Fetal Abdomen & Pelvis Flashcards
(88 cards)
1
Q
When does the primordial gut form, and what does it develop from?
A
- Forms during the 6th menstrual week
Begins as a hollow tube with:
* Primordial mouth (stomodeum)
* Anal pit (proctodeum)
Surrounding tissues of the yolk sac and allantois fuse to form the umbilical cord
2
Q
What are the three parts of the primitive GI tract?
A
- Foregut
- Midgut
- Hindgut
3
Q
What structures are included in the foregut?
A
- Esophagus
- Stomach
- Liver
- Biliary tract
- Pancreas
- Part of duodenum
4
Q
What is the arterial supply for the foregut?
A
Celiac Artery
5
Q
What structures are included in the midgut?
A
- Distal duodenum
- Jejunum,
- Ileum
- Cecum
- Appendix
- Ascending colon
- Proximal transverse colon
6
Q
What is the arterial supply for the midgut?
A
Superior mesenteric artery
7
Q
What structures are included in the hindgut?
A
- Distal transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Upper anal canal
- Urogenital sinus
8
Q
What is the arterial supply for the hindgut?
A
Inferior mesenteric artery
9
Q
What happens if physiologic herniation does not return into the abdomen by 12 weeks?
A
Omphalocele
- Failure of intestinal loop to return from the umbilical cord to the abdominal cavity
- Results in herniated bowel and other viscera through the umbilical ring
- Covered by an avascular membrane (amnion)
- Occurs in 2.5 per 10,000 births
- Often associated with chromosomal abnormalities and malformations
- Has a high mortality rate (\~25%)
ities may occur
10
Q
What organs are identifiable early in the second trimester?
A
- By early 2nd trimester, abdominal organs reach normal adult position
- Liver, kidneys, and adrenal glands are easily identified
- Anechoic structures: gallbladder (GB), stomach, and blood-filled vessels
- Spleen and pancreas are difficult to visualize
11
Q
What organs are identifiable early in the third trimester?
A
- Fluid- or meconium-filled colon and collapsed small bowel may be visible
Measurement tip: In transverse view, place calipers outside the soft tissue surrounding the bony structures
12
Q
What is evaluated in the transverse plane of the fetal abdomen on ultrasound?
A
- Establishes fetal lie
- Determines abdominal situs
- Compares stomach position to the apex of the heart
- Normal finding: Both stomach and heart apex should be on the left side
13
Q
What is spine vs. skin integrity?
A
Skin (left) and spine (right)
14
Q
What structures are assessed in the transverse plane of the fetal abdomen?
A
- Spine
- Skin integrity
Biometry measurements
* Stomach
* Liver
* Portal venous system
15
Q
A
16
Q
What are these structures?
A
- Umbilical vein (intrahepatic segment)
- Liver
- IVC
- Descending aorta
- Spleen
- Fetal stomach
17
Q
A
18
Q
What are the key sonographic features of the fetal liver?
A
- It is a large, homogeneously echogenic organ located on the right.
- It grows throughout pregnancy.
- It is the most prominently visible structure in the fetal abdomen.
- The left lobe fills most of the left upper quadrant, lying anterior to the spleen and fluid-filled stomach.
19
Q
What are the key features of the umbilical cord?
A
- The allantois eventually becomes the umbilical vein and arteries.
- The cord normally contains 2 umbilical arteries and 1 vein.
- In 1% of singleton pregnancies, a single umbilical artery may occur.
- A 2-vessel cord is more common in twins.
- A 2VC is associated with GI, renal, or cardiac abnormalities and increased risk of trisomies.
20
Q
What trends are seen in umbilical artery Doppler indices as gestational age increases?
A
Doppler indices decrease as the fetus matures (more diastolic flow):
S/D ratio (systolic/diastolic):
* At 20 weeks, 50th percentile = 4.0
* At 30 weeks, 50th percentile = 2.83
* At 40 weeks, 50th percentile = 2.18
* RI (Resistive Index) decreases from 0.756 to 0.609
* PI (Pulsatility Index) decreases from 1.270 to 0.967
21
Q
What are the key sonographic features of the fetal gallbladder?
