Amnion refers to a membranous structure which covers and protects the embryo. It forms inside the chorion. The amnion usually fuses with the outer chorion by around 14 weeks of gestation.
The amnion can be visualised in most pregnancies before the 12th week of...
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
The basal plate is a synonym for the maternal side of the placenta. The fetal side of the placenta is termed the chorionic plate.
Some pathologies and processes are localized to the basal plate, and evaluation of the basal plate is a part of placental grading.
The broad ligament is the lateral folds of the parietal peritoneum which reflect over the upper genital tract.
The broad ligament extends from the lateral aspect of the uterus to the lateral pelvic wall and can be divided into three main components - the mesosalpinx, mesovarium a...
Sequential morphological ultrasound changes of the endocervical canal with cervical incompetence can be remembered using the mnemonic:
Trust Your Vaginal Ultrasound
T-shaped (normal internal cervical os)
The cervix or uterine cervix is the lower constricted segment of the uterus providing the passage between the uterus proper and the vagina.
The cervix is somewhat conical in shape, with its truncated apex directed posteriorly and inferiorly. The inferior aspect of the cervix pro...
The chorion is one of the embryonic membranous structures than encloses both the fetus as well as the amnion. The chorion begins to form chorionic villi towards its outer surface, which initially serves to provide nutrition to the developing embryo.
Part of the chorionic villi arborize more ex...
The chorionic plate is a synonym for the fetal side of the placenta. The maternal side of the placenta is termed the basal plate.
Some pathologies and processes are localized to the chorionic plate, and evaluation of the chorionic plate is a part of placental grading.
There are many classification systems for congenital utero-vaginal anomalies. These include:
Buttram and Gibbons classification 2
American Fertility Society (AFS) classification
Modified Rock and Adam - AFS classification
Modified Rock and Adam - AFS classification
This classification divid...
The corpus luteum is a temporary endocrine structure involved in ovulation and early pregnancy.
During ovulation, the primary follicle forms the secondary follicle and subsequently the mature vesicular follicle.
At ovulation the follicle ruptures expelling the ovum into the fallopian tube. The...
A dominant ovarian follicle refers to the follicle that enlarges to release an ovum during a menstural cycle. Usually approximately 10 Graafian follicles begin to mature where one becomes a dominant follicle and the rest become atretic ovarian follicles. After release of the ovum the remainder o...
The ductus arteriosum (or arteriosus) is the thick short conduit for blood to bypass the non-ventilated lungs in the fetus. It is located between and connects the proximal left pulmonary artery and the undersurface of the aortic arch distal to the origin of the last branch of the arch, at the ao...
Ductus venosus (DV) is a narrow, trumpet-shaped vessel which is seen in the fetal liver connecting the umbilical vein directly to the caudal inferior vena cava. The vessel plays a critical role in the fetal circulation by shunting oxygenated and nutrient-rich umbilical venous blood from the plac...
Fetal circulation differs from the adult circulation due to the presence of certain vessels and shunts.
These shunts will close after birth, and most of these fetal vessels will be seen as remnants in the adult circulation. The function of these shunts is to direct oxygen-rich venous blood to ...
The foramen ovale (or ovalis) is the opening in the interatrial septum in the fetal heart that allows blood to bypass the right ventricle and non-ventilated lungs, shunted from the right atrium to the left atrium. Specifically it represents the opening between the upper and lower portions of the...
Hemivertebra is a type of vertebral anomaly and results from a lack of formation of one half of a vertebral body. It is a common cause of congenital scoliosis.
The estimated incidence is at ~0.3 per 1000 live births 2.
It falls under the spectrum of segmentation anoma...
Intramembranous ossification describes the process of ossification from mesenchymal cells (stem cells) without a cartilaginous template and is involved in the healing process of fractures. The stages of intramembranous ossification osteogenesis are as follows:
mesenchymal cells differentiate in...
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 ovarian artery is a paired structure and is the main gonadal artery in females.
The ovarian artery arises anterolaterally from the aorta just inferior to the renal arteries and superior to the inferior mesenteric artery.
Descends caudally in the retroperitone...
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...
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 fenestrata is one of the variations in placental morphology, which is characterised by one or more areas of focal placental atrophy lacking villi and covered only by the chorion membrane.
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...
Renal agenesis refers to a congenital absence of one or both kidneys. If bilateral (traditionally known as the classic Potter syndrome) the condition is fatal, whereas if unilateral, patients can have a normal life expectancy.
Unilateral renal agenesis affects approximately 1 in ...
Retroplacental complex (RPC) is the region behind the placenta and is composed of decidua basalis and portions of myometrium including the maternal veins which drain the placenta.
visualised post 20 weeks of gestation
seen as an echo-poor, subplacental region...
The rhombencephalon, or hindbrain is a primary vesicle of the neural tube.
During the fifth week of embryological development the rhombencephalon further subdivides into the secondary brain vesicles, the metencephalon and the myelencephalon 1.
The metencephalon goes on to form th...
Single umbilical artery (SUA) results when there is a congenital absence of either the right or left umbilical artery. In the usual situation, there are paired umbilical arteries. For unknown reasons, the absence of the left umbilical artery is much more common (~70%).
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
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...
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...
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 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...
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...
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 ...
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 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...
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...
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...