Obstetric ultrasound Flashcards
first trimester ultrasound should include visualization of
location and appearance of gestational sac, presence or absence of a yolk sac and embryo, crown-rump-length, cardiac activity, fetal number, fetal neck region for nuchal translucency, uterus and adnexa
second and third trimester ultrasound should include visualization of
fetal presentation, amniotic fluid volume, cardiac activity, placental position, fetal measurements (biometry), fetal number, fetal anatomic survey, maternal cervix and adnexa
potential cavitation and tissue disruptive effects from ultrasound are most significant in what trimester when embryologic tissues are tiny and loosely tethered
first
thermal effects from ultrasound are more significant in what trimester, when bone is present increasing sound absorption and heating
second and third trimesters
serum pregnancy test is defined as positive with values of
above 5 mIU/ml
first trimester ultrasound covers the period from conception to the end of
13th menstrual week
Normal or not: no visible ultrasound findings up to 5 weeks GA
normal
size of GS at approximately 5 weeks GA
2-3 mm
true or false: absence of intradecidual sign or double decidua sign does not exclude an intrauterine pregnancy
true
yolk sac appears at approximately what week and provides provides a definitive evidence of a gestational sac
5.5 weeks GA (>8 mm mean sac diameter)
embryo is visible at what week
6 weeks, with mean sac diameter of 10 mm
embryonic cardiac activity is visible at what week
6 weeks GA
normal embryonic heart rate at 6.2 to 7 weeks is how many beats per minute
100-120
after 7 weeks, embryonic heart rate is
137-144 bpm
first ultrasound evidence of intrauterine pregnancy is visualization of a
gestational sac
tiny well-defined cystic structure implanted within the echogenic decidua seen as early as 4.5 weeks
intradecidual sign
refers to the endometrium of pregnant uterus
decidua
normal appearance of gestational sac
smoothly contoured, round or oval, fluid-containing structure positioned within the endometrium near the fundus of the uterus
normal gestational sac has an echogenic border of
greater than 2 mm thick, which represents the choriodecidual reaction
double decidua sign is produced by
visualization of 3 layers of decidua early in pregnancy
lines the endometrial cavity
decidua vera/parietalis
covers the gestational sac
decidua capsularis
contributes to the formation of the placenta at the site of implantation
decidua basalis
free margin of the gestational sac consists of
chorion and decidua capsularis
normal thickness of chorion and decidua capsularis
at least 2 mm thick
first structure seen with US within the gestational sac and is definitive in identifying a gestational sac
yolk sac
it is a 2 to 6 mm diameter, spherical, cystic structure that is connected to the mid-gut of the embryo by a thin stalk, the vitelline duct
yolk sac
remnant of the connection of the vitelline duct (aka omphalomesenteric duct) to the distal ileum
meckel diverticulum
earliest site of blood cell formation in the embryo. it floats freely in fluid between the amniotic and chorionic membranes
yolk sac
yolk sac should always be visualized in normal pregnancy in gestational sacs of what size of MSD by transvaginal utz
8 mm MSD
yolk sac disappears at what Gestational age
12 weeks
plate-like structure at the periphery of yolk sac
embryo
embryo develops in the _____, while the yolk sac resides in the ______
embryo- amniotic cavity; yolk sac- chorionic cavity
the appearance of two adjacent cystic structures, the amnionic sac containing the embryo and yolk sac has been termed the
double bleb sign
embryos as small as how many mm can be detected by transvaginal utz
2 mm
the embryo, amniotic cavity and chorionic cavity enlarge proportionally untill about how many weeks
10 weeks GA
fetal urine production starts at what week
10 weeks
at 10 weeks, the amniotic cavity then enlarges faster than the chorionic cavity with fusion of the amnion and chorion at what week
14 to 16 weeks
develops on the ovary at the site of dominant follicle from which ovulation ocurred
corpus luteum
secretes estrogens, progesterones and other hormones that are essential for establishing and maintaining pregnancy
corpus luteum
immediately following ovulation, the corpus luteum appears as an area of
focal hemorrhage in the ovary
At what weeks GA does the hindbrain (rhombencephalon) forms a prominent cystic structure, which represents a normal cystic phase
6-8 weeks GA
Rudimentary brain structure that becomes the normal fourth ventricle and posterior fossa
Rhombencephalon
At what week does the gut herniates into the base of the umbilicus forming a physiologic omphalocele seen as protruding midline anterior abdominal wall mass 6-9 mm in size
9-11 weeks
diagnosis of pregnancy failure: no embryonic heartbeat with CRL of ___ mm
> /= 7mm
diagnosis of pregnancy failure: no embryo with mean sac diameter of ___ mm
> /= 25 mm
diagnosis of pregnancy failure:no embryo with heartbeat of ___ weeks after US that showed a gestational sac without a yolk sac
> /= 2 weeks
diagnosis of pregnancy failure: no embryo with heartbeat ___ days after US that showed a gestational sac with a yolk sac
> /= 11 days
suspicious but not diagnostic of pregnancy failure (pregnancy of uncertain viability): crown-rump-length of ___ mm with no heartbeat
<7 mm
suspicious but not diagnostic of pregnancy failure (pregnancy of uncertain viability): MSD of ___ mm with no embryo
16-24 mm
suspicious but not diagnostic of pregnancy failure (pregnancy of uncertain viability): no embryo with heartbeat ____ days after US that showed a gestational sac without a yolk sac
7-13 days
suspicious but not diagnostic of pregnancy failure (pregnancy of uncertain viability): no embryo with heartbeat ___ days after US that showed a gestational sac with a yolk sac
7-10 days
empty amnion. pregnancy failure or pregnancy of uncertain viability
pregnancy of uncertain viability
suspicious but not diagnostic of pregnancy failure (pregnancy of uncertain viability): yolk sac size
larger than 7 mm
less than 5 mm difference between mean sac diameter and CRL. pregnancy failure or pregnancy of uncertain viability?