A
- Inactive in utero
- Teardrop shape
- Seen in 84% of fetuses, located at the undersurface of the liver
- One of three normal fluid-filled structures: gallbladder, stomach, bladder
- Any other fluid-filled structure may be abnormal
- Fetal gallstones are rare, but may appear in the 3rd trimester
22
Q
What does the absence of the gallbladder raise suspicion for?
A
Biliary atresia
23
Q
Where is the fetal aorta seen on ultrasound, and what does it terminate into?
A
- The aorta and branching renal arteries are seen in the fetal retroperitoneum
- The aorta terminates into the umbilical arteries in the pelvis
24
Q
How is the fetal stomach visualized on ultrasound?
A
- Seen as an ovoid or spherical fluid collection
- Located in the left upper quadrant of the fetal abdomen
25
What should be done if the fetal stomach bubble is not seen on ultrasound?
* The **stomach bubble** is normally visible after **16 weeks**
* If absent, **rescan after 20 minutes**
* If still not visible, **suspect esophageal atresia**
26
How does the fetal small intestine typically appear on ultrasound?
* Appears **mixed echogenic** with **cystic/hypoechoic texture**
* Echogenicity is **less than that of skeletal structures**
27
What is echogenic bowel and what is it associated with?
* **Echogenic bowel** is diagnosed when the bowel appears **as bright as bone** on ultrasound
* It is considered a **soft marker** for **chromosomal anomalies**, especially **Trisomy 21 (Down syndrome)**
28
What should you do if echogenic bowel is suspected on ultrasound?
* **Turn down the gain**
* **Compare bowel echogenicity to bone** to assess if it is abnormally bright
29
What are normal ultrasound findings for the fetal **small and large bowel**?
* **Peristalsis** should be seen by the **late second trimester**
* **Large bowel (colon)** becomes visible by **22 menstrual weeks**, appears **relatively hypoechoic**, and lies **near the kidneys**
* **Meconium** (bile, vernix, fetal hair, desquamated cells) may make the bowel appear **highly echogenic**
* However, **it should not be more echogenic than bone**
30
What measurements indicate bowel obstruction in the fetus?
* **Small bowel**: **> 7 mm**
* **Large bowel (colon)**: **> 20 mm**
* Dilated bowel on ultrasound may indicate **intestinal obstruction**
31
What are the sonographic features of the fetal diaphragm, and why is it important?
* The **diaphragm** is a **muscular dome** separating the **thoracic and abdominal cavities**
* Appears as a **hypoechoic band** between the **echogenic lungs** and **echogenic liver**
* It is a **useful landmark** for identifying **herniation defects**
32
What pelvic structures are evaluated in fetal ultrasound, and how can the rectum be distinguished?
* Iliac bones
* Sacrum
* Symphysis pubis
* Urinary bladder
* Rectum
* Small bowel
* Pelvic vessels
The **rectum lies posterior to the bladder** and has **similar echogenicity**
* If the **bladder is empty or small**, the **colon may be mistaken** for the bladder
33
What are the key sonographic features of the fetal bladder and their significance?
* Usually visible **transabdominally from 12 weeks of gestation**
* Normally empties every **30 to 45 minutes**
* **Filling** of the bladder implies **normal renal function**
* **Helps exclude bilateral renal agenesis**
34
What are three important non-specific clues that may indicate fetal anomalies on ultrasound?
* **Polyhydramnios**
* **Oligohydramnios**
* **Elevated AFP (alpha-fetoprotein)**
These clues help guide a **targeted examination** for possible **underlying fetal anomalies**, even when they are **unsuspected before the anatomy scan**.
35
How is polyhydramnios classified by DVP and AFI measurements?
