Fetal anomaly scan
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The document provides guidance on performing and interpreting a fetal anomaly scan in the second trimester. It outlines key structures to examine in the brain, head, face, thorax, heart, abdomen and gastrointestinal system. Normal anatomy is described along with variants and common anomalies. For the brain, it details the standard thalamic, ventricular and cerebellar views and structures to assess such as ventricle size and cavum septi pellucidi. Common cranial anomalies like holoprosencephaly and Dandy-Walker malformation are also outlined.
Fetal anomaly scan
- 1. FETAL ANOMALY SCAN Dr SHAROJ KHAN 1st yr RESIDENT NMCTH, BIRGUNJ
- 2. Alternate names for the study include second trimester anatomy scan, or TIFFA (targeted imaging for fetal anomalies)
- 3. FETAL BRAIN In 2nd trimester 3 standard views plane Thalamic Ventricular cerebellar
- 4. CRANIAL STRUCTURES TO NOTE AT ROUTINE SCAN Measurement of biparietal diameter and head circumference Head shape Bone density Falx and interhemispheric fissure Ventricle size and appearance Cavum of the septi pellucidi (CSP) Thalamus Cerebellum and vermis Cisterna magna Nuchal fold Median view for corpus callosum and vermis
- 5. transverse view at the thalamus- hypothalamus complex (t) contains the slit like midline third ventricle. The area behind the thalamus and between the occipital lobes is the ambient cistern (arrow), which contains cerebrospinal fluid (CSF) but is rendered echogenic because of strands of meninges supporting the brain structures. insula is a short, brightly echogenic line (thick arrow) containing the middle cerebral artery branches. It is surrounded by white matter that is hypoechoic . The echogenic band between thalamus and insula is the basal ganglia. Anteriorly are the tips of the anterior frontal horns of the lateral ventricles (v), and between them is cavum septi pellucidi (c) THALAMIC VIEWview
- 6. Displays the thalamus, third ventricle, fornices, basal ganglia, insula, and ambient cistern and is used to measure the biparietal diameter (BPD), occipitofrontal diameter (OFD), and head circumference (HC) smooth straight interhemispheric fissure is visible on this . If the fissure appears irregular, then abnormalities of the corpus callosum and other cerebral structures should be suspected
- 7. VENTRICULAR VIEW AT 18 WEEKS The ventricular view is slightly higher than the thalamic view and shows the bodies and, more important, the atria of the lateral ventricles as well as the interhemispheric fissure The atrium of the occipital horn is filled with echogenic choroid
- 8. choroid fills more than 60% of atrium width between the medial ventricle wall and the choroid is less than 3 mm
- 9. CEREBELLAR VIEW Obtained by rotating the transducer from the thalamic view so that the cerebellar hemispheres (arrows) in the posterior fossa come into view, connected in the midline by the slightly more echogenic and narrower vermis. The cisterna magna (m) is visible between the cerebellum and the occipital bone.
- 10. TRANSVERSE CEREBELLAR DIAMETER . It is measured as the maximal diameter between the cerebellar hemispheres on an axial scan. The TCD is not thought to be significantly altered by the presence of IUGR
- 11. This view shows the cerebellum, cisterna magna, cavum septi pellucidi (CSP), and frequently the anterior horns of the lateral ventricles. Up to about 24 weeks, the transverse cerebellar diameter corresponds to gestational weeks. The cisterna magna is the cerebrospinal fluid (CSF) space behind the cerebellum and is measured between the cerebellar vermis and inner occipital bone on an axial plane that includes the anterior end of the CSP and the midplane of the cerebellum. It is normally 2 to 10 mm.
- 13. Cisterna magna obliteration suggests Chiari II malformation and spina bifida. Excessive enlargement may be seen with mega– cisterna magna, Blake pouch cyst, vermian dysplasia, Dandy-Walker syndrome, and arachnoid cysts.
