
    • Germ cell tumors originate from cells around the follicle (the germ cell lineage).

  • Ovarian hormones and cycle (hormonal regulation)

    • Pituitary hormones:
    • FSH (follicle-stimulating hormone): stimulates follicle growth (follicular development).
    • LH (luteinizing hormone): stimulates the dominant follicle to ovulate.
    • Ovarian hormones and cell sources:
    • Granulosa cells produce estrogen (via aromatization of androgens).
    • Theca interna cells produce androgens (e.g., testosterone, androstenedione) which granulosa cells convert to estrogen.
    • Corpus luteum produces progesterone (and some estrogen) after ovulation; supports secretory endometrium.
    • Phases of the ovarian cycle:
    • Follicular phase: follicles grow under FSH influence.
    • Ovulation: release of the oocyte when the dominant follicle ruptures (LH surge).
    • Luteal phase: corpus luteum forms and secretes progesterone; ends with either pregnancy or corpus albicans if not pregnant.
    • Corpus luteum and corpus albicans
    • Corpus luteum forms after ovulation; can be associated with intrauterine pregnancy.
    • If not pregnant, corpus luteum regresses to corpus albicans (white body).
    • Follicle development and dominance
    • Multiple follicles grow during the proliferative/follicular phase; one becomes the dominant follicle.
    • The rest undergo atresia (atresia).
    • Dominant follicle size commonly around 2–2.5 cm; registry references may use up to 3 cm as a cutoff beyond which a follicle is considered a cyst.
    • Ovulation indicators on ultrasound
    • Cumulus oophorus sign: a secondary small cyst within a dominant follicle indicating imminent ovulation; typically observed within ~24–36 hours of ovulation.
    • Post-ovulation changes (cremulation): scalloped irregular wall around the follicle as it collapses; fluid may collect in the posterior cul-de-sac.
    • Dominant follicle around 2–2.5 cm (some references say up to 3 cm as a threshold for cystification).
    • Endometrial phases (visible side-by-side with ovarian phases)
    • Menstrual phase: thin endometrium; multiple small follicles in ovary.
    • Proliferative phase: endometrium thickens; three-line sign; dominant follicle preparing to ovulate.
    • Secretory phase: thick, hyperechoic endometrium with posterior enhancement; corpus luteum present.
    • Correlation: endometrium phases align with ovarian cycle phases; ovulation occurs around day 14 in a typical cycle.

  • Ultrasound appearance of the ovaries

    • Normal ovary: homogeneous echotexture; simple follicles appear anechoic (fluid-filled) with posterior acoustic enhancement.
    • Medulla may be more echogenic than cortex, but not required.
    • Follicles: anechoic structures within the cortex.
    • Postmenopausal ovaries: smaller and often atrophic with few or no follicles; require careful differentiation from bowel.
    • Techniques to differentiate ovary from bowel in difficult cases:
    • Use color Doppler to delineate borders and vessel pattern.
    • Check for peristalsis to identify bowel.

  • Ovarian ultrasound measurements and thresholds

    • Ovarian volume calculation: V = L imes W imes H imes 0.523 where L, W, H are length, width, and height.
    • Abnormal ovarian volume threshold: > 22 mL is considered abnormal.
    • Volume measurement method: use calcs package on ultrasound machine when available; otherwise, multiply L × W × H × 0.523 by hand.
    • Size-asymmetry concern: if one ovary is more than twice the size of the other, this is abnormal (red flag).

  • The ovarian cycle and endometrium correlation (summary recap)

    • Hormone drivers:
    • FSH stimulates follicle growth; LH triggers ovulation; ovarian hormones include estrogen and progesterone.
    • Follicular phase features:
    • Multiple follicles visible; rising estrogen; endometrium proliferates (proliferative phase).
    • Ovulation features:
    • Dominant follicle reaches around 2–2.5 cm (up to 3 cm in some references); cumulus oophorus sign present.
    • Ovulation around day 14 (variable).
    • Luteal phase features:
    • Corpus luteum forms; endometrium secretory; potential corpus luteum cyst.
    • Endometrial phase references (for imaging correlation):
    • Menstrual phase on left side (thin endometrium) corresponding to early follicular activity.
    • Proliferative phase (three-line sign) corresponds to follicular growth and pre-ovulation.
    • Secretory phase corresponds to luteal phase with thick, echogenic endometrium.

