Snowstorm sign in obstetric imaging is classically seen in complete hydatiform mole. It is characterized by the presence of many hydropic villi which gives the ultrasonographic appearance of a central heterogeneous mass having a solid, hyperechoic area and interspersed with a multitude of cystic...
Snowstorm sign may refer to:
snowstorm sign: complete hydatiform mole (ultrasound)
snowstorm sign: extracapsular breast implant rupture (ultrasound)
snowstorm sign: thyroid pulmonary metastases (chest radiograph)
Obstetric and gynecological 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 thi...
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...
The spectrum of abnormal placental villous adherence describes the degree to which there is an invasion of chorionic villi into the myometrium because of a defect in the decidua basalis.
the commonest type of placental invasion (~75% of cases)
occurs in ~1 in 7...
Spina bifida is a type of neural tube defect/spinal dysraphism which can occur to varying degrees of severity. It is often considered the most common congenital CNS malformation.
Spina bifida in its strictest sense means defective fusion of the vertebral posterior elements, leading...
Spinal dysraphisms refer to a broad group of malformations affecting the spine and/or surrounding structures in the dorsum of the embryo. They are a form of neural tube defect.
The neural tube is formed by the lengthwise closure of the neural plate, in the dorsum of the embryo.
Spondylocostal dysostosis (SCDO) is a rare condition characterized by short-trunk dwarfism secondary to developmental anomalies of the vertebrae and ribs. Previously the condition Jarcho-Levin syndrome (also known as spondylothoracic dysostosis) was grouped together with spondylocostal dysostosi...
Spontaneous rupture of membranes (SROM) refers to rupture of fetal membranes occurring on its own (in contrast with artificial rupture of membranes). When this occurs before ~37 weeks in gestation, it is then termed spontaneous premature rupture of membranes (SPROM) which is the usual cause of p...
Stenosis of the uterine cervix is the pathologic narrowing of the uterine cervix. The term cervical stenosis is clinically defined as cervical narrowing that prevents the insertion of a 2.5 mm wide dilator through the cervical os.
One-fifth of patients have a history of exposure t...
Stickler syndrome refers to a group of disorders primarily affecting connective tissue.
Several gene mutations have been identified dependent on specific subtypes which include:
Stickler syndrome type I: COL2A1
Stickler syndrome type II: COL9A1
Stickler syndrome type III: COL11A1
Straight umbilical cord implies, as the name suggests, an umbilical cord with no coils.
The reported incidence of a straight cord is about 3.7-5% of all pregnancies.
the entire length of the umbilical cord shows no evidence of coiling
Strawberry skull refers to the shape of the head on an antenatal ultrasound.
In general, strawberry skull is considered one of the non-specific 'soft markers' for abnormal fetal development. It is considered more closely associated with trisomy 18 (Edward syndrome).
Subamniotic hemorrhage is considered a type of perigestational hemorrhage.
Subamniotic hematomas are classical placental pathological lesions resulting from the rupture of chorionic vessels (allanto-chorionic vessels) close to the cord insertion.
A subamniotic hemorrhage is contain...
Subchorionic cysts are often considered a subtype of placental surface cyst (commonest type). They are often multiple and may be present in ~5-7% of term placentas 2. Occasionally they can compress chorionic or amniotic vessels leading to adverse fetal outcome.
Subchorionic hemorrhage occurs when there is perigestational hemorrhage and blood collects between the uterine wall and the chorionic membrane in pregnancy. It is a frequent cause of first and second trimester bleeding.
It typically occurs within the first 20 weeks of gestation. W...
Subgaleal hematoma 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 f...
A succenturiate lobe is a variation in placental morphology and refers to a smaller accessory placental lobe that is separate to the main disc of the placenta. There can be more than one succenturiate lobe.
The estimated incidence is ~2 per 1000 pregnancies. Some authors suggest f...
Symmetrical intrauterine growth restriction is a type of intrauterine growth restriction (IUGR) where all fetal biometric parameters tend to be less than expected (below the 10th percentile) for the given gestational age. Both length and weight parameters are reduced.
Please, refer to the artic...
Syndactyly (plural: syndactylies) 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...
