11-13 week antenatal (nuchal translucency) scan is considered a routine investigation advised for the fetal well-being as well as for early screening in pregnancy (see antenatal screening).
It includes multiple components and is highly dependent on the operator. Traditionally three factors are ...
Three-dimensional (3D) ultrasound is a technique that converts standard 2D grayscale ultrasound images into a volumetric dataset. The 3D image can then be reviewed retrospectively. The technique was developed for problem-solving (particularly in obstetric/gynecologic exams) and to potentially re...
Aarskog syndrome or Aarskog–Scott syndrome (also known as the facio-digito-genital syndrome) is a rare anomaly characterized by short stature in association with a variety of structural anomalies involving mainly the face, distal extremities, and external genitalia.
Aase-Smith syndrome (or Aase syndrome) is an extremely rare congenital disorder characterized by anemia and skeletal deformity.
Aase-Smith syndrome has a prevalence of less than 1 per 1,000,000 persons. There have only been 20 reported cases.
A mnemonic for causes of abdominal distension (6 Fs) is:
F: fulminant mass
Abdominal ectopic pregnancies are an extremely rare type of ectopic pregnancy.
They are thought to represent ~1% of all ectopic pregnancies 6 with an estimated incidence of 1:1000-10,000 births.
It is often thought that they most frequently result from a tubal rupture ...
The abdominal pain in pregnancy MRI protocol encompasses a set of MRI sequences for assessment of causes of non-traumatic abdominal pain in pregnancy.
Note: This article aims to frame a general concept of an MRI protocol for the assessment of the abdomen in pregnancy. Protocol specifics will va...
Abdominoschisis (plural: abdominoschises) refers to a split or defect in the abdominal wall. Some authors use the term synonymously with a gastroschisis. When the defect continues into the thoracic region it is termed a thoracoabdominoschisis. A large abdominoschisis is considered part of the li...
Abnormal ductus venosus waveforms can arise in a number of conditions ranging from aneuploidy to vascular malformations and fetal tumors. "A wave" reversal can be seen in 5% of euploid fetuses 9.
Abnormal waveforms in fetal ductus venosus flow assessment can occur in a number of situ...
An eccentrically-located gestational sac towards the fundus of the uterus is the normal sonographic appearance; however, an abnormally eccentric gestational sac on ultrasound may be apparent due to a number of causes
interstitial ectopic pregnancy 1
normally implanted pregnancy i...
An abnormally low sac position can result from several possibilities which include
cervical ectopic pregnancy
Cesarean scar ectopic pregnancy
fundal fibroid or other mass compressing the sac downward
Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorized based on whether or not they are related to pregnancy. Etiologies may also be classified based on whether the patient is premenopausal or postmenopausal.
Agenesis of the ductus venosus (ADV) is a rare fetal vascular anomaly.
According to the data obtained from the screening tests performed at 11-14 weeks of pregnancy, its incidence is reported to be 1/2500 12.
In a large case series, Acherman et al. 13 defined five drai...
Non-visualization of the fetal stomach on ultrasound can occur with various physiological as well as pathological processes. It becomes a significant sonographic observation >14 weeks of gestation (about the time the fetus begins to swallow).
physiological emptying: transient
In a fetal sonographic assessment, an absent nasal bone is a feature that can sometimes be used as a surrogate marker for fetal aneuploidy.
It is assessed on a midline sagittal view. In this section, the nasal bone is often seen as a bright echogen...
An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.
The septum pellucidum is partly or entirely absent in 2 or 3 individuals per 100,000 in the general population.
An absent septum pelluc...
Absent end-diastolic flow (AEDF) in an umbilical artery Doppler assessment is a useful feature which indicates underlying fetal vascular stress if detected in mid or late pregnancy. It is often classified as Class II in severity in abnormal umbilical arterial Dopplers 9.
Absence of the yolk sac in the presence of an embryo on a transvaginal ultrasound is considered abnormal, and in general is associated with subsequent embryonic death.
An acardiac twin, also known a recipient twin, refers to the haemodynamically disadvantaged twin of a twin-pair in the setting of twin reversed arterial perfusion (TRAP) sequence. The acardiac twin undergoes secondary atrophy and is non-viable.
Acardiac twinning is thought to affe...
Acardius acormus is a morphologic subtype of an acardiac twin in a twin reversed arterial perfusion (TRAP) sequence. This entity is the least common of the four subtypes, comprising of cephalic structures only. It is seen in approximately 5% of cases.
