A monochorionic monoamniotic (MCMA) twin pregnancy is a subtype of monozygotic twin pregnancy. These fetuses share a single chorionic sac, a single amniotic sac and, in general, a single yolk sac.
It accounts for the minority (~5%) of monozygotic twin pregnancies and ~1-2% of al...
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
Fetal intra-abdominal cystic lesions can arise from a number of physiological and pathological causes.
fetal gastric dilatation / fetal gastric bubble (can be pathological if there is a gastric outlet obstruction
normal fetal gallbladder
No colour flow
Intrauterine contraceptive devices (IUCD) are one of the most frequently used methods of contraception throughout the world. It prevents pregnancy by:
thinning the endometrial lining
preventing sperm motility
There are two main types of IUCDs:
non-hormonal metallic (...
A dizygotic (DZ) twin pregnancy is a type of twin pregnancy where two seperate ova are independantly fertilised by two seperate sperm resulting the two seperate zygotes. These twins are known as fraternal twins. They may or may not be of the same gender.
Dizygotic twins are the m...
The second trimester scan is a routine ultrasound examination in many countries that is primarily used to assess fetal anatomy and detect the presence of any fetal anomalies.
The second trimester extends from 13 weeks and 0 days to 27 weeks and 6 days of gestation although the majority of thes...
Myelomeningocele, also known as spina bifida cystica, is a complex congenital spinal anomaly that results in spinal cord malformation (myelodysplasia).
It is one of the commonest congenital CNS anomalies and thought to occur in approximately 1:500 of live births 5. There may be a...
A transverse abdominal view is one of the standard views on fetal echocardiography and is very useful for assessing situs abnormalities. In case of situs solitus (normal situs), the stomach is on the left and liver on the right. The descending aorta lies anterior and to the left of the spine whi...
A standard fetal echocardiogram consists of several specific views which can be obtained to optimise visualisation of different structures and anomalies. They include:
abdominal situs view / transverse view of abdomen
four chamber view
left ventricular outflow tract view (or a fi...
Congenital goitre is a rare cause of neck swelling in neonates and is demonstrated as diffuse/nodular thyroid gland enlargement.
It is a common endocrine disease in newborns and affects approximately 1:2000-4000 live births.
There may be a difficult vaginal...
Syndactyly refers to a congenital fusion of two or more digits. It may be confined to soft tissue (soft tissue syndactyly / simple syndactyly) or may involve bone (bony syndactyly / complex syndactyly).
The overall estimated incidence is at ~1 per 2,500 to 5,000 live births 6,8. T...
Brachydactyly (BD) essentially refers to short digits. It is often inherited as an autosomal dominant trait (all the types). The clinical spectrum can widely range from minor digital hypoplasia to complete aplasia. As a group, it most commonly involves the middle phalanx 2.
Single or multiple b...
Congenital hypothyroidism (CHT), previously known as cretinism, can be of thyroidal or central (hypothalamic/pituitary) origin and can have a widely diverse molecular aetiology.
Most children are asymptomatic at birth and are diagnosed after screening. In untreated CHT pa...
Mesoblastic nephroma, also sometimes known as a congenital mesoblastic nephroma (CMN) or fetal renal hamartoma, is, in general, a benign renal tumour that typically occurs in utero or in infancy.
It is the commonest neonatal renal tumour. Diagnosis is usually made in the antenatal...
Subgaleal haematoma describes scalp bleeding in the potential space between the periosteum and the galea aponeurosis. It is a rare but possibly lethal emergency.
Moderate to severe presentations occur in 1.5 of 10 000 live births. It most commonly occurs after vacuum-assisted and ...
Cephalohaematomas are traumatic subperiosteal haematomas of the skull that are usually caused by birth injury. They are bound between the periosteum and cranium, and therefore cannot cross sutures. Being bound by a suture line distinguishes them from subgaleal haematoma, which can cross sutures....
Congenital limb amputations are a limb anomaly that usually occur due to disruption of vascular supply.
Congenital amputations occur in 0.5 (range 0.03-1) per 1000 live births 2.
Slightly more common in the upper limb (60%) than in the lower limb (40%) 2.
The lemon sign, noted on antenatal imaging, is one of the many notable fruit-inspired signs. It is a feature when there appears to be an indentation of the frontal bone (depicting that of a lemon). It is classically seen as a sign of a Chiari II malformation and also seen in the majority (90-98%...
