In obstetric imaging, the fetal transverse cerebellar diameter (TCD) is often measured as an additional fetal biometric parameter. It is measured as the maximal diameter between the cerebellar hemispheres on an axial scan. The value of the transverse cerebellar diameter in mm's is considered rou...
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...
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 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...
Triple screening refers to a screening blood test that is used to screen pregnant women for possible neural tube defects, Down syndrome and trisomy 18 in the developing fetus. It measures:
An abnormal test result doesn't indic...
Triploidy is a rare lethal chromosomal (aneupliodic) abnormality caused by the presence of an entire extra chromosomal set.
It is considered the 3rd commonest fatal chromosomal anomaly 7. While it is thought to affect as much as 1-2% of conceptions, the vast majority are thought ...
Trisomies are chromosomal anomalies which usually occur due to non-disjunction. The vast majority of affected fetuses being spontaneously aborted, often very early during gestation. Only three are compatible with extra-uterine life (T13, T18, T21), and only one beyond early infancy (T21).
Trisomy 22 is an aneuploidic chromosomal anomaly which is usually fatal unless in mosaic forms.
Duplication of the short arm (p) and a small section of the long arm (q) of chromosome 22 can give result to the cat-eye syndrome - Schmidt-Fraccaro syndrome.
True umbilical cord knots are a rare occurrence and as the name suggests represent a knot formation in the umbilical cord.
They occur in less than 1% of pregnancies.
a long umbilical cord
excessive fetal movements
The "T sign" is really the absence of a twin-peak sign (or lambda (λ) 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 t...
Tubal ectopic pregnancy (or adnexal ectopic pregnancy) is the most common location of an ectopic pregnancy.
It is the most common type of ectopic by far, accounting for 93-97% of cases.
Although the fallopian tube has many anatomical parts, for the purposes of ectopic ...
Tubal ring sign, also referred to as bagel sign or blob sign, one of the ultrasound signs of a tubal ectopic. It comprises of an echogenic ring which surrounds an unruptured ectopic pregnancy. It is said to have a 95% positive predictive value (PPV) for ectopic pregnancy.
Turner syndrome, also known as 45XO or 45X, is the most common of the sex chromosome abnormalities in females.
The incidence is estimated at 1:2000-5000 of live births, although the in utero rate is much higher (1-2% of conceptions) due to a significant proportion of fetuses with...
Twin anaemia polycythaemia sequence (TAPS) is considered a variant of the twin to twin transfusion syndrome (TTTS).
TAPS may occur spontaneously in up to 5% of monochorionic twins and may also develop after incomplete laser treatment in twin-to-twin transfusion syndrome cases 2.
Twin embolisation syndrome (TES) is a rare complication of a monozygotic twin pregnancy following an in utero demise of the co-twin.
It was traditionally thought to result from the passage of thromboplastic material into the circulation of the surviving twin which causes ischaemic st...
Twin growth discordance is a term used in obstetric imaging to describe a significant size or weight difference between the two fetuses of a twin pregnancy. To be classified as a growth discordance, some consider that the estimated fetal weight (EFW) of the smaller twin should fall under the 10t...
A twin growth disparity is a closely related term to twin growth discordance. In a twin growth disparity, there may be a significant size or weight difference between the two fetuses but estimated fetal weight of smaller twin does not fall below the 10th centile. ( In contrast to twin growth dis...
The twin peak sign (also known as the lambda (λ) sign) is a triangular appearance of the chorion insinuating between the layers of the intertwin membrane and strongly suggests a dichorionic twin pregnancy. It is best seen in the first trimester (between 10-14 weeks) 5. While the presence of a tw...
Twin pregnancies are the most common multifetal pregnancies.
Multifetal pregnancies account for ~ 1% of all pregnancies but are seen in much higher numbers in populations where in vitro fertilisation (IVF) is a common practice, most of which are twin pregnancies.
Twin reversed arterial perfusion (TRAP) sequence is considered a severe variant of the twin to twin transfusion syndrome (TTTS). The hallmark of this condition which only happens in monochorionic pregnancies is the lack of placental perfusion of one of the twins (so-called acardiac twin), with a...
Twin to twin transfusion syndrome (TTTS) is a potential complication that can occur in a monochorionic twin (either MCDA or MCMA) pregnancy.
This complication can occur in ~10% (range 15-25%) of monochorionic pregnancies giving an estimated prevalence of ~1:2000 of all pregnancie...
The two diameter pocket (TDP) method is an alternative method of assessing amniotic fluid volumes on ultrasound. However, it is not thought to be good predictor of adverse neonatal outcome 2.
According to this method 1-2:
TDP <15 cm2: indicative of oligohydramnios
An umbilical arterial aneurysm (UAA) is an extremely rare but potentially lethal vascular anomaly which is usually detected in utero.
It tends to favour the placental end of the umbilical artery in the cord.
Concurrently associated anomalies are thought to b...
Umbilical arterial (UA) Doppler assessment is used in surveillance of fetal well-being in the third trimester of pregnancy. Abnormal umbilical artery Doppler is a marker of uteroplacental insufficiency and consequent intrauterine growth restriction (IUGR) or suspected pre-eclampsia.