**Mild:**
* DVP: **>8 to <12 cm**
* AFI: **>24 to <30 cm**
**Moderate:**
* DVP: **≥12 to <16 cm**
* AFI: **≥30 to <35 cm**
**Severe:**
* DVP: **≥16 cm**
* AFI: **≥35 cm**
36
What measurements define oligohydramnios?
* **AFI (Amniotic Fluid Index): ≤ 5 cm**
* **DVP (Deepest Vertical Pocket): < 2 cm**
37
Poly vs. Oligo
38
What are the four important herniation abnormalities in fetal development?
* Omphalocele
* Gastroschisis
* Limb-body wall complex
* Cloacal exstrophy
39
What is an omphalocele and how does it appear sonographically?
* **Midline abdominal wall defect**
* Involves **extrusion of gut** into the **base of the umbilical cord**
* The herniated organs are **covered by a membrane** made of **parietal peritoneum and amnion**
40
What are common associated abnormalities with omphalocele?
* **Trisomies 13, 18, 21**
* **Beckwith-Wiedemann Syndrome**
* **Pentalogy of Cantrell**
* **Turner Syndrome**
**Cloacal exstrophy** – severe defect with exposed abdominal organs
**Cardiac abnormalities**, including:
* Transposition of great vessels
* Atrial and ventricular septal defects
* Tetralogy of Fallot
* Pulmonary artery stenosis
* Double-outlet right ventricle
* Coarctation of the aorta
41
What causes an omphalocele and why is prenatal diagnosis important?
* Caused by the **failure of the intestines to return to the abdomen by 12 weeks** during the **second stage of intestinal rotation**
* Has a **high incidence of associated anomalies and chromosomal abnormalities** (50%)
* **Prenatal diagnosis is essential** to avoid **rupture of the omphalocele sac during delivery**, which can lead to **sepsis**
42
What are the sonographic signs of an omphalocele?
* **Complex mass** extending from the **anterior abdomen**, **contiguous with the umbilical cord**
* **Membranous sac** covering the **herniated organs**
* Contents may include **fluid-filled bowel loops, mesentery, omentum, liver, pancreas, spleen**
* **Smaller-than-expected abdominal circumference**
* Associated with **polyhydramnios**
43
What is gastroschisis and how is it different from omphalocele?
* **Anterior abdominal wall defect** usually **adjacent to the umbilical cord**
* Typically involves **herniation of small bowel only**
* **No membrane** covering the herniated bowel
* **Not associated with chromosomal anomalies**
* **High survival rate** and **successful treatment**
* Unlike omphalocele, **gastroschisis is usually isolated** and lacks a protective sac the cord insertion through which abdominal viscera herniates
44
What is the commonality of associated anomalies with gastroschisis?
Usually isolated without other anomalies
* Intestinal malrotation
* Intestinal atresia
* Intestinal stenosis
* IUGR
45
What sono signs indicate gastroschisis?
* Thick-walled free-floating loops of bowel
* No membranous sac covering the hernia
* Cord insertion identified adjacent(lateral to the herniation defect
* Smaller than expected abdominal circumference
* May be associated with polyhydramnios
46
Omaphacele vs Gastroschisis
47
What is the primary defect seen in Limb-Body Wall Complex (Body Stalk Anomaly)?
* **Lethal** anomaly involving the anterior abdominal wall
* Caused by **left-sided abdominoschisis**
* **Absent umbilical cord**
* **Abdominal viscera exteriorized** and **attached directly to the placental surface**
48
What are the possible causes of Limb-Body Wall Complex and its prognosis?
**Causes:**
* Rupture of the **amniotic membrane**
* Early **ischemic insult** due to vascular abnormalities
* Disruption in the formation of **anterior embryologic folds**
**Prognosis:**
* **Lethal condition** — typically results in death **before or shortly after birth**
49
What abnormalities are commonly associated with Limb-Body Wall Complex?
