Mesomelia refers to a shortening of the middle (intermediate) portion of a limb.
mesomelia-synostoses syndrome (MSS) or mesomelic dysplasia with acral synostoses1
Ellis van-Creveld syndrome 2
Metatropic dysplasia refers to a rare subgroup of the skeletal dysplasias. It is part of the wider category of rhizomelic dwarfism. Disorders in this group include:
lethal metatropic dysplasia (type 2) or hyperchondrogenesis
lethal hyperplastic metatropic dysplasia (type 1...
Microcephaly (plural: microcephalies) is a descriptive term meaning a small head and is associated with numerous disorders of diverse etiology. It is usually associated with microencephaly (plural: microencephalies) (small brain). For the purpose of this article, the two will be used interchang...
Microgenia is a term meaning a small chin. It is somewhat related to but distinct from the term micrognathia which means a small mandible.
Microgenia can be isolated or be associated with a number of anomalies which include
campomelic dysplasia 1
The term micrognathia describes a small mandible.
A small mandible occurs secondary to abnormalities of the first branchial arch which in turn are caused by deficient or insufficient migration of neural crest cells and usually occur around the 4th week of gestation.
Microphthalmia essentially means small eyes. It is characterized by a small eye within a small orbit. It can be unilateral or bilateral. It is sometimes defined as a globe with a total axial length (TAL) that is at least two standard deviations below the mean for age.
Midfacial hypoplasia is a type of congenital facial anomaly and can be feature of a number of congenital syndromic anomalies. These include:
chromosome 1p36 deletion syndrome 2
chromosome 18q deletion syndrome
fetal alcohol syndrome
fetal valproate s...
Miller-Dieker syndrome (MDS) or is a rare chromosomal anomaly and is one of the conditions considered part of lissencephaly type I (classic) 6. It is the form of lissencephaly that is most recognizable on prenatal imaging due to its severity 5.
Mirror syndrome or triple edema or Ballantyne syndrome is a rare disorder affecting pregnant women. It refers to the unusual association of fetal and placental hydrops with maternal pre-eclampsia and edema.
History and etymology
It was first described in 1892 by John William Ballantyne.
A miscarriage is the spontaneous termination of a pregnancy before 20 weeks gestation. Fetal death after week 20 is termed fetal death in utero (FDIU).
The term miscarriage is preferred by many over 'abortion' due to the use of the latter for therapeutic pregnancy termination, and ...
A missed miscarriage, sometimes termed a missed abortion 3, is a situation when there is a non-viable fetus within the uterus, without symptoms of a miscarriage.
Ultrasound diagnosis of miscarriage should only be considered when either a mean gestation sac d...
Mixed gonadal dysgenesis (MGD) is a type of gonadal dysgenesis characterized by gonadal asymmetry, and/or sex chromosomal mosaicism, as well as retained Müllerian ducts.
Depending on the chromosomal composition, patients may have testes and/or streak gonads.
A monochorionic diamniotic (MCDA) twin pregnancy is a subtype of monozygotic twin pregnancy. These fetuses share a single chorionic sac but have two amniotic sacs and two yolk sacs.
It accounts for the vast majority (70-75%) of monozygotic twin pregnancies although only ~30% of a...
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...
A monochorionic twin pregnancy is a type of monozygotic twin pregnancy where the twins share a single chorion. Depending on the sharing of the amnion this can be divided into two types.
monochorionic monoamniotic (MCMA) pregnancy: single amnion
monochorionic diamniotic (MCDA) pregnancy: two am...
A mono nostril falls under the midline facial defects which arise from cleavage anomalies. It can occur as part of many underlying conditions such as
holoprosencephaly: particularly alobar holoprosencephaly
Several other facial anomalies can be associated ...
A monozygotic (MZ) twin pregnancy results from the division of single zygote following fertilisation and shares similar genetic materials. These twins are therefore always of the same gender.
MZ twins account for approximately 30% of all twin pregnancies 1. The estimated incidence...
Müllerian duct anomalies (MDAs) are congenital abnormalities that occur when the Müllerian ducts (paramesonephric ducts) do not develop correctly. This may be as a result of complete agenesis, defective vertical or lateral fusion, or resorption failure.
MDAs are estimated to occur...
Multiple placental cystic spaces can be seen in many conditions:
within the placenta
true placental cysts
allantoic ducts cysts
hydropic degeneration of placenta
placental mesenchymal dysplasia
adjacent the placenta
The multiple pterygium syndrome(s) (MPS) refers to a group of disorders which are collectively characterized by multiple soft tissue webs (or pterygia) across the neck and various joints.
They can be broadly classified into two main groups
lethal multiple pterygium syndrome
non lethal multipl...
MURCS association refers to the combination of:
MU: Müllerian duct aplasia
R: renal aplasia /renal agenesis
CS: cervicothoracic somite dysplasia
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...
The Naegele's formula is simple arithmetic method for calculating the EDD (estimated date of delivery) based on the LMP (last menstrual period).