- 14. VARIANTS (USUALLY NORMAL) Choroid Plexus Cysts Choroid plexus cysts (CPCs) are cystlike spaces in the choroid plexus and are due to entrapment of CSF within an infolding of neuroepithelium.
- 15. BLAKE POUCH CYST It is a thin-walled cystic structure commonly seen in the midline of the posterior fossa behind the lower portion of the cerebellar vermis and brainstem
- 16. CAVUM VELI INTERPOSITI Cavum veli interpositi (CVI) is a small cystic collection in the midline, seen below the splenium of the corpus callosum, behind the upper brainstem and above the region of the pineal gland
- 17. VENTRICULOMEGALY Ventricular Measurement. Image showing the appropriate position of calipers to measure the lateral ventricle. Done by transverse measurement of the atrium of the occipital horn. .
- 18. Fetal ventriculomegaly is defined as: >10 mm across the atria of the posterior or anterior horn of lateral ventricles at any point in the gestation alternatively, a separation of more than 3 mm of the choroid plexus from the medial wall of the lateral ventricle may be used
- 20. Hydrocephalus (HC) refers to enlarged ventricles associated with increased intracranial pressure and thus is typically associated with head enlargement. lateral ventricular diameter >15 mm
- 21. ERRORS OF DORSAL INDUCTION CNS development begins with development of the notochord, which subsequently induces the dorsal development of the neural plate, which closes to form the neural tube, which becomes the spinal cord and part of the brain. Errors of dorsal induction can result from many different genetic and teratogenic factors and affect development of the dorsal neural plate and closure of the neural canal (neurulation).
- 22. ERRORS OF DORSAL INDUCTION Anencephaly and Exencephaly Anencephaly follows failure of closure of the rostral neuropore leading to failed cranial vault development and unprotected exposed brain tissue (exencephaly)
- 23. CEPHALOCELE AND ENCEPHALOCELE A cephalocele is a herniation of intracranial structures through a defect in the cranium or skull base. It is termed cranial meningocele when it contains only meninges and CSF and encephalocele when it contains brain tissue.
- 24. ERRORS OF VENTRAL INDUCTION Errors of ventral induction occur in the rostral end of the embryo and result in brain abnormalities of the prosencephalon, mesencephalon, and rhombencephalon and usually also affect facial development.
- 25. HOLOPROSENCEPHALY Holoprosencephaly (HPE) is a complex brain malformation resulting from incomplete separation of the prosencephalic diverticulum into right and left cerebral hemispheres. 3 types… ALOBAR SEMILOBAR LOBAR
- 26. POSTERIOR FOSSA AND CEREBELLUM Dandy-Walker Malformation Classic DWM is a triad of - partial or complete vermian agenesis, - cystic enlargement of the fourth ventricle, and - elevated tentorium Oblique axial view at 34 weeks shows enlarged cisterna magna with keyhole deformity in this fetus with DWM.
- 27. MEGA–CISTERNA MAGNA Mega–cisterna magna (MCM) refers to an enlargement of the cisterna magna beyond 10 mm with intact vermis Mega– cisterna magna (*) axial view. Note the clear fluid content and the lateral Blake cyst walls (arrows) with echogenic subarachnoid fluid lateral to the walls.
- 28. SPINA BIFIDA Cranial Signs Associated With Open Spina Bifida
- 29. FETAL FACE
- 30. The sagittal facial profile view is acquired whenever possible and should demonstrate the presence and normal configuration of the nasal bone, lips, chin, and forehead Axial views of the orbits can be obtained to verify that both globes are present, of normal size, and at a normal distance apart Axial images of the maxilla and alveolar ridge can be obtained to determine if a cleft primary palate is present
- 31. The palate separates the nasal cavity from the oral cavity. The secondary palate is difficult to visualize on 2-D sonography but may be evaluated with special 3-D sonographic views
- 32. SONOGRAPHY OF THE NORMAL FETAL FACE Profile of the face of a 18-week fetus shows a normal nasal bone (long arrow), maxilla (arrowhead), and mandible (short arrow).