* **Neural tube defects**
* **Facial clefts**
* **Encephalocele**
* **Exencephaly**
* **Caudal regression syndrome**
**Limb anomalies** such as:
* **Clubfoot**
* **Oligodactyly** (missing digits)
* **Brachydactyly** (short digits)
* **Syndactyly** (webbed digits)
* **Arthrogryposis** (joint contractures)
* **Amelia** (absent limbs)
50
What are the sono findings of Limb-Body Wall Complex?
* **Grossly and dramatically abnormal appearance**
* **Fetus appears tethered to the placenta**, no free movement
* **No free-floating cord** (**short or absent umbilical cord**)
* **Herniation of liver and abdominal viscera**
* **No membrane present**
* **Scoliosis**
51
What is cloacal exstrophy?
* A **rare birth defect** involving abnormal development of the **cloaca**
* Results in the **urinary, genital, and intestinal tracts merging into one common channel**
* Involves **anomalies of the rectum and urinary bladder**
52
What are the components of the triad of congenital anomalies in cloacal exstrophy?
* Lower abdominal wall defect
* Exstrophy of the bladder
* Omphalocele
## Footnote
Distribution of this formation results in extensive abnormalities **of the lower abdominal wall.**
53
What is gastrointestinal atresia?
* **Narrowing** of the hollow lumen of the gut from esophagus to anus
* **Fluid accumulation proximal to the obstruction**
**Types:**
* **Esophageal atresia** → **No stomach or small stomach**
* **Duodenal atresia** → **"Double-bubble" sign**
* Associated with **polyhydramnios** (POLY)
54
What is esophageal atresia?
**Esophageal atresia** refers to the **interruption of the esophageal lumen**, typically occurring **in the chest**.
55
What sono signs indicate esophageal atresia?
* Polyhydramnios
* IUGR
* Failure to demonstrate stomach on serial sonograms
56
What is the most common type of esophageal atresia?
The most common type of esophageal atresia is **Type C: Esophageal atresia with tracheoesophageal fistula (TEF)** between the **trachea and distal esophageal segment**, accounting for **85%** of cases.
57
Why can't the presence of a stomach bubble rule out esophageal atresia?
Because in **85% of cases**, esophageal atresia is associated with a **tracheoesophageal fistula (Type C)**, allowing **amniotic fluid to reach the stomach** and create a visible bubble, even in the presence of **polyhydramnios**.
58
What are the sonographic signs of duodenal atresia, and what syndrome is it often associated with?
* **"Double-Bubble" sign**: fluid-filled stomach and proximal duodenum
* **Polyhydramnios** is always present
* May not be apparent until **24 weeks** gestation
* **30–50%** of cases are associated with **Down syndrome (Trisomy 21)**
## Footnote
Interruption of the GI tract in descending and
inferior portions of the duodenum
59
What sonographic findings suggest small bowel obstruction in a fetus?
* **Bowel loop > 7 mm** in the second trimester
* **Hyper-peristalsis**
* **Gross fetal abdominal distension**
* **Intra-abdominal calcifications**
* **Polyhydramnios**
* Consider **intestinal atresia** when these findings are present.
60
What are the sonographic signs of fetal small bowel obstruction?
* **Multiple dilated fluid-filled bowel loops**
* **Small bowel inner diameter > 7 mm**
* **Abdominal distention** (AC measurement greater than expected for gestational age)
61
What is meconium peritonitis and what causes it?
Meconium peritonitis is an **inflammatory reaction** caused by the **spillage of sterile, but irritating fetal meconium (stool)** into the **peritoneal cavity** due to a **bowel rupture**, leading to a secondary inflammatory response visible on a sonographic exam.
62
What are the **sonographic findings** associated with **meconium peritonitis**?
* **Echogenic bowel**
* **Fetal ascites**
* **Intraperitoneal calcifications**
* **Meconium pseudocysts**
* **Polyhydramnios**
63
What is the clinical significance of echogenic fetal bowel (EFB) on ultrasound?