Acardius anceps is a morphologic subtype of the acardiac twin in a twin reversed arterial perfusion (TRAP) sequence. This entity is the most well differentiated of the four subtypes, with a partly formed head, thorax, and abdomen. It is seen in approximately 10% of cases.
Acardius anephus is a morphologic subtype of an acardiac twin in the twin reversed arterial perfusion (TRAP) sequence. In this entity, no cephalic or structures are present, but the lower limbs are preserved. This is the most common subtype, seen in 60-75% of cases1.
Acheiria refers to absence of one or both hands and can occur in a number of situations, including:
amniotic band syndrome: particularly if unilateral
Cornelia de Lange syndrome 1
fetal hydantoin syndrome 2
Rare defect occurring in 1:65 000 live births.
Achondrogenesis refers to a group of rare and extreme skeletal dysplasias.
The estimated incidence is 1:40,000 with no recognized gender predilection.
It is classified as an osteochondrodysplasia, meaning deficiency of both bone and cartilage development.
Acrania is a rare lethal congenital anomaly characterized by an absence of the calvaria.
The estimated incidence is at ~1:1000 pregnancies 4.
The condition is thought to result from abnormal migration of mesenchymal tissue, which normally covers the cerebral hemisphe...
Acrania anencephaly sequence or acrania–exencephaly–anencephaly sequence is the progression from a relatively normal-appearing exposed brain due to an absent cranium (acrania) to an amorphous brain mass (exencephaly) to no recognisable brain tissue (anencephaly) 1.
The acrania ane...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterized by:
calvarial anomalies: e.g. craniosynostoses
digital anomalies: syndactyly and polydactyly
While there can be some overlap in features, they can be primarily classified into the fo...
Acrocephalosyndactyly syndromes (ACS) are a rare group of disorders collectively characterized by:
calvarial anomalies, e.g. craniosynostoses
digital anomalies, e.g. syndactyly
While there can be some overlap in features, they can be primarily classified into the following maj...
Acute abdominal pain is a common acute presentation in clinical practice. It encompasses a very broad range of possible etiologies and diagnoses, and imaging is routinely employed as the primary investigative tool in its modern management.
A subgroup of patients with acute abdomina...
Acute fatty liver of pregnancy (AFLP) is a rare pregnancy-associated condition that tends to manifest in the 3rd trimester of pregnancy or early postpartum period.
The estimated incidence is at around 1:7000-20,000 births.
Patients may present with nausea,...
Acute non-traumatic abdominal pain in pregnancy requires a considered imaging approach due to the increased risks of fetal demise associated with undiagnosed diseases such as perforated acute appendicitis. Ultrasound is the first-line modality due to its wide availability and ability to diagnose...
The Adams-Oliver syndrome (AOS) is a rare disorder characterized by aplasia cutis congenita (missing hair and/or skin) and variable degrees of terminal transverse limb defects.
polymicrogyria: can be associated with a variant of Adams-Oliver syndrome 3
Agenesis of the diaphragm is a congenital diaphragmatic developmental anomaly where all or part of diaphragm fails to form. It can sometimes be thought of as an extreme form congenital diaphragmatic herniation 1.
The agenesis can either be unilateral or bilateral. Herniation of abdom...
Acquired immunodeficiency syndrome (AIDS) embryopathy is characterized by a group of dysmorphic features, which manifests either before or after birth in offsprings of women who are infected by HIV virus. The diagnosis, however, is in disfavour according to some authors 2.
Allantoic cysts are a type of true cyst of the umbilical cord.
The allantois forms from the part of the fetal yolk sac that eventually becomes the primitive hindgut (the cloaca). The cloaca divides into the hindgut posteriorly and the urogenital sinus anteriorly. The allantois remain...
Alpha-fetoprotein (AFP) is an important plasma protein synthesized by the yolk sac and fetal liver. In adults, its main utility is as a tumor marker, primarily for hepatocellular carcinoma or teratoma. Functionally it is the fetal homologue of albumin i.e. it acts as a major carrier protein in t...
Amelia refers to a skeletal dysplasia characterized by the complete agenesis of an upper or lower extremity or all four limbs. It may be associated with other congenital anomalies, i.e. omphalocele and diaphragmatic hernias 3.
Amelia is a very rare congenital anomaly with an incid...
Amniocentesis, also known as amniotic fluid testing or AFT, is a diagnostic or therapeutic medical procedure primarily used in prenatal diagnosis of chromosomal abnormalities and fetal infections.