  • Doppler and flow assessment in ovarian imaging

    • When evaluating masses, Doppler can provide helpful information about vascularity.
    • Typical resistive and pulsatility index (RI and PI):
    • RI = (PSV − EDV) / PSV
    • PI = (PSV − EDV) / Mean velocity
    • Example calculations (from slides):
    • Example 1: PSV = 44, EDV = 5.61 → RI = (44 − 5.61)/44 ≈ 0.87.
    • Example 2: PSV = 16.8, EDV = 7.83, Mean = 11.2 → PI = (16.8 − 7.83)/11.2 ≈ 0.8.
    • Clinical interpretation notes from the lecture:
    • There are conflicting statements about what RI/PI values imply for malignancy; some sources say RI < 0.4 or PI < 1 may suggest malignancy, while others suggest RI > 0.4 and PI > 1 as normal. The lecturer emphasized that these indices are not always sensitive and depend on cycle phase.
    • Doppler assessment should be performed in the appropriate cycle window (typically within the first 10 days to avoid luteal-phase normalization of flow).
    • Low-resistive flow is typical during the luteal phase due to corpus luteum blood supply, while higher resistance is observed in the follicular/proliferative phases.
    • Practical tips for image acquisition:
    • Enable color and spectral Doppler; adjust scale to detect slow flow (power Doppler may help in very slow flow states, such as torsion).
    • Compare bilateral ovaries; use color to better delineate borders and vascularity.

  • Functional ovarian cysts and related cystic pathologies

    • Functional cysts (ovarian follicles that did not ovulate or persist post-ovulation):
    • Follicular cysts: follicles that did not ovulate; typically anechoic, thin-walled, posteriorly enhancing; usually <5 cm but can grow larger; generally benign.
    • Corpus luteum cysts: form after ovulation, may be simple or complex; thick-walled; may produce progesterone; can be bilateral or unilateral.
    • Thecal-lutein cysts: large bilateral multiloculated cysts associated with high hCG (often in trophoblastic disease or assisted reproduction).
    • Hemorrhagic corpus luteum cysts: hemorrhage within corpus luteum; internal echoes possible; can look complex; risk of mistaken ectopic pregnancy; color Doppler helps.
    • Complex cysts and adnexal masses:
    • Complex masses have both cystic and solid components; look for solid nodules, thick septations, and vascularity; require careful evaluation for potential malignancy.
    • Dermoid cyst (mature teratoma): a common benign germ cell tumor; can contain fat, hair, teeth; often with heterogeneous appearance; may have Rokitansky nodule; typically benign.
    • Endometrioma (chocolate cyst): localized endometriosis within the ovary; classically cyst with homogeneous low-level echoes; may appear as a complex cyst; often called chocolate cyst due to contents.
    • Other complex adnexal masses and conditions:
    • Endometriosis can involve ovaries and cul-de-sacs; endometriomas are localized ovarian endometriosis; overall endometriosis is outside the uterus (endometrial tissue outside uterus).
    • Pelvic inflammatory disease (PID) can create complex adnexal masses.
    • Peritoneal inclusion cysts: septated fluid collections in posterior cul-de-sac due to prior surgery or PID; often septated, multi-chambered collections.
    • Paraovarian cysts (Gardner’s duct cysts): para-ovarian cysts arising from remnants of Wolffian ducts; can occur near the ovary or vagina.
    • Ovarian remnant: after oophorectomy, residual ovarian tissue can persist and function.
    • Pedunculated fibroids: fibroids with a stalk can mimic an ovarian mass; differentiation by location relative to uterus and stalk anatomy.

  • Benign cysts and common tumors (epithelial, germ cell, stromal categories)

    • Epithelial tumors (originating from epithelial surface/tunica albuginea): include mucinous cystadenoma (benign, usually cystic, large; most common cystic ovarian tumor; often unilateral; age range roughly 13–45; multiple variants).
    • Germ cell tumors (originating from germ cells surrounding the follicle): include dermoid/dermoid cyst (mature teratoma) and other germ cell tumors; often benign in the mature form but can be malignant in others.
    • Stromal tumors (connective tissue origin): include granulosa cell tumors (can be benign or malignant); sometimes hormone-active.
    • Practical charting exercise described in lecture: fill a chart with examples of ovarian tumors by category (epithelial, germ cell, stromal) including names, benign/malignant status, typical age range, laterality (unilateral/bilateral), ultrasound appearance, and special facts (e.g., mucinous cystadenoma being the most common cystic tumor; granulosa cell tumors can be benign or malignant).

  • Pediatric and menopausal ovarian considerations

    • Pediatric ovaries: may show small follicles normally; occasional follicles can be seen pre-puberty.
    • Postmenopausal ovaries: generally atrophic with few or no follicles; smaller size makes differentiation from bowel important; tips include turning on color Doppler and looking for peristalsis to distinguish bowel; bowel motion helps avoid misidentification as an ovary.
    • Menopausal changes: atrophic ovaries; different morphology; consider benign vs malignant features with caution; malignancy may present with enlarged ovaries and ascites in some scenarios.

