Anomaly Scan - The Fetal Survey
Dr. Subrata Bhattacharya*
Post-graduate Trainee (Final Year) Deptt. of Obs, & Gynae, Silchar Medical College & Hospital Silchar, Assam. *
Introduction
Ever since Sir Ian Donald obtained pictures of a fetus with a static B-scan ultrasound close to half a century ago, this method of diagnosis has made a dramatic improvement and revolutionized the management of obstetric patients. With the advent of Doppler-both spectral and color, harmonic imaging and three-dimensional ultrasound (3 DU) and its two modes: static and real-time (live 3 DU, also called 4 DU), we can gain a lot of information from a well-performed scan. However, before the universal use of obstetric ultrasound, most of the congenital malformations were revealed at the time of delivery. It was an unprecedented and unfortunate period for all - the parent's obstetrician and the neonatologist. Presently, it is possible to survey good number of fetal and placental abnormalities along with changes in the amniotic fluid with a reasonable certainty. Henceforth, there is a need for every obstetrician to be well-acquainted with the diagnosis, prognosis and early intervention/management of these abnormalities. Till date, this non-invasive diagnostic procedure is considered safe even with repeated use.
Timing of Anomaly Scan
In countries like UK, Norway, Canada - routine second trimester scans are performed between 16-20 weeks gestation. Some countries do an early scan at 11-14 weeks gestation for the early detection of pathologies like Anencephaly, Nuchal translucency (NT), large encephaloceles, Holoprosencephaly, Ectopia cordis, conjoined twins, etc. A detailed anomaly scan should be made at 18-20 weeks gestation and minor aberrations should not be ignored as they can reveal many chromosomal disorders/syndrome complexes.

Anencephaly was the first fetal anomaly to be caught in utero by ultrasonography.

The minimum standard for a "20-week" anomaly scan
Gestational age can be established by measurement of Bi-parietal diameter (BPD), Head circumference (HC) and Femur length (FL); the inclusion of Abdominal circumference (AC) would be optional.
Fetal Normality
  • Head shape + Internal structures - Cavum pellucidum,cerebellum,ventricular size at atrium (<10 mm)
  • Spine: longitudinal and transverse
  • Abdominal shape and content at level of stomach
  • Abdominal shape and content at level of kidneys and umbilicus
  • Renal pelvis (<5 mm AP measurement)
  • Longitudinal axis - abdominal-thoracic appearance(diaphragm/bladder)
  • Thorax at level of 4 chamber cardiac view
  • Arms - three bones and hand (not counting fingers)
  • Legs - three bones and foot (not counting toes)

The optimal standard for the "20-week" anomaly scan
If resources allow, the following could be added to the features listed above:
  • Cardiac outflow tracts
  • Face and lips
Common fetal anomalies diagnosed with Anomaly Scan
  • Brain - Anencephaly, Hydrocephalus, Neural tube defects, Encephalocele, Ventriculomegaly, CNS tumors, Choroid plexus cyst.
  • Spine - Spina bifida, Kyphoscoliosis, Sacrococcygeal teratoma
  • Face and Neck - Cleft lip/palate, Cystic hygroma, Absent Nasal bone, Micrognathia, Macroglossia, Goiter
  • Chest defects - Pulmonary Hypoplasia, Congenital Diaphragmatic hernia, Cystic adenomatoid malformation
  • Cardiovascular defects
  • Anterior wall defects - Gastroschisis, Omphalocele, Ectopia vesicae, Body stalk anomaly, Pentalogy of Cantrell
  • Gastrointestinal - Duodenal atresia, Fetal ascites, Hepatosplenomegaly
  • Genito-urinary - Renal developmental variants, Ureteropelvic junction obstruction, Multicystic dysplastic kidneys, PUV, Ureterocele, Urachal anomalies
  • Ambiguous genitalia, Hypospadias
  • Musculoskeletal - Achondroplasia, Osteogenesis imperfecta, Thanatophoric dysplasia, Club foot, Rocker bottom foot, Clinodactyly, Polydactyly, Syndactyly.
Conclusion
The incidence of obstetric sonography in the western countries ranges 90-100 percent. Unfortunately, the scenario in our country and especially in this region is to the other extreme. Absence of access to antenatal care, poverty and ignorance compounds the poor situation further. Every obstetrician should advice and arrange for a routine anomaly scan a around 18-20 weeks and, thus, utilize this noble and effective diagnostic tool for better management of the mother and the fetus.
References :
  1. Donald School: Textbook of Ultrasound in Obstetrics and Gynecology, Eds. Asim Kurjak, Frank A. Chervenak, First Edition, 2004, Jaypee Brothers Medical Publishers (P) Ltd., New Delhi, India.
  2. Fernando Arias: Practical Guide to High-Risk Pregnancy and Delivery, Second Edition, 1993, Mosby (Elsevier), USA.
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