Small prenatal fetal ultrasound abnormalities
There are 800,000-1.2 million new births of congenital anomalies in China every year, accounting for 4-6% of the total Chinese birth population. The majority of fetal morphological and structural anomalies can be detected by preliminary systematic ultrasound screening at 18-22 weeks of gestation. In addition to the obvious serious anomalies, the ultrasound findings also include some microscopic anomalies (also known as potential chromosomal abnormality markers). There is a correlation between these micro-anomalies and fetal chromosomal abnormalities (mostly aneuploid aneuploid) reported in the literature. With limited time for outpatient communication, it is often difficult for the doctor to give an exhaustive explanation, and there is much confusion among pregnant women who have these problems. Pan Shaneng, Department of Obstetrics and Gynecology, Tiantai County People’s Hospital
Common microscopic abnormalities include increased cervical hyaline layer width, choroidal plexus cyst, ventricular dilatation, widened renal pelvis, single umbilical artery, intracardiac strong echogenic spot, short femur, strong echogenic intestine, nasal bone abnormality, small jaw deformity, etc.
1.Nuchal translucency width (NT).
NT refers to the maximum thickness of soft tissue between the skin layer and fascial layer at the back of the fetal neck, reflecting the accumulation of lymphatic fluid in the subcutaneous tissue. Before 14 weeks of gestation, the fetal lymphatic system is not well developed, and some lymphatic fluid collects in the lymphatic sacs or lymphatic vessels of the neck, forming NT. After 14 weeks, the lymphatic system is well developed, and the accumulated lymphatic fluid rapidly drains to the internal jugular vein, and NT disappears. 16 weeks later, it is called nuchal skin fold thick.
NT should be performed at 10-14 weeks. The sonographic picture shows a non-echoic subcutaneous layer in the neck. The commonly used criteria are: ≥2.5 mm at 10-14 weeks of gestation is considered abnormal; ≥6 mm at 14-22 weeks is considered abnormal. The criteria may be relaxed in advanced age.
Genetic, anatomical abnormalities or infections causing lymphatic reflux disorders are the causes of NT widening, and some of them may develop into cervical lymphatic hydrocystic hygroma (cystic hygroma) by mid-pregnancy. It has been reported that 10% of early NT widening is combined with chromosomal abnormalities, mainly trisomy 21, trisomy 18, trisomy 13 and 45X0 (Turner’s syndrome). In addition, non-chromosomal anomalies such as cardiac anomalies, fetal edema, thoracic dominant lesions, skeletal dysplasia, and recipient of twin-birth transfusion syndrome should be excluded. Overall, about 80%-90% of NT abnormalities are transient lesions and the fetus is normal.
2. choroid plexus cyst (CPC).
The choroid is located in the lateral ventricle, the third ventricle, and the fourth ventricle, and is the site of cerebrospinal fluid production. CPC, which is a cyst in the choroid plexus, is thought to be caused by folds of the neuroepithelium within the choroid, containing cerebrospinal fluid and cellular debris, and can be single or multiple, and can cause ventricular dilatation if the cerebrospinal fluid circulation is blocked. It has also been suggested that most cysts have a hemangioma-like capillary network and stroma, which are pseudocysts.
CPC occurs in 1%-2% of normal fetuses and may appear transiently but disappears at 20 weeks. The sonogram is a round or oval anechoic structure seen within a homogeneous strongly echogenic choroidal plexus, mostly 3-5 mm in size, and the diagnosis should be considered for those found after 18 weeks with a diameter of 10 mm or more. The chance of chromosomal abnormalities in pure CPC is between 1 and 2.4%.
Simple CPC disappears in late pregnancy and is in the vast majority not combined with other abnormalities. If other abnormalities are combined, especially multiple malformations, the chance of chromosomal abnormalities is high, including trisomy 18, trisomy 21, etc.
3. ventricular dilatation (ventriculomegaly).
Cerebrospinal fluid is produced by the intraventricular choroid plexus and enters the third ventricle via the interventricular foramen, then flows into the fourth ventricle via the middle cerebral aqueduct, and then enters the subarachnoid space via the middle and lateral foramina. Various causes cause obstruction of cerebrospinal fluid circulation and accumulation in the ventricles, resulting in ventricular dilatation. A marked ventricular dilatation with a lateral ventricular width of ≥15 mm is called hydrocephalus. It is mostly due to narrowing of the midbrain aqueduct, and the causes include chromosomal abnormalities, inflammation, and mass compression.
After 20 weeks of gestation, lateral ventricles or cerebellar medullary pools with a width of more than 10 mm should be alerted to hydrocephalus and should be followed closely. When the width is >10 mm and <15 mm, it is called mild ventriculomegaly. The incidence is between 1.5 and 22 per 1,000, mostly not due to obstruction of the ventricular system. Further detailed examination of extracranial lesions, such as agenesis of the corpus callosum and cardiac malformations, should be performed. Note that about 5-10% of fetuses with isolated mild ventricular dilatation are chromosomal abnormalities, among which trisomy 21 children are more common.
