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Obstetrics & Gynaecological Radiology

  1. Ultrasonography in pregnancy

By Transvaginal ultrasonography (TVS) the earliest sign of pregnancy in the form of gestational sac seen at 5th menstrual week, corresponds to predicted beta-hCG levels of 1000m IU/ml.

  1. QDefinite visualization on endovaginal ultrasound:
    1. At 46 days GA (6.5 weeks)
    2. Mean sac diameter of 16 mm
    3. CRL 5 mm = 6.2 weeks
  2. Definite visualization on transabdominal scan:
    1. At 55 days GA (8 weeks)
    2. QMean sac diameter of 25 mm
  3. Ultrasound milestones:
    1. Gestational sac only = 5.0 weeks                 
    2. Gestational sac + yolk sac = 5.5 weeks
    3. QHeart beat ±embryo < 5 mm = 6.0 weeks          
    4. Accuracy ±0.5 week

QHeart begins to contract at a CRL of 1.5–3 mm = 22 days GA=36 days MA

  1. Parameters for estimation of fetal age by ultrasound
    1. Gestational sac size
    2. Parameter used for dating between 6 and 12 weeks menstrual age. Identified as early as 5 weeks on transabdominal scan.Accuracy:7 days.
    3. CRL (crown-rump length)
    4. Used upto 12 weeks MA
    5. Identified by 7 weeks MA on transabdominal scan.
    6. Accuracy: 5–7 days
    7. Biparietal diameter (BPD)
      1. Excellent parameter for estimating GA in 2nd trimester > 12 weeks MA.
      2. Less reliable for dating in 3rd trimester because of increasing biologic variability.
    8. Abdominal circumference (AC)
      1. Measured at level of vascular junction of umbilical vein with left portal vein ("hockey-stick" appearance)
      2. Better predictor of fetal weight than BPD.
    9. Femur length (FL)
      1. QThe length of diaphysis of fetal femur is often used for gestational age prediction and given accurate estimate of gestational age in third trimester.

Mean gestational sac diameter by tvs (mm)

Predicted age (weeks)

Predicted hcg range (m iu/ml)

2 (Earliest seen)



















QFor USG in pregnancy frequency of USG probe used is 3.5–5 MHz.

The earliest embryonic structure however is yolk sac that is detectable by USG, which can be seen using TVS during 5th menstrual week itself.

The earliest unequivocal sign of pregnancy using sonographic evaluation is demonstration of the “gestational sac”.


QIn a normal early pregnancy, the yolk sac should be visible sonographically by a mean gestational sac diameter of 8 mm transvaginally and 20 mm transabdominally.
Similarly, an embryo should be visible sonographically by a mean gestational sac diameter of 16 mm transvaginally and 25 mm transabdominally.

The gestation in the uterine cavity starts with formation of choriodeciduo after blastocyst implantation into the endometrium surrounded by echogenic gestational sac measuring 0.1 mm known as intradecidual sign where endometrial thickening occurs first, followed by visualization of following on the ultrasound study:

  1. Gestational sac w/o embryo or yolk sac = 5 weeks
  2. Gestational sac + yolk sac w/o embryo= 5.5 weeks
  3. Heart beat embryo < 5 mm = 6 weeks.Q

Recording the presence or absence of fetal life can generally be accomplished by real-time ultrasound by 6th week (TAS) or 5th week (TVS) counting from first day of last menstrual period.

The routine use of doppler in pregnancy remains controversial, with concern about the increased power intensities when compared with imaging levels and with the widespread use of TVS.

  1. First trimester = Best to assess is CRL, Second trimester = Best to assess is BPD and FL,
  2. Third trimester = Best to assess is BPD, FL, AC and HC.
  3. BPD > 9.2 cm indicate foetal lung maturity.Q
  4. Ultrasonic evidence of embryo can be seen as early as sixth week.Q
  5. Radiological demonstration of foetal skeleton can be done at > 16 weeks.Q
  6. Placenta well demo by 12 weeksQ
  1. Transvaginal USG (TVS):
    1. It is more informative in first trimester.
    2. In TVS images are of enhanced quality (5–7.5 MHz transducer).
    3. Full bladder is not required.
    4. QIt is superior to transabdominal USG in placenta previa.

QUse of transvaginal probe can detect the following events by one week earlier then transabdominal.

  1. Gestational ring                -  5th week
  2. Fetal poles                        -  6th week
  3. Yolk sac                            -  6th week
  4. Cardiac pulsation               -  7th week
  5. Embryonic movement        -  8th week
  1. High Yield Facts
    1. If a pregnant patient presents with vaginal bleeding, pelvic pain, and uterine tenderness, placental abruption must be excluded.
    2. The most dreaded complication of oligohydramnios is pulmonary hypoplasia.
    3. Omphalocele has a worse prognosis than gastroschisis because the former is associated with an increased incidence of chromosomal abnormalities leading to other structural abnormalities.

QMRI has no ionizing radiation, hence relatively safe in pregnancy but its absolute safety in pregnancy is still unknown.

  1. Modalities For Detection of Gynecologic Lesions
    1. USG
      It is considered one of the most sensitive modalities for detection of gynecologic lesions and is the imaging modality of choice in the initial evaluation of a pelvic mass. Relative advantages of US include its ready availability, lower cost, lack of ionizing radiation, and ability to scan rapidly in multiple planes. Its disadvantages include operator dependency, inability to evaluate adjacent bony structures, inability to adequately characterize tissue, and limiting patient factors such as obesity or incomplete bladder filling. US limitations also include occasional difficulty in separating a pelvic mass from bowel loops and differentiating adnexal from uterine masses.

