Pelvic Ultrasound: Concepts and Anatomy

Pelvic Ultrasound: Basic Concepts and Anatomy

Basic Ultrasound Terminology

• Anechoic: Without internal echoes, appears black (e g., fluid, cysts, vessels, bladder)
• Hyperechoic: Displays bright echoes (e.g., bone, fat, air, ligaments, diaphragm)
• Hypoechoic: Less bright than surrounding tissues
• Isoechoic: Equal brightness to surrounding tissues
• Homogeneous: Refers to uniform texture
• Heterogeneous: Non-uniform texture

Scanning Fundamentals

• Sagittal Plane:
  • Entry: Anterior or posterior.
  • Visuals: Anterior, posterior, superior, and inferior aspects
• Transverse Plane:
  • Entry: Multiple points.
  • Visuals: Anterior, posterior, right lateral, and left lateral aspects
• Coronal Plane:
  • Entry: Lateral.
  • Visuals: Lateral, medial, superior, and inferior views

Patient Preparation and History

• Transabdominal Ultrasound: Requires a full bladder achieved with 32 ounces of water
• Transvaginal Ultrasound: Needs an empty bladder, verbal consent, and a chaperone if the examiner is male
• History: Review prior records (imaging reports, lab results, biopsies) and reproductive history using TPAL format (Term, Preterm, Abortion, Living children)

Pelvic Vascular Anatomy

Arterial Supply: - Major vessels: Begins with common iliac bifurcation at the superior margin of the sacrum, leading to external and internal iliac arteries - Uterine Blood Supply: Paired uterine arteries with a branching pattern including uterine (serosal), arcuate (myometrial), and radial (deep myometrial) arteries - Straight/basal arteries supply basal endometrial layer, and spiral arteries supply functional endometrial layer

• Venous Drainage: Mirrors arterial supply, drains to internal iliac veins, then IVC, except the left ovarian vein drains to the left renal vein

Pelvic Organs

Urinary System: - Bladder's location is in the anterior pelvis. Shape is pyramid when empty, dome when full. Wall layers are mucosa, submucosa, muscular, serosa. - Ureters route from kidney to bladder, anterior to internal iliac artery and posterior to ovary; not normally visible unless obstructed - Urethra: Muscular tube, bladder to genitals, for expelling urine

Clinical Considerations for Pelvic Ultrasound

• Common indications are pelvic pain and menstrual irregularities like dysmenorrhea, amenorrhea, menorrhagia, metrorrhagia; also infertility and postmenopausal bleeding
• Contraindications involve certain limitations

Technical Aspects

Infection Control: Transvaginal probe requires a sterile cover and proper disinfection with glutaraldehyde (20 min) or Trophon machine (7 min); never autoclave Documentation: Must include patient position, scanning approach, organ measurements, vascular assessment, and any pathological findings

Gynecologic Anatomy and Sonography

Pelvic Anatomy Overview

Anatomical Spaces: - Anterior cul-de-sac (uterovesical pouch): Between bladder and uterus - Posterior cul-de-sac (pouch of Douglas): Between rectum and uterus - Space of Retzius: Anterior to bladder and posterior to symphysis pubis Uterine Location: Posterior/inferior to the bladder and anterior to the rectum

Uterine Anatomy

Basic Structure: - Major Parts: Fundus (dome), body (corpus), isthmus, and cervix - Wall Layers: Endometrium (innermost), myometrium (middle), and perimetrium (outermost) Endometrial Characteristics: - Layers: Functional zone (sheds during menstruation) and basal zone (deep basal layer) - Sonographic Appearances: Vary with menstrual phase (thin, linear, echogenic, under 4 mm), periovulatory (trilaminar, 10-16 mm), and secretory (homogeneous, 16-18 mm) Uterine Positions: Version is cervix orientation to vagina, flexion is body orientation to cervix

Normal Measurements

Uterine Dimensions: - Adult Measurements: Length (6-9 cm), AP (2.5-3.5 cm), width (3-4 cm) - Changes in uterus size with respect to prepubertal or postmenopausal phase

Ovarian Anatomy

Basic Structure: - Dimensions: Maximum normal size is 3x2x2 cm; volume is calculated as L×W×H/2; reproductive age max is 6 cc - Anatomical Parts: Including germinal epithelium, tunica albuginea, cortex, medulla, follicles, and corpus luteum/albicans Blood Supply: Arterial (direct from aorta, ovarian branches of uterine arteries) and venous (right to IVC, left to left renal vein)

Sonographic Evaluation

Uterine Scanning - key views necessary Congenital Anomalies - mullerian duct development Clinical Applications: - Normal Variants: Postmenopausal changes include atrophic endometrium, tubular uterus, and equal cervix/body ratio

Gynecologic Anatomy and Physiology

Fallopian Tube Anatomy

• Alternative Names: Oviducts, salpinges (singular: salpinx), uterine tubes
• Dimensions: 7-14 cm Length, 1 - 4 mm Diameter
• Bilateral extension from cornua

Anatomical sections:

 - Interstitial (Intramural): Located within uterine horn, the proximal portion.
- Isthmus: Located in the narrow portion, between the interstitial and ampulla.
- Longest/most tortuous segment : Ampulla, which is common site for fertilization and ectopic pregnancy.
- Infundibulum: Most distal section with  funnel-shaped opening, connects to fimbriae.
- Fimbriae: Finger-like projections, helps to  guide oocyte into the tube.

• Structural Layers (Outside to Inside): Serosal, muscularis, mucosal

Fallopian Tube Pathology

• Condidtions: Salpingitis, Bacterial inflammation (STDs), causes infertility, symptoms range from none to pelvic pain. Fluid Collections:

• Hydrosalpinx: Appears anechoic and tubular, comprised of Clear fluid .