4, posterior cranial fossa pool widening (enlarged cisterna magna).
Also known as enlarged posterior cranial fossa pool and enlarged Magna sac, it refers to the distance between the fetal cerebellar pool and the anterior-posterior diameter of the medial aspect of the skull ≥ 10 mm.
Widening of the posterior cranial fossa pool is associated with fetal haploinsufficiency, especially trisomy 18, and is also seen in arachnoid cysts and Dandy-Walker malformation. In the absence of other coexisting anomalies, follow-up with ultrasound and other imaging studies is feasible.
5. Pyelectasis or pelvic separation (pyelectasis/hydronephrosis).
Urinary tract obstruction leads to retention of urine in the renal pelvis and calyces, and ultrasound shows dilated anterior and posterior diameters of the renal pelvis. Severe pyelectasis can result in atrophy of the renal parenchyma and an increase in kidney size.
Renal pelvic effusion has been reported to be detected in 2%-2.8% of normal fetuses and 17%-25% of trisomy 21 children. Anterior-posterior diameter of renal pelvis separation (APD) values of ≥4 mm at 15-20 weeks, ≥5 mm at 20-30 weeks, and ≥7 mm at 30-40 weeks may present as fetal anomalies and should be followed until after birth.
Other organic lesions include pelvic ureteral junction stenosis, ureteral bladder junction stenosis or ureteral dilatation due to vesicoureteral reflux, posterior urethral valves, Prune-belly syndrome (urethral obstruction resulting in a huge fetal bladder with extremely thin bladder wall and fetal abdominal wall), etc.
6.Single umbilical artery (SUA).
The normal umbilical cord contains two umbilical arteries and one umbilical vein, but SUA means that there is only one umbilical artery, the incidence is about 1%, and the left side is more common than the right side. The larger one is the umbilical vein and the smaller one is the umbilical artery, which is slightly larger than the normal lumen. SUA can occur singly, but is not uncommon in combination with chromosomal anomalies and other malformations, and is seen in approximately 50% of children with trisomy 18 and 10%-50% of children with trisomy 13. Further fetal echocardiography is recommended clinically.
7. Intracardiac strong echogenic spot or intracardiac focal strong echo (echogenic intracardiac focus,EIF).
EIF is a point-like isolated focal echogenicity in the free area of one ventricular cavity that corresponds to the papillary muscle or tendon area on a four-chamber cardiac image, and its echogenic intensity is similar to that of the fetal bone (rib cage). It may be solitary or multiple, with the left ventricle being the most common, gradually diminishing with increasing gestation and disappearing by the age of 1 year at the latest. It may be associated with inflammation, thickening and calcification of the papillary tendon cords, but it is a normal variant and is common in Asians.
The incidence of EIF on ultrasound at 18-22 weeks of normal gestation is 2-5%, with a risk rate of 16%-30% in trisomy 21 children and 39% in trisomy 13 children; EIF with other ultrasound abnormalities increases the risk; alone, the chance of fetal abnormalities is low; the incidence of fetal chromosomal abnormalities with EIF is about 1/600 when the maternal age is ≥31 years. Echocardiography is recommended.
8. short femur length.
Long bone dysplasias are considered to be one of the features of chromosomal abnormalities, and the femur is the only long bone that is routinely measured on obstetric ultrasound scan. If the femur is measured at less than the fifth percentile of the corresponding gestational week, but other growth indicators are normal, this is a high priority. 19% of trisomy 21 children have short femurs. With a BPD/FL greater than 1.5, 54%-70% of trisomy 21 children can be detected. Short femur in middle and late pregnancy is also seen in chondrodysplasia, IUGR, infants younger than gestational age, and congenital proximal femoral defects (PFFD).
9. Strong echogenic bowel (hyperechogenic bowel).
It is not a disease but a sonographic manifestation, which refers to the enhancement of fetal intestinal echogenicity with intensity close to or higher than that of bone echogenicity, commonly found in the small intestine of mid-pregnancy fetuses and the colon of late-pregnancy fetuses. The incidence in mid- and late-term pregnancies is 1%. Most fetal follow-up results are ultimately normal, but a significant proportion of fetuses are confirmed to have abnormalities, such as chromosomal abnormalities, gastrointestinal abnormalities, intestinal obstruction, meconium peritonitis, cystic fibrosis, intra-amniotic hemorrhage, and intrauterine infection.