Bladder flap haematoma is a haematoma between the uterus and posterior wall of bladder. They may be small (more commonly) or large (>5 cm, less common).
Small haematomas may be asymptomatic. Large ones may present with lower abdominal pain, dysuria, anaemia and fever (if ...
Induced fetal demise as the name suggests, refers to an iatrogenically-induced fetal demise, most often by injection of a pharmacologic agent.
selective or non-selective reduction of one of the fetuses in a multifetal pregnancy
fetal demise is often induced before medical or surgi...
Fetal ascites refers to the accumulation of free fluid in the fetal abdomen. It is often considered under the same spectrum of hydrops fetalis.
any condition that results in hydrops fetalis
additional causes include
bowel perforation (e.g. meconium peritoniti...
Skeletal dysplasia (also known as osteochondrodysplasia) refers to any abnormality in bone formation. There is a very wide clinicopathological spectrum and any part of the skeleton can be affected.
The overall prevalence is estimated at ~2 per 10,000 live births 3.
Antenatal choroid plexus cysts are benign and are often transient typically resulting in utero from an infolding of the neuroepithelium.
They should not be confused with adult choroid plexus cysts (which are very commonly found at autopsy and likely degenerative), large intraventricular simpl...
Echogenic fetal bowel is an observation in antenatal ultrasound imaging, in which fetal bowel appears to be brighter than it is supposed to be. It is a soft marker for trisomy 21 and has several other associations. When observed, it needs to be interpreted in the context of other associated abno...
Fetal ovarian cysts refer to an ovarian cyst detected antenatally in a female fetus. They are relatively uncommon and are usually diagnosed in the 3rd trimester 5.
From autopsy studies they are found in up to 30% of fetuses 1.
The exact aetiology is not well known at t...
Heterotopic pregnancy is a rare situation when there is an intra-uterine and extra-uterine (i.e. ectopic) pregnancy occurring simultaneously.
The estimated incidence in the general population is estimated at 1:30,000 (for a naturally conceived pregnancy 7). The incidence among pat...
Choriocarcinoma is an aggressive, highly vascular tumour. When it is associated with gestation, it is often considered part of the spectrum of gestational trophoblastic disease; it is then termed gestational choriocarcinoma. When it occurs in the absence of preceding gestation, it is termed non-...
Obstetric and gynaecological ultrasound is rampant with numerous cut off values. Some of these get revised over the years. The following list is a useful aid to refer to and revise.
rate of increase of a mean sac diameter per day in early pregnancy
generally accepted value for a th...
Autosomal recessive polycystic kidney disease (ARPKD) is one of many paediatric 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 hyp...
The Spalding sign refers to the overlapping of the fetal skull bones caused by collapse of the fetal brain. It appears usually a week or more after fetal death in utero.
This finding was originally described by Alfred Baker Spalding (1874-1942), an American obstetrician 2, on abdominal radiogr...
IUCD (Intrauterine contraceptive device) related uterine perforations are one of the causes of uterine perforation. It is rare, but a serious complication of an IUCD insertion, and is often clinically silent.
The incidence rate is reported at ~2 in 1000 2.
Gestational trophoblastic disease (GTD) results from the abnormal proliferation of trophoblastic tissue and encompasses a wide spectrum of diseases, including:
invasive mole ~10%
choriocarcinoma (gestational choriocarcinoma) ~1%
placental site t...
Coexistent molar pregnancy refers to an extremely rare situation where there is a molar pregnancy occurring simultaneously with normal intra-uterine pregnancy.
The estimated incidence is at ~1:10,000-100,000 gestations (for a complete hydatidiform mole and a normal pregnancy) 2.
Conjoined twin pregnancy are rare occurrence resulting from failure of a zygote to separate completely after 13 weeks. This results in the twins being physically joined.
The prevalence of conjoined twins ranges from 1:50,000 to 1:200,000. They are more common in parts of Southeast...
Fanconi anaemia is a rare disorder characterised by progressive bone marrow failure, various congenital abnormalities, and predisposition to malignancies (often acute myeloid leukaemia). It is considered the commonest type of inherited marrow failure syndrome 7.
Fanconi anaemia sh...
Scar endometriosis is a term given to endometriosis occurring in a Caesarian section scar. It can be located in the skin, subcutaneous tissue, rectus muscle/sheath, intraperitoneally, or in the uterine myometrium (within uterine scar).