pregnancy of uncertain viability
if findings tagged as pregnancy of uncertain viability, follow-up US examination in ____ days is appropriate
7-10 days
risk factors for ectopic pregnancy
tubal ligation, previous tubal surgery, PID, previous ectopic pregnancy, presence of an IUD, endometriosis, in vitro fertilization, history of smoking prior to conception, previous endometrial or myometrial surgery
abortion is termination of pregnancy before ___ weeks GA
20 weeks GA
up to how many percent of spontaneous abortions have chromosomal abnormalities
60%
refers to the occurrence of vaginal bleeding and uterine cramping with a closed cervical os in early pregnancy
threatened abortion
refers to presence of residual products of conception within the uterus
incomplete abortion
fetus has died but remains within the uterus
missed abortion
habitual abortion is defined as ____ successive spontaneous abortions
3 or more
pregnancy in which the embryo has dies and is no longer visible, or never developed
anembryonic pregnancy or blighted ovum
gestational sac is considered abnormal if it demonstrates the following features
large size (> 25 mm MSD), without an embryo or yolk sac, distorted shape, irregular contour, thin or weak choriodecidual reaction, absence of a double decidual sac or abnormal position
this feature of the gestational sac have reported a 100% specificity and positive predictive value for identification of nonviable pregnancy
large sac size without visualized yolk sac or embryo and a distorted sac contour
term used for the presence of an intrauterine gestational sac with no embryonic heartbeat and no findings of definite pregnancy failure
intrauterine pregnancy of uncertain viability
describes the situation of a woman with a positive urine or serum pregnancy test and no intrauterine or ectopic pregnancy on TVS examination
pregnancy of unknown location
At what gCG level is a viable intrauterine pregnancy unlikely
> /= to 3000 IU/mL
a nonspecific intrauterine fluid collection with smooth rounded or oval contours and with no yolk sac or embryo and normal adnexa most likely represents a
an intrauterine pregnancy, however, ectopic pregnancy is not completely excluded. intrauterine fluid may represent a gestational sac
if pregnancy is uncertain if intrauterine or not, follow-up US and hCG determination should be done in how many weeks
7-10 weeks as long as the patient is hemodynamically stable
major cause of pregnancy related maternal deaths
ectopic pregnancy
those susceptible to ectopic pregnancy include
history of PID, tubal surgery, endometriosis, ovulation induction, previous ectopic pregnancy or use of IUD
most ectopic pregnancies occur in the
fallopian tube
ectopic pregnancy in the fallopian tube usually occurs at what area
ampulla
uncommon sites for ectopic pregnancy
interstitial portion of fallopian tube, abdominal cavity, ovary and cervix
most specific finding of ectopic pregnancy
live embryo with heartbeat outside of the uterus
US findings in ectopic pregnancy include demonstration of an extrauterine gestational sac appearing as a fluid containing structure with an echogenic right, called the
tubal ring sign
true or false: corpus luteal cysts always arise from the ovary
true
blood in the uterine cavity produces cystic-appearing mass termed a _____ seen in 10 to 20% of ectopic pregnancies
pseudogestational sac
a true gestational sac is differentiated from a “pseudosac” by the presence of
yolk sac or embryo
a ____ sign suggests a true gestational sac, but is not always reliable
double decidua sign
pseudosacs are located _____ within the uterine canal whereas a normal gestational sac is ______
pseudosacs- centrally, true gestational sac- eccentrically implanted within the decidua
Doppler studies demonstrate _____ with pseudosacs and _____ with true gestational sacs
absent or minimal peritrophoblastic flow with pseudosacs and high-velocity, low impedance flow with true gestational sacs
ectopic pregnancy in this location is associated with high incidence of severe maternal hemorrhage
intersitital
implantation in this region of the fallopian tube (myometrial portion) allows development of pregnancy up to 16 weeks with large supplying arteries, A fundal gestational sac is eccentric and the adjacent myometrium is thinned to less than 5mm. it can be confused with a pregnancy in one horn of bicornuate uterus
interstitial
ectopic pregnancy in this region is common with IUD in place
ovarian
ectopic pregnancy in this region is associated with marked increase in maternal mortality because of growth of the pregnancy is unrestricted
abdominal
ectopic pregnancy in this region shows an hourglass shaped uterus
cervical
medical management of ectopic pregnancy
oral methotrexate or local injection of methotrexate or potassium chloride