  • Ovarian pathology: key features and differential diagnoses

    • Simple cysts: benign, anechoic, thin-walled, posterior enhancement; may fill entire ovary; pre- and postmenopausal thresholds differ for intervention.
    • Complex cysts: mixed solid and cystic; contain internal echoes; may have septations; risk stratification essential to differentiate benign vs malignant.
    • Solid masses: more common in reproductive years; risk of malignancy increases with age; overall, about 1 in 15 solid masses are malignant in premenopausal age group; higher probability with older age.
    • Masses with ascites: suggest malignant potential; but ascites can also be present with ectopic pregnancy; documentation of pregnancy status essential.
    • Ovarian cancers: often present late due to vague symptoms; may have CA-125 elevation; BRCA gene mutations increase risk; risk of bilateral involvement; staging ranges from I to IV.
    • Endometriosis vs adenomyosis:
    • Endometriosis: ectopic endometrial tissue outside uterus; endometrioma (chocolate cyst) in the ovary is a localized manifestation.
    • Adenomyosis: endometrial tissue within the myometrium (uterus), not outside uterus; differentiate from endometriosis for management.
    • Pseudomyxoma peritonei: malignant ascites associated with certain cancers; extensive peritoneal involvement with mucinous ascites.

  • Ovarian torsion: emergency and imaging features

    • Ovarian torsion = twisting of the ovary around its vascular pedicle; can be partial or complete.
    • Clinical presentation: acute severe pelvic pain, sometimes with nausea/vomiting; right-sided torsion is more common.
    • Imaging features: enlarged ovary with edema, thickened wall; decreased or absent arterial flow on Doppler; early signs include edematous follicles; whirlpool sign on color Doppler (twisted pedicle) may be seen; absence of color flow indicates advanced torsion and risk of infarction.
    • Management: urgent surgical evaluation; ovarian preservation if possible, but detorsion may be necessary to prevent irreversible damage.
    • In torsion cases with a large cyst, the cyst may predispose to twisting; aspiration might be considered to reduce mass effect when surgery is planned.
    • Imaging techniques to maximize diagnostic confidence: use color, spectral Doppler, and power Doppler to characterise flow; adjust color scale to detect slow flow; compare bilateral ovaries; assess for pelvic fluid.

  • Differential diagnosis and mass assessment workflow (clinical reasoning)

    • When encountering an adnexal mass, consider: benign cysts, hemorrhagic cysts, corpus luteum cysts, endometriomas, teratomas, paraovarian/ Gartners duct cysts, hydrosalpinx, PID, ovarian torsion, and malignant tumors.
    • Key imaging cues:
    • Simple cyst: anechoic, thin wall, posterior enhancement; benign typically; size thresholds guide management.
    • Complex cyst: mixed content; thick septations or solid components raise suspicion for malignancy; need correlation with clinical history and tumor markers.
    • Solid mass with papillary projections or nodularity, thick septations, and papillary structures raises malignancy concern.
    • Features that raise suspicion for malignancy: solid components, thick septations, mural nodules, papillary projections, ascites, and bilateral disease; however, tumors can be bilateral or unilateral.
    • Tumor markers and genetics: CA-125 elevation associated with ovarian cancer; BRCA1/BRCA2 mutations increase risk; familial history important for risk stratification.
    • Staging and reporting: use standardized malignancy assessment frameworks (e.g., ORADS-like charts and ACR guidelines) to classify adnexal masses and guide management.

  • Staging and prognosis notes for ovarian cancer (high-level)

    • Stage I: limited to ovaries.
    • Stage II: pelvic involvement.
    • Stage III: peritoneal implants outside the pelvis; includes peritoneal metastases.
    • Stage IV: distant metastases (e.g., liver).
    • Prognosis worsens with higher stage and presence of ascites or peritoneal carcinomatosis.

  • Practical notes and exam-style reflections

    • Common exam prompts include: identifying dominant follicle vs follicular cyst; recognizing cumulus oophorus and its implications for imminent ovulation; differentiating corpus luteum cysts with ring of fire on color Doppler; understanding endometrial phase correlations to ovarian cycles.
    • Key measurements and calculation practice: calculate ovarian volume from provided dimensions; interpret if the volume is within normal range; identify a red flag when volumes are disproportionate between ovaries.
    • Normal vs abnormal Doppler expectations: luteal phase tends to have low resistive flow due to corpus luteum perfusion; follicular phase may show higher resistance; the cycle day can significantly affect RI/PI interpretation, so timing matters for accurate assessment.