- 33. ORBIT Best seen in axial or coronal view. The orbits should be symmetrical in size and the outer and inner interorbital distances within a normal range. Normal orbits in axial view (cursors: +, outer orbital distance; x, inner orbital distance).
- 34. Hypotelorism Hypotelorism is defined as an abnormally small distance between the orbits Hypertelorism Hypertelorism is defined as widely spaced eyes
- 35. LENS Congenital Cataracts Congenital cataracts may be diagnosed on prenatal sonography, which will show a rounded echogenic mass in the anterior portion of the globe. Causes of congenital cataracts include genetic disorders, infection, syndromes, and microphthalmia
- 36. NASAL BONE assessed on a midsagittal view of the fetal face. Ideally three echogenic lines should be seen. The difficulty in defining nasal bone hypoplasia has historically lead to the development of various criteria, based on measurements such as BPD: nasal bone ratio , gestational age-adjusted nasal bone length, or a single cut-off definition (0.25 cm)
- 37. PT/NBL RATIO NBL= Nasal Bone Length PT= Prenasal thickness N=0.35-0.8 Chromosomal abnormalities=>0.8
- 38. ABSENT NASAL BONE In fetuses with trisomy 21 The absence of a nasal bone at secondtrimester sonography, or abnormally short nasal bone measurements in combination with other markers of, increases detection of aneuploidy
- 39. LIP & PALATE In general, an upper lip defect may be seen and is best appreciated on angled coronal scanning. A vertical hypo-echoic region through the fetal upper lip usually represents the defect in cleft lip. The palate can be examined in the transverse (axial) plane. 3D ultrasound may further assist in diagnosis. It is good practice to comment on fetal swallowing in real time at the time the scan is performed.
- 42. In the second trimester, the nuchal fold thickness is measured in the suboccipital bregmatic plane. A measurement of 6 mm or greater from 15 to 22 weeks is associated with an increased risk of trisomy 21. The measurement is taken in the midline from the outer edge of the occipital bone to the outer edge of the skin.
- 43. THORAX
- 44. The shape should be regular with a smooth transition to the abdomen. The ribs should have normal curvature without deformities. Both lungs should appear homogeneous and without evidence of mediastinal shift or masses. The diaphragmatic interface can often be visualized as a hypoechoic dividing line between the thoracic and abdominal content (e.g. liver and stomach) Sagittal view of torso at 13 weeks. Note liver (Li), lungs (Lu), and diaphragm (arrow).
- 45. DIFFERENTIAL DIAGNOSIS OF ECHOGENIC LESION IN FETAL THORAX
- 46. FETAL HEART
- 47. CHECK AT A GLANCE 2 ventricles/ walls of equal size 2 atria/ walls of equal size Foramen ovale moving in left atrium Pulmonary veins entering left atrium Motion of mitral valves(left side) regular Motion of tricuspid valves(right side) regular Continuity of interventricular septum
- 48. The basic cardiac screening examination is interpreted from a four-chamber view of the fetal heart. A normal regular rate ranges from 120 to 160 beats per min. The heart should be located in the left chest (same side as the fetal stomach) if the situs is normal. A normal heart is usually no larger than one-third of the area of the chest and is without pericardial effusion. The heart is normally deviated by about 45±20◦ towards the left side of the fetus.
- 49. Normal position and axis of the heart. The heart is predominantly in the left side of the chest, with the apex of the heart pointing leftward. Dual-screen image shows the stomach also on the left side.
- 50. Dextroposition of fetal heart caused by a large, congenital pulmonary airway malformation. Transverse image through the fetal chest shows the heart displaced to the right, but the apex (arrow) remaining leftward. LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; S, stomach. Dual-
- 51. The apical four-chamber view may also be used as a starting point when evaluating normal cardiac anatomy A slight cephalad advancement will show an apical five-chamber view, which is useful in assessing continuity of the ascending aorta with the left ventricle Continued cephalad movement should result in visualization of the bifurcating pulmonary artery and its relationship to the right ventricle.