up to how many percent of ectopic pregnancies resolve spontaneously
15%
in general, quantitative hCG levels are expected to double approximately every
2 days
develop because of venous bleeding from separation of the margin of placenta
subchorionic hemorrhage
in subchorionic hemorrhage, hematoma collects preferentially beneath the ____ becuase it is more easily separated from the myometrium than the placenta
chorion
nonspecific term that refers to small collections of blood at the site of attachment of the chorion to the endometrium. these are in essence small areas of subchorionic hemorrhage that occur early in pregnancy
implantation bleeding
retained products of conception has a variant appearance of thickened endometrium of up to
> 10 mm
group of neoplasms that range from benign to highly malignant in which all are derived from abnormal placental tissues and occur as sequelae to pregnancy
gestational trophoblastic disease
both benign and malignant GTD tumors produce
hCG
woman over age ___ with a prior history of molar pregnancy are at increased risk for GTD
40
most common and most benign form of GTD
hydatidiform mole
form of H.mole that involves the entire placent, lacks a fetus and is diploid in karyotype
complete/classic mole
form of H.mole that involves only a portion of the placenta and is associated with an abnormal fetus that is triploid in karyotype (due to fertilization of an ovum by 2 sperm
partial mole
true or false: molar pregnancy may occassionally appear as an anechoic fluid collection that mimics anembryonic pregnancy
true
seen as large, septated, bilateral cysts massively enlarging the ovaries in 25- 65% cases of molar pregnancy
theca lutein cysts
theca lutein cysts result from
hyperstimulation of the ovaries by high circulating levels of hCG and are most commonly seen in molar pregnancy in the second trimester
refers to invasion of molar tissue into, but usually not beyond the myometrium
invasive mole (chorioadenoma destruens)
highly aggressive malignancy that forms only trophoblast without any villous structure. it is locally invasive and spreads into the myometrium and parametrium, and hematogeneously metastasizes to any site of the body
choriocarcinoma
serum hCG levels that rise or plateau in the 8-10 weeks following evaluation of molar pregnancy suggest
invasive or metastatic gestational trophoblastic disease
clinical dating of pregnancy is based on
LMP, PE assessment of uterine size
sonographic dating of pregnancy
based on measurements of fetal parameters used to document growth
these terms are usually considered to be synonymous terms and are based on the average 28-day menstrual cycle
gestational age and menstrual age
used inthe first trimester to estimate GA when no embyro is visualized
gestational sac
mean sac diameter is accurate to within approximately ___ week of menstrual age
1 week
measured from the top of the head to the bottom of the torso of the visualized embryo or fetus
crown rump length
CRL is useful until about __ weeks GA, when other measurements become more accurate
12 weeks
biparietal diameter and head circumference is measured at what level on an axial image of the fetal head
at the level of 3rd ventricle and thalamus
elongated skull
dolicocephaly
round skull
brachycephally
relatively independent of head shape
HC
abdominal circumference is measured at what level
level of intrahepatic portion of umbilical vein
true or false: GA estimates are most accurate in early pregnancy and become progressively less accurate as the pregnancy advances
true
a fetus or newborn i considered SGA if its weight is below the ___ percentile for GA
10th
pattern of growth impairement occurs early in the ____ trimester and tends to be symmetrical
second
growth impairment that are asymmetrical occurs in
late second and third trimester
at what trimester of growth impairment does the fetal abdomen may become disproportionally small relative to the head and femur because of diminished glycogen stores in the fetal liver and decreased or absent subcutaneous fat
late second and third trimester
cause of 80% of intrauterine growth retardation that is prone to asymmetric growth restriction
uteroplacental insufficiency
multiparameter approach for IUGR include
estimated fetal weight, amniotic fluid volume and presence of absence of maternal hypertension
IUGR is diagnosed confidently when the EFW is below the ___ percentile
5th
when EFW is betweent the 5th and 20th percentile, IUFR is diagnosed if these are also present
oligohydramnios, maternal hypertension
normal fetal weight gain in the third trimester is ____ g/week
100 to 200 grams/week
oligohydramnios has an AFI of
5 cm or less
test to identify compromised fetuses
biophysical profile
