Begins at inferior narrowing of uterus (isthmus)

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  Supravaginal portion: Endocervix

  
  
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  Vaginal portion: Ectocervix

Endocervical canal: Spindle-shaped cavity communicates with uterine body and vagina

Internal os: Opening into uterine cavity

External os: Opening into vagina

Largely fibrous stroma with high proportion of elastic fibers interwoven with smooth muscle

Endocervical canal lined by mucus-secreting columnar epithelium

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  Epithelium in series of small, V-shaped folds (plicae palmatae)

Ectocervix lined by stratified squamous epithelium

Squamocolumnar junction near external os but exact position variable

Nabothian cysts commonly seen

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  Represent obstructed mucus-secreting glands

Entire cervix is extraperitoneal

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  Anterior: Peritoneum reflects over dome of bladder above level of internal os

  
  
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  Posterior: Peritoneum extends along posterior vaginal fornix, creating rectouterine pouch of Douglas (cul-de-sac)

Arteries, veins, nerves, and lymphatics

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  Arterial supply

  
  
  
  
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    Descending branch of uterine artery from internal iliac artery

  
  
  
  
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  Venous drainage

  
  
  
  
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    To uterine vein and drains into internal iliac vein

  
  
  
  
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  Lymphatics

  
  
  
  
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    Drain into internal and external iliac lymph nodes

  
  
  
  
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  Innervation

  
  
  
  
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    Sympathetic and parasympathetic nerves from branches of inferior hypogastric plexuses

  
  

Variations with pregnancy

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  Nulliparous: Circular external os, arterial waveform shows high resistivity index (RI)

  
  
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  During pregnancy: Changes become apparent by ~ 6 weeks of gestation

  
  
  
  
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    Softened and enlarged cervix due to engorgement with blood with decreased RI of uterine artery

    
    
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    Hypertrophy of mucosa of cervical canal: Increased echogenicity of mucosal layer

    
    
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    Increased secretion of mucous glands: Increased volume of mucus ± mucus plug in cervical canal

  
  
  
  
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  Parous: Larger vaginal part of cervix, external os opens out transversely with anterior and posterior lips

Variations with age: Cervix grows less with age than uterus

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  Neonatal: Adult configuration due to residual maternal hormonal stimulation

  
  
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  Infantile: Cervix predominant with cervix:corpus length ratio ~ 2:1

  
  
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  Prepubertal: Cervix:corpus length ratio ~ 1:1

  
  
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  Reproductive: Uterus predominant, cervix:corpus length ratio ≥ 1:2

  
  
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  Postmenopausal: Overall reduction in size

Anterior

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  Supravaginal cervix: Superior aspect of posterior bladder wall

  
  
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  Vaginal cervix: Anterior fornix of vagina

Posterior

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  Supravaginal cervix: Rectouterine pouch of Douglas

  
  
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  Vaginal cervix: Posterior fornix of vagina

Lateral

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  Supravaginal cervix: Bilateral ureters

  
  
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  Vaginal cervix: Lateral fornices of vagina

Ligamentous support: Condensations of pelvic fascia attached to cervix and vaginal vault

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  Transverse cervical (cardinal) ligaments

  
  
  
  
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    Fibromuscular condensations of pelvic fascia

    
    
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    Pass to cervix and upper vagina from lateral walls of pelvis

  
  
  
  
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  Pubocervical ligaments

  
  
  
  
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    2 firm bands of connective tissue

    
    
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    Extend from posterior surface of pubis, position on either side of neck of bladder and then attach to anterior aspect of cervix

  
  
  
  
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  Sacrocervical ligaments

  
  
  
  
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    Fibromuscular condensations

    
    
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    Attach posterior aspect of cervix and upper vagina from lower end of sacrum

    
    
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    Form 2 ridges, 1 on either side of rectouterine pouch of Douglas

  
  

Transabdominal scan

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  Mucus within endocervical canal usually creates echogenic interface

  
  
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  In periovulatory phase, cervical mucus becomes hypoechoic due to high fluid content

  
  
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  Mucosal layer: Echogenic

  
  
  
  
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    Thickness and echogenicity show cyclical changes similar to endometrium

  
  
  
  
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  Submucosal layer: Hypoechoic

  
  
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  Cervical stroma: Intermediate to echogenic

Transvaginal scan

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  Angle of insonation should be optimized for best visualization

  
  
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  Imaging may be improved with withdrawal of probe into midvagina

Transperineal scan

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  Useful for evaluation of cervical shortening and incompetence after premature rupture of membranes or preterm labor

  
  
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  Useful when transvaginal scan cannot be tolerated

Important in local staging of cervical cancer

Uniform intermediate signal on T1WI

Zonal anatomy on T2WI

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  Endocervical canal: High signal

  
  
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  Cervical stroma: Predominately low signal, contiguous with junctional zone

  
  
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  Outer layer of smooth muscle (variably present): Intermediate signal

  
  
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  Parametrium: Variable signal intensity

  
  
  
  
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    Cardinal ligament and associated venous plexuses high signal

    
    
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    Sacrocervical ligament low signal