• Pyosalpinx: Shows internal echoes, comprised of Pus.

• Hematosalpinx: Shows low-level echoes, comprised of Blood.

The Menstrual Cycle:

• Cycles Involved: Ovarian cycle, uterine (endometrial) cycle, hormonal cycle.

• Timing: 28 days - average duration , menses is 1-5 days, and day 14 for ovulation.

• Hormonal Control:

  • GnRH from Hypothalamus controls anterior pituitary
  • FSH leads to Follicle development
  • LH triggers ovulation
  • Estrogen is driven by theca/granulosa cells, used in the first half of cycle, promotes endometrial thickening.
  • Progesteroneis used the by corpus luteum, in the second half of cycle, maintains endometrial thickness.

Ovarian Cycle Phases:

• Characteristics of Follicular Phase (Days 1-14): Follicle development, estrogen production, ends with ovulation
• Follicle's Components: -Fluid-filled center, theca cells, oocyte, granulosa cells (sonographic marker)
• Phases of Ovulation:
  • Triggered by LH surge, Graafian follicle rupture,release oocyte, possible mittelschmerz pain

Luteal Phase (Days 15-28)

development, corpus luteum formation, progesterone production, maintains endometrium. Outcomes

restart  if no pregnancy: Corpus albicans,Progesterone decline cycle

The Endometrial Cycle

Three Phases:

• The functional layer is shed in the menstrual Phase.
• Sonographic Appearances driven During The proliferative Phase:
  • Early : Thin, enchogenic
  • Late: 3 line sign.
• Post ovulatory and Progesterone maintained during the secretory phase:
  • Thick and uniformly echogenic.

Sonographic Considerations

• usually not visible and may see proximal segments on TV- Normal findings of fallopian tubes .

• cysts > 3 cm, , Follicles < 3 cm-,Corpus luteum development-Ovarian Structures
  

• Changes Throughout Cycle
• Early proliferative : Thin, echogenic -Endometrial Appearance: late proliferative is three-line sign , secretory is echogenicity with uniform thickness.

Clinical Applications

Important follicle sizing measurements :

• Tube small < cm , Follicle sizes and cyst measurements> 3

• enlarded -Tube pathology enlarged Abnormal Signs

• cycle irregular and sign Abnormal fluid collections

• abnormal endometrial Anovulation signs

Fetal Embryologic Development

Basic Cell Development and Reproduction

- Types of Cells

• Gametes (Haploid cells - 23 chromosomes)
• Female: Ova/oocytes
• Male: Spermatozoa (viable up to 72 hours)
• Human cells (Diploid - 46 chromosomes) -23 from mother (22 + X) -23 from father (22 + X or Y)
  • Cell Division Processes:
• Meiosis: Creates gametes (23 chromosomes)
• Mitosis: Creates diploid cells (46 chromosomes)

Early Pregnancy Development

• Timeline.

  • Fertilization timeline of after 24-26 hours of post-ovulation. Implants - Location: Ampulla of fallopian tube at day 7,
  • Early Developmental Stages :Single-cell starts from fertilized ovum zygote. Blastomere. 2-4 cell stages stages Morula mass of dividing cells. Blastocyst. Organised cell collection.

• Pregnancy Dating

  • Age Calculations: Conceptual Age that starts from conception. Gestational dating from LMP adds up to 2 weeks of developmental periods. Embryo and uterus Zygote. Conception till to implantation implantation(12 days.Embiryo till week 10.After week 10 into fetus

• Trimester Division: - (1st trimester) 1-12 weeks, (2nd trimester) 13-26 weeks, (3rd trimester) 27-42 weeks.

Structures Of Early Pregnancy.

Blastocyst Components- Components:

Trophoblast - Key Structures: produces Hcg .Lining(outer layer of the Yolk sac . Becomes the inner mass(embryonic sack , Amnion.

• Decidual Development - develops within one week :Basalis implantation site, and then Capsularis surrounding the blastocyst which transforms into Verae uninvolved tissue.
• Pregnancy significance sonographically -Decidual formation, not so specific must check correlation between and age :Checkup must occur with HCG

Features Of Pregnancy

Production to assess early functions from placenta Detectable at day 23 of maintained detectable by day 23(menstrual age), maintains corpus, levels of around Normal 48 levels,peaks at 10, to 20 mmil

- Sonographic Correlation

Discriminatory (transvaginal and trans abdominal) :Transvaginal levels that measures between 12/18mm : Transabdominal : Possible detection with between 500mil Sonographic Finds During Early Pregnancy :First indication is gestational. :Forms in either mid shape in the uterus ,the growth rate :1mm by day Gestational Sac - Characteristics: Double Decidual sign that includes requires the yolk sac, required 8mm MSD

Extraembryonic Membranes Components

Amnion: Fluid-filled Protective sac . Yolk sac: Provides blood cell formation. Allantois Provides umbilical vessels through development

Specifics Of Yolk Sac

Detaches at around 8 weeks Becomes unviable :Disappears by 12 weeks-normal

• Normal size < 6mm Indicates - viability (90% accuracy)-.
• Note most indications

Placental Development

1. Formation Of Structure : -Components involved with basal maternal, and frondosum fetal structure -Provides energy -Functionalities :Oxygen transfer, nutrient ,waste Hormone- HCG

2. Includes

The spiral, endometrial veins, formation components of circulation (maternal).

• Fevessels, developed Development vessels within the circulation

• development Formation Layer:

  • Endolining -Three Germs Digestive/ respiratory
  • Mesoderm: muscles and bone

• Ectoderm and neurological system Key formation from fetal of shape 10 weeks-Organ rudiments

Warnings For consideration

  pregnancy of size from sac Gestational Characteristics