The umbilical cord is a fetal organ that connects the placenta to the developing fetus and is a vital passage for nutrients, oxygen and waste products to and from the fetus.
The umbilical cord inserts into the centre of the placental bulk and into the fetus at the umbilicus. Variations in inse...
Umbilical cord coiling index is defined as a number of coils per one centimetre of length of the cord. The normal index is one coil for a length of five centimetres. If the number of coils is more per centimetre it is called as a hypercoiled and less than it is called as a hypocoiled umbilical c...
Umbilical cord cysts can refer to any cystic lesion associated with the umbilical cord. They can be single (commoner) or multiple.
They may be seen in ~3% of pregnancies in the first trimester 8.
Umbilical cord cysts can represent either true or false cysts:
Umbilical cord entanglement is a feature which can mean either one or more loops of the cord being encircled around any part of the fetal body 3 or two umbilical cords getting entangled with each other. In the latter situation, it is a classical feature of a monochorionic-monoamniotic twin pregn...
Umbilical cord haematoma describes the formation of a haematoma secondary to bleeding from the umbilical cord.
The haematomas can be either spontaneous or iatrogenic. Spontaneous bleeding is very rare and documented to be around 0.02% of pregnancies. Majority of the cases are iatroge...
Umbilical cord knot is a term given to denote either
true umbilical cord knot: often the term "umbilical cord knot" is used to describe this entity 1
false umbilical cord knot: usually of no clinical significance
umbilical cord entanglement
Umbilical cord prolapse is a situation where the umbilical cord protrudes into the cervical canal.
The estimated incidence is at ~ 0.2-0.5% of all pregnancies 4,5.
Recognised associations include
multifetal pregnancy: twin gestation
Umbilical cord pseudocysts are a type of cystic lesion occurring in relation to the umbilical cord.
Although the true incidence not accurately known, they are comparatively much more common than true umbilical cord cysts.
The pseudocyst basically comprises of mucoid de...
Umbilical cord thrombosis is a potentially fatal complication and can mean either a thrombosis of the umbilical vein or either or both the umbilical arteries. Umbilical vein thrombosis occurs more frequently than thrombosis of one or both umbilical arteries (umbilical arterial thrombosis)
The umbilical vein is the conduit for blood returning from the placenta to the fetus until it involutes soon after birth.
The umbilical vein arises from multiple tributaries within the placenta and enters the umbilical cord, along with the (usually) paired umbilical arteries. Once it enters the...
Umbilical vein varix (UVV) refers to a focal dilatation of the umbilical vein.
UVVs were initially thought to have a high association with other anomalies which include:
chromosomal anomalies: 5-12% with FIUVV 2,3
underlying congenital cardiovascul...
Umbilical venous dilatation is a rare entity and often tends to occur as an isolated finding 4.
Dilatation of the umbilical vein can arise from a number of pathologies:
umbilical venous varix (UVV): particularly if focal
fetal hydrops: a focal dilatation due to an umbilical venous varix with...
Umbilical venous flow in the physiological situation comprises of a monophasic non-pulsatile flow pattern in the umbilical vein with a mean velocity of 10-15 cm/s. The presence of pulsatility implies a pathological state unless in the following situations:
early in pregnancy: up to ~13 weeks ge...
Urethral agenesis (or urethral atresia) refers to a situation where there is a congenital absence of the urethra. It can be a cause of fetal obstructive uropathy.
prune belly syndrome 5
bladder agenesis 2
May show a dilate...
The uterine artery is seen bilaterally and is a branch of the anterior division of the internal iliac artery.
It runs medially in the pelvis, within the base of the broad ligament, to the outer surface of the uterus. From lateral to medial it has a descending, transverse ...
Uterine artery embolisation (UAE) is an interventional radiological technique to occlude the arterial supply to the uterus and is performed for various reasons.
Uterine artery embolisation has been practised for more than 20 years for controlling haemorrhage following delivery / aborti...
Uterine artery embolisation (UAE) is used as an alternative to hysterectomy in selected patients and MRI assessment is key in allowing not only pre-procedure assessment but also assessing post-procedural outcome.
For a general discussion of the underlying condition refer to the article on ute...
Uterine artery flow notching refers to phenomenon observed in uterine arterial Doppler ultrasound assessment.
The presence of notching after 22 weeks is associated with several other conditions including adverse pregnancy outcomes. These include
pregnancy induced hyper...
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 ...
Uterine dehiscence is, usually, used to refer to the process of gradual myometrial rupture without a rupture of membranes. However, the term is used synonymously with uterine rupture by some authors. It is often described in the context of C-section scar where it is also termed an incisional deh...
Uterine duplication anomalies are a group of Müllerian duct anomalies where fusion of the Müllerian duct associated structures fail to some degree:
uterus didelphys: class III
bicornuate uterus: class IV (second commonest duplication anomaly)
septate uterus: class V (commonest duplication ano...