four parameters that assess for acute hypoxia
reactive fetal heart rate (nonstress test), respiratory activity, gross motor movements, fetal tone
one parameter thatn evaluates for chronic hypoxia
amniotic fluid volume
in BPS, a score of 2 in one parameter is given for
normal response
a BPS score of 0 in one parameter means
abnormal
fetus is at extreme risk for fetal demise within 1 week if the BPS score has a total of
0-2
there is no immediate risk if the BPS total score is
8 or 10
umbilical artery circulation to the placenta is normally ___ impedance manifest by high blood flow velocities in late diastole on spectral Doppler waveforms
low impedance
fetal arterial doppler findings of ____, is strongly predictive of severe fetal compromise
systolic to diastolic ratio of 4 or greater, or absence of forward flow in diastole
ominious finding in fetal arterial Doppler indicative of high risk for fetal demise within 1 to 7 days if the fetus is left in utero
reversal of flow in diastole
carries more than 80% of fetal cerebral blood flow and is accessible to Doppler interrogation
middle cerebral artery
in normal fetal brain, MCA circulation shows a
high vascular resistance pattern with little or no forward flow in late diastole
fetal macrosomia is defined as EFW above the
90th percentile for GA or a fetal weight above 4000 g
risk factors for fetal macrosomia
DM, maternal obesity, previous history of macrosomic infant, excessive weight gain during pregnancy
complications of macrosomia manifest at delivery include
shoulder dystocia, traumatic delivery, fractures, brachial plexus injury, perinatal asphyxia, neonatal hypoglycemia and meconium aspiration
most common solid pelvic masses encountered during pregnancy
uterine leiomyomas
most common cystic pelvic masses found in pregnancy
corpus luteal cysts
internal hemorrhage in the corpus luteal cysts may cause increase in size of up to
10-15 cm in size
most of the corpus luteal cysts regress by how many weeks
16 to 18 weeks GA
forms due to an exaggerated corpus luteum response to high levels of hCG. they appear as bilateral multicystic enlargement of the ovaries. occurs with GTD, pregnancy more than one fetus, or associated with the use of ovulation-inducing drugs
theca lutein cysts
single most common cause of a poor neonatal outcome
preterm delivery
normal cervical length throughout gestation
26 to 50 mm
cervical length is measured in
sagittal plane between the internal os marked by a V-shaped notch and the external os marked by a triangular echodensity
dilatation of the cervical canal of ___mm is indicative of cervical incompetence
> 8mm
normal placenta is first apparent on US at what week, as a focal thickening at the periphery of the gestational sac
8 weeks
disc like shape of the placenta becomes evident at what week
12 weeks
by this week, the placenta appears finely granular and homogeneous with a smooth covering chorionic membrane along its fetal surface
18 weeks
prominent sonographic landmark of placenta
retroplacental complex of decidual and myometrial veins
as gestation advances, placenta appears
more heterogeneous, with focal echolucencies owing to venous lakes and area of fibrin deposition
normal placenta has a maximum thickness of __ cm and a minimal thickness of ___ cm
maximum thickness of 4 cm and minimal thickness of 1 cm
thick placentas are associated with
maternal diabetes, maternal anemia, hydrops from immune and nonimmune causes, chronic uterine infections and placental abruption
thin placentas are associated with
preeclampsia, placental insufficiency and trisomies 13 and 18
present when a part or all of the placenta covers the internal cervical os
placenta previa
risk factors for placenta previa include
scarring of the lower uterine segment associated with previous cesarean sections, previous placenta previa and multiple previous pregnancies
placenta previa usually present with ____ in the 3rd trimester
painless vaginal bleeding
present when placental blood vessels or the umbilical cord are adherent to the membranes that cover the cervix
vasa previa
risk factors for vasa previa
placenta previa, low-lying placenta, multiple gestation, succenturiate lobe , velamentous cord insertion
an accessory placental lobe separate from the main placenta
succenturiate lobe
umbilical cord inserts into the chorioamniotic membranes at the margin of the placenta
velamentous cord insertion
defined as the premature separation of a normally positioned placenta from the myometrium
placental abruption
placental separation is associated with
hemorrhage from maternal vessels at the base of the placenta
subchorionic hemorrhage is also called
marginal abruption
retroplacental hemorrhage is usually arterial or venous
arterial
abnormal adherence of the placenta to the uterine wall