A small amount of amniotic fluid (15-20 ml), which contains fetal tissue, is extracted from the am...
Amnion refers to a membranous structure which covers and protects the embryo. It forms inside the chorion. The amnion usually fuses with the outer chorion by around 14 weeks of gestation.
The amnion can be visualized in most pregnancies before the 12th week of...
An amnioreduction is a procedure where an amniocentesis is performed for intentional reduction of amniotic fluid volume. This is sometimes performed in the context of extreme polyhydramnios (particularly in the recipient twin in twin to twin transfusion syndrome).
Amniotic bands refer to free-floating blind-ending amnion with an intact chorionic membrane. In certain situations, they lead to amniotic band syndrome. They should not be confused with amniotic shelves which refer to the presence of amnion folding around pre-existing uterine adhesions. Some adv...
Amniotic band syndrome (ABS) comprises of a wide spectrum of abnormalities, all of which result from entrapment of various fetal body parts in a disrupted amnion. Due to the randomness of entrapment, each affected individual has the potential to form a unique deficit.
An amniotic fluid discordance is usually defined as a difference in amniotic fluid volumes in a twin pregnancy. It is a predictor of poor fetal outcome in twin pregnancy related complications.
Causes of amniotic fluid discordance include:
twin-twin transfusion syndrome
The amniotic fluid index (AFI) is an estimate of the amniotic fluid volume in a pregnant uterus. It is part of the fetal biophysical profile.
the uterus is divided into four imaginary quadrants with the linea nigra and a mediolateral line running through the umbilicus acting as the ...
Amniotic fluid in the first trimester has been estimated from weeks 7-12. Although the amniotic fluid index (AFI) is calculated in the second trimester, one can get an idea of whether the amount of amniotic fluid is too much or too little at an earlier time point.
The amniotic fluid volume is r...
Amniotic fluid volume (AFV) is a function both of the amount of water transferred to the gestation across the placental membrane, and the flux of water across the amnion.
Change in volume through gestation
The AFV undergoes characteristic changes with gestation. It progressively ri...
Amniotic shelf (also known as an amniotic sheet 4) refers to a sheet like projection that can result from uterine synechiae that has been encompassed by the expanding chorion and amnion. In contrast to amniotic bands, they are not thought to be associated with any fetal deformity.
Ampullary ectopic pregnancy is the commonest type of tubal ectopic pregnancy and accounts for ~70% of such cases. According to one study, the disruption of the tubal wall was less than as in isthmic ectopic pregnancy 2.
Amyoplasia congenita is a syndrome characterized by multiple specific congenital joint contractures, associated with substitution of muscular tissue by fibrosis and adipose tissue.
The estimated incidence is at 1: 10000 live births. There may be a higher prevalence with twin preg...
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
Anembryonic pregnancy is a form of a failed early pregnancy, where a gestational sac develops, but the embryo does not form. The term blighted ovum is synonymous with this but is falling out of favor and is best avoided.
The patient may be asymptomatic, presenting for an...
Getting a film with anembryonic pregnancy in the radiology fellowship examination is one of the many exam set-pieces that the candidate must be prepared for.
Transabdominal and transvaginal pelvic ultrasound shows a uterus with an intrauterine gestational sac. MSD is at least 25 m...
Anencephaly is the most severe form of cranial neural tube defect (NTD) and is characterized by an absence of cortical tissue (although the brainstem and cerebellum may be variably present) as well as an absence of the cranial vault. The morphological spectrum within anencephaly ranges from holo...
Aneuploidy refers to an abnormal number of chromosomes, and is a type of chromosomal abnormality.There are large number potential aneuploidic anomalies. The most common three in obstetric practice are:
trisomy 21: commonest aneuploidic anomaly
Angular pregnancies are those in which implantation occurs eccentrically along the fundus of the endometrial cavity, along with the lateral upper angle or cornua of the uterus.
In contrast to interstitial tubal pregnancy, angular pregnancies have a more medial location and are considered an int...
Anhydramnios is a term where there is a complete or near-complete lack of amniotic fluid (sometimes referred to as "liquor volume").
Anhydramnios can result in a number of situations:
fetal renal tract anomalies
Potter syndrome (bilateral renal agenesis): most common
Anophthalmia refers to a complete absence of ocular development. It is often considered to represent the most severe form of microphthalmia.
It can occur in three different situations:
primary anophthalmia: complete absence of eye tissue due to a failure of the part of the brain tha...