* **Isolated finding in up to 70%** of cases
* **Associated with trisomy** and other clinically significant problems
* **Requires thorough evaluation** of all fetal systems
* **Rule of thumb:** Normal fetal bowel is **less echogenic than bone**, especially the **iliac bone**
of fluid in the abdomen that mimics ascites
64
What are the three sonographic parameters assessed when evaluating the fetal liver?
1. **Size**
2. **Parenchymal heterogeneity**
3. Presence of **solid or cystic** components
65
What is hepatomegaly, and what are its possible associations and sonographic findings in a fetus?
* **Hepatomegaly** is the **enlargement of the fetal liver**.
It may be associated with:
* **Rh isoimmunization**
* **Congenital infection**
* Certain **syndromes**
**Sonographic finding**: Liver fills the **epigastrium** and **right upper quadrant (RUQ)**.
66
What does loss of hepatic parenchymal homogeneity indicate on fetal ultrasound, and what is the normal appearance of the fetal liver?
**Loss of hepatic parenchymal homogeneity** may suggest **liver pathology or abnormality**.
**Normal fetal liver** is:
* **Moderately homogeneous**
* **Solid in appearance**
Contains **multi-sized anechoic structures** representing:
* **Hepatic arteries**
* **Hepatic veins**
* **Portal veins**
* **Biliary system**
67
What associated abnormalities can cause loss of parenchymal homogeneity in the fetal liver, and what does this sonographic finding suggest?
Associated abnormalities include:
* **Hepatitis**
* **Ischemic insults**
* **Portal and hepatic venous thromboembolism**
* **Infections** such as **cytomegalovirus**, **herpes simplex**, **varicella zoster**, and **toxoplasmosis**
**Sonographic Appearance:**
* **Loss of parenchymal homogeneity** is a key sign that may **indicate the presence** of one or more of these conditions.
68
What does the presence of a solid hepatic mass on fetal ultrasound typically indicate, and what types of neoplasms are included?
A **solid hepatic mass** is **almost always an ominous sonographic sign**.
It may represent **benign or malignant neoplasms**, including:
* **Hemangioma**
* **Mesenchymal hamartoma**
* **Hepatoblastoma**
* **Metastases (mets)**
69
What are the sonographic signs of a solid hepatic mass?
**Focal, echogenic**, or **complex mass** in the **liver**
**Doppler** shows **arterial blood supply** with either **high or low resistance**
70
What are the characteristics and causes of cystic hepatic masses on fetal ultrasound?
* **Uncommon findings** and usually of **little clinical significance**
* Most are **biliary in origin**, such as **hepatic cysts**
A **choledochal cyst** is a **rare disorder** of **biliary tract development**
* It shows **dilated bile ducts** entering the cyst
* It is a **congenital segmental cystic dilatation** of the **intrahepatic** or **extrahepatic bile ducts**, most commonly affecting the **main portion of the extrahepatic duct (ED)**
71
What are the sonographic signs of a cystic hepatic mass?
* **Well-circumscribed**, **anechoic mass** within the **liver**
* **Separate from the gallbladder (GB)**
* Shows **posterior acoustic enhancement**
72
What should be considered when hepatic calcifications are found on fetal ultrasound?
* **Relatively common** finding
* **Site**, **size**, and **distribution** of the lesions are key for **management decisions**
* If **calcifications are the only finding** and **infection tests are negative**, the **prognosis is promising**
* Important to assess for additional findings such as **liver involvement**, **abdominal or retroperitoneal masses**, and **ascites**
73
What infections are commonly associated with hepatic calcifications in the fetus?
**Cytomegalovirus (CMV)** – a common **herpesvirus**, caused by **human cytomegalovirus (HCMV)**
* * **Toxoplasmosis**
* **Rubella**
* **Syphilis**
* **Herpes simplex**
74
What are the sonographic patterns of hepatic calcifications?