- 52. A three-vessel and trachea view should be visualized . This view allows evaluation of the main pulmonary artery–ductus arteriosus confluence, the transverse aortic arch, and the SVC. Comparison of vessel size, confirmation of vessel presence, and determination of blood flow direction with color Doppler can all be accomplished at this level.
- 53. FETAL GIT AND ABDOMINAL WALL
- 54. Abdominal organ situs should be determined. The fetal stomach should be identified in its normal position on the left side. Bowel should be contained within the abdomen and the umbilical cord should insert into an intact abdominal wall. Abnormal fluid collections of the bowel(e.g.enteric cysts,obvious bowel dilatation)should be documented.
- 55. Aside from the left-sided stomach, a fetal gallbladder may be seen in the right upper quadrant next to the liver, although this latter finding is not a minimum requirement of the basic scan. Any other cystic structuresseenintheabdomenshould promptreferralfor a more detailed scan. The fetal umbilical cord insertion site should be examined for evidence of a ventral wall defect such as omphalocele or gastroschisis. Cord vessels may also be counted using gray- scaleimaging as an optional component of the routine anomaly survey.
- 57. ABSENT STOMACH BUBBLE Physiological Emptying: Transient Lack of amniotic fluid to swallow Oligohydraminos Anhydraminos Impaired fetal swallowing Esophageal Atresia Obstructing oropharyngeal Mass Facial clefts Congenital Diaphragmatic hernia
- 58. ESOPHAGUS Esophageal Atresia The main sonographic signs of esophageal atresia include absent or small stomach , polyhydramnios, and the esophageal pouch sign (fluid collection in the blind end of the esophagus
- 59. DOUBLE BUBBLE SIGN Another bubble adjacent to stomach bubble other than Gastric Bubble D/D Duodenal Atresia Choledochal cyst Duplication cyst
- 60. DILATED BOWEL >7mm in small bowel >20 mm in large bowel OBSTRUCTION
- 61. LIVER The fetal liver is clearly visualized in the upper abdomen in the second half of gestation
- 62. ABDOMINAL WALL The most common types of abdominal wall defects are gastroschisis and omphalocele. Other, less common types include bladder exstrophy cloacal exstrophy, ectopia cordis, and more severe ventral body wall defects including pentalogy of Cantrell, body stalk anomaly, and abdominoschisis in amniotic band syndrome.
- 63. persistence of the midgut herniation beyond 12 weeks or the presence of content other than intestine (e.g., liver) in the herniation should be considered as evidence of true abdominal wall defect (i.e., omphalocele).
- 64. Gastroschisis is a relatively small (<4 cm in most cases), fullthickness paraumbilical defect of the abdominal wall, most often located to the right of the umbilicus. Free-floating loops of bowel in the amniotic fluid are the key finding on ultrasound.
- 65. Bladder exstrophy refers to infraumbilical abdominal wall defect that results from incomplete closure of the lower abdominal wall and the anterior wall of the bladder
- 66. FETAL UROGENITAL TRACT Measurement of Renal pelvis AP diameter Inner to inner aspect of pelvis Upper limit 4-5 mm in 2nd trimester Look for Renal cystic disease
- 67. Fetal bladder visible after 12 wk Over distended bladde B/l Hydro-uretero nephrosis Obstructive uropathy
- 68. In the second trimester the kidneys often appear as isoechoic structures adjacent to the fetal spine on transabdominal sonography As the fetus matures, corticomedullary differentiation becomes more obvious, especially in the third trimester
- 69. Transabdominal scan at 19 weeks in the transverse plane shows the kidneys (arrows) as paired isoechoic structures adjacent to the fetal spine, with a small amount of fluid in the renal pelvis.