Antenatal screening of Down syndrome (and other less common aneuploidies) should be available as a routine component of antenatal care. It allows families to either adjust to the idea of having a child with the condition or to consider termination of pregnancy.
For a general description of Down...
Antenatal screening and diagnosis are currently available for a few selected genetic conditions, including trisomy 21 (Down syndrome), trisomy 18 (Edward syndrome), trisomy 13 (Patau syndrome) and neural tube defects.
For an overview of the conditions and their manifestations, please refer to t...
Antenatal soft ultrasound markers are fetal sonographic findings that are generally not abnormalities as such but are indicative of an increased age adjusted risk of an underlying fetal aneuploidic or some non chromosomal abnormalities.
Most of the described features do not constitute a structu...
Antepartum hemorrhage (APH) refers to vaginal bleeding during the second half of pregnancy (> 20 weeks gestation). APH may occur in varying degrees from mild to severe, with concomitant risk to mother and baby and potential to result in severe maternal/fetal compromise, including death.
The anterior cervical angle is a novel ultrasound parameter that is being used as a predictor of spontaneous preterm birth.
The angle between the uterine wall and the cervical canal is measured during the first and the second trimester by a transvaginal ultrasound. It is measured u...
An aortic arch view is one of the additional views performed on fetal obstetric ultrasound - fetal echocardiography. It is an oblique sagittal view which is obtained similar to a left anterior oblique angiogram or the sagittal arch view obtained in CT arteriography. The isthmus, after the origin...
Aorto-ventricular tunnel (AVT) is an extremely rare form of congenital heart disease, representing an anomalous extracardiac communication between the ascending aorta and the left or right ventricles.
In most cases the anomalous communication is between the aorta and the left ventr...
Apert syndrome (also known as type I acrocephalosyndactyly) is a syndrome that is predominantly characterized by skull and limb malformations.
The estimated incidence is 1 case per 65-80,000 pregnancies.
increased paternal age has been proposed 6
Apgar score was originally described by Virginia Apgar (American anaesthesiologist, 1909-1974) in 1952.
Helpfully, her surname is also a useful mnemonic for remembering the 5 factors: each is graded as 0, 1 or 2 with a total possible score of 10. The lower the score the worse the prognosis.
Apple-peel intestinal atresia, also known as type IIIb or Christmas tree intestinal atresia, is a rare form of small bowel atresia in which the duodenum or proximal jejunum ends in a blind pouch and the distal small bowel wraps around its vascular supply in a spiral resembling an apple peel. Oft...
Aprosencephaly is an extremely rare anomaly fetal cerebral development the derivatives of the telencephalon as well as the diencephalon are absent or dysplastic, while more caudal structures are normal or mildly deformed. It falls under the aprosencephaly / atelencephaly spectrum (AAS).
A fetal arachnoid cyst is term given when an arachnoid cyst is diagnosed in utero. For a general discussion of arachnoid cysts refer to the parent article.
They can be classified as being primary or secondary 2.
primary (congenital) arachnoid cysts: result from a benign accumulation...
Arhinia refers to congenital failure of the external nose, nasal cavity, and olfactory apparatus to develop. It is an extremely rare condition that can be detected on prenatal ultrasound or MRI.
Arhinia may occur in a syndromic setting (such as ethmocephaly), but it has been repor...
Arthrogryposis (multiplex congenita) is a clinical or imaging descriptor that denotes congenital non-progressive joint contractures involving two or more body regions.
Mostly reported in individuals of Asian, African and European descent with equal incidence in males and females ...
An artificial rupture of membranes (AROM) is a procedure that can be used for the induction of labor.
A sterile, plastic, thin hook is brushed against the membranes just inside the cervix (termed a membrane sweep) This causes the fetal head to move down against the cervix, usually r...
Asphyxiating thoracic dysplasia, also known as Jeune syndrome, is a type of rare short limb skeletal dysplasia, which is primarily characterized by a constricted long narrow thoracic cavity, cystic renal dysplasia and characteristic skeletal features. It is also sometimes classified as one of th...
Asymmetrical intrauterine growth restriction is a type of intrauterine growth restriction (IUGR) where some fetal biometric parameters are disproportionately lower than others, as well as falling under the 10th percentile. The parameter classically affected is the abdominal circumference (AC).
Asymmetric ventriculomegaly, interhemispheric cyst, and dysgenesis of the corpus callosum (AVID) is a triad of congenital cerebral anomalies.
markedly asymmetric enlargement of the lateral ventricles may be the initial finding on routine fetal morphology ultrasound.
