Comprehensive OB/GYN Ultrasound Review and Study Notes

ULTRASOUND STUDY GUIDE: CORE OB/GYN SONOGRAPHY

THE UTERUS AND VAGINA

  • Overview of the Uterus

    • The uterus is a hollow, muscular, pear-shaped organ situated in the female pelvis.
    • It serves crucial roles in three major biological functions: menstruation, pregnancy, and childbirth.
    • Uterine Layers
    • 1. Endometrium: The innermost lining of the uterus.
    • 2. Myometrium: The middle muscular layer of the uterus; the prefix "myo-" denotes muscle.
    • 3. Perimetrium: The outer layer of the uterus; the prefix "peri-" means around or surrounding.
    • Anatomical Location
    • Posterior to the urinary bladder.
    • Anterior to the rectum.

  • Anatomical Divisions of the Uterus

    • Fundus: The most superior and widest portion of the uterus.
    • Body (Corpus): The largest portion of the uterus, situated between the fundus and the cervix.
    • Isthmus: The narrow area connecting the body to the cervix. During pregnancy, this is referred to as the lower uterine segment (LUS).
    • Cervix: The lower portion of the uterus that projects into the vagina.

  • Normal Variations in Uterine Anatomy

    • Anatomy varies based on size, shape, position, and orientation, influenced by age, parity (number of pregnancies), and pathology.
    • Age-Related Size and Ratio Changes
    • Pre-pubertal age: The uterus is small and infantile. The cervix is longer than the body, with a cervix-to-body ratio of 2:12:1.
    • Reproductive age: The uterus reaches its maximum size. The body is longer than the cervix, with a cervix-to-body ratio of 1:21:2. It significantly enlarges during pregnancy to accommodate the fetus.
    • Postmenopausal age: The uterus undergoes atrophy, a process of regression and size reduction due to decreased estrogen levels.
    • Uterine Positions and Orientations
    • Anteverted: The most common position; the entire uterus tilts forward toward the bladder.
    • Anteflexed: The uterus is bent forward at the level of the cervix.
    • Retroverted: A normal anatomical variation where the uterus tilts backward toward the spine.
    • Retroflexed: The uterus is bent backward at the cervix; the body folds back on the cervix due to a bend rather than just a tilt.
    • Levoverted: The uterus tilts toward the left side of the pelvis.
    • Levoflexed: The uterus flexes toward the left side.
    • Dextroverted: The uterus tilts toward the right side of the pelvis.
    • Dextroflexed: The uterus flexes toward the right side.

  • Vascular Anatomy of the Uterus

    • Blood Supply Pathway
    • Oxygenated blood arrives via the uterine arteries, which arise from the internal iliac arteries.
    • Arcuate Arteries: These encircle the uterus within the myometrium. They are sonographically visible as hypoechoic structures in the myometrial periphery.
    • Radial Arteries: These branch from the arcuate arteries and penetrate centrally into the myometrium toward the endometrium.
    • Straight Arteries: These branch from radial arteries to supply the basal layer (zona basalis) of the endometrium.
    • Spiral Arteries: These branch from radial arteries to supply the functional layer (zona functionalis) of the endometrium. They change during the cycle: they appear coiled and longer during the secretory phase and constricted during menstruation.
    • Venous Drainage
    • Blood returns via the uterine veins, which drain into the internal iliac veins.

  • Congenital Uterine Anomalies (Müllerian Duct Anomalies)

    • These result from abnormal formation, fusion, or resorption of the Müllerian ducts during fetal development.
    • Risk Factor: Exposure to diethylstilbestrol (DES), a synthetic estrogen, in utero.
    • Specific Anomalies
    • Arcuate uterus: A mild indentation or concavity of the uterine fundus; a common variation.
    • Unicornuate uterus: Only one Müllerian duct develops. It is half the size of a normal uterus and has only one fallopian tube.
    • Bicornuate uterus: Features two distinct uterine horns, creating a heart-like shape.
    • Septate uterus: The uterine cavity is divided by a septum.
    • Didelphys uterus: Known as a "double uterus"; occurs when Müllerian ducts develop into two separate uterine cavities.

