USG in Obs & Gyn

1. Moderator-
DR. M.C. BANSAL
Professor
DEPTT. OF OBS & GYN
NIMS MEDICAL COLLEGE & HOSPITAL
DR. RIDHI KATHURIA
PG 2ND year
DEPTT OF OBS & GYN
NIMS MEDICAL COLLEGE & HOSPITAL
JAIPUR

3.  Obstetric ultrasound examination at any stage in pregnancy serves two
important functions: Diagnostic and Screening.
 While many major fetal defects can be diagnosed in the first trimester, the
diagnostic accuracy of an ultrasound scan is significantly greater in the mid-second
trimester due to the larger size and more advanced development of the
fetus

4. HCG Levels for normal Pregnancy.
NOTE: The quantitative maternal serum
beta HCG peaks at approximately 10 weeks
and then reduces.
Initial confirmation
of pregnancy is
done by a Urine for
Pregnancy Test kit.
The kit detects hCG
beta subunit in
urine in
concentration as
low as 25 mIU/ml.

5. The First Trimester is defined as the first 12 weeks of
pregnancy following the last normal menstrual period
(some authors refer to early pregnancy as 0 - 10 weeks).
It can be divided into a number of phases, each of which
has typical clinical issues. These phases are:
Conceptus phase : 3 - 5 weeks
Embryonic phase : 6 - 9 weeks
Fetal phase : 10 - 12 weeks

6. Ultrasound during this period is predominantly concerned with the following clinical issues:
1. Dating of the pregnancy
MSD : mean sac diameter
CRL : crown rump length (most accurate)
2. Early pregnancy failure
Threatened abortion
Missed abortion
Inevitable abortion
Incomplete abortion
Complete abortion
An-embryonic pregnancy / Blighted Ovum
3. Confirming intrauterine pregnancy (IUP)
Double Decidual Sac Sign
Intradecidual Sign
Double Bleb Sign
4. Ectopic pregnancy
5. Nuchal lucency

7. • GS is the earliest sonographic finding in pregnancy.
• It will be difficult to see if the mother has a
retroverted uterus or fibroids.
• The GS is an echogenic ring (formed by
chorio-emryonic cells) surrounding an
anechoic centre (as fluid filled).
• An ectopic pregnancy will appear the same but it
will not be within the endometrial cavity.
• The GS is not identifiable until approximately 4 1/2
weeks with a transvaginal scan.
• Gestational sac size should be determined by
measuring the mean of three diameters. These
differences rarely effect gestational age dating by
more than a day or two.
5 week gestation
Yolk Sac Only seen.
The yolk sac will be visible before a
clearly definable embryonic pole.

8. Mean Sac Diameter measurement is used to determine
gestational age before a Crown Rump length can be clearly measured.
The average sac diameter is determined by measuring the length, width
and height then dividing by 3.

10. A Yolk Sac is first anatomical structure identified within
the gestational sac.
It plays a critical role in embryonal development by providing
nutrients, serving as the site of initial haematopoiesis and
contributing to the development of gastrointestinal and
reproductive systems

11. The yolk sac appears during the 5th week.
It is the second structure to appear after the GS.
It should be round with an anechoic centre.
It should not be calcified, misshapen or >5mm from the inner to inner
diameter.
Yolk sacs larger than 6 mm are usually indicative of an abnormal
pregnancy.
Failure to identify (with transvaginal ultrasound) a yolk sac when the
gestational sac has grown to 12 mm
is also usually indicative of a failed pregnancy.

