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Imaging in obstetrics & gynaecology part 2

USG in Obs & Gyn

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Imaging in obstetrics & gynaecology part 2

  2. 2.  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
  3. 3. 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.
  4. 4. 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
  5. 5. 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
  6. 6. • 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.
  7. 7. 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.
  8. 8. 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
  9. 9. 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.
  10. 10. 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.
  11. 11. 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).
  12. 12. • 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
  13. 13.  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.
  14. 14. 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.
  15. 15. • 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.
  16. 16. Outside to Outside Measurements
  17. 17. 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 .
  18. 18. 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.
  19. 19. 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.
  20. 20. 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.
  21. 21. 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.
  22. 22. 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
  23. 23. 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.
  24. 24. ANAL DEFECTS 1. Atresia 2. Imperforate Anus VERTEBRAL DEFECTS 1. Hypoplastic Vertebrae 2. Hemi-vertebrae 3. Scoliosis
  25. 25. TRACHEO-ESOPHAGEAL DEFECTS 1. T.O Fistula 2. Esophageal Atresia CARDIAC DEFECTS 1. VSD 2. ASD 3. TOF 4. TpGV 5. Truncus Arteriosus
  26. 26. 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
  27. 27. Nuchal lucency is measured on a sagittal section through the fetus.
  28. 28. 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
  29. 29. 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).
  30. 30. The nuchal translucency cannot be adequately assessed if there is - Unfavourable fetal lie Unfavourable gestational age - CRL < 45 or > 84 mm.
  31. 31. Most likely a case of Hydrops Fetalis- 1.Incresed NT. 2.Oedema under the skin. 3.Evidence of Ascites.
  32. 32. 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
  33. 33. • 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.
  34. 34. • Irregular Sac. • Hyperechoic collection within the sac.
  35. 35. • 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.
  36. 36. 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
  37. 37. 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.
  38. 38. Shows an empty uterus with no fetal components or products of conception
  39. 39. Retained Products of Conception, still seen within the uterine / cervical cavity.
  40. 40. 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
  41. 41. 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
  42. 42. 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
  43. 43. 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
  44. 44. 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
  45. 45. Transvaginal scan showing fluid with debris at the cul-de-sac Empty endometrium with a normal size
  46. 46. 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)
  47. 47. 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
  48. 48. - 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
  49. 49. - 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
  50. 50. Round Skull shadow. Middle Fossa in focus here.
  51. 51. Cavum Septum Pellucidum Lateral Lobe Thalamus Cisterna Magna Vermis Choroid Plexus
  52. 52. 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”
  53. 53. 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
  54. 54. • 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.
  55. 55. • 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.
  56. 56. 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)
  57. 57. 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
  58. 58. •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
  59. 59.  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.
  60. 60. 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 .
  61. 61. • 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
  62. 62.  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%.
  63. 63. 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
  64. 64. Single ventricle- Horseshoe shaped appearance. Hemispheres are fused to form a mass around the ventricle.  Thalami are fused & no Falx Cerebri is seen.
  65. 65. Horseshoe Shaped Appearance
  67. 67. 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.
  68. 68. 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
  70. 70. • 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.
  71. 71. 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
  72. 72. 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.
  73. 73. DANDY WALKER VARIANT Partial vermian hypoplasia with partial obstruction to the fourth ventricle, but without enlargement of the posterior fossa
  75. 75. 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.
  76. 76. 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
  77. 77. 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)
  78. 78. • 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)
  79. 79. 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.
  81. 81. 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).
  82. 82. 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.
  83. 83. 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%.
  84. 84. 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.
  85. 85. 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.
  86. 86. 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.
  87. 87. 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.
  88. 88. Measuring the Outer Orbital Diametre Measuring the Inter Orbital Diametre
  89. 89. Profile used to see the Nose, Upper Lip, Lower Lip, Chin, Philtrum, Glabella. Profile used to see the Orbits, the Inta-Orbital Distance (IOD).
  91. 91. CLEFT PALATE
  92. 92. Sagittal scan & post mortem fetus showing- PROMINENT FOREHEAD RETROGNATHIA
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  100. 100. PWOhaWt’sE YRoPuOr MINeTss 2a0g1e?0
  101. 101. 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