10. Increased or decreased fetal eye spacing.
Excessive or small orbital distance in both eyes is commonly associated with some anomalous syndrome. A rough estimate of the central orbital distance (mm) is approximately equal to the number of weeks of gestation and can be judged accordingly. The fetal canthus index = (inner canthus/outer canthus) × 100, when the canthus index ≥ 38, the canthus index is too large, which can be seen in trisomy 13, trisomy 18, trisomy 21; when the canthus index < 20, the canthus index is too small, which can be seen in forebrain holoprosencephaly (whole forebrain holoprosencephaly), juxtacranial malformation, microcephaly, often also the manifestation of trisomy 13, trisomy 21.
11.Fetal nasal hypoplasia and absence of nasal bone.
The fetal nasal bone starts to develop in the 6th week of embryonic life and ossifies by membranous osteogenesis in 9-11 weeks. 1.4% of normal fetuses have absent nasal bone. In approximately 50-60% of trisomy 21 children, nasal bone defects are detected on ultrasound screening at 10-14 weeks. Fetal nasal widening or narrowing can also be seen in a variety of chromosomal abnormalities. For example, anterior anencephaly and ocular hyperfusion in fetuses with juxtacranial anomalies may manifest as single nostril, elephantine nose and abnormal nasal position.
The standard measurement plane is the median sagittal plane in the horizontal position of the fetus, which shows a thin line of strong echogenicity in the nasal bridge. It is important to note that nasal bone defects can occur in a small percentage of chromosomally normal fetuses, and the background prevalence of nasal bone defects in chromosomally normal populations depends on the ethnicity and facial features of the parents.
12. Increased or decreased distance between the corners of the fetal mouth.
The distance between the two corners of the fetal mouth correlates with gestational age. The increased distance between the corners of the mouth is 2 standard deviations higher than normal and is seen in a variety of chromosomal abnormalities. The decrease in the distance between the corners of the mouth, which is lower than 65% of normal fetuses of the same gestational age, is also often a clinical manifestation of chromosomal and genetic syndromes.
13. Fetal mandibular developmental malformations.
The anomalous mandible (agnathia) or small mandibular anomaly (micrognathia/micrognathism/small jawz/small chin) is often one of the frequent anomalies of chromosomal anomaly syndromes. The fetus with micrognathia has a reduced anterior-posterior and left-right diameter of the mandible, which is significantly lower than that of a normal fetus of the same gestational age.
Ultrasonography can clearly show the horseshoe-shaped mandible. In the past, visual inspection of the facial contour was more subjective, but nowadays, the jaw index is used to determine this. The mandibular index (jaw index) = (anterior-posterior mandibular diameter / biparietal diameter) × 100. mandibular index <21 in small mandibular deformities, commonly seen in trisomy 18, trisomy 21, 45XO, 5P deletion, etc. Chromosomal abnormalities have been reported in about 66% of small mandibular fetuses, and autopsy reports the presence of small jaw anomalies in 80% of triploid children.
14. Amniotic film.
Ultrasonography during pregnancy reveals a strongly echogenic band of light floating in the amniotic fluid within the amniotic sac, called amniotic sheet also known as uterine adhesion folds (uterine shelf). This is caused by the presence of adhesion scars in the uterine cavity and the growth of amniotic and chorionic membranes along the stretched scars. It is thicker because it contains two layers of chorionic villus and two layers of amnion, so it is strongly and distinctly echogenic. The incidence has been reported in the literature as 0.6%, although it is not uncommon in recent years and should be related to the increasing number of uterine operations in women of childbearing age. Amniotic slices do not adhere to the fetus and are not associated with fetal malformations, so no special treatment is indicated. However, care should be taken to differentiate it from other intrauterine band echoes, such as amniotic band syndrome, incomplete longitudinal uterine septum, contoured placenta, and amniotic sac separation in multiple fetuses.
The causes of fetal anomalies are diverse, and there is no effective prevention method in medical science, but only through early diagnosis and timely termination of pregnancy. Ultrasonography is the first choice for early diagnosis of fetal anomalies. Some of these microscopic anomalies appear early and persist, some are transient, some appear irregularly, and some are late onset lesions. Although many fetuses with chromosomal abnormalities do not show any signs on ultrasound images. However, as soft-markers of chromosomal abnormalities, they can provide clues for careful screening of fetal anomalies and alert the operator to scrutinize the fetus for combined abnormalities elsewhere. For continued pregnancies, the sonographic changes should be reviewed periodically.
Although the probability of problems occurring in the isolated presence of the above-mentioned phenotypes is small and the sensitivity and specificity are not high; however, for those pregnant women who are older and have abnormal serologic screening (PAPP-A, α-FP, β-hCG, uE3, inhibin-A) results and combined with other high-risk factors, chorionic villus biopsy (10-13 weeks) and amniocentesis (16-22 weeks) should eventually be performed, in addition to MRI. In addition to MRI, the diagnosis should be clarified by karyotyping after fetal cell extraction by interventional methods such as chorionic villus biopsy (10-13 weeks), amniocentesis (16-22 weeks) and umbilical cord puncture.