Syntelencephaly, also known as middle interhemispheric variant (MIHV), is a mild subtype of holoprosencephaly that is characterized by an abnormal midline connection of the cerebral hemispheres between the posterior frontal and parietal regions.
Syntelencephaly is a congenital ma...
A telephone receiver deformity is a characteristic bowing of the shaft of the long bones, usually the humeri or femora, seen in thanatophoric dysplasia.
Terminal myelocystoceles are an uncommon form of spinal dysraphism representing marked dilatation of the central canal of the spinal cord, herniating posteriorly through a dorsal spinal defect. The result is a skin-covered mass in the lower lumbar region, consisting of an ependyma-lined sac.
Thalidomide embryopathy refers to a syndrome resulting from in utero exposure to thalidomide, and is characterized by multiple fetal anomalies. Fetal exposure to thalidomide occurred primarily from 1957 to 1961, when it was used as a treatment for nausea in pregnant women.
Thanatophoric dysplasia is a lethal skeletal dysplasia. It is the most common lethal skeletal dysplasia followed by osteogenesis imperfecta type II.
The estimated incidence is around 1:25,000-50,000 3.
It results from a mutation coding for the fibroblast gro...
Theca lutein cysts (TLC), also known as hyperreactio luteinalis (HL), are a type of functional ovarian cysts. They are typically multiple and seen bilaterally.
They are thought to originate due to excessive amounts of circulating gonadotrophins such as beta-hCG. Hyperplasia of the th...
The Pre-Conception and Pre-Natal Diagnostic Techniques (Prohibition Of Sex Selection) Act (PCPNDT) is a statute enacted to stop the female feticide 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...
The third trimester in a gestation is the final trimester in a human pregnancy which is usually taken as extending from 28 weeks and 0 days of gestation to term (~38-40 weeks).
History and etymology
Trimester was first seen in English in 1821, a direct borrowing from the French word trimestre,...
Thoracopagus conjoined twins are, as the name suggests, conjoined twins united at their thorax.
Fusion is typically face-to-face, at the upper thorax to the umbilicus with a common sternum, diaphragm, and upper abdominal wall. Very often a common pericardial sac is present as well as a degree o...
Threatened miscarriage (or threatened abortion) is mainly a clinical term, used when a pregnant woman in first 20 weeks of gestation presents with spotting, mild abdominal pain and contractions, with a closed cervical os 3.
It occurs in 20-25% of pregnancies and is associated with...
The three vessel and trachea view (also known as 3VT view or arrow view) is one of the fetal echocardiography views. In this view, aortic and ductal arches are combined into the DAo and appear as a V-shaped confluence. Both arches tend to be of similar size and are located towards the left of th...
Thrombocytopenia with absent radius (TAR) syndrome is primarily characterized by the following two features:
absent fetal radii (bilaterally) with the presence of both thumbs
The condition is extremely rare with an estimated incidence of 0.4 per 100,000 bi...
Tracheal atresia (TA) is an extremely rare anomaly and refers to a congenital absence of the trachea.
There may be a greater male predilection 5.
Tracheal atresia falls under the spectrum of laryngeal-tracheo-bronchial atresia which in turn results either from an obstr...
Transient abnormal myelopoiesis (TAM) is a phenomenon that can happen in the fetuses or neonates with trisomy 21. The condition can mimic leukemia.
The estimated incidence is at ~10% of newborns with trisomy 21 3.
In the context of kno...
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 indica...
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 ...
The trisomies are chromosomal anomalies which usually occur due to non-disjunction. The vast majority of affected fetuses are spontaneously aborted, often very early during gestation. Only three are compatible with extrauterine 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.
Trisomy 8 is a chromosomal anomaly where there is three copies of chromosome 8. Complete trisomy 8 causes severe effects on the developing fetus and can be a cause of miscarriage. However, trisomy 8 can occur as a mosaic form, Warkany syndrome, that can be compatible with life.
Trisomy 8 mosaicism or Warkany syndrome is less severe variant of trisomy 8 and individuals with a low proportion of affected cells may exhibit a comparatively mild range of physical abnormalities and developmental delay. They are more likely to survive into childhood and adulthood but can exhib...
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 has been described in several different pathologies:
T sign (obstetrics)
upper T sign (brain)
lower T sign (brain)
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 an echogenic ring that 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...