placenta accreta
invasion of the uterine wall by the placenta is referred to as
placenta increta
penetration of the uterine wall by the placenta is
placenta percreta
usually present in placenta accreta, approximately 88% of cases
placenta previa
benign vascular placental mass supplied by the fetal circulation
chorioangioma
most common tumor of the placenta
chorioangioma
normal umbilical cord consists of
two arteries and one vein surrounded by wharton jelly
normal diameter of umbilical cord
1-2 cm
single artery umbilical cord is associated with what anomalies
cardiac, urinary tract, CNS malformations, omphalocele, trisomy 13 and 18
outer layer of placenta
chorion
inner layer of placenta
amnion
chorion and amnion are separated by fluid until what week before it fuses
14 to 16 weeks
true or false: occassional persistence of chorioamniotic separation into third trimester is believed to be of no clinical significance
true
caused by early disruption of the amnion, enabling the fetus to enter the chorionic cavity
amniotic band syndrome
early disruption of amnion in amniotic band syndrome happens at what week
before 10 weeks GA
membranous structures that project into the uterine cavity
amniotic sheets/uterine synechia
dialysate of maternal serum in early pregnancy
amniotic fluid
major source of amniotic fluid as pregnancy advances
fetal urine
turnover of amniotic fluid occurs every how many hours
3 hours
fetus swallows amniotic fluid at a rate of ___ cc/24 hours
450 cc
essential in promoting normal development and maturation of fetal lungs
amniotic fluid
suspended particles in amniotic fluid visualized by US are attributable to
normal vernix, blood or meconium
AFI is measured by
measuring the vertical diameter of the deepest pockets of fluid in the 4 quadrants of uterus and adding these values together
normal AFI
5 to 20 cm
polyhydramnios represent excessive amount of amniotic fluid greater than
2L at delivery, AFI of more than 20 cm or a single fluid pocket greaster than 8 cm
if there is failure of fetal abdomen to be in contact with both anterior and posterior uterine wall after 24 weeks GA, this can be considered
polyhydramnios
associated anomalies with polyhydramnios include
anencephaly, encephalocele, GI obstruction, abdominal wall defects, achondroplasia and hydrops (isoimmunization)
oligohydramnios is diagnosed with AFI of
less than 5 cm, largest fluid pocket is less than 1 cm
major complication of severe oligohydramnios is
fetal lung immaturity
fetus sharing a placenta
monochorionic
each fetus having its own placenta
dichorionic
twins that share a single amniotic cavity
monoamniotic
have the highest morbidity, including conjoined twinning and intertwining of umbilical cords
monoamniotic
definitive proof of lower-risk dichorionic twinning
two separate placentas, determination that the twins are of different sex
chorionicity is best determined at what weeks
11 to 14 weeks GA
presence of two yolk sacs is evidence of
diamniotic twins
about half of diamniotic twins will have
fused placenta
visualization of membranes separating twins confirms
diamniotic twins
twins that have usually vascular anastomoses at the placental level, making them at risk for twin transfusion syndrome and twin embolization syndrome
monochorionic twins
shunting of blood from one twin to the other through vascular connections in the placenta
twin-to-twin transfusion syndrome (TTTS(
tiny AV anastomosis in the placenta that allow slow transfusion of blood from the donor twin to recipient twin resulting in anemia in the donor and polycythemia in the recipient
twin anemia-polycythemia sequence (TAPS)
placenta may show an echogenic thickened section supplying the donor and a thin hypoechoic section supplying the recipient
twin anemia-polycythemia sequence (TAPS)
large AV anastomosis usually near a common cord insertion site results in a pump twin who perfuses a severely malformed acardiac twin
twin reversed arterial perfusion sequence (TRAP)
in TRAP sequence, high output cardiac failure develops in what twin
pump twin who is driving blood thru both fetuses
blood products from the dead twin are shunted through placental interconnections to the live twin, resulting in disseminated intravascular coagulopathy and multifocal tissue infarction
twin embolization syndrome
majority of serious structural birth defects can be detected at what GA
18 to 22 weeks
defined as having one or more extra, or missin, chromosomes in a cell
aneuploidy
most common aneuploidies
trisomy 21, 18 and 13
first trimester aneuploidy screening is generally performed between
11 and 14 weeks
first trimester aneuploidy screening include
NT measurement, serum free B-hCG or total hCG and pregnancy-associated plasma protein A anylate levels (PAPP-A)
