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Obstetric and Gynecology Atlas and Gallery

Hundereds of carefully categorized obgyn illustrations, and real life ultrasound scan images and clips from clinical practice with desription, user comments lightbox..etc.

 
 
Fetal Abdomen
 
Transverse and longitudinal views are useful to evaluate the following:

1- Abdominal wall: AC, UC insertion

2- Stomach

3- Diaphragm

4- Upper abdomen: Liver, Gall bladder, spleen

5- Lower abdomen: Bowel

6- Kidneys

7- Urinary Bladder

8- Genitalia

 

1. Abdominal wall: Outline of the abdominal wall seen complete with no defects

 

1.a.Abdominal circumference measure (AC) at level of umbilical vein should correlate with gestational age and other fetal measures (more than 2 weeks lag needs level III ultrasound scan assessment). Fetal growth restriction would affect the size of fetal liver and hence the AC measure.

To obtain an accurate measure for AC it has to be in a transverse section in the fetal abdomen, not oblique view. This plain is at the level of the umbilical vein when it is within the liver (almost J-shaped) since visualization of the umbilical vein more anteriorly is only possible with oblique view.

 

1.b.Umbilical cord insertion: Detection of a normal cord insertion excludes a vast majority of anterior abdominal wall defects. The umbilical arteries can further be traced on both sides of the fetal urinary bladder whereas the larger umbilical vein can be traced into the liver substance as it joins the portal system and the ductus venosus can be identified as the communication between the UV and the IVC.

 

Defects may be:

- Gastroschisis: Para-umbilical defect usually to the right side of an intact umbilical cord. The defect is usually small but a complete defect with absence of all layers on the abdominal wall resulting in "free bowel" herniating into the amniotic sac with no sac covering.

- Omphalocele: Midline abdominal wall defect with herniation of abdominal content covered with amnion and peritoneum. THe umbilical cord inserts into the membranes.

 

 

2. Stomach appears as a fluid filled structure at the upper left part of the abdomen on the same side of the cardiac apex.

Defects may be:

Absent stomach (confirmed in more than one scan) may be due to:

- Displaced into the chest (diaphragmatic hernia) or displaced into and abdominal wall defect.

- Oesphageal atresia (there may be fluid collection in the oesphagus with polyhydramnious)

- Anhydramnios (there will be no AF as well)

- Microgastria

Dilated fetal stomach / bowel loops may be due to:

-Normal

-Atresia at a distal point:

*Duodenal atresia: Dillated stomach and duodenum = Double bubble sign

*Small bowel atresia: Dilated bowel loops (>7mm) without dilated stomach

*Anorectal atresia: Hyperechoic content in the rectal pouch, there may be no dilated loops of bowel.

 (dudenal, jeujenal..tec)

Midline or right sided stomach: GIT rotation

 

 

 

3. Diaphragm: seen as a line separating chest from abdomen in longitudinal view,

Defects may be:

Absence of diaphragm causes right or left diaphragmatic hernia with herniation of abdominal structures into the chest, this commonly changes the axis and position of the fetal heart.

 

4. Liver, spleen and Gall bladder:

- The liver occupies the majority of the upper abdomen in the fetus.

- The smaller spleen is seen as the homogenous organ posterior to the stomach.

- The gall bladder is seen in the right upper abdomen at the inferior edge of the liver,  the gall bladder taker a teardrop shape (unlike the umbilical vein which is uniform and more to the midline).

Defects may be:

- Hepatomegaly are recorded in fetal anemia, glycogen storage disease and fetal infections,

- Shrunken liver (leading to decreased abdominal circumference) is seen in cases of fetal growth restriction

- Gall stones have been recorded as well as choledochal cyst.

- Spleenomegaly almost always denotes fetal infection.

 

5. Bowel: Apart from liver, spleen, stomach, urinary bladder, the rest of the abdomen is occupied by the bowel which appears as an area of midlevel or increased echogenecity.

 

Defects may be:

*Dilated: see above

*Echogenic bowel (as echogenic as iliac crest) is considered a soft tissue marker of chromosomal anomalies.

 

 

6.Kidneys: Normal size is expressed best as a ration of AC to kidney circumference which is 0.27 to 0.30 at any time of pregnancy.