The reported incidence of abdominal scar endo...
Uteroplacental blood flow assessment is an important part of fetal well-being assessment and evaluates Doppler flow in the uterine arteries and rarely the ovarian arteries.
In a non-gravid state and at the very start of pregnancy the flow in the uterine artery is of high pulsatility ...
Hydrops fetalis is excessive extravasation of fluid into the third space in a fetus which could be due to heart failure, volume overload, decreased oncotic pressure, or increased vascular permeability. Hydrops is defined as the accumulation of fluid +/- oedema involving at least two fetal compon...
Nuchal translucency is the normal fluid-filled subcutaneous space identified at the back of the fetal neck during the late first trimester and early second trimester (11.3-13.6 weeks).
It should not be confused with the nuchal fold, which is seen in the second trimester.
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...
Uterine bleeding during pregnancy is a common clinical presentation that often necessitates obstetric ultrasound for the assessment of the haemorrhage, and of fetal well being.
The potential causes vary with the stage of gestation.
Bleeding in the first trimester
Haemorrhagic corpus luteal cysts result from bleeding into corpus luteal cysts.
Commonly described findings include:
complex adnexal mass
adnexal thick-walled cystic lesion with lace-like strands
adnexal thick-walled cystic lesion with low-level echoes with...
Dandy-Walker variant (DWv) is a less severe posterior fossa anomaly than the classic Dandy-Walker malformation (DWM) and is considered being on the lesser end of the disease spectrum in the Dandy-Walker continuum.
This term was created to include those malformations that do not mee...
Clinodactyly is a descriptive term that refers to a radial angulation at an interphalangeal joint in the radio-ulnar or palmar planes. It typically affects the 5th finger.
The estimated incidence is highly variable dependent on sampling and has been reported to range between 1-18...
Angular pregnancies are those in which implantation occurs eccentrically along the fundus of the endometrial cavity, along 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 intraute...
Radial ray anomalies comprise of a large spectrum of upper limb anomalies which range from partial (radial hypoplasia) to a complete (radial aplasia) deficiency of the radius with or without accompanying deficiency of the thumb bones.
They can be associated with a numbe...
The vagina is a midline fibromuscular tubular organ positioned in the female perineum extending superiorly from the vulva, to the cervix and uterus in the pelvis.
The vagina is 8-10 cm in length, extending posterosuperior from the vestibule through the urogenital diaphragm to th...
Pulmonary sequestration, also called accessory lung, refers to the aberrant formation of segmental lung tissue that has no connection with the bronchial tree or pulmonary arteries. It is a bronchopulmonary foregut malformation (BPFM).
There are two types:
intralobar sequestration (ILS)
Encephalocele, also known as meningoencephalocele, is a form of neural tube defect and a type of cephalocele where brain tissue and overlying meninges herniate out through a defect in the cranium.
It should be distinguished from cranial meningocele in which the lesion contains onl...
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...
Ethmocephaly refers to a rare type of midline cranio-facial anomaly that is characterised by the presence of extreme hypotelorism, arhinia and a midline proboscis.
holoprosencephaly 1,2: particularly alobar holoprosencephaly
A rocker bottom foot (also known as a congenital vertical talus) is a congenital anomaly of the foot. It is characterised by a prominent calcaneus/heel and a convex rounded sole.
It results from a dorsal and lateral dislocation of the talonavicular joint.
The traumatic abruptio placenta scale (TAPS) was devised to stratify placental injury findings on CT. Since placental abruption is a concern in a pregnant patient who has undergone traumatic injury, CT is occasionally the first imaging modality used to evaluate the placenta.
0: normal homogeneo...
Facial clefts comprise of a wide spectrum of pathologies that result from failure of fusion in the facial region during the embryonic/early fetal period. The result is a gap in the fetal face. These clefts can affect the lip, philtrum, alveolus, and hard and soft palate to varying degrees.
Cleft lip and palate is one of the commonest of neonatal facial anomalies. In ~80% of cases, the two features tend to occur together 6.
It is estimated to occur with an incidence of ~1 in 700-to-1000 live births 1. This can increase to 4% for a sibling of a previously affected fet...
Isolated inferior vermian hypoplasia (IIVH), also referred as part of Dandy-Walker variant (DWV), is a congenital malformation characterised by partial absence of the inferior portion of the cerebellar vermis.