normal echolucent space between the spine and overlying skin at the back of fetal neck
nuchal translucency
normal nuchal translucency measures
less than 3 mm
at what CRL is nuchal translucency may be measured
CRL of 45 to 84 mm
quadruple marker screen is best performed between what weeks
16 and 18 weeks GA
four maternal plasma substances measured in the quad screen are
hCG, AFP, dimeric inhibin A and unconjugated estriol
penta screen testing include
hCG, AFP, dimeric inhibin A and unconjugated estriol, hyperglycosylated hCG
evaluates short segments of fetal DNA derived from placenta in maternal plasma
cell-free DNA screening
nuchal fold measurement associated with down syndrome
> or = to 5 mm
nuchal fold is measured at what trimester
second, 18-22 weeks GA
absent nasal bone is associated with
trisomies 21, 13 and 18
echogenic intracardiac focus is associated with
down syndrome
short femur and humerus (<0.9) is associated with
down syndrome
pyelectasis refers to size of renal pelvis of up to
> or = to 4 mm
pyelectasis is associated with
down syndrome
hyperechoic bowel is associated with
down syndrome
refers to thickness of skin overlying the back of the neck and occipital bone seen in the second trimester when NT is no longer present
nuchal fold
nuchal fold is measured at the level of
thalamus and cerebellar hemispheres
nuchal fold is measured between the
occipital bone and skin surface
nuchal fold thickness is considered reliable only between what weeks
15 and 20 weeks GA
chorionic villous sampling is performed between
10 and 13 weeks GA by transcervical or transabdominal US-guided needle puncture of the placenta
amniocentesis is generally performed bewteen
15 and 20 weeks GA
most common chromosome abnormality, increasing in incidence and currently occuring in 1 of 800 births
trisomy 21
major structural defects in down fetuses include
congenital heart disease (endocardial cushion defect, VSD, TOF), duodenal atresia, ventriculomegaly and tracheoesophageal atresia
second most common chromosome abnormality occuring in 1 in 3000 births
trisomy 18
chromosome abnormality associated with IUGR, complex congenital heart disease, choroid plexus cyst, congenital diaphragmatic hernia, omphalocele, neural tube defects, Dandy-walker complex, clenched hands and single UA
trisomy 18
third ventricle appears as a single echogenic line to a slit-like structure less than ___ mm in width
3.5
axial plane at the level of the ventricular atria
transventricular plane
dominant landmark of transventricular plane is
echogenic choroid plexus, which normally fills the atrium nearly complete
measurements of atrial diameter made perpendicular to the walls do not normally exceed ___ mm
10 mm
axial scan in approximately 10 to 15 degrees of inclination from the canthomeatal line
transcerebellar plane
anatomic landmarks of transcerebellar plane
inferior portion of 3rd ventricle, cerebellar hemispheres outlined by fluid in the cisterna magna
normal cisterna magna measures
2-11 mm in width
a small cisterna magna (<2mm) suggests a
Chiari II malformation, or massive ventriculomegaly
large cisterna magna may be due to
normal variant (mega-cisterna magna) or indicate Dandy walker malformation, arachnoid cyst or cerebellar hypoplasia
categories of ventriculomegaly
obstructive hydrocephalus (osbtruction to flow of CSF), cerebral atrophy (ex vacuo), maldevelopment (agenesis of corpus callosum)
diagnosis of ventriculomegaly include
atrium of > 10 mm, separation of choroid plexus from ventricular wall by > 3mm and a “dangling choroid”
most common cause of ventriculomegaly in the fetuses are
chiari II malformation and aqueductal stenosis
absent skull conditions
anencephaly, amniotic band syndrome, acrania
absent or incomplete falx with cortical mantle condition
holoprosencephaly
absent or incomplete falx without cortical mantle condition
hydranencephaly
extracranial cysts
cystic hygroma, encephalocele, meningocele
bilateral intracranial cysts
hydrocephalus
midline intracranial cysts
Dandy-walker, arachnoid cyst, Vein of Galen Aneurysm
Unilateral intracranial cysts
arachnoid cyst, porencephalic cyst, unilateral hydrocephalus
most common fetal neural tube defect
anencephaly
include absence of cranial vault and cerebral hemispheres above the lebel of the orbits
anencephaly
fluid and/or brain tissue filled sacs that protrude through a defect in the bony calvarium
cephaloceles
cephaloceles are commonly seen in what region of the brain
occipital
cephalocele that only contain CSF
meningocele
cephalocele that contain CSF and brain tissue
encephalocele
refers to a spectrum of spinal abnormalities resulting from failure of complete closure of neural tube
spina bifida
nonfusion of vertebral arches with intact skin
spina bifida occulta