12. Visualization of a yolk sac is useful in distinguishing an intrauterine pregnancy (IUP) from a
pseudo gestational sac, a decidual cast cyst or a blighted ovum, as it is only seen in theIUP.
A yolk sac should always be seen when themean sac diameter (MSD) is 20 mm on trans-abdominal
scanning and usually seen trans-vaginally with an MSD of 8 - 10 mm.
In general if the MSD is 16 mm or greater and no fetal pole / yolk sac can be identified on
trans-vaginal scanning then this suggests a non-viable pregnancy (an-embryonic pregnancy).
Repeat scanning with an larger MSD and serial quantitative beta-HCGs is however thought
prudent.
In a normal early pregnancy, the diameter of the yolk sac should usually be < 6 mm while its
shape should be near spherical.
Visualisationmultiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g twins.
Natural course
As the pregnancy advances, the yolk sac disappears and is often
sonographically not detectable after 14 weeks.

13. Double Decidual Sac Sign (DDSS) is a useful feature
on early pregnancy ultrasound in distinguishing between
an early intrauterine pregnancy (IUP) and
a pseudogestational sac.
It consists of the Decidua Parietalis (that lining the
uterine cavity) and Decidua Capsularis (lining the
gestational sac) and is seen as two concentirc rings
surrounding an anechoic gestational sac.
Where the two adhere, is the Decidua Basalis, and is the
site of future placental formation.
With good quality high frequency transvaginal scanning
a yolk sac should also be present at this time.
Should a definite IUP not be confirmed on sonography
then repeat scanning and serial quantitative beta-HCGs are
required, until either an IUP is established, an ectopic
pregnancy is visualised or beta-HCGs return to zero
(implying miscarriage).

15. • A Double Bleb Sign is a sonographic
feature where there is visualisation of a
gestational sac containing a yolk
sac and amniotic sac giving an
appearence of two small bubbles.
• The embryonic disc is located between
the two bubbles.
• It is an important feature of an
intrauterine pregnancy and thus
distinguishes a pregnancy form
a pseudogestational sac or decidual cast
cyst.
• It should not be confused with
the double decidual sac sign.
Yolk sac
Embryonc
Disc
Amniotic sac

16.  The CRL is a reproducible and accurate method for measuring and dating a fetus.
 Early ultrasonographers used this term (CRL) because early fetuses also adopted the
sitting in the chair posture in early pregnancy.
 After 12 weeks, the accuracy of CRL in predicting gestational age diminishes and is
replaced by measurement of the fetal biparietal diameter.
 In at least some respects, the term "crown rump length" is misleading: there is no fetal
crown and no fetal rump to measure in 1st trimester.

17. Until 53 days (9weeks) from the LMP, the most caudal portion of the fetal cell
mass is the Caudal Neurospone, followed by the tail.
Only after 53 days (9weeks) is the fetal rump the most caudal portion of the fetus.
Until 60 days (10.5 weeks) from the LMP, the most cephalad portion of the fetal
cell mass is initially the Rostral Neurospore, and later the cervical flexure.
After 60 days (10.5 weeks), the fetal head becomes the most cephalad portion of
the fetal cell mass.
What is really measured during this early development of the fetus is the
longest fetal diameter.
From 6 weeks to 9 1/2 weeks gestational age, the fetal CRL
grows at a rate of about 1 mm per day.

18. • Crown Rump Length (CRL) measurement
in a 6 week gestation.
• A mass of fetal cells, separate from the yolk
sac, first becomes apparent on transvaginal
ultrasound just after the 6th week of
gestation.
• This mass of cells is known as the Fetal
Pole.
• The fetal pole grows at a rate of about 1
mm a day, starting at the 6th week of
gestational age.
• Thus, a simple way to "date" an early
pregnancy is to add the length of the fetus (in
mm) to 6 weeks.
• Using this method, a fetal pole measuring 5
mm would have a gestational age of 6 weeks
and 5 days.

19. Outside to Outside Measurements

20. Using a transvaginal approach the fetal heart beat can be seen flickering before the
fetal pole is even identified.
It will be seen alongside the yolk sac.
It may be below 100 beats per minute but this will increase to between 120- 180 beats
per minute by 7 weeks.
In the early scans at 5-6 weeks just visualising a heart beating is the important thing.
Failure to identify fetal cardiac activity in a fetus whose overall length is greater than
4 mm (approx 4.5 weeks)is an ominous sign .
Sometimes there is difficulty in distinguishing between the maternal pulse and fetal
heart beat. Often technicians will take the mothers pulse at the same time to check if
it is the fetus or the mothers .