Atelencephaly (also termed atelencephalic microcephaly) is a rare and extreme disorder with only a handful of published cases. In this anomaly, the derivatives of the telencephalon are absent or dysplastic, while more caudal structures are normal or mildly deformed. It falls under the aprosencep...
Atelosteogenesis refers to a heterogeneous group of lethal skeletal dysplasias that are characterized by aplasia/hypoplasia of the humeri, femora and spine.
atelosteogenesis type I (boomerang dysplasia)
atelosteogenesis type II
atelosteogenesis type III 4
Atypical ectopic pregnancy generally refers to an ectopic pregnancy which occurs outside the fallopian tube.
interstitial ectopic: 3% (often also termed cornual ectopic), also essentially a type of tubal ectopic
cornual ectopic (<1%)
ovarian ectopic: 0.5-1% (ovarian pregna...
Autosomal recessive polycystic kidney disease (ARPKD) is one of many pediatric cystic renal diseases.
On imaging, it usually presents on ultrasound with enlarged echogenic kidneys with multiple small cysts. Liver involvement with coarse echotexture, biliary tract cystic changes, and portal hype...
The banana sign is one of the many notable fruit inspired signs.
This sign is seen on axial imaging through the posterior fossa of fetuses with associated conditions such as Chiari II malformation and/or spina bifida.
In Chiari II malformation, the banana sign describes the way the cerebellum...
A Bandl ring may be seen during imaging of a patient in labor.
It is considered to be an uncommon finding in modern obstetrics (0.01-1.26%).
It is a pathologic retraction ring at "Barnes boundary line", which separates the upper contractile portion of the uterus from l...
Band like structures in the gestational sac is not an uncommon finding in the first trimester or second trimester ultrasound scans and can represent a number of varying conditions
Barth syndrome (BTHS), also known as 3-methylglutaconic aciduria type II, is an extremely rare X-linked multisystem disorder that is usually diagnosed in infancy.
Barth syndrome has an estimated prevalence of 1 in 300,000-400,000 live births.
It is characte...
The basal plate is a synonym for the maternal side of the placenta. The fetal side of the placenta is termed the chorionic plate.
Some pathologies and processes are localized to the basal plate, and evaluation of the basal plate is a part of placental grading.
Beta-hCG (bHCG or β-hCG) is a sex hormone found in the mother's blood serum that can be used to help interpret obstetric ultrasound findings.
Beta-hCG levels may be used in three ways in the clinical setting of pregnancy:
qualitatively, for presence/absence of fetal tissue
more often determin...
A bilobed placenta also referred to as bipartite placenta, is a variation in placental morphology and refers to a placenta separated into two near equal-sized lobes. If more than two lobes are present, it is termed a trilobed, four-lobed and so on. If the second lobe is smaller than the main lob...
The binocular distance (BOD) is a measurement between the two lateral (outer) canthi of each eye. It is sometimes used as a accessory fetal biometric parameter where it is often documented on both 2nd trimester anatomy scans on axial brain scans. The largest diameter of the orbit should be used ...
Biparietal diameter (BPD) is one of the basic biometric parameters used to assess fetal size.
BPD together with head circumference (HC), abdominal circumference (AC), and femur length (FL) are computed to produce an estimate of fetal weight. In the second trimester this may be extrapolated t...
Birth fractures of the clavicle occur in 0.5-1% of vaginal deliveries and are the most frequent birth-related fracture. They are most commonly seen following normal, uncomplicated births but there is recognized increased incidence with high birth weight babies, forceps delivery and shoulder dyst...
Birth trauma (a.k.a. birth injury) relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
The Bishop score is a criterion for successful induction of labor, vaginal delivery and includes the age of gestation, parity, presenting part of the fetus, previous history of childbirths and consent of the patient. This score decides whether a patient needs cervical ripening or not 1,4.
Bladder exstrophy (also known as ectopia vesicae) refers to a herniation of the urinary bladder through an anterior abdominal wall defect. The severity of these defects is widely variable.
The estimated incidence of bladder exstrophy is 1:10,000-50,000 live births 3,5. There is a ...
Bladder flap hematoma is a hematoma between the uterus and posterior wall of urinary bladder. They may be small (more commonly) or large (>5 cm, less common).
Small hematomas may be asymptomatic. Large ones may present with lower abdominal pain, dysuria, anemia and fever ...