  • The Endometrium

    • Layers
    • Zona functionalis: The superficial layer that is shed during menstruation.
    • Zona basalis: The deep, thin layer that remains and does not shed.
    • Sonographic Appearance by Phase
    • Menstruation: Appears as a thin, bright line.
    • Early Proliferative Phase (Days 5-9): Appears as a thin, echogenic line.
    • Late Proliferative Phase (Days 10-14): Displays the "three-line sign" (one central echogenic line, surrounding hypoechoic areas, and two outer parallel hyperechoic lines).
    • Secretory Phase (Days 15-28): The thickest stage; uniformly echogenic; may cause posterior acoustic enhancement.
    • Measuring the Endometrium
    • Use a sagittal (longitudinal) view.
    • Measure thickness from the basal layer of one side to the basal layer of the opposite side (including both anterior and posterior layers).
    • Do not include myometrium or intrauterine fluid in the measurement.
    • Reference Ranges
      • Proliferative Phase: 4−8 mm4-8\,mm.
      • Secretory Phase: Up to 16 mm16\,mm.
      • Menstrual Phase: Thin/Difficult to measure.
      • Postmenopausal with bleeding: Less than 5 mm5\,mm is normal.
      • Postmenopausal without bleeding: Less than 8−11 mm8-11\,mm is normal.

  • Assessing Uterine Metrics

    • Average Nulliparous Size: 7.5 cm7.5\,cm length, 5 cm5\,cm width, 2.5 cm2.5\,cm thickness.
    • Measurement Technique
    • Length (Sagittal): From the top of the fundus to the external cervical os.
    • Width (Transverse): The widest part of the mid-uterus.
    • Depth/AP (Sagittal): Anterior-to-posterior wall at the thickest part, perpendicular to length.

  • Intrauterine Fluid Collections

    • Hydrometra: Clear, serous fluid (anechoic) in the uterus.
    • Hydrometracolpos: Clear fluid (anechoic) in both uterus and vagina.
    • Hematometra: Blood (low-level internal echoes) in the uterus.
    • Hematometracolpos: Blood (low-level internal echoes) in both uterus and vagina.
    • Pyometra: Pus (complex internal echoes) in the uterus.

  • The Cervix

    • Cervical Anatomy and Function
    • Connects the uterine cavity to the vagina. Protects against infection and supports pregnancy.
    • Endocervix: Inner lining of the cervical canal.
    • Exocervix: Outer layer of the cervix.
    • Internal cervical os: Opening into the uterus.
    • External cervical os: Opening into the vagina.
    • Sonographic Assessment: Measured from internal os to external os. In pregnancy, a normal length is at least 3 cm3\,cm.

  • The Vagina and Congenital Anomalies

    • Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome: Partial or complete absence of the vagina, often with uterine anomalies. Ovarian function is typically normal.
    • Imperforate Hymen: The hymen has no opening, leading to hematocolpos (blood accumulation) at puberty.
    • Vaginal Duplication: Often associated with uterine duplication.

  • Uterine Pathology: Leiomyoma (Fibroids)

    • Definition: Benign smooth muscle tumors of the myometrium.
    • Risk Factors: African American ethnicity, obesity, hypertension, and family history.
    • Presentation: Menorrhagia (heavy bleeding), pelvic pain/pressure, urinary frequency, dysuria, and enlarged uterus.
    • Sonographic Appearance: Well-defined, hypoechoic masses showing posterior acoustic shadowing.
    • Locations
    • Intramural: Within the myometrium (most common).
    • Submucosal: Projects into the uterine cavity; distorts the endometrium; can impact pregnancy.
    • Subserosal: Grows on the uterine surface; distorts the contour.
    • Pedunculated: Attached by a stalk; risk of torsion leading to necrosis and acute pain.