Turtle sign may refer to the ultrasound turtle sign or a clinical sign of fetal shoulder dystocia in which the fetal head retracts 3. The head bobbing, emerging and then pulling back could be conceptualized as similar to a turtle pulling it's head into and out of it's shell. The sign does not ne...
Twin anemia polycythemia 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 embolization 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 ischemic str...
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.
A twin pregnancy can be broadly cate...
Twin reversed arterial perfusion (TRAP) sequence is a rare complication of monochorionic pregnancies. It develops when the following conditions are present:
1. lack of a well-formed heart in one of the twins (so-called acardiac twin), and
2. a superficial artery to artery placental anastomosis...
Twin to twin transfusion syndrome (TTTS) is a potential complication that can occur in a monochorionic (either MCDA or MCMA) twin 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 a 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 favor the placental end of the umbilical artery in the cord.
Concurrently associated anomalies are thought to be...
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 placental insufficiency and consequent intrauterine growth restriction (IUGR) or suspected pre-eclampsia.
Umbilical arterial pulsatility index (UA-PI) is a parameter used in umbilical arterial (UA) Doppler assessment. It is calculated by subtracting the end-diastolic velocity (EDV) from the peak systolic velocity (PSV) and then dividing by the time-averaged (mean) velocity (TAV):
PI = (PSV - EDV) ...
Umbilical arterial systolic/diastolic (S/D) ratio is a parameter used in obstetric imaging as part of umbilical arterial (UA) Doppler assessment. It is the ratio between the systolic velocity and the diastolic velocity.
Reference range varies through the stage of pregnancy. If...
The umbilical artery gives rise to both a nonfunctional remnant of the fetal circulation and an active vessel giving supply to the bladder. In the adult, the obliterated area of the vessel is identifiable as the medial umbilical ligament and the patent segment is the superior vesical artery.
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 center of the placental bulk and into the fetus at the umbilicus. Vari...
Abnormalities of the umbilical cord can be classified into 1:
umbilical cord coiling
hypocoiled umbilical cord
hypercoiled umbilical cord
straight umbilical cord
umbilical cord length abnormalities
long umbilical cord
short umbilical cord
umbilical cord thickne...
Umbilical cord coiling index is defined in terms of the number of 360-degree spiral course of umbilical vessels. This can be described in two main ways:
the number of coils per one centimeter of length of cord.
Normocoiled: one coil for a length of five centimeters.
Hypercoiled: more than one...
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 hematoma describes the formation of a hematoma secondary to bleeding from the umbilical cord.
The hematomas 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 iatrogenic...
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.
Recognized 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 is not accurately known, they are comparatively much more common than true umbilical cord cysts.
The pseudocyst basically comprises of mucoid...
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) 8.
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. Since a normal umbilical vein supplies a continuous forward flow of oxygenated blood to the fetal heart, the presence of pulsatility...
The umbilicus is the fibrous remnant of the fetal attachment of the umbilical cord after birth.
All layers of the anterior abdominal wall fuse at the umbilical ring, a small round defect in the linea alba located just inferior to the midpoint between the xiphoid process of the st...
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...
Urinary tract dilatation (UTD) classification was a proposed unified classification of urinary tract dilatation for prenatal and postnatal care. This classification was formed with the collaborations from 8 societies (The American College of Radiology (ACR), the American Institute of Ultrasound ...
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 embolization (UAE) is an interventional radiological technique to occlude the arterial supply to the uterus and is performed for various reasons.
Uterine artery embolization has been practised for more than 20 years for controlling hemorrhage following delivery/abortion,...
Uterine artery embolization (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 a 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 hyp...
Uterine artery pseudoaneurysm (UAP) is a rare cause of secondary postpartum hemorrhage.
UAP usually presents as delayed (secondary) postpartum hemorrhage, that is per vaginal bleeding which occurs more than 24 hours and up to 6 weeks postpartum. However, some reported ca...
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 inversion is a rare condition in which the uterus is essentially turned inside out. There are two types: "puerperal" (within six weeks of childbirth) and "non-puerperal". The reason for uterine inversion is unclear. In the puerperal form, it is theorized that excessive traction on the um...
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 0.05% 6.
Uterine rupture is usually an acute presentation with hemodynamic instability and abdominal discomfo...