QIn premenopausal women, since the normal dominant follicles can range up to 3 cm (or sometimes greater), simple ovarian cysts smaller than 3 cm need no follow-up and typically resolve spontaneously.

  1. CT
    The major use of CT is in staging advanced pelvic malignancies. CT is superior to US in demonstrating tumor involvement of the parametrium, pelvic sidewall, adjacent bony structures, and pelvic and para-aortic lymph nodes. Limitations of CT include the use of ionizing radiation and contrast material, limited tissue contrast resolution, and image degradation by metallic clips or prostheses.
  2. MRI
    It is a promising imaging modality in the evaluation of pelvic neoplasia. It provides superior tissue contrast and delineation between tumor and normal tissue compared to US and CT. MRI adds only minor additional information over US in the evaluation of cystic lesions and fluid collections; therefore, US remains the initial imaging modality because of lower cost and easy availability. MRI is the imaging modality of choice when supplemental information is needed following initial US if the sonogram is inadequate, if the origin of the pelvic mass is not established, or when evaluation of the full extent of a noncystic lesion is desired. In the differential diagnosis of recurrent tumor versus fibrosis, MRI can offer tissue specificity.

QCEMRI is now supposed to be investigation of choice for pre-operative evaluation of endometrial and cervical cancer.

It is helpful in differentiating adenomyomatosis from uterine fibroids.


MRI can generally distinguish between septate and bicornuate uteri. A septate uterus will have a smooth outer contour and a fibrous septum. A bicornuate uterus will display a depression, 1 cm or greater of the outer contour of the fundus, and a thicker, more muscular septum.

Laparotomy is the primary procedure used to establish the diagnosis and provide accurate staging. Less-invasive studies may help define the extent of spread, including chest x-rays, abdominal CT or MRI scans, and abdominal and pelvic sonography. Symptoms of bladder or renal dysfunction are evaluated by cystoscopy or intravenous pyelography.

  1. Causes Of An Increased Nuchal Translucency
    1. Chromosomal abnormalities
    2. Cardiac abnormalities
    3. Diaphragmatic hernia
    4. Exomphalos
    5. Skeletal dysplasias
    6. Noonan's Syndrome
    7. Myotonic dystrophy
    8. Spinal muscle atrophy
    9. Smith-Lemli-Opitz syndrome
    10. Congenital adrenal hyperplasia
Quick specifics-breast and obgy

Stepladder sign

Linguine sign

Breast implant rupture

Spalding sign

Robert sign

Intrauterine fetal demise

Snowstorm pattern

Molar pregnancy

Rosary sign

Pearl necklace sign


Intestitial line sign

Ectopic pregnancy

Double decidua sign

Early normal intrauterine gestation

Breast in a breast


Extra Edge

Arnold-Chiari I malformation

Chiari I malformation (cerebellar ectopia and seen in adulthood)

Definition: Descent of otherwise normal cerebellar hemispheres below the foramen magnum, usually involving tonsils.

Features: Peg like, pointed tonsils displaced into upper cervical canal

  1. 0-10 years  6 mm at least
  2. 10-30 years   5 mm
  3. 30-40 years   4 mm

Associated anomalies: Syringomyelia (30-60%), hydrocephalus (20-25%), basilar invaginations (25-50%), Klippel-Feil syndrome (5-10%) and atlanto-occipital assimilation (1-5%)

Chiari II malformation (childhood)

Definition: Descent of dysplastic cerebellar hemisphere below the foramen magnum, usually involving inferior vermis, which is everted instead being inverted, causing 4th ventricle to reduce to a coronal cleft and medulla oblongata to elongate and kink.




Skull and Dura



Spine and Cord

Calvarial defects

(Lacunar skull Lückenschädel)


Small posterior fossa


Beaked tectum


Heart-shaped incisura


Hypoplastic tentorium


Gaping foramen magnum


Concave clivus and petrous ridge

Inferior displaced (90%) vermis




Medullary spurs kink like 4th vent.

Fenestrated falx

Interdigitated gyri


Towering cerebellum




Callosal agenesis


Hydrocephalus Batwing frontal horns



Elongated tube-Incomplete / abse nt C1 arch



Large mass intermedia



Myelomeningocele (100%)





Extra Edge

Dandy-Walker Malformation: Features

  1. Skull and dura
    1. Large posterior fossa (increase volume)
    2. High tentorial insertion (lambdoid torcular inversion)
    3. High transverse sinus
  2. Ventricles and CSF spaces
    1. Fourth ventricle floor present
    2. Ventricle open dorsally to large posterior fossa cyst Hydrocephalus in 80% cases
  3. Cerebellum, vermis, brain stem
    1. Vermian cerebellar hemispheric hypoplasia
    2. Vermian remnant anterosuperiorly everted above cyst
  4. Cerebellar hemispheres winged anterolaterally in front of cyst, heterotopias and cerebellar dysplasia also may occur
    1. Brain stem may be hypoplastic, compressed
  5. Associated CNS anomalies
    1. Corpus callosal agenesis (20-25%) Heterotopias, gyral anomalies, schizencephaly Cephaloceles.

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