Uterine enlargement can occur in a number of situations from both diffuse and focal processes. These include:
gestation related events
normal intrauterine pregnancy
molar pregnancy - gestational trophoblastic disease
postpartum uterus - still larger than usual
Uterine perforation represents a serious complication that can occur as a result of any type of intrauterine procedure or implantation. Some authors use the term uterine rupture synonymously with the term uterine perforation.
IUCD insertion: IUCD related uterine perforation
Uterine rupture is a rare but nevertheless potentially catastrophic complication that can occur in pregnancy.
The incidence rate in pregnancy is at 0.05% 6.
Uterine rupture is usually an acute presentation with haemodynamic instability and abdominal disc...
The uterine tube, also known as the Fallopian tube or less commonly the oviduct, is a paired hollow tube that bridges between each ovary and the uterus and functions to convey the mature ovum from the former to the latter. If conception occurs, it normally does so within the tube. It can be affe...
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 ...
The uterus is a hollow, thick-walled, muscular organ of the female reproductive tract that lies in the lesser pelvis.
The uterus has an inverted pear shape. In the adult, it measures about 7.5 cm in length, 5 cm wide at its upper part, and nearly 2.5 cm in thickness. It weighs ...
VACTERL is an acronym that describes a non-random constellation of congenital anomalies. It is not a true syndrome as such and is equivalent to the VATER anomaly.
The estimated incidence is 1 in 10,000-40,000 births 3.
The acronym VACTERL derives from:
V: vertebral an...
The VACTERL-H association is a rare non-random association which bears the features of the standard VACTERL association with added fetal hydrocephalus.
Unlike the standard VACTERL association which is sporadic, the VACTERL-H is hereditary with both X-linked 3 and autosomal recessive 2 inheritan...
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...
There can be several variations with cord insertion into the placenta:
central insertion (~90%): normal situation
eccentric cord insertion: lateral insertion of the umbilical cord >2 cm from the placental margin
term sometimes used synonymously with marginal cord insertion
marginal cord inse...
There can be many variations in the fetal presentation which is determined by which part of the fetus is projecting towards the internal cervical os. This includes:
cephalic presentation: fetal head presenting towards the internal cervical os, considered normal and occurs in the vast majority o...
There can be several variations in placental morphology. These include:
single lobed discoid placenta (single disc): most common scenario
bilobed placenta: two near equal size lobes
succenturiate lobe(s): one of more smaller accessory lobes
circumvallate placenta: rolled placental edges with...
Vasa praevia is a term given when there are abnormal fetal vessels within the amniotic membranes that either cross or run in extremely close proximity to the internal cervical os.
Vasa previa can be of two types
type I (present in ~ 90% of cases with vasa praevia 3): abnormal fetal ...
Vein of Galen aneurysmal malformations (VGAMs), probably better termed as median prosencephalic arteriovenous fistulas, are uncommon intracranial anomalies that tend to present dramatically during early childhood with features of a left-to-right shunt and high-output cardiac failure.
Velamentous cord insertion is one of the types of abnormal umbilical cord insertion into the placenta.
The estimated incidence is ~1% in singleton and 9-15% in twin pregnancies, respectively 11. It is also more common in placenta previa than in normally located placentas. The prev...
Ventricular septal defects (VSD) represent defects in the interventricular septum that allow a haemodynamic communication between the right and left ventricles. It typically results in a left-to-right shunt.
They represent one of the most common congenital cardiac anomalies and ma...
Evaluation of vermian lobulation is essential in assessment of the vermian maturity. MRI is a useful tool in assessment of the fetal posterior fossa.
Normal Vermian lobulation by weeks 1:
By 21 weeks - Prepyramidal fissure can be seen between the tuber and pyramis.
21 to 22 weeks - Preculmina...
Radiological evaluation of the posterior fossa is an essential part of the routine fetal assessment, including vermian maturity assessment.
Ultrasonography is a readily available diagnostic tool in the assessment of the fetal posterior fossa but is sometimes limited due t...
Vitamin B9 (folate or folic acid) is a water-soluble vitamin that is vital for the synthesis of several amino acids, the purines adenosine and guanine and the pyrimidine thymine (three of the four nucleotide bases and hence critical for the synthesis of nucleic acids.)
The antimicrobial drug cl...
Walker-Warburg syndrome (WWS), sometimes known as HARDE syndrome, is an extremely rare lethal form of congenital muscular dystrophy. It is primarily characterised by:
fetal hydrocephalus: almost always present
neuronal migrational anomalies: agyria (cobblestone lissencephaly / lissencephaly ty...
Wharton jelly refers to the gelatinous substance within the umbilical cord.
Wharton jelly is derived from extra-embryonic mesoderm and is largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulphate) while containing smaller amounts of fibroblasts and macropha...
Wolf-Hirschhorn syndrome (WHS) is an extremely rare chromosomal anomaly characterised by partial deletion of the p arm of chromosome 4 (4p16.3).
agenesis of the corpus callosum
cleft lip + / - palate...
Yolk sac is the first anatomical structure identified within the gestational sac. It plays a critical role in embryonal development by providing nutrients, serving as the site of initial haematopoiesis, providing endocrine, metabolic and immunological functions and contributing to the developmen...