21. The very early embryonic heart
will be a subtle flicker.
This may be measured using M-Mode(
avoid Doppler in the first
trimester due to risks of
bioeffects).
Initially the heart rate may be
slow.
Compare to the maternal heart
rate to confirm that one is not
seeing an arteriole.

23. 8 weeks
A normal 8 week foetal
pole.
One should see a
definable head and
body.
The beginning of the
limb buds.
The fetal heart should
be easily visible.
Subtle body movements
can often be seen.

24. NOTE- Demarcation between the
Chorion & Amnion
The 2 sacs are clearly visible.
The outer chorion with the
developing placenta and the
inner amnion which will
"inflate" with the production
of fetal urine, to adhere to the
chorion obliterating the
residual yolk sac.
The normal small mid-gut
hernia into the cord is still
visible (pink shading).
This is the result of normal
midgut proliferation and will
resolve by 11 weeks as the
fetus lengthens.
This physiological occurrence
should not be confused with
an omphalocele.

25. The Nuchal Translucency is a
measurement performed during a
specific period in the first
trimester (11.3-13.6 weeks).
It should not be confused
with Nuchal Thickness which is
measured in the second trimester.
An increased nuchal translucency
is thought to relate to dilated
lymphatic channels.

26. It can being associated with a number of anomlaies including :
ANEUPLOIDY
Trisomies – 13, 18, 21.
Turner syndrome
NON-ANEUPLOIDIC STRUCTURAL DEFECTS &
SYNDROMES
Congenital Diaphragmatic Herniation
Congenital Heart Disease
Omphalocoele
Skeletal Dysplasias
Smith-Lemli-Opitz Syndrome
VACTERL association

27. VACTERL association (also VATER syndrome) is a non-random
association of birth defects.
The reason it is called an association, rather than a syndrome is that
while the complications are not pathogenetically related they tend to
occur together more frequently than expected by chance.
No specific genetic or chromosome problem has been identified.
Can be seen with some chromosomal defects such as Trisomy 18 and is
more frequently seen in babies of diabetic mothers.
Most likely caused by multiple factors.

28. ANAL DEFECTS
1. Atresia
2. Imperforate Anus
VERTEBRAL DEFECTS
1. Hypoplastic Vertebrae
2. Hemi-vertebrae
3. Scoliosis

29. TRACHEO-ESOPHAGEAL
DEFECTS
1. T.O Fistula
2. Esophageal Atresia
CARDIAC DEFECTS
1. VSD
2. ASD
3. TOF
4. TpGV
5. Truncus Arteriosus

30. LIMB DEFECTS
1. Hypoplastic /
Dysplastic thumb
2. Polydactyly
3. Syndactyly
4. Radial Aplasia
RENAL DEFECTS
1. Single Umbilical
Artery
2. Incomplete formation
of kidney(s).
3. Outflow obstruction
4. Severe reflux

31. Nuchal lucency is measured on a sagittal section through the
fetus.

32. Use of the correct technique is essential
 The fetus should be transverse (sagittal) in the imaging plane
The vertebral column should be facing the bottom of the screen.
 Fetal head should not be extended or flexed
 Fetus should be floating free of the uterine wall (i.e. amniotic fluid should be
seen between its back and the uterus)
 Only the lucency is measured (again differing from nuchal thickness)
 Ideally only the head and upper thorax should be included in the measurement
 The level of magnification should be appropriate (fetus should occupy most of
the image) enabling 1mm changes in measurement possible.
 The " + " calipers should be used for measurement
 The widest part of the measurement should be taken

33. 1. Only values obtained when CRL values are between 45-
84 mm are considered valid.
2. The lucent region is generally not septated.
3. The thickness rather than the appearance (morphology) is
considered to be directly related to the incidence of
chromosomal and other anomalies.
4. A normal value is usually less than roughly 2.5-3.0 mm in
thickness however it is
maternal age dependent and
needs to be matched to exact
gestational age and crown rump
length (CRL).