The term Dandy-Walker variant was created to include those malformations...
A normal fetal heart rate (FHR) usually ranges from 120 to 160 beats per minute (bpm) in the in utero period. It is measurable sonographically from around 6 weeks and the normal range varies during gestation, increasing to around 170 bpm at 10 weeks and decreasing from then to around 130 bpm at ...
Marginal cord insertion is a type of abnormal cord insertion.
The estimated incidence is at ~7% 1 of singleton pregnancies but ~25% of twin pregnancies. Hence, it is very important to locate the umbilical cord in all patients, particularly in high-risk pregnancy.
Arthrogryposis (multiplex congenita) is a clinical or imaging descriptor that denotes congenital non-progressive joint contractures involving two or more body regions.
It is thought to occur in approximately 1:3000-10,000 live births 6,8.
It can result from a number o...
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...
Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorised based on whether or not they are related to pregnancy. Aetiologies may also be classified based on whether the patient is premenopausal or postmenopausal.
Haematometrocolpos refers to a blood-filled distended uterus and vagina usually due to an anatomical mechanical obstruction precluding the evacuation of the menstrual blood.
The estimated incidence in teenagers is at ~1 in 1000-2000 5.
imperforate hymen: in ~2...
Uterine artery pseudoaneurysm (UAP) is a rare cause of secondary postpartum haemorrhage.
UAP usually presents as delayed (secondary) postpartum haemorrhage, that is per vaginal bleeding which occurs more than 24 hours and up to 6 weeks postpartum. However, some reported ...
Endometrial thickness is a commonly measured parameter on routine gynaecological ultrasound and MRI. The appearance, as well as the thickness of the endometrium, will depend on whether the patient is of reproductive age or postmenopausal and, if of reproductive age, at what point in the menstrua...
A congenital (primary) megaureter encompasses causes of an enlarged ureter which are intrinsic to the ureter, rather than as a result of a more distal abnormality; e.g. bladder, urethra (see secondary megaureter). It includes:
obstructed primary megaureter
refluxing primary megaureter
The "T sign" is really the absence of a twin-peak sign (or lambda sign) and is used in ultrasound assessment of a multifetal pregnancy.
It refers to the lack of chorion extending between the layers of the intertwin membrane, denoting a monochorionic pregnancy. The intertwin membrane comes to an...
Fetal heart beat can be detected as early as 34 days (just under 6 weeks) gestation on good quality, high frequency transvaginal ultrasound, as a crown rump length (CRL) of as little as 1-2 mm.
If a fetal heartbeat cannot be identified with a CRL ≥7 mm using transvaginal scanning, then embryona...
Cornelia de Lange syndrome (CdLS) is an extremely rare clinically heterogenous developmental disorder of unknown aetiology.
The estimated incidence is at ~1:10,000-160,000 births ref. There is no recognised racial or gender predilection 8.
The syndrome carries ...
Retained products of conception (RPOC) refer to the persistence of placental and/or fetal tissue in the uterus following delivery, termination of pregnancy or a miscarriage.
Retained products of conception complicate ~1-5% of all pregnancies (routine vaginal deliveries 12).
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 ...
Exencephaly is a lethal congenital fetal brain developmental anomaly (neural tube defect) considered to be a precursor to anencephaly in the acrania-exencephaly-anencephaly sequence.
It is characterised by calvarial absence and loss of fetal brain tissue to variable degrees and is co...
HELLP syndrome is a pregnancy-related condition and is an abbreviation for:
elevated liver enzymes and
It is considered a severe and life-threatening form of pre-eclampsia although it can occur without co-existing pre-eclampsia.
The estimated inciden...
Trauma is a leading cause of mortality in pregnancy. Pregnancy increases the incidence and severity of abdominal trauma in females.
Trauma affects up to 7% of pregnancies, and the incidence of pregnancy in level 1 trauma patients is estimated to be ~2% 1.
The broad ligament is the lateral folds of the parietal peritoneum which reflect over the upper genital tract.
The broad ligament extends from the lateral aspect of the uterus to the lateral pelvic wall and can be divided into three main components - the mesosalpinx, mesovarium a...
Eclampsia is a condition involving seizures and hypertension in pregnancy. It is thought to result from hypertensive encephalopathy 1.