protruding sacs with spinal cord or nerve roots
myelomeningocele
totally open spinal defect
myeloschisis
spina bifida most commonly occurs in
lumbosacral region
US findings include outward splaying, rather than inward convergence of the laminae, defect in the soft tissue overlying the bony abnormality and a protruding sac containing fluid and often neural tissues
spina bifida
functional neuromuscular defect associated with spina bifida
club foot deformities and dislocated hips
refers to bossing of frontal bones
lemon sign
produced by compression of the cerebellar hemispheres into a banana shape
banana sign
chiari II is associated with ___ 95% of the time
myelomeningocele
consist of caudal displacement of cerebellar tonsils, pons and medulla, fourth ventricle is elongated, posterior fossa is small and cisterna magna is obliterated
chiari II
spectrum of disorders characterized by a failure of prosencephalon to divide and form the separate right and left hemispheres and thalami
holoprosencephaly
includes facial anomalies namely hypotelorism, cyclopia, proboscis
holoprosencephaly
most severe form of holoprosencephaly and demonstrates absence of the falx and interhemispheric fissure with a single midline ventricle
alobar holoprosencephaly
refers to total detruction of cerebral cortex, believed to be caused by the occlusion of ICA
hydranencephaly
maldevelopment of the roof of the 4th ventricle. cisterna magna is enlarged and communicates directly with 4th ventricle through its absent roof. posterior fossa is enlarged and tentorium is elevated. cerebellar hemispheres are usually hypoplastic. hydrocephalus is usually present
Dandy-walker malformation
arachnoid cysts and large cisterna magna are differentiated from Dandy-walker malformation
lack of communication with the 4th ventricle
true or false: choroid plexus cysts themselves cause no clinical problem and nearly always resolve
true
choroid plexus cysts are associated with what aneuploidy
trisomy 18
true or false: choroid plexus cysts are not associated with Down syndrome
true
most common type of cleft lip and palate
lateral cleft
associated anomalies with cleft lip and palate
polydactyly, congenital heart disease and trisomy 21
median cleft lip or palate is associated with
holoprosencephaly
fluid collection in the fetal neck caused by failure of the lymphatic system to develop normal connections with venous system in the neck
cystic hygroma
in US, it demonstrates a bilateral nuchal cystic mass with a prominent midline septum that represents the nuchal ligament
cystic hygroma
cystic hygroma is associated with
down syndrome, turner syndrome, trisomy 18 and 13
refers to pathologic accumulation of fluid in body cavities and tissues
fetal hydrops
caused by blood group incompatibility between mother and fetus that causes pathologic fluid accumulation in body cavities and tissues
immune hydrops
hydrops that is caused by a host condition including cardiac disorders, infections, chromosomal anomalies, twin pregnancy, urinary obstruction and umbilical cord complications
nonimmune hydrops
treatment for immune hydrops
fetal transfusion
disorder in which abdominal contents protrude into the thorax through defects in the diaphragm
congenital diaphragmatic hernia
majority of congenital diaphragmatic hernia occurs on what side
left
mortality is hight in fetuses with congenital diaphragmatic hernia due to
pulmonary hypoplasia
congenital hamartomatous lesion of the lung that usually affects one lobe
cystic adenomatoid malformation
CAM type in which single or multiple cysts are present larger than 2 cm
type 1
CAM type with multiple smaller cysts of uniform size less than 2 cm
type 2
CAM type with lesions appearing as echogenic solid masses because the cysts are microscopic
type 3
mass of lung tissue supplied by systemic arteirs and separated from its normal bronchial and pulmonary vascular connections
pulmonary sequestration
type of pulmonary sequestration that is contained within the pleural covering of an otherwise normal lobe of the lung. pulmonary venous drainage is maintained
intralobar
pulmonary sequestration type that appears as accessory lobes, contained within their own pleura and supplied by both systemic arteries and veins
extralobar
more common form of pulmonary sequestration
intralobar
major cause of neonatal morbidity and mortality and is the most common major anomaly in the neonate affecting 1 in 200 live births
fetal cardiac anomalies
routine screening views of the heart include
four-chamber heart view, RVOT, LVOT
in four-chamber view of heart in US, apex of normal heart is directed at the left anterior chest wall at how many degrees on the same side of the fetal stomach
45 degree angle
in the fetal heart, which is bigger in size, atria or ventricles?