34. The nuchal translucency cannot be adequately
assessed if there is -
Unfavourable fetal lie
Unfavourable gestational age - CRL < 45 or > 84 mm.

36. Most likely a case of
Hydrops Fetalis-
1.Incresed NT.
2.Oedema under the
skin.
3.Evidence of
Ascites.

38. Interpretation
• Detection rates for aneupliodic
anomalies with nuchal translucency
alone approaches 80 - 90 % with a
false positive rate of ~ 5%.
Correlation With Serum Markers
• To increase the clinical accuracy of nuchal
lucency, it can be correlated with
serum markers such as
• maternal B-HCG
• alpha feto protein (AFP)
• pregnancy associated plasma protein A
(PAPP-A)
• oestriol
Further work up
• If abnormal > further work up is
carried out which includes
• Amniocentesis and / or Chorionic Villus
sampling
• Fetal echocardiography
Natural course - progression
• As the second trimester approaches, the
region of nuchal translucency might either
• Regress :
– if chromosomally normal, a large
proportion of fetuses will have a normal
outcome
– spontaneous regression does not however
mean a normal karyotype
• Evolve into a
– Nuchal Oedema
– Cystic Hygroma

40. • A CRL of ≥ 7mm without a heart
beat on a transvaginal ultrasound
confirms the diagnosis
(by RCOG criteria).
• Additional clues are presence of
abnormal hyperechoic material
within the uterine cavity and an
irregular gestational sac.
• If there is an absence of heart beat in a
fetus that is less than 7mm, the diagnosis
of miscarriage cannot be made with
certainty.
• This scenario is termed "Pregnancy Of
Uncertain Viability (PUV)", and
followup with ultrasound (generally in 7-
10 days) and serial bHCG recommended.

41. • Irregular Sac.
• Hyperechoic collection
within the sac.

42. • Refers to the presence of an
open cervix in the context of
bleeding in the first trimester
of pregnancy.
• Essentially, a threatened
abortion progresses to an
inevitable abortion if cervical
dilatation occurs. Once tissue
has passed through the
cervical os, this will then be
termed an incomplete
abortion and ultimately
a complete abortion.

43. A subchorionic
haemorrhage is often
seen, but unless large
does not carry a poor
prognosis.
Features which do
predict poor outcome
include:
• Fetal bradycardia : <
80 - 90 bpm
• Small or
Irregular Gestational
Sac : MSD - CRL < 5 mm
• Large Subchorionic
Haemorrhage

45. One important difference is to be deduced between an
actual irregular sac & a sac which appears irregular due to
Braxton-Hick’s contractions.
The former one, will not change its shape to become
normal with time.
However, the later, will change shape with time. The
patient is allowed to lay at rest for few minutes & put
the probe again to confirm. A changed contour of the
sac / regular appearing sac on 2nd look, helps the
jeopardy.

46. Shows an empty
uterus with no
fetal
components or
products of
conception

47. Retained
Products of
Conception, still
seen within the
uterine / cervical
cavity.

48. BLIGHTED OVUM
An anembryonic
pregnancy may be
diagnosed when there
is no fetal
pole identified on
trans-vaginal scanning
the size of the gestational
sac is such that a fetal pole
should be seen
MSD ≥ 25 mm (by RCOG
criteria)
There is little or no
growth of the gestational
sac between interval scans
Normally the MSD
should increase
by 1 mm per day
If MSD is too small to
ascertain viability on the
initial ultrasound, a follow
up scan in 10-14 days
should differentiate early
pregnancy from a failed
pregnancy

49. Other ancillary features include
 Absent yolk sac when MSD > 8 mm
Poor decidual reaction : often < 2 mm
 Irregular gestational sac shape
 Abnormally low sac position