  • Other Uterine and Vaginal Pathologies

    • Leiomyosarcoma: Rare, aggressive malignant tumor of smooth muscle. Larger, faster-growing, and more heterogeneous than fibroids; shows cystic degeneration.
    • Endometriosis: Endometrial-like tissue found outside the uterus, common on ovaries as "chocolate cysts" (endometriomas). Symptoms include painful bowel movements, menorrhagia, and dysmenorrhea.
    • Endometrial Hyperplasia: Thickening due to excess estrogen (obesity, PCOS, HRT, Tamoxifen). Thresholds: >14 mm>14\,mm (premenopausal), >5 mm>5\,mm (postmenopausal with bleeding).
    • Endometrial Polyps: Benign growths on the inner wall. Cause heavy or intermenstrual bleeding. Appear as focal (solitary) or diffuse (multiple) endometrial thickening.
    • Endometrial Carcinoma: Most common malignancy of the female genital tract. Features: postmenopausal bleeding (90%90\% of patients), elevated CA 125, thickened/heterogeneous endometrium.
    • Adenomyosis: Endometrial tissue grows into the myometrium. Results in a thickened junctional zone, heterogeneous myometrium, and myometrial cysts.
    • Precocious Puberty: Puberty onset before age 8 in girls. Uterus and ovaries increase in size; functional cysts may present.
    • Nabothian Cyst: Benign, asymptomatic, round, anechoic cysts within cervical tissue.
    • Cervical Stenosis: Narrowing of the cervical canal, often following other pathology. Causes pelvic pain, infertility, or amenorrhea.
    • Cervical Carcinoma: Malignant tumor often linked to HPV. Types: Squamous Cell Carcinoma (80−90%80-90\%) and Adenocarcinoma (10−20%10-20\%).
    • Gartner Duct Cyst: Benign, anechoic lesion in the vaginal wall (lateral sides).

THE OVARIES

  • Ovarian Anatomy

    • External Structure: Outer surface is germinal epithelium; beneath it is the tunica albuginea.
    • Internal Structure
    • Cortex: Outer layer containing ovarian follicles and the corpus luteum.
    • Medulla: Central part containing loose connective tissue and neurovascular structures.
    • Arterial Supply
    • Ovarian Arteries: Branch from the abdominal aorta; travel within the suspensory ligament (infundibulopelvic ligament).
    • Uterine Arteries: Anastomose with ovarian arteries.
    • Venous Drainage (Critical Asymmetry)
    • Right ovarian vein: Drains directly into the Inferior Vena Cava (IVC).
    • Left ovarian vein: Drains into the left renal vein.

  • Physiology and the Ovarian Cycle

    • Controlled by GnRH (hypothalamus) and LH/FSH (pituitary).
    • Hormones produced by Ovaries
    • Estrogen: Regulates cycle and secondary characteristics.
    • Progesterone: Produced by the corpus luteum to support potential pregnancy.
    • Cycle Phases
    • Follicular Phase: FSH stimulates growth. The dominant (Graafian) follicle reaches 2.0−2.5 cm2.0-2.5\,cm.
    • Ovulation: Occurs around Day 14 (in a 28-day cycle) following an LH surge. Mittelschmerz refers to mid-cycle pain.
    • Luteal Phase: The corpus luteum forms. If no pregnancy, it becomes the corpus albicans.

  • Sonographic Assessment

    • Appearance: Homogeneous, medium-level echotexture.
    • Volume Calculation: Ovarian Volume=(Length×Width×Height)×0.523\text{Ovarian Volume} = (\text{Length} \times \text{Width} \times \text{Height}) \times 0.523.
    • Normal Measurements (Premenopausal): Approximately 3.5×2.5×1.5 cm3.5 \times 2.5 \times 1.5\,cm.

  • Ovarian Pathologies: Cysts and Benign Neoplasms

    • Follicular Cysts: Results from a follicle failing to release an egg. Sonographically simple, anechoic, 3−8 cm3-8\,cm.
    • Corpus Luteum Cysts: Form after ovulation. Can be complex/hemorrhagic; shows the "ring of fire" sign on color Doppler.
    • Theca Lutein Cysts: Largest functional cysts, always bilateral. Result from high hCG (molar pregnancy, OHSS, multiple gestations). Appearance: "honeycomb" or "cluster of grapes."
    • Paraovarian Cysts: Simple, fluid-filled sacs adjacent to the ovary but not arising from it.
    • Dermoid Cysts (Cystic Teratoma): Germ cell tumor containing hair, fat, bone, or teeth. Key signs: "Tip of the iceberg" and "Dermoid mesh."
    • Thecoma: Benign stromal tumor (theca cells). Often postmenopausal. Associated with Meig’s syndrome (benign tumor, ascites, pleural effusion).
    • Granulosa Cell Tumor: Produces excess estrogen. Causes pseudoprecocious puberty or postmenopausal bleeding.
    • Mucinous Cystadenoma: Large, multilocular cysts filled with gelatinous substance.
    • Androblastoma (Sertoli-Leydig): Produces androgens, leading to virilization (hirsutism, masculization).
    • SALT Mnemonic: Sertoli-Leydig, Androgens, Ladies, Testosterone effects.
    • Ovarian Fibroma: Solid, hypoechoic mass with posterior attenuation. Associated with Meig’s syndrome.
    • Endometrioma ("Chocolate Cyst"): Ectopic endometrial tissue on the ovary. Contains thick, dark fluid. Sonographically: low-level internal echoes ("ground glass").
    • Serous Cystadenoma: Common benign tumor filled with watery fluid. Features papillary projections.