atria; ventricles are equal in size and slightly smaller
LVOT view is obtained by
angling the transducer from the position of four chamber view toward the right shoulder
on this view of the heart on US, the aortic valve and origin of the aorta from the left ventricle are seen
LVOT view
RVOT view is obtained by
angling the transducer slightly from the LVOT view
on this view of the heart on US, the origin of pulmonary artery to the bifurcation into right and left pulmonary arteries are seen
RVOT view
normal liver appearance in fetus, which lobe is larger
left
half the fetal blood that it carries goes directly to the IVC via ductus venosus
umbilical vein
venous supply of the fetal liver is from
left portal vein
appearance of fetal adrenal gland
up to 20 times larger in relative size because of the “fetal zone”
swallowing begins at what week
11 to 12 weeks GA
fetal stomach should be filled with swallowed fluid by
18 weeks GA
peristalsis in small bowel loops can be seen at what trimester
3rd
visualized fetal small bowel loops are normally of what size
6 mm in diameter, less than 15 mm in length
colon is visualized at what week
after 20 weeks
the colon progressively fills with meconium but does not exceed what size
23 mm in diameter
length of normal kidney in mm is approximately equal to
GA in weeks
if stomach is absent, patient may be reexamined after how many hours
1 hour
causes of absent fetal stomach include
obstruction (esophageal atresia, chest mass), impaired swallowing (facial clefts and neuromuscular disorders), low amniotic fluid volume and stomach in an abnormal location (diaphragmatic hernia)
descriptive fluid distention of the stomach and proximal duodenum
double bubble
fluid distention of the duodenum is abnormal and indicative of
duodenal atresia or stenosis, annular pancreas or volvulus
in double bubble sign, what aneuploidy may be present
down syndrome
dilatation of fetal small bowel of greater than 6 mm may be due to
jejunal or ileal atresia or stenosis, volvulus, meconium ileus, enteric duplication
causes small bowel obstruction by impaction of abnormally thick meconium in the distal ileum
meconium ileus
meconium ileus is nearly always associated with
cystic fibrosis
results from perforation of a bowel segment due to spillage of meconium into the peritoneal cavity causing a sterile peritonitis that results in calcifications on peritoneal surfaces, loculated fluid-filled masses within the peritoneal cavity (meconium pseudocysts), ascites, bowel dilation and polyhydramnios
meconium peritonitis
cause of meconium peritonitis is commonly not identified but may be due to
vascular insult to small bowel. meconium ileus (cystic fibrosis), bowel atresia, volvulus
echogenic bowel may be due to
cystic fibrosis, chromosome abnormalities (trisomy 21 and 18), small bowel atresia, volvulus and fetal viral infection (CMV)
most common cause of hydronephrosis in fetus are
ureteropelvic junction obstruction, ectopic ureterocele, posterior urethral valves
definitive evidence of significant hydronephrosis
renal pelvis greater than 10 mm AP diameter or greater than 50% of the AP diameter of kidney in axial section or unequivocal caliectasis
minimal dilation of the renal pelvis is most often due to
physiologic vesicoureteral reflux
physiologic vesicoureteral reflux is normal during what trimester
second and third
a fluid filled renal pelvis larger than 3 mm warrants attention because it may be a sonographic marker of
aneuploidy (Down syndrome) or an early indicator of congenital urinary obstruction
elective postnatal US of equivocal cases of mild dilation of renal pelvis should be done how many weeks of age to avoid underestimation of hydronephrosis because of the normal oliguria that occurs during early postnatal period
1 to 2 weeks
appears as multiple noncommunicating renal cysts of varying sizes
multicystic dysplastic kidneys
polycystic kidney disease with nonfunctioning kidneys, associated with severe oligohydramnios and is not compatible with life
multicystic dysplastic kidneys
massive enlargement of both kidneys associated with oligohydramnios suggests ___. kidneys are predominantly echogenic with sonolucent rim
autosomal recessive polycystic disease
kidneys are enlarged but lack sonolucent rim of autosommal polycystic kidney disease
autosomal dominant polycystic kidney disease
affected kidneys are hydronephrotic, with increased parenchymal echogenicity and parenchymal cysts of varying sizes. kidneys may be dysplastic without cysts being evident on US
obstructive uropathy such as posterior urethral valves
results from a defect in the anterior abdominal wall nearly always on the right side of umbilicus. bowel herniates through the defect and floats freely in the amniotic fluid with no covering membrane
gastroschisis
true or false: gastroschisis is most commonly an isolated defect without chromosomal anomaly or risk of recurrence
true
more serious abdominal wall defect that is about equal in frequency to gastroschisis. defect is midline at the umbilicus with herniation of abdominal contents into the base of umbilical cord
omphalocele
in omphalocele, what commonly herniates
liver and bowel
the membrane that covers the omphalocele consits of
peritoneum and amnion
most common site for teratoma
sacrococcygeal
commonly affected gender in teratoma
female
ratio of FL to footh length of less than 1 suggest
skeletal dysplasia
an FL to foot length ratio of more than 1 suggest
constitutionally small or growth-retarded fetus
most common lethal skeletal dysplasia
thanatophoric dwarfism
this include small thorax, cloverleaf skull, large head, hydrocephalus, and polyhydramnios
thanatophoric dwarfism
an autosomal dominant trait that is lethal in homozygous form and nonlethal in heterozygous form. shows proximal limb shortening in US
achondroplastic dysplasia
heterogeneous group of disorders with both autosomal dominant and recessive inheritance patterns. hallmark of disease is osteoporosis, that manifest as diminished bone echogenicity. additional findings include bone thickening with fractures and callus formation, bone boweing, small chest and protuberant abdomen
osteogenesis imperfecta
clenched hands with overlapping index fingers suggests
trisomy 18
polydactyly and polycystic kidneys suggest
Meckel-Gruber syndrome
hypoplasia of middle phalanx of fifth digit in association with femur and humerus shortening suggests
down syndrome