51. ECTOPIC GESTATION
UTERUS
Empty uterine cavity / no evidence of intra-uterine pregnancy
Pseudogestational sac / decidual cyst - may be seen in 10 – 20 %
of ectopic pregnancies
Decidual cast
TUBE AND OVARY
Simple adnexal cyst : 10% chance of an ectopic
Complex adnexal cyst / mass : 95% chance of an tubal ectopic
Tubal ring sign :
95% chance of an tubal ectopic if seen
described in 49 % of ectopics and in 68 % of unruptured ectopics
Ring of fire sign : can be seen on colour Doppler in a tubal ectopic

52. PERITONEAL CAVITY
Free pelvic fluid / Haemoperitoneum in
the Pouch Of Douglas
The presence of free intra peritoneal
fluid in the context of a positive beta
HCG and empty uterus is
~ 70% specific for an ectopic
pregnancy
~ 63% sensitive for an ectopic
pregnancy
Live Pregnancy : 100% specific, but only
seen in a minority of cases

53. TUBAL ECTOPIC : 93 - 97%
Ampullary Ectopic : most common : ~ 70 % of tubal ectopics and ~ 65 - 68 %
of all
ectopics
Isthmal Ectopic : ~ 12 % of tubal ectopics and ~ 11 % of all ectopics
Fimbrial Ectopic : ~ 11 % of tubal ectopics and ~ 10 % of all ectopics
ATYPICAL ECTOPIC PREGNANCIES
Interstitial Ectopic - cornual ectopic : 3 - 4 % : also essentially a
type of tubal
ectopic
Ovarian Ectopic - ovarian pregnancy : 0.5 - 1%
Cervical Ectopic - cervical pregnancy : rare < 1 %
Scar Ectopic : site of previous Caesarian section scar : rare

55. Transvaginal scan showing fluid
with debris at the
cul-de-sac
Empty endometrium
with a normal size

56. Color and spectral doppler
demonstrates a right anechoic tubal mass
with tracings similar to fetal heart rate "RING OF FIRE" SIGN
The presence of Ring of Fire sign, confirms
the anechoic shadow to be a GS.
(HYPERVASCULAR RING)

58. 2nd trimester scan is a routinely performed ultrasound examination
on all pregnancies .
This scan emphasizes on fetal anatomy and therefore is also called
a
2nd Trimester Anatomy Scan
OR
Fetal Anomaly Scan
OR
TIFFA (Targeted Imaging For Fetal Anomalies) Scan.
Period extends from 13 weeks 0 days
to 27 weeks 6 days

59. - Integrity / Shape
- Ventricles, Choroid Plexus, Mid Brain, Posterior Fossa
- Profile, Orbits (including Interocular Diameter
And Binocular Diameter), Upper Lip
- Nuchal Thickness
- Transverse As Well As Longitudinal Views
Fetal Heart Rate / Rhythm
Four Chamber View
Outflow Tract Views
Aortic Arch View

60. - Thoracic Shape, Size, Lungs, Diaphragm
- Stomach (including Situs), Liver, Kidneys, Bladder,
Abdominal Wall, Umbilicus
- Echogenicity, Measurements, Hands, Movements
In addition to this, Standard Fetal Biometric Parameters
as well as the following features are also assessed
Fetal Lie
Placental Position
Liquor Volume
Cord : Number Of Cord Vessels

61. Round Skull shadow.
Middle Fossa in focus
here.

62. Cavum Septum
Pellucidum
Lateral Lobe Thalamus
Cisterna
Magna
Vermis
Choroid Plexus

63. Measured at a focus which shows, both the
THALAMI & the CAVUM SEPTUM
PELLUCIDUM, preferably with the Sylvian
Fissure, in the same image.
Both the thalami when seen together, as two
anechoic structures, represent the
“Trishool Sign”

64. Accuracy – 7-10 days upto 24 weeks & 2-3 weeks during the 3rd trimester.
Measurement
The outer table of the skull on the superior end of the image upto the inner table
of the skull at the inferior end of the image
BPD

65. • Not useful when the head shape is abnormal i.e, elongated (Dolicocephaly) or
excessively round (Brachecephaly).
• Better to use the parameter of CEPHALIC INDEX (CI), instead of BPD
alone.
• Also, the CI remains constant during the 3rd trimester.
Cephalic Index (CI) = Bipareital Diameter (BPD) / Occipitofrontal Diameter (OFD) X 100
• BPD is commonly effected by fetal position. Eg. Breech presentation.