  • Malignant Ovarian Disease and Other Conditions

    • Serous Cystadenocarcinoma: Most common malignant ovarian epithelial tumor. Features thick septations and solid components; elevated CA 125.
    • Mucinous Cystadenocarcinoma: Can lead to pseudomyxoma peritonei (mucin spread in the peritoneal cavity).
    • Dysgerminoma: Equivalent to male seminoma. Most common ovarian malignancy in childhood; elevated LDH and hCG.
    • Yolk Sac Tumor (Endodermal Sinus Tumor): Highly aggressive; elevated alpha-fetoprotein (AFP).
    • Metastasis (Krukenberg Tumors): Secondary tumors often from the GI tract (stomach). Characterized by mucin-secreting signet-ring cells.
    • Ovarian Torsion: Rotation of the ovary cutting off blood supply. Symptoms: acute unilateral pain, vomiting. Sign: "Whirlpool sign" on ultrasound.
    • Polycystic Ovary Syndrome (PCOS / Stein-Leventhal): Hormonal disorder. Sonographic sign: "String of pearls" (12+ follicles, 2−9 mm2-9\,mm) or volume >10 mL>10\,mL.
    • Ovarian Hyperstimulation Syndrome (OHSS): Complication of fertility treatment. Features enlarged ovaries with multiple theca lutein cysts and ascites.

THE FALLOPIAN TUBES

  • Anatomy and Divisions

    • Pair of 10−12 cm10-12\,cm tubes. Origin: Uterine cornua.
    • Infundibulum: Funnel-shaped end near the ovary with fimbriae.
    • Ampulla: Widest section; the primary site of fertilization.
    • Isthmus: Narrow part connecting to the uterus.
    • Interstitial (Intramural) Segment: Passes through the uterine muscular layer.

  • Pathology of the Fallopian Tubes

    • Pelvic Inflammatory Disease (PID): Infection spreading from vagina/cervix. Leads to salpingitis. Fitz-Hugh-Curtis Syndrome is a complication involving perihepatitis (liver capsule inflammation).
    • Pyosalpinx: Accumulation of pus in the tube; appears dilated with echogenic debris.
    • Hydrosalpinx: Blockage leads to clear fluid accumulation; appears thin-walled and anechoic.

SUPPORTING PELVIC STRUCTURES

  • Ligaments

    • Broad Ligament: Peritoneal fold encasing the uterus, tubes, and ovaries. Sections: Mesometrium (largest), Mesosalpinx (tubes), Mesovarium (ovaries).
    • Round Ligament: Maintains uterine anteversion; extends to the labia majora.
    • Uterosacral Ligament: Provides posterior support from cervix to sacrum.
    • Cardinal Ligament: Major support; extends from cervix/vagina to pelvic sidewalls.

  • Pelvic Spaces and Muscles

    • Bony Pelvis: Sacrum, coccyx, and innominate bones (ilium, ischium, pubis). Divided by the linea terminalis into the False (superior) and True (inferior) pelvis.
    • Muscles
    • Iliopsoas: Lateral/anterior; contains a central echogenic tendon.
    • Levator Ani: Main support of the pelvic floor; weakness leads to prolapse.
    • Obturator Internus: Triangular, near obturator foramen.
    • Piriformis: Flat, triangular; from sacrum to greater trochanter.
    • Potential Spaces for fluid collection
    • Space of Retzius (Retropubic): Between pubic symphysis and bladder.
    • Vesicouterine Pouch: Between bladder and uterus.
    • Pouch of Douglas (Rectouterine / Posterior Cul-de-sac): Between uterus and rectum; the most dependent recess where fluid most commonly collects.