Ultrasound — MCQs

Ultrasound Indian Medical PG Practice Questions and MCQs

Question 91: Ultrasound diagnoses all the following except?

A. Anencephaly
B. Down syndrome (Correct Answer)
C. Placenta previa
D. Hydatidiform mole

Explanation: **Explanation:** The correct answer is **Down Syndrome (Option B)** because ultrasound is a **screening tool**, not a definitive diagnostic tool, for chromosomal abnormalities. 1. **Why Down Syndrome is the correct answer:** While ultrasound can identify "soft markers" associated with Down syndrome (Trisomy 21)—such as increased **Nuchal Translucency (NT)** in the first trimester, an absent nasal bone, or cardiac defects—these findings are only suggestive. A definitive diagnosis requires **karyotyping** or chromosomal analysis via invasive procedures like Amniocentesis or Chorionic Villus Sampling (CVS). 2. **Why the other options are incorrect:** * **Anencephaly:** This is a structural neural tube defect characterized by the absence of the cranial vault and cerebral hemispheres (the "Frog-eye appearance"). It is easily diagnosed via ultrasound as early as 10–12 weeks. * **Placenta Previa:** Ultrasound is the **gold standard** for localizing the placenta. It can clearly visualize the relationship between the placental edge and the internal os of the cervix. * **Hydatidiform Mole:** Ultrasound is diagnostic for molar pregnancies, typically showing a characteristic **"Snowstorm appearance"** (a vesicular mass with multiple small cystic spaces) and the absence of a fetus in a complete mole. **High-Yield Clinical Pearls for NEET-PG:** * **Nuchal Translucency (NT):** Measured between 11 and 13+6 weeks. A value >3mm is highly suspicious for aneuploidy. * **Snowstorm Appearance:** Classic USG sign for Hydatidiform mole. * **Frog-eye/Mickey Mouse Appearance:** Classic USG sign for Anencephaly. * **Double Bubble Sign:** USG finding in Duodenal Atresia, often associated with Down Syndrome.

Question 92: What is the best investigation for diagnosing minimal right pleural effusion?

A. Right lateral decubitus X-ray
B. CT scan
C. Ultrasound (USG) (Correct Answer)
D. Left lateral decubitus X-ray

Explanation: **Explanation:** The diagnosis of pleural effusion depends on the sensitivity of the imaging modality to detect small volumes of fluid. **Ultrasound (USG)** is the correct answer because it is highly sensitive and can detect as little as **5–20 mL** of pleural fluid. It is superior to conventional radiography for identifying minimal effusions, differentiating fluid from pleural thickening, and identifying loculations. **Analysis of Options:** * **A & D (Lateral Decubitus X-ray):** While more sensitive than an upright PA view (which requires ~200 mL to show costophrenic angle blunting), a lateral decubitus film still requires approximately **25–50 mL** of fluid to be visible. For a right-sided effusion, a **Right** lateral decubitus view is used (fluid layers down). * **B (CT Scan):** CT is the "gold standard" for characterizing pleural anatomy and can detect very small amounts of fluid (~10 mL). However, it is not considered the "best" initial investigation due to high radiation dose, cost, and lack of portability compared to USG. **High-Yield Pearls for NEET-PG:** 1. **Sensitivity Thresholds:** * **USG:** 5–20 mL (Most sensitive bedside tool). * **Lateral Decubitus X-ray:** 25–50 mL. * **Upright PA X-ray:** 175–200 mL (blunting of costophrenic angle). * **Lateral X-ray (Upright):** 75 mL (blunting of posterior costophrenic sulcus). 2. **USG Sign:** The "Quad sign" and "Sinusoid sign" are classic sonographic findings of pleural effusion. 3. **Clinical Utility:** USG is the investigation of choice for **guiding thoracocentesis**, significantly reducing the risk of iatrogenic pneumothorax.

Question 93: What is the single most sensitive marker of intrauterine growth restriction on ultrasonography?

A. Abdominal Circumference (AC) (Correct Answer)
B. Amniotic Fluid Index (AFI)
C. Femur Length (FL)
D. Biparietal Diameter (BPD)

Explanation: **Explanation:** **Abdominal Circumference (AC)** is the single most sensitive ultrasound parameter for diagnosing Intrauterine Growth Restriction (IUGR). The physiological basis lies in the fact that the fetal liver is the first organ to be affected by chronic placental insufficiency. IUGR leads to a depletion of fetal glycogen stores in the liver and a reduction in subcutaneous fat. Since the AC measurement primarily reflects the size of the liver and the thickness of the abdominal wall fat, it decreases significantly before other skeletal parameters are affected. **Analysis of Options:** * **Amniotic Fluid Index (AFI):** While oligohydramnios (low AFI) is a common association and a sign of fetal distress in IUGR, it is a non-specific marker and can occur due to various other causes (e.g., PROM, renal anomalies). * **Femur Length (FL) & Biparietal Diameter (BPD):** These are markers of skeletal growth. In "Asymmetrical IUGR" (the most common type), the fetus exhibits "brain-sparing," meaning the head and long bones continue to grow while the body remains small. Therefore, BPD and FL remain relatively preserved until the late stages of growth restriction. **Clinical Pearls for NEET-PG:** * **Most sensitive single parameter:** Abdominal Circumference (AC). * **Most sensitive ratio:** HC/AC ratio (Head Circumference/Abdominal Circumference). This ratio is elevated in asymmetrical IUGR. * **Earliest sign of IUGR on Doppler:** Increased resistance/pulsatility index in the **Umbilical Artery**. * **Gold Standard for Monitoring:** Umbilical Artery Doppler is the best tool for managing IUGR and deciding the timing of delivery.

Question 94: At what gestational week is accurate diagnosis of anencephaly typically seen on ultrasound?

A. 6 weeks of gestation
B. 8 weeks of gestation
C. 10 weeks of gestation
D. 14 weeks of gestation (Correct Answer)

Explanation: **Explanation:** Anencephaly is a lethal neural tube defect characterized by the absence of the cranial vault (acrania) and the cerebral hemispheres. The diagnosis relies on the visualization of the ossified skull vault. **Why 14 weeks is the correct answer:** While the precursor to anencephaly (exencephaly) can sometimes be suspected earlier, the definitive diagnosis of anencephaly is typically made at **11–14 weeks**. By 14 weeks, the **ossification of the