MR imaging has shown that cytotoxic oedema and posterior reversible encephalopathy syndrome are common in eclampsia. The severity of...
An oesophageal atresia refers to an absence in the contiguity of the oesophagus due to an inappropriate division of the primitive foregut into the trachea and oesophagus. This is the most common congenital anomaly of the oesophagus.
It is thought to occur in ~1:3000-4500 live bir...
Ectopia cordis is an extremely rare congenital malformation where the heart is located partially or totally outside the thoracic cavity. The four main ectopic positions are:
adjacent to the thorax: ~60%
The estimated pre...
Hemivertebra is a type of vertebral anomaly and results from a lack of formation of one half of a vertebral body. It is a common cause of congenital scoliosis.
The estimated incidence is at ~0.3 per 1000 live births 2.
It falls under the spectrum of segmentation anoma...
Echogenic intracardiac focus (EIF) is a relatively common sonographic observation that may be present on an antenatal ultrasound scan.
They are thought to be present in ~4-5% of karyotypically normal fetuses. They may be more common in the Asian population 5.
Sacrococcygeal teratoma (SCT) refers to a teratoma arising in the sacrococcygeal region. The coccyx is almost always involved 6.
It is the commonest congenital tumour in the fetus 11 and neonate 3. The incidence is estimated at ~1:35000-40000. There is recognised female predilecti...
11-13 week antenatal 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 dependant on the operator. Traditionally three factors are used to calculate the ...
A fetal interhemispheric cyst refers to an interhemispheric cyst diagnosed in utero. It is seen as a cystic collection located in the interhemispheric fissure, with or without communication with the ventricular system.
agenesis of the corpus callosum: strong association...
Chiari II malformation, also known as Arnold-Chiari malformation, is a relatively common congenital malformation of the spine and posterior fossa characterised by myelomeningocoele (lumbosacral spina bifida aperta) and a small posterior fossa with a descent of the brainstem and cerebellar tonsil...
Schizencephaly is a rare cortical malformation that manifests as a grey matter lined cleft extending from the ependyma to the pia mater.
Some authors do not use the term schizencephaly, preferring to group these disorders under the blanket term of porencephaly. For the purpose of t...
Ian Donald (1910-1987) was a Scottish obstetrician who pioneered the diagnostic use of ultrasound in medicine.
Ian Donald was born in Lisgeard, Cornwall, United Kingdom on 27th December 1910 6. His father was a general practitioner. In 1925 his family moved to South Africa where he ...
Omphalocoeles, or exomphalos, are congenital midline abdominal wall defects at the base of the umbilical cord insertion with herniation of gut (or occasionally other content) out of the fetal abdomen.
The estimated occurrence can be up to 1:4000 of live births 3.
The expanded amnion sign has been described as a poor prognostic sign in early pregnancy, suspicious though not diagnostic of failed early pregnancy. Any visible embryo that is surrounded by an amnion (visible on transvaginal ultrasound) should also have a heartbeat, regardless of crown-rump len...
Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder which has many features similar to Marfan syndrome.
The disease is characterised by skeletal manifestations and vasculopathies. Although Loeys-Dietz syndrome shares many similarities with Marfan syndrome, the course ...
NB - Please consult original article(s) and discuss with you local radiology department/radiation physicist before making any clinical decision.
Although exposure to the gravid uterus is to be avoided when ever possible, and only deliberately performed after careful weighing up of the pros and ...
Lithopaedions, also referred as stone babies, are a rare phenomenon which occurs most commonly when a fetus dies during an ectopic pregnancy.
The estimated incidence is at ~ 1.5 to 1.8% of abdominal ectopic pregnancies 4.
If the deceased fetus is too large to be re-abs...
Pre-eclampsia is a disorder of pregnancy involving new-onset hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg) and involvement of one or more other organ systems.
Pre-eclampsia affects up to 8% of pregnancies 1.
diabetes mellitus 2
chronic hypertension ...
Placental abruption refers to a premature separation of the normally implanted placenta after the 20th week of gestation and before the 3rd stage of labour. It is a potentially fatal complication of pregnancy and is a significant cause of third-trimester bleeding / antepartum haemorrhage.
A complete miscarriage is defined as a cessation of vaginal bleeding with no evidence of retained products of conception or a gestation sac in a woman who previously had an ultrasound confirmed intrauterine pregnancy.
Shows an empty uterus with no fetal compon...