ULTRASOUND SOFT MAKRERS
HYPOPLASTICS NASAL BONE / ABSENT NASAL BONE
Hypoplastics nasal bone refers to a sonographic observation where the fetal nasal bone appears smaller in the midsagittal view of the fetal face. The prevalence rate is about 1.15%. 0.5-1.2% of normal fetuses have been found to have a hypoplastic nasal bone on a routine 2nd trimester scan, compared to 43-62% of fetuses with Down syndrome.
Absent nasal bone refers to a sonographic observation where fetal nasal bone is missing in the midsagittal view or nasal bone is missing on the retronasal triangle. The prevalence rate of absent is about 0.13%. Absent nasal bone is a feature that can sometimes be used as a surrogate marker for fetal aneuploidy like Down syndrome.
THICKENED NUCHAL TRANSLUCENCY (NT)
Nuchal translucency is the normal fluid-filled space between the back of the fetal skin and the overlying skin. This is one of the most sensitive and specific individual markers of fetal disorders. Increased NT may be associated with other rarer chromosomal abnormalities, structural abnormalities, genetic syndromes and fetal infections.
THICKENED NUCHAL FOLD
Thickened nuchal fold is an increased thickness of the skin at the base of a fetal neck. The nuchal fold thickness is considered normal if less than 6mm between 18 and 24 weeks gestation. It is found via ultrasound in 1-2 percent of normal pregnancies between 15 and 20 weeks' gestation. An increased thickness corresponds to increased risk for aneuploidy and other fetal abnormalities. Increased thickness of the nuchal fold is a soft marker associated with multiple fetal anomalies.
Ventriculomegaly is the dilatation of ventricle which is ≥ 10 mm. The severity of ventriculomegaly can be further classified as, mild fetal ventriculomegaly: lateral ventricular diameter between 10-12 mm; moderate fetal ventriculomegaly: 12.1-15 mm; severe fetal ventriculomegaly (also sometimes classified as fetal hydrocephalus): lateral ventricular diameter >15 mm. Many fetuses with mild ventriculomegaly have a normal outcome, however, there are also a large number of congenital syndromes associated with enlarged ventricles. Included central nervous system abnormalities like abnormal corpus callosum and septo-optic dysplasia, or some chromosomal abnormalities like trisomy 13, 18 and 21.
The prognosis and management depend on the presence of associated abnormalities.
CHOROID PLEXUS CYST
Choroid plexus cysts are benign, transient, and common. It is organs in cerebral ventricular system that produce cerebrospinal fluid. This appears as a cyst inside the choroid plexus at the time of ultrasound. A choroid plexus cyst can be likened to a blister and is not consider a brain abnormality. It is seen in 0.3-3.6% of 2nd-trimester fetuses and it is a weak marker for trisomy 18. Choroid plexus cysts are found in about one third of the time in fetuses with trisomy 18. Isolated choroid plexus cyst is not associated with trisomy problem. It requires no treatment, as 90% will resolve on their own by the 28th week of gestation. Even when an otherwise healthy child is born with a choroid plexus cyst, the baby will likely develop normally.
INTRACARDIAC ECHOGENIC FOCI
Echogenic foci is small bright dot in ventricle of heart. This is a relatively common sonographic observation that maybe present on an antenatal ultrasound scan. This is presented in 4-5% of scans at the 2nd trimester and this is more common in Asians. It is more often to be seen in low risk patients. Most of the intracardiac echogenic foci are unilateral. The most frequent location of the echogenic foci is at the left ventricle, out of all the 4 cardiac chambers. It is usually single and less than 3mm. It is considered a benign variant when it is isolated. However, this maybe associated trisomy problem like Down syndrome and trisomy 13) in high risk pregnancy.
ABERRANT RIGHT SUBCLAVIAN ARTERY
Aberrant right subclavian artery is a blood vessel arises from the distal portion of the aortic arch and courses from the left side of the upper chest, behind the esophagus and the trachea, to the right upper arm. It is a frequent condition, seen in 1.5% of the chromosomally normal fetuses and is considered a normal variant. Most of the people with ARSA have no symptoms. ARSA are most likely not aware that they have this variant. By itself, ARSA is not a very worrying finding. Some of the cases may be associated with chromosomal abnormalities with Down syndrome and Di George syndrome. However, in most cases of ARSA, no chromosomal defect is identified and no genetic cause of the ARSA is determined.
PERSISTENT RIGHT UMBILICAL VEIN
Right umbilical vein means the portal vein is curved towards the stomach, the fetal gallbladder is located medially to umbilical vin – between the umbilical vein and the stomach. The incidence is about 0.2% to 0.5%. This is the most common form among fetal venous system anomalies. The recent studies have highlighted that this anomaly does not increase the rate of chromosomal anomaly or syndromic pattern frequency.The prognosis is excellent if isolated.
Pericardial effusion is the fluid collection surrounding all or part of the heart. The incidence is about 2% of pregnancy. 50-80% of fetuses have trace fluid (< 2 mm) on careful search. It is generally accepted pericardial fluid thickness greater than 2mm as abnormal. Trace fluid along 1 ventricular wall is a normal finding. However, fetal pericardiac effusion can occure as a component of hydrops fetalis. This may also associated with aneuploidy, fetal infection, fetal anemia, cardiac malformation and genetic syndrome.
Hydronephrosis is the widening of the renal pelvis and is a common finding on ultrasound scans performed during pregnancy. The normal measurement of the renal pelvis is 0-7mm. If the measurement is more than this, it is called hydronephrosis (or renal pelvic dilatation).
Echogenic bowel is an ultrasound finding where the fetal intestines appear brighter than expected. Prevalence of echogenic bowel is about 0.4 to 2%. Echogenic bowel can be detected by ultrasound usually around 20 weeks of pregnancy. 82.5% of cases of EB are considered normal variant at is often associated with normal, healthy babies. However, there are several medical problem that can cause echogenic bowel. It may be associated with chromosomal abnormalities, genetic syndrome, fetal infection, structural abnormalities and intrauterine growth restriction.
SINGLE UMBILICAL ARTERY
In the usual situation, there are pair of umbilical arteries in the umbilical cord. When there is a congenital absence either left or right umbilical artery, we called it 2 vessels cord or single umbilical artery. The estimated prevalence is 1 in 100 of pregnancies. This may be associated with intrauterine growth restriction.