Renal structure is examined to show a renal pelvis that may contain small amount of fluid (urine) surrounded by renal medulla that appears hypoechoic then the outer more echoic renal cortex.

 

Anomalies of fetal kidney involves agenesis, cystic kidneys and backpressure hydronephrotic changes.

- Agenesis is the absence of one or both kidneys

- Cystic kidneys = Potters disease which is of three types:

 -  Potter Type I = Infantile Polycystic kidneys:
This is an autosomal recessive condition. The responsible gene is in the short arm of chromosome 6. In this condition, the markedly enlarged kidneys are filled with numerous small cortical cysts and dilated collecting ducts. 
Features include: Oligohydramnios, bilaterally enlarged and homogeneously hyperechogenic kidneys.
- Potter Type II = Fetal Multicystic Renal dysplasia:
In the majority of cases, this is a sporadic abnormality but chromosomal abnormalities (mainly trisomy 18), genetic syndromes and other defects are present in about 50% of the cases. In fetal multicystic renal dysplasia the collecting tubules become cystic and the diameter of the cysts determines the size of the kidneys, which may be enlarged or small.  
Ultrasonographically, the kidneys are replaced by multiple irregular cysts of variable size with intervening hyperechogenic stroma. The disorder can be bilateral, unilateral or segmental; if bilateral, there is associated anhydramnios and the bladder is ‘absent’.
- Potter Type III = Renal Dysplasia; 
Potter type III renal dysplasia is characterized by markedly enlarged irregular kidneys with innumerable cysts of variable sizes interspersed amongnormal or compressed renal parenchyma. It is the common morphological expression of autosomal dominant adult polycystic kidney disease (APKD) and of other Mendelian disorders such as tuberous sclerosis, Jeune syndrome, Sturge–Weber syndrome, Zellweger syndrome, Lawrence Moon Biedl syndrome and Meckel–Gruber syndrome. 
Both kidneys are generally equally enlarged and only rarely is one involved so slightly that it remains of normal size. Look for other cysts in the liver, pancreas, spleen or lungs and search for cerebral aneurysms after birth.

- Hydronephrotic changes

Mild hydronephrosis is defined by the presence of an anteroposterior diameter of the pelvis of > 4 mm at 15–19 weeks, > 5 mm at 20–29 weeks and > 7 mm at 30–40 weeks.
Moderate and marked hydronephrosis is defined by anteroposterior pelvic diameter of more than 10 mm and pelvicalyceal dilatation, is usually progressive and in more than 50% of cases surgery is necessary during the first 2 years of life.
Hydronephrosis can also be classified according to aetiology and prognosis into:
Transient hydronephrosis may be due to relaxation of smooth muscle of the urinary tract by the high levels of circulating maternal hormones, or maternal–fetal overhydration. In the majority of cases, the condition remains stable or resolves in the neonatal period. 
True Hydronephrosis: there may be an underlying ureteropelvic junction obstruction or vesicoureteric reflux that requires postnatal follow-up and possible surgery. 

 

 

7.Urinary bladder; appears at the lower abdomen as a cystic structure. To differentiate the urinary bladder from other cysts; the UB changes in volume over time and the and visualization of the umbilical arteries along the lateral wall of the bladder confirms it as the urinary bladder.

Defects may be:

As the urinary bladder changes in volume it can occasionaly be seen as distended or absent in any single scan, thus, any of these findings should be confirmed by either re-scan after a minimum of 30 minutes.

Overdistended urinary bladder:

Bladders persistently larger than 15 mm in longitudinal diameter and associated with oligohydramnios, posterior urethral dilation (key-hole sign),  ureteral or renal pelvic dilation may be due to Posterior Urethral Valve (PUV), urethral atresia.

Absent Urinary bladder (non-visulaization of urinary bladder) can be due to renal agenesis, Potter disease, epispadias, bladder exstrophy, cloacal exstrophy, or bilateral ectopic ureters. Associated findings may be lower abdominal bulge, small penis with anteriorly displaced scrotum, low umbilical insertion, and widening of the iliac crests.

8. Genitalia can be detected as early as 14 weeks, is best viewed with both femurs seen in one view and search between thighs for external genital structures. Do not mention the gender if you do not see labia in a female fetus (do not diagnose female fetus by exclusion).

Anomalies may involve:

- Ambiguous genitalia may be identified

- Hydrocele of fetal testes is easily seen.