66. • The cephalic index gives an idea of the fetal head shape.
• It can change according to various situations such as
1. Presentation : e.g. Breech presentation
2. Ruptured membrances
3. Presence of a twin pregnancy
• The usual range is variable depending on various sources
and different demographic groups.
• Often the mean value is taken ~ 78 (range 74 - 83)
• An grossly decreased cephalic index suggests Dolichocephaly while a grossly
increased one can suggest Brachycephaly.

67. OCCIPITO-FRONTAL DIAMETER
Measured between the most prominent part of
the occipital bone & the frontal bone.
The area in focus is the same which shows both
the thalami, as in BPD.
Anterior Horn Of The Lateral Ventricle (Va)
Posterior Horn Of The Lateral Ventricle (Vp)
Hemisphere (Hem)

68. Recently , a lot of stress is
being laid on measuring of
the TCD.
It is believed to be effected
at last and the least in cases
of IUGR

69. •Transcerebellar
Diameter (TCD)
•Cisterna Magna (CM)
•Nuchal Fold (NF)
Measured from the outer margin of one
cererbellar hemisphere to the outer margin of
the other cerebellar hemisphere, including
both the hemispheres & the vermis

70.  The area of scan is the same as that for BPD & OFD measures, i.e the
thalami & cavum septum should be seen.
 An ellipsoid should be used to mark out the fetal skull at its outer borders
(as far as possible).
Unaffected by
head shape.
Towards the end of
pregnancy, it is the
best indicator of
Gestational Age.
Not effected in
IUGR, until
vary late stages.

71. The brain tissue, except the a portion of the brainstem is completely
absent/fails to develop.
No skull vault / cranium is seen.
FROG EYES SIGN – two hollows, that of the orbits are seen
prominently.
ACRANIA – the term is used when the
cranium is absent & major part of the
brain tissue is present .

73. • The choroid plexus within the
dilated ventricles are relatively
small & looses contact with the
medial & lateral wall.
• A very common appearance of
choroids plexus is DANGLING
CHOROID.
• A separation of upto 5 mm from
ventricular wall may be considered
normal.
Lateral ventricle with greater than
10mm diameter is suspicious of
VENTRICULOMEGALY.
10-12 mm is taken as borderline.
Ventriculomegaly is diagnosed surely,
when the choroid plexuses lose contact
with one / both walls

75.  May be Unilateral or Bilateral.
Usually transient & benign.
 Seen in fetus normally between
16 – 21 weeks, after which they start
regressing.
 Normally not seen after 25 weeks.
Association with chromosomal
anomaly is less than 1%.

76. Rare congenital brain malformation, resulting from incomplete
separation of the two hemispheres.
The three main sub types, in order
of decreasing severity are :
1. Alobar Holoprosencephaly
2. Semilobar Holoprosencephaly
3. Lobar Holoprosencephaly

77. Single ventricle- Horseshoe shaped
appearance.
Hemispheres are fused to form a mass
around the ventricle.
 Thalami are fused & no Falx Cerebri is
seen.

78. Horseshoe Shaped Appearance

79. ALOBAR HOLOPROSENCEPHALY

80. LOBAR PROSENCEPHALY
a. Nearly complete separation of
the hemispheres with the falx.
b. Anteriorly, the frontal horns of
lateral ventricles are fused (so is
the frontal brain parenchyma).
Thus, attaining a triangular
shape.
c. Septum pellucidum is absent.
d. Thalami are separate.