  • Quick reference questions (study prompts)

    • What is the dominant follicle size typically around? Approximately 2 ext{ to } 2.5 ext{ cm} (some institutions may use 3 ext{ cm} as a threshold).
    • How do you calculate ovarian volume? V = L imes W imes H imes 0.523; abnormal if V > 22 ext{ mL}.
    • Which vein drains the right and left ovaries? Right ovarian vein → IVC; left ovarian vein → left renal vein.
    • What is cumulus oophorus, and what does it indicate? A smaller cyst indicating imminent ovulation within ~24–36 hours.
    • What is a chocolate cyst? An endometrioma, a cyst in the ovary filled with endometrial tissue (deposits of blood and tissue, giving a chocolate-like appearance).
    • What features suggest a malignant adnexal mass on ultrasound? Thick septations, solid components, mural nodules, papillary projections, and ascites; a complex mass with suspicious features warrants further workup and correlation with tumor markers.
    • What is the Ring of Fire sign? Color Doppler appearance around a corpus luteum indicating normal physiology; indicates vascular ring around the cyst.
    • How do you differentiate bowel from an ovary in imaging? Look for peristalsis, and use color Doppler to delineate borders; bowel will show movement whereas ovary should be relatively non-mobile; sometimes lowering the color scale helps reveal borders.

  • Summary of practical takeaways

    • Ovaries are variable in position and size; landmarks include external iliac vessels and uterus; movement is influenced by uterine position and prior surgeries.
    • Ultrasound appearances vary with age and cycle phase; follicles are anechoic; corpus luteum has thick walls and can be hemorrhagic; ring of fire is a normal Doppler finding around corpus luteum.
    • Functional cysts are common; complex cysts require careful evaluation for malignancy risk, with correlation to clinical history and tumor markers.
    • Doppler RI and PI provide supportive information but are not sole determinants of malignancy; interpretation should account for cycle phase and the overall imaging phenotype.
    • Ovarian torsion is a surgical emergency; recognize signs of absent or reduced flow, enlarged edematous ovary, and whirlpool sign on color Doppler.
    • Benign cystic tumors (e.g., mucinous cystadenoma) are common; dermoid/teratoma is a common germ cell tumor; granulosa cell tumors can be benign or malignant; knowledge of tumor categories helps in differential and charting for exams.

  • Key terminology recap

    • Corpus luteum, corpus albicans, cumulus oophorus, cremulation, ring of fire, three-line sign, endometrium phases (menstrual, proliferative, secretory), atresia, endometrioma (chocolate cyst), peritoneal inclusion cyst, paraovarian/Gartner duct cyst, whirlpool sign, pseudomyxoma peritonei.

  • Quick formulas to memorize

    • Ovarian volume: V = L imes W imes H imes 0.523
    • Resistive index: RI = rac{PSV - EDV}{PSV}
    • Pulsatility index: PI = rac{PSV - EDV}{Mean}
    • Dominant follicle size to monitor: around 2 ext{–} 2.5 ext{ cm} (some references allow up to 3 cm)
    • Postmenopausal ovarian abnormality threshold: not explicitly numeric, but smaller ovaries with lack of follicles and careful evaluation for bowel vs ovary is essential.

  • Ethical and clinical implications discussed

    • Accurate differentiation between benign and malignant adnexal masses is critical to avoid unnecessary surgery and to ensure timely cancer treatment.
    • In pregnancy-related scenarios (e.g., suspected hemorrhagic corpus luteum vs ectopic), ensure pregnancy tests are performed to guide management.
    • Counseling patients about fertility considerations in cases of torsion or major ovarian pathology.
    • The exam expectations include familiarity with a range of ovarian tumors, their imaging appearances, patient age ranges, and typical laterality, as well as use of standardized charts (e.g., ORADS/ACR-like schemes) for mass characterization.

  • Note on study resources

    • Use the provided slides and textbook references to fill out chart categorizing ovarian tumors by epithelial, germ cell, and stromal origins.
    • Be familiar with common patterns (e.g., mucinous cystadenoma as a common cystic tumor; dermoid/teratoma; endometrioma).
    • Review the difference between endometriosis (ectopic endometrial tissue outside the uterus) and adenomyosis (endometrial tissue within the myometrium).

  • Final takeaway

    • Comprehensive ovarian ultrasound requires integration of anatomy, cycle physiology, Doppler flow assessment, and careful differential diagnosis to guide management and ensure patient safety. Always correlate imaging findings with clinical history, pregnancy status, and laboratory markers when applicable.