* **Diffuse**: **Small**, **multiple echogenic foci** within the **liver parenchyma** that may or may not cast **acoustic shadows**
* **Focal**: **Large, focal calcifications** in the **liver parenchyma** that **cast acoustic shadows**
* **Extrahepatic**: **Small, multiple echogenic foci** scattered over the **peritoneal layer** of the liver that may or may not cast **acoustic shadows**
75
What are typical gallbladder (GB) abnormalities seen in fetal ultrasound?
* **GB is visualized in 82–100%** of fetuses during the **2nd and 3rd trimester**
* After **28 weeks**, it’s common to see **echogenic material** in the **GB lumen**
* This is usually an **incidental finding** with **no significant concern**, and the cause is **unknown**
76
What are the sonographic signs of **echogenic filling** in the fetal gallbladder?
* **Echogenic foci** within the **fetal gallbladder (GB)**
* May cast **posterior acoustic shadow** or **ring-down artifact**
* Indicates possible **gallstones** or **sludge**
77
What does **fetal biliary sludge** look like on ultrasound, and what is its clinical significance?
* Seen in the **third trimester**
* **Gallbladder filled with echogenic sludge**
* **No other anomaly** typically found
* **Sludge resolves spontaneously after birth**
78
What does a **septated fetal gallbladder** indicate on prenatal ultrasound?
* Observed in the **third trimester**
* **Sagittal ultrasound** shows **several septa** within the GB
* **No associated fetal anomalies** pre- or postnatally
79
What are the two main types of splenic abnormalities seen in fetal ultrasound?
* **Rare and few** in occurrence
* **Splenomegaly**: caused by **infections** the fetus has been exposed to, such as **cytomegalovirus**
* **Splenic cysts**: can be **primary** or **pseudocysts**
80
What are the sonographic signs of a splenic cyst?
* **Well-circumscribed**, **anechoic lesion** in the **splenic parenchyma**
* Shows **posterior acoustic enhancement**
81
What causes fetal ovarian cysts and how common are they?
* **Stimulation to the fetal ovaries** from the **mother’s hormones** can cause cyst formation
* Cysts can **fill the entire pelvic region**
* **Unilateral** cysts are **more common** than bilateral
82
What are the sonographic signs of a fetal ovarian cyst?
* Appears as a **simple cystic mass** in the **fetal pelvis**
* Located **separately from the GI tract, kidney, ureter, and bladder**
* **Fetus is identified as a female**
* May be **difficult to distinguish** from **urachal or mesenteric cysts**
83
What should you suspect if you see a mass in the sacral area on fetal ultrasound?
* **Think teratoma!**
* Most are **benign**, but may **grow large** and **threaten fetal viability**
84
What are the two main types of sacral teratomas?
1. **Pre-sacral teratomas**: arise from the **anterior sacrum** and grow into the **fetal pelvis**
2. **Sacroccocygeal teratomas**: arise from the **posterior sacrococcygeal area** and **project exophytically** into the **amniotic cavity**
85
What are some associated abnormalities with sacral teratomas?
* **Myelomeningocele**
* **Vertebral anomalies**
* **Hydrops fetalis**
* **Ureteral obstruction**
* **GI obstruction**
* **Tumor rupture**
* **Dystocia** (difficult labor and/or birth)
86
What are the typical sonographic signs of a sacral teratoma?
* **Complex, large mass** in the **fetal pelvis** arising from the **fetal rump**
* May contain **cystic**, **solid**, and **calcific components**
87
What is pseudoascites and how can it be mistaken for true ascites?
* **Pseudoascites** is a **hypoechoic band** around the **anterior abdominal surface**
* It represents the **abdominal musculature** of the fetus
* It may **resemble true ascites** due to its **low-level echogenicity**
88
What are the diagnostic criteria for identifying pseudoascites?
* **Confined to the anterior and anterolateral abdomen**
* **Traceable to the ends of the fetal ribs**
* **Not found in peritoneal recesses**
* Does **not outline the falciform ligament** or **umbilical vein**
* Does **not outline intra-abdominal structures** like the **bowel** or **intra-abdominal extrahepatic umbilical vein**