81. The basic structure of the
cerebral lobes are present,
but are fused most
commonly anteriorly and
at the thalami and there is
partial diverticulation of
brain.
o Absence Of Septum Pellucidum
oMonoventricleWith Partially Developed
Occipital And Temporal Horns
o Rudimentary Falx Cerebri : Absent Anteriorly
o Incompletely Formed Interhemispheric Fissure
o Partial Or Complete Fusion Of The Thalami
o Absent Olfactory Tracts And Bulbs
o Agenesis Or Hypoplasia Of The Corpus
Callosum
o Incomplete Hippocampal Formation

82. SEMILOBAR
HOLOPROSENCEPHALY

83. • Due to B/L occlusion of the Internal Carotid Arteries.
• Resulting infarction of the entire brain, except the Posterior Fossa,
which is supplied by the Vertebral Arteries.
• It appears as a large empty cranial vault filled with fluid without any
cortical brain parenchyma matter, within.

85. DANDY-WALKER CONTINUUM consists of a group of anomalies where
there is a posterior fossa cyst which communicates with the fourth ventricle as
well as abnormal development of the vermis.
There are numerous forms, and the classification is contentious.
The forms which are typically included in the Dandy-Walker
spectrum include:
Dandy-Walker Malformation (Classic)
Dandy-Walker Variant
Other included conditions
Fourth Ventriculocoele
Blake’s Pouch Cyst
Mega Cisterna Magna

86. Classically Dandy Walker malformation
consists of the triad of :
1. Hypoplasia of the vermis
2. Cystic dilatation of the fourth ventricle
extending posteriorly.
3. Enlarged posterior fossa
Antenatal ultrasound may falsely over
diagnose the condition if scanned before 18
weeks due to the vermis not being properly
formed before that time.

87. DANDY WALKER
VARIANT
Partial vermian hypoplasia
with partial obstruction to
the fourth ventricle, but
without enlargement of the
posterior fossa

88. CLASSICAL
DANDY WALKER
MALFORMATION
DANDY WALKER
VARIANT
MEGA
CISTERNA MAGNA

89. Relatively common congenital
malformation of the spine and
posterior fossa characterised by
lumbosacral spina bifida aperta /
myelomeningocoele and a small
posterior fossa with descent of the
brain stem.

90. Classical signs described on ultrasound include:
LEMON HEAD SIGN
BANANA CEREBELLUM SIGN
There may also be evidence of fetal Ventriculomegaly due to obstructive
effects as a result of downward cerebellar herniation.
Additionally many of the associated malformations (e.g. Corpus Callosal
Dysgenesis) may be identified

91. Classical
LEMON HEAD SIGN
Breech in continuity of the skin over the
spinal cord, suggestive of Spina Bifida
(seen here at the lumbosacral area, as evident by
the bladder seen in front of the spine)

93. • Varying degrees of protrusion of the Vermis, 4th Ventricle &
Medulla through the Foramen Magnum, into the spinal cord.
• As a result, Cisterna Magna can be obliterated or reduced.
• Cerebellar hemispheres come closer producing a BANANA SIGN.
• Hydrocephalus due to obstruction in lower ventricular area
causing varying degrees of ventricular dilatation.
• Fetal bones angulate inwards, producing the LEMON HEAD
SIGN.
(may be seen with Encephalocoele & Thanatophoric Dysplasia)

95. Several diagnostic points should be remembered
about this sign:
1. When obtaining images of the calvarium, the
transducer should not be angled downward
anteriorly, as the fetal orbits may simulate the
lemon sign.
2. Seen more often in fetuses less than 24 weeks
and may not be present in older fetuses
(usually disappears after 24 weeks 4 ).
3. This may be due to the decreased pliability of
the fetal calvarium with advancing gestational
age or the increased intracranial pressure with
associated hydrocephalus
4. This sign may be rarely seen in normal
patients
( ~ 1 % of cases) and in those with other non-neural
axis abnormalities.
It is seen on axial
imaging
(usually antenatal
ultrasound, although
antenatal MRI will also
demonstrate this sign)
through the head
and relates to
concavity
(not just flattening)
of the frontal bones.