- 70. RENAL LENGTHS AT 14-42 WEEKS’ GESTATION
- 73. “Lying Down” Adrenal Sign. Longitudinal scan through the renal fossa shows absence of the kidney and the flattened adrenal gland (arrows). The lying-down adrenal sign is an indication of renal agenesis or ectopia.
- 74. AUTOSOMAL RECESSIVE POLYCYSTIC KIDNEY DISEASE Usually, but not always, ultrasound shows evidence of ARPKD by 24 to 26 weeks’ gestation
- 75. Autosomal Recessive Polycystic Kidney Disease (Early Presentation). (A) and (B) Coronal and transverse scans of a 22-week fetus show bilateral large, diffusely hyperechoic kidneys (calipers) with loss of corticomedullary differentiation
- 76. Algorithm for Sonographic Evaluation of Hyperechogenic Kidneys.
- 77. HORSESHOE KIDNEY Findings include abnormal longitudinal axis of both kidneys and a bridge of renal tissue connecting the lower poles on fusion anomaly of the kidney Horseshoe Kidney. (A) Coronal image in a 19-week fetus shows the bridge of renal parenchyma (arrow) connecting the lower poles of the kidneys, anterior to the aorta (Ao). (B) Axial image shows, in addition to the fused isthmus (arrow), the abnormal anterior orientation
- 78. GENITAL TRACT In the second trimester, fetal sex determination is based on direct visualization of the external genitalia: the penis and scrotum in males, and the labia majora and minora, represented by two or four parallel lines, respectively, in females
- 79. FETAL MUSCULOSKELETAL SYSTEM upper limb humera, including humeral length (HL) radius/ulna: both sides fingers and thumbs, including hand opening lower limb both femora, including femoral length (FL) as part of biometric assessment both tibia/fibula: saggital views to demonstrate orientation of the ankles to screen for talipes. both feet
- 80. Extremity Measurements standard practice is to assess femur length (FL) as part of the evaluation of fetal size and morphology. Although measurement of all the long bones is not required in a routine obstetric ultrasound, an overall evaluation of the fetal skeleton should be performed to ensure the presence and bilateral symmetry of the tubular bones.
- 81. Bone scanned throughout long section Look for any bowing, angulation, fracture Club foot Number of fingers
- 83. NORMAL EXTREMITY LONG-BONE LENGTHS AND BIPARIETAL DIAMETERS AT DIFFERENT MENSTRUAL AGES
- 84. PATTERN OF LIMB SHORTENING Rhizomelia…………proximal Mesomellia…………Middle Acromelia…………………Distal Micro……………Enntire limb
- 85. Normal Femur and Spectrum of Abnormal Appearances. (A) Normal femur: measure the longest length, excluding the proximal and distal epiphyses and the specular reflection of the lateral aspect of the distal femoral epiphysis (arrow). (B) Normal femur in the near field, with straight lateral border versus the curved medial border in the far field of the transducer. (C) Isolated hypoplastic left femur (arrowhead), with normal tibia (black arrow) and foot (white arrow). (D) Osteogenesis imperfecta type I. Isolated femoral fracture with acute angulation (arrow). (E) Campomelic dysplasia. Mild shortening and a gently curved ventral femoral bowing (arrow). (F) Osteogenesis imperfecta type IIA. Bowed femur with multiple discontinuities representing fractures.
- 86. (G) Hypophosphatasia. Severe micromelia (relatively broad metaphysis, short diaphysis) . (H) Thanatophoric dysplasia. Curved, “telephone receiver” femur.
- 88. PLACENTA
Editor's Notes
- #4: These 3 planes can detect more than 95% disorders of brain
- #10: visible in this view are the thalamus, third ventricle, anterior horns, and cavum septi pellucidi
- #38: PT = 0.393 × NBL +1.71 (R=0.63; p<0.01).
- #53: Three-vessel and trachea view shows the correct orientation of the main pulmonary artery–ductus arteriosus confluence (P), the transverse aortic arch (A), and the superior vena cava (S). This view also shows the two great vessels correctly positioned on the left side of the trachea (T).