To the date of the first day of the LMP (e.g. 22nd June 2008):
add seven days (i.e 29th)
subtract 3 months (i.e March)
add one year (i.e 2009)
The Nager syndrome (also known as acrofacial dysostosis) is a rare congenital syndrome primarily characterized by facial and skeletal features
Recognized features include:
lower lid ptosis
A narrow fetal thorax on antenatal ultrasound can be present with a number of anomalies which include:
Jeune syndrome - asphyxiating thoracic dysplasia
short rib polydactyly syndro...
Neu-Laxova syndrome is a lethal autosomal recessive multiple malformation syndrome with a heterogeneous phenotype.
The clinical spectrum can be quite wide and includes:
dermal / cutaneous
severe skin restriction
decreased fetal movement
Neural tube defect (NTD) refers to the incomplete closure of the neural tube in very early pregnancy, resulting in cranial defects or spinal dysraphism.
The neural tube comprises of a bundle of nerve sheath which closes to form brain caudally and spinal cord rostrally. The closure should occur ...
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 gestational choriocarcinoma, this is a much rarer situation.
In women, they often tend to occur in the ovary. Most ovarian non-gestational choriocarcinomas occur in mix...
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-visualization of the fetal gallbladder is often a transient finding and in most cases, the gallbladder can be eventually detected. However non-visualization can be rarely associated with certain pathological conditions.
agenesis of the gallbladder
Noonan syndrome (NS) is a genetically and phenotypically heterogeneous 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 10. As individuals have normal numbe...
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 summarize 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 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 Gynecology imaging for students curriculum represents a core set of common pathologies seen on the wards, in theater and in the emergency O&G patient.
Fundamental to most imaging of the O&G patient is an und...
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 occurrence 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.
Esophageal atresia refers to an absence in the continuity of the esophagus due to an inappropriate division of the primitive foregut into the trachea and esophagus. This is the most common congenital anomaly of the esophagus.
It is thought to occur in ~1:3,000-4,500 live births 3...
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...
Omphaloceles, 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 ...
Oral-facial-digital syndromes (OFDS) are a group of rare genetic developmental disorder that affects the mouth, face, digits and also may cause some problems on the central nervous, kidney and the other organs.
Some publications have classified at least 13 forms of OFDS based on...
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 (between L2 and L3).
Descends caudally ...
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, endometriosis, in vitro fertilisation-embryo transfer 3, and previous adnexal surgery 4. Pa...
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 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 throm...
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 extremely rare chromosomal anomaly.
It may be more prevalent in births from women of advanced age 4.
Phenotypic expression can significantly vary from multiple anomalies resulting in perinatal death to the more charact...
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.
Patau syndrome along with Down syndrome (trisomy 21) and Edward syndrome (trisomy 18) 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 hemorrhage refers to hemorrhage that occurs around the fetus during the gestational period. The spectrum of hemorrhage includes:
chorionic hemorrhage: caused by the separation of the chorion from the endometrium
subchorionic hemorrhage: most common type, occurs between the cho...
Getting a film with perigestational hemorrhage in the exam is one of the many exam set-pieces that can be prepared for.
Transabdominal and transvaginal (TV) pelvic ultrasound shows an anteverted uterus with an intrauterine gestational sac. MSD is 20 mm in TV study with a single, l...
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 periurethral 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
male genitourinary trac...
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 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 beyond...
Placenta fenestrata is one of the variations in placental morphology, which is characterized 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 (or abruptio placentae) refers to a premature separation of the normally implanted placenta after the 20th week of gestation and before the 3rd stage of labor. It is a potentially fatal complication of pregnancy and is a significant cause of third-trimester bleeding/antepartu...
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 “aging” of the placenta. It commonly increases with gestational age.
Delayed placental calcification
Accelerated placental calcification
normal placental maturity
maternal thrombotic disorder...
Placental chorioangiomas are benign vascular tumors of placental origin. It is the most common tumor of the placenta and is usually found incidentally.
The estimated incidence is at ~1% of all pregnancies 3.
In most cases, chorioangiomas are asymptomatic, a...
Placental chorioangiomatosis is an extremely rare condition where numerous placental chorioangiomas involve the placenta. The individual chorioangiomas can be of varying size.
Recognized complications include
precipitation of fetal hydrops 2
fetal cerebral embol...
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 can be categorized by location:
within the placental tissue (placental septal cysts)
under the fetal ...
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.
In a DCDA pregnancy, there are no vascular anastomoses between the twin placentae...
Placental grading (Grannum classification) refers to an 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 advers...
Placental infarction refers to a localized area of ischemic 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 bloo...
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 characterized by enlargement of the placenta with multiple bunches of grape-like vesicles that can resemble a molar pregnancy by ultrasound and gross pathologic examination.
This is an often underdiagnosed ...
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 mosaicism. When the fetal cells are normal in chromosomal composition, this is then known as con...
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 tumor (PSTT) is rare and one of the least common (~ 0.2% 7) forms of the 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 ...
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 tumor.
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 consistent w...
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 a 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...
There are many tumors that can involve the placenta.
These can be of very different pathology and can include
placental chorioangioma (considered the most common primary tumor of the placenta 1)
placental site trophobla...
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...