97. DOLICOCEPHALY BRACHYCEPHALY
CLOVER LEAF SKULL
(Thanatotropic Dysplasia)

98. NUCHAL THICKNESS
is a parameter that is
measured in a second
trimester scan (18 - 22
weeks)
and
it is not to be confused
with Nuchal
Translucency (which is
measured in the first
trimester).

99. The nuchal thickness is measured on an axial section through the
head and the level of the thalami, cavum septi pellucidum &
cerebellar hemispheres
(i.e in the same plane that is used to assess posterior fossa structures).
One caliper should be placed at the skin, and the other against the
outer edge of the bone of the occiput.

100. An abnormal value is one that is more
than 6 mm in thickness.
A thick nuchal fold is often considered the most sensitive and most
specific (best) 2ndtrimester marker for Down syndrome with false positive
rates as low as 1%.

101. The increase in nuchal fold thickness can be due to-
Scalp Edema - Down’s Syndrome, IUFD, Hydrops Fetalis.
Lymph- Cystic Hygroma.
Brain Matter - Early Encephalocoele.
Fat – Macrosomia.

102. Associations
• ANEUPLOIDY
– Trisomies
– Turner syndrome
• CONGENITAL
HEART DISEASE
NATURAL COURSE
Most thickened nuchal folds
tend to resolve towards the
third trimester but that does
not decrease the increased
risk of aneuploidic anomalies.

103. The arrow shows a cystic growth arising from the
neck (posteriorly).
16 week fetus with a septate cystic mass in
the posterior and lateral aspect of the fetal
neck.

104. Color Doppler image shows that this mass is
not the cord or part of it.
Fetal head shows evidence of
mild scalp edema (early fetal
hydrops).
The fetal spine and calvarium
show no bony defects, thus
ruling out the possibility of
fetal meningocele or myelo-meningocele,
encephalocele etc.

107. Measuring the Outer
Orbital Diametre
Measuring the
Inter Orbital Diametre

108. Profile used to see the Nose, Upper
Lip, Lower Lip, Chin, Philtrum,
Glabella.
Profile used to see the Orbits, the
Inta-Orbital Distance (IOD).

110. MICROGNATHIA
SEVERE
HYPER-TELORISM

111. CLEFT PALATE

112. Sagittal scan & post mortem fetus
showing-
PROMINENT
FOREHEAD
RETROGNATHIA

117. Fountain Geyser
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124. PWOhaWt’sE YRoPuOr MINeTss 2a0g1e?0

125. The abdominal circumference (AC) is a transverse section
(coronal) through the fetal abdomen at the level where the
umbilical vein enters the liver. The AC may be measured
directly, or calculated from the AP and transverse abdominal
measurements. Both techniques give good results. Although
the AC can be used to calculate gestational age, it is more
useful in determining fetal weight. Combined with the BPD,
with or without the fetal femur length, reliable formulas can
be used to predict fetal weight.
Level I and Level II Scanning (Screening vs Targeted
Scanning)
Level I (screening) scanning consists of the basic evaluation
listed above. It is usually relatively simple to perform, readily
available, and relatively inexpensive. More detailed scanning
(Level II, or targeted scan) requires higher resolution (more
expensive) equipment and sonographic skills that are more
limited in their availablity and significantly more expensive.
Indications for a Level II scan may include:
Suspicious findings on a Level I scan
History of prior congenital anomaly
Insulin dependent diabetes or other medical problem that
increases the risk of anomaly.
History of seizure disorder, particularly if being treated with
medications known to increase the risk of anomaly.
Teratogen exposure
Elevated MSAFP
Suspected chromosome abnormality
Symmetric IUGR
Fetal arrhythmia
Oligohydramnios, hydramnios
Advanced maternal age