Neural tube defect (NTD) refers to the incomplete closure of the neural tube in very early pregnancy.
The neural tube comprises of a bundle of nerve sheath which closes to form brain at the anterior end and spinal cord at the posterior end. The closure should occur at around the 28th day of co...
The neurenteric canal or canal of Kovalevsky is the transient communication of the amnion through notochordal canal to the yolk sac during notochordal formation at day 16-17.
Abnormalities during this stage produce the neurenteric cyst spectrum.
The Noack syndrome is a type of acrocephalopolysyndactyly. It is now considered a variant of the Pfeiffer syndrome 2.
Non-gestational choriocarcinoma is choriocarcinoma occurring in the absence of a preceding gestation. As opposed to a gestational choriocarcinoma, this is a much rarer situation.
In women they often tend to occur in ovary. Most ovarian non-gestational choriocarcinomas occur in mixed...
Non-invasive perinatal testing (NIPT) is an antenatal screening technique which has relatively recently come into practice. It relies on the detection of small amounts of cell free fetal DNA to be detected in the maternal bloodstream, hence allowing prenatal genetic diagnosis to occur by way of...
Non visualisation of the fetal gallbladder is often a transient finding and in most bases can be eventually detected. However it can be rarely associated with certain pathological conditions.
agenesis of the gallbladder
Noonan syndrome (NS) is a genetically and phenotypically heterogenous non aneuploidic congenital RASopathy. Affected individuals can bear some clinical features similar to that of Turner syndrome.
The estimated incidence is at ~1 in 1000-2500 11. As individuals have normal number...
Noonan syndrome with multiple lentigines, previously known as LEOPARD syndrome (LS), is a rare autosomal dominant RASopathy that has many similarities to Noonan syndrome.
Despite a change in formal name, the 'LEOPARD' acronym is still useful to summarise the clinical feat...
Nuchal cord is a term given to the situation where there are one or more loops of umbilical cord wrapped around the fetal neck for ≥360°.
The prevalence is dependent on the extent of coiling and range from ~25% for a single loop to 2.5% for a double loop to ~0.5% for more than two...
The nuchal fold is a normal fold of skin seen at the back of the fetal neck during the second trimester of pregnancy. Increased thickness of the nuchal fold is a soft marker associated with multiple fetal anomalies, and is measured on a routine second trimester ultrasound.
Nuchal translucency is the normal fluid filled subcutaneous space identified at the back of the fetal neck during in 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.
The obstetric curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core obstetric knowledge.
Topics pertaining to the normal and abnormal pregnancy, the gravid uterus and fetal environment, placenta, normal fetal development and fet...
This is a basic article for medical students and other non-radiologists
Obstetrics and Gynaecology imaging for students curriculum represents a core set of common pathologies seen on the wards, in theatre and in the emergency O&G patient.
Fundamental to most imaging of the O&G patient is an un...
Obstructive cystic renal dysplasia, or Potter type IV cystic renal disease, is a potential complication that can occur from prolonged obstruction of the bladder outlet or urethra during gestation.
Ureteric obstruction during active nephrogenesis results in cystic renal dysplasia; th...
The OEIS complex refers to the combined occurence of:
bladder exstrophy / cloacal exstrophy
an imperforate anus
and spinal anomalies: e.g
The estimated occurrence is at around 1-200,000 to 400,000 live births 1,8.
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...
Oligohydramnios refers to a situation where the amniotic fluid volume is less than expected for gestational age. Often these fetuses have <500 mL of amniotic fluid.
The estimated prevalence can be up to ~6% of pregnancies 4.
The causes of oligohydramnios are pr...
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.
An omphalomesenteric duct cyst is a type of true umbilical cord cyst.
The omphalomesenteric duct serves as a communication between the midgut and yolk sac In early embryonic life and usually obliterates between the 9-18th week of gestation. The omphalomesenteric duct cyst is an embry...
Omphalopagus twins are joined at the front and at the level of the umbilicus.
Commonly involved structures are lower thorax fusion and liver fusion. Pericardium may be common, but the heart is never shared. Stomach and the proximal small intestines are usually separate but the small intestines ...
Oro-facial-digital syndromes (OFDS) are a generic name for a variety of genetically heterogeneous disorders that result in malformations of the mouth, teeth, jaw, facial bones, hands, and feet.
There are several (at least 13 2 ) recognised subtypes which include:
OFDS type I: G...
The ovarian artery is a paired structure and is the main gonadal artery in females.
The ovarian artery arises anterolaterally from the aorta just inferior to the renal arteries and superior to the inferior mesenteric artery.
Descends caudally in the retroperitone...
Ovarian ectopic pregnancies are rare (1-3%) when compared to other types of ectopic pregnancy such as tubal ectopic.
Risk factors include pelvic inflammatory disease, IUCD use and endometriosis. Pathogenesis is debated and lies between:
fertilisation of the ovum in th...
Ovarian hyperstimulation syndrome (OHSS) is a complication of ovarian stimulation treatment (ovarian induction therapy) for in vitro fertilisation. Rarely, it may also occur as a spontaneous event in pregnancy (see spontaneous ovarian hyperstimulation later in the article).
The clinical syndrom...
Ovarian vein thrombosis (actually most often a thrombophlebitis) occurs most commonly in postpartum patients and can result in pulmonary emboli. A presentation is usually with acute pelvic pain in the postpartum period, then termed puerperal ovarian vein thrombosis or postpartum ovarian vein th...
Overlapping fetal fingers is an antenatal ultrasound observation where the fetal fingers are seen to overlap each other. It may be seen seen with a concurrent clenched fetal hand. If the hand is clenched typically the 2nd finger is seen to overlap the 3rd 4.
a well re...
Pallister-Killian syndrome (PKS) is an extremly rare chromosomal anomaly.
It may be more prevalent in woman of advanced age 4.
It is a polymalformative complex with tetrasomy of isochromosome 12p although many cases are mosaic.
The majority of cases are th...
Parapagus twins are conjoined twins that lie side-by-side with ventrolateral fusion.
This type of conjoined twins usually shares the umbilicus, abdomen, and pelvis. The conjoined pelvis may have a single symphysis pubis and one or two sacra.
The lower gastrointestinal tract (single colon and...
Partial hydatidiform mole is a type of hydatidiform mole, which in turn falls under the spectrum of gestational trophoblastic disease.
Clinical signs and symptoms such as abdominal pain, cramps of the lower abdomen and vaginal bleeding during pregnancy are common but non...
Parturition-induced pelvic instability is a rare condition seen in women following vaginal delivery.
The incidence of symphyseal rupture after vaginal delivery ranges from one in 600 to one in 30,000 deliveries 1.
Predisposing factors include multiparity, complicated delivery, ...
Patau syndrome (also known as trisomy 13) is considered the 3rd commonest autosomal trisomy.
This along with Down syndrome (T21) and Edward syndrome (T18) are the only three trisomies to be compatible with extrauterine life. However, few infants live more than a few days.
The Pena-Shokeir syndrome (PSS) is an autosomal recessive nonaneuploidic condition with some clinical features being similar to that of trisomy 18. The condition is most often lethal.
The estimated incidence is at ~1 in 12,000 births.
Features include 2,4:
The pentalogy of Cantrell is an extremely rare phenomenon with an incidence estimated at around 6 per million live births 3.
It encompasses the following 5 main features 1.
ectopia cordis (abnormal location of heart)
pericardial defect or sternal cleft
Perigestational haemorrhage refers to haemorrhage that occurs around the fetus during the gestational period. The spectrum of haemorrhage includes:
chorionic haemorrhage: caused by the separation of the chorion from the endometrium
subchorionic haemorrhage: most common type, occurs between th...
Getting a film with perigestational haemorrhage in the exam is one of the many exam set-pieces that can be prepared for.
Transabdominal and transvaginal pelvic ultrasound show an anteverted uterus with an intrauterine gestational sac. MSD is 20 mm in TV study with a single, live e...
Perinatal lethal hypophosphatasia (PLH) is the most severe form of hypophosphatasia. If untreated, it is lethal in all cases.
The estimated incidence is at ~1:100,000 live births.
As with all hypophosphatasia cases, this is due to a mutation in chromosome 1q3...
There are several peri-urethral cystic lesions. These include:
female genitourinary tract:
Gartner duct cyst
epidermal inclusion cyst of the vagina
Skene duct cyst
Bartholin gland cyst
endometrial cyst of perineal - vulval - vaginal region
A persistent right umbilical vein (PRUV) is an uncommon vascular anomaly which is often detected in utero.
The estimated prevalence is ~2 per 1000 births 1,2.
In the normal situation, the right umbilical vein begins to obliterate in the ~4th week of gestation and disap...
Phocomelia is an extremely rare congenital skeletal disorder that characteristically affects the limbs. It can affect either the upper limbs or lower limbs or both. Phocomelia is also a descriptive term to describe the characteristic limb anomalies occurring with its associated conditions.
Physiological gut herniation is a natural phenomenon that occurs in early pregnancy. It usually occurs from around 6-8 weeks up until 12-13 weeks in-utero, after which the bowel returns to the abdominal cavity.
It occurs as a result of the bowel (particularly ileum) growing faster ...
The placenta is a fetal organ of pregnancy, responsible for providing nutrition and oxygen to the fetus as well as excretory functions.
Placenta is formed by fetal and maternal components 2:
maternal component: decidua placentalis is the inner portion of the placenta, which is for...
Placenta accreta (PA) is both the general term applied to abnormal placental adherence and also the condition seen at the milder end of the spectrum of abnormal placental adherence. This article focuses on the second, more specific definition.
In a placenta accreta, the placental villi extend b...
Placenta fenestrata is one of the variations in placental morphology, which is characterised by one or more areas of focal placental atrophy lacking villi and covered only by the chorion membrane.
Placenta increta is an intermediate level in the spectrum of abnormal placental villous implantation and accounts for ~20% of such cases. The placental villi extend beyond the confines of the endometrium and invade the myometrium.
The estimated incidence is increasing (likely rel...
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.
Getting a film with placental abruption (premature separation of placenta from uterus) in the exam is one of the many exam set-pieces that can be prepared for.
Transabdominal and transvaginal pelvic ultrasound show a single live fetus with gestational age of 27 weeks. The cervix i...
Placental calcification has been considered a manifestation of “ageing” of the placenta. It commonly increases with gestational age.
Delayed placental calcification
Accelerated placental calcification
normal placental maturity
maternal thrombotic disorde...
Placental chorioangiomas are benign vascular tumours of placental origin. It is the most common tumour of the placenta and is usually found incidentally.
The estimated incidence is at ~1% of all pregnancies 3.
In most cases, chorioangiomas are asymptomatic,...
Placental chorioangiomatosis is an extremely rare condition where numerous placental chorioangiomas involve the placenta. The individual chorioangiomas can be of varying size.
Recognised complications include
precipitation of fetal hydrops 2
fetal cerebral embo...
Placental cyst refers to a simple cystic lesion that develops in relation to the placenta.
Their estimated prevalence is at 2-20% of all pregnancies.
They may be divided into two types dependant on location:
within the placental tissue (placental septal cyst...
Placental evaluation with MRI is a problem-solving technique that can be used if ultrasound evaluation is insufficient or confusing. Even if the placenta is not the main point of evaluation, it is useful to understand the appearance of the placenta on obstetric imaging for other causes.
Placental fusion is a phenomenon that can occur in a twin pregnancy. This can occur to varying degrees. Determination of chorionicity on ultrasound can sometimes be difficult if there has been a placental fusion.
Placental grading (Grannum classification) refers to a ultrasound grading system of the placenta based on its maturity. This primarily affects the extent of calcifications. In some countries the use of placental grading has fallen out of obstetric practice due to a weak correlation with adverse ...
Placental infarction refers to a localised area of ischaemic villous necrosis. It is a significant cause of placental insufficiency.
A localized infarction can occurs in up to ~12.5% (range 5-20%) of all gestations.
It usually results from an interrupted maternal blo...
Placental insufficiency is a term given to a situation where the placenta cannot bring enough oxygen and nutrients to the growing fetus.
Fetuses may present with intra-uterine growth restriction (IUGR) (especially asymmetrical IUGR).
It can be primarily caused...
Placental mesenchymal dysplasia (PMD) is a rare, benign condition that is characterised by enlargement of the placenta with multiple bunch of grape-like vesicles that can resemble a molar pregnancy by ultrasound and gross pathologic examination.
This is an often underdiagnosed an...
Placental mosaicism is a situation where there discrepancy between the chromosomal makeup of the cells in the placenta. According to one study fetal mosaicism was found in 50% of cases with placental mosacism. When the fetal cells are normal in chromosomal composition, this is then known as conf...
A placental septal cyst is a placental cyst typically located in the mid-placenta. It forms between the cotyledons of the placenta. The cysts contain gelatinous material and are usually 5-10 mm in diameter. They may be present in 10-20% of placentas from full term uncomplicated pregnancies.
A placental shelf refers to a ridge of placental tissue freely abutting the margin. It may represent part of a circumvallate placenta, although an early second-trimester placental shelf can be a common, benign and transient finding 1.
Placental shelves detected in early second-trimester are tho...
Placental site trophoblastic tumour (PSTT) is a rare and one of the least common (~ 0.2% 7) forms of gestational trophoblastic disease (GTD).
PSTT typically occurs in women of reproductive age with the average age around 30. It may occur after a normal pregnancy, molar pregnancy o...
Placental surface cysts are often related to cystic change in an area of subchorionic fibrin. They can be variable in size.
subchorionic cyst: commonest type 2
amniotic epithelial inclusion cyst
Most placental surface cysts are associated with a normal pregnancy outco...
A placental teratoma is a very rare placental tumour.
A placental teratoma is benign and almost never associated with congenital deformities in the fetus.
May show a heterogeneous mass at the placental margin. Hyperechoic foci consisten...
Placental thickness tends to gradually increase with gestational age in a linear fashion. Sonographically, this can be seen to be approximately 1 mm per week and the thickness of the placenta can be used to approximate gestational age:
approximate gestational age (in weeks) = placental thicknes...
Placental trophotropism refers to a phenomenon where there is dynamic migration of the placenta at its insertion through gestation. The placenta tends to grow in areas of good blood supply and nutrition and atrophies in areas with poor blood supply and poor nutrition. It may play a role in the d...
There are many tumours that can involve the placenta.
These can be of very different pathology and can include
placental chorioangioma (considered the most common primary tumour of the placenta 1)
placental site trophob...
Placental venous lakes refer to a phenomenon of formation of hypoechoic cystic spaces centrally within the placenta. Finding placental lakes during a second trimester ultrasound scan is not associated with any uteroplacental complication or with an adverse pregnancy outcome. They can, however, b...
Placenta membranacea, also known as a placenta diffusa, is an extremely uncommon variation in placental morphology in which the placenta develops as a thin membranous structure occupying the entire periphery of the chorion.
The estimated incidence is ~1:20,000-40,000 pregnancies 1...
Placenta percreta is a term given to the most severe but least common form of the spectrum of abnormal placental villous adherence, where there is a transmural extension of placental tissue across the myometrium with serosal breach. It carries severe maternal as well as fetal risks.
Placenta praevia is a term given to an abnormally low position of the placenta such that it lies close to, or covers the internal cervical os.
It is a potentially life-threatening condition for both mother and infant, which may result in exsanguination. As such, antenatal diagnosis is essentia...
Placentomegaly is a term applied to an abnormally enlarged placenta.
It can be associated with number of maternal and fetal disorders which include:
chronic intrauterine infections
Platyspondyly is a radiographic feature and refers to flattened vertebral bodies throughout the axial skeleton.
Platyspondyly can be feature of many conditions which include:
severe Gaucher disease 1
Polydactyly refers to the situation where there are more than the usual number of digits (five) in a hand or foot. It can be broadly classified as:
pre-axial polydactyly: extra digit(s) towards the 1st digit (radially)
post-axial polydactyly: extra digit(s) towards 5th digit (ulnar)
Polyhydramnios refers to a situation where the amniotic fluid volume is more than expected for gestational age.
It is generally defined as:
amniotic fluid index (AFI) >25 cm
largest fluid pocket depth (maximal vertical pocket (MVP)) greater than 8 cm 6: although some centres particularly in A...
Polysyndactyly refers to the combined presence of polydactyly as well as syndactyly involving either the hands or feet.
Polysyndactyly can be associated with a number of syndromes which includes:
type I: Noack syndrome
type II: Carpenter syndrome (typically...
Post-axial polydactyly refers to polydactyly where the additional digit is on the ulnar margin of the hand, or lateral to the 5th toe.
Post-axial polydactyly is more common than pre-axial polydactyly, with an estimated incidence of 1 in 3000.
Post dates fetus is when there is prolonged gestation when the fetus remains in-utero beyond 2 weeks beyond expected date of delivery (>42 weeks gestation).
The reported frequency is at approximately 3-12% of pregnancies.
Posterior urethral valves (PUVs), also referred as congenital obstructing posterior urethral membranes (COPUM), are the most common congenital obstructive lesion of the urethra and a common cause of obstructive uropathy in infancy.
Posterior urethral valves are congenital and only...
Although described as a separate condition, postpartum angiopathy is a subset of reversible cerebral vasoconstriction syndrome (RCVS). It is also known as postpartum angiitis and puerperal vasospasm. Please refer to the main article for a broad discussion on these reversible cerebral vasoconstri...
Post partum haemorrhage (PPH) refers to uterine bleeding after delivery and remains one of the major worldwide causes of maternal mortality.
A post partum haemorrhage can be board classified as primary or secondary.
Primary post partum haemorrhage
This is the most ...
The Potter sequence is a constellation of findings demonstrated postnatally as a consequence of severe, prolonged oligohydramnios in utero.
It consists of:
pulmonary hypoplasia: often severe and incompatible with life
growth restriction (IUGR)
abnormal facies (Potter f...
Preconception and prenatal diagnostic techniques (prohibition of sex selection) act (PCPNDT) is a statute enacted to stop the female foeticide that has resulted in declining female sex ratio in India.
As per census 2011, adult sex ratio in India is 943 females per 1000 males and child sex ratio...
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 ...
Pregnancy-associated plasma protein-A (PAPP-A) is a protein found in the maternal circulation and is produced by the placenta. The PAPP-A gene has been assigned to human chromosome 9q33.1 and contains 22 exons 5. PAPP-A values tend to rise exponentially during pregnancy and the reference range d...
Pregnancy of uncertain viability (PUV) is a term given to an intrauterine pregnancy in a situation where there are not enough criteria (usually on ultrasound grounds) to confidently categorise an intrauterine pregnancy as either viable or a failed pregnancy.
The term pregnancy of unknown location is assigned when neither an intrauterine pregnancy (IUP) or an ectopic pregnancy is identified on transvaginal ultrasound in the context of a positive pregnancy test.
pelvic pain, vaginal bleeding
positive pregnancy test
Pregnancy-related osteonecrosis , also known as pregnancy-related avascular necrosis, is a common cause of femoral head osteonecrosis. Since the femoral head is deficient in blood supply, it is particularly vulnerable to osteonecrosis.
The pathophysiology is thought to be due to venous stasis a...
Pregnancy with intrauterine contraceptive device (IUCD) is uncommon and IUCD is a highly effective contraception method. Chances of pregnancy to occur is highest during the 1st year of IUCD usage and there are chances of adverse outcomes during pregnancy.
Pregnancy with IUCD may o...
Premature rupture of membranes (PROM) refers to a rupture of the amniotic sac and chorion (membranes) occurring prior to the onset of uterine contractions. When this occurs prior to 37 weeks it is then termed a pre term premature rupture of membranes (PPROM). By this definition, PROM is classifi...
Pre-placental abruption or haemorrhage can be subamniotic or subchorionic in location.
most often painless
Symptoms may be similar to placental abruption in other locations, however, it may not have as poor a prognosis as other placental abruption.
Pre-term labour refers to spontaneous delivery of the fetus prior to 37 weeks of gestation. This is regardless of estimated fetal weight.
shortened cervical length
presence of cervical funneling
dilatation or internal cervical os: cons...
Preterm premature rupture of membranes (PPROM) refers to rupture of membranes prior to 37 weeks of gestation.
It is thought to occur in 0.4-2% of all pregnancies. It however may account for up to one-third of all preterm births (particularly in the United States 5).
A primary fetal hydrothorax (PFHT) is a rare situation and refers to a primary accumulation of fetal pleural fluid without any underlying abnormality. It can present with a wide spectrum of severity and can be uni or bilateral.
The estimated prevalence is at ~ 1:10,000-15,000 preg...
Proboscis is a rare congenital anomaly where an anterior appendage-like structure is seen projecting from the midline fetal face/forehead. Depending on the exact location, this has further been classified into various subtypes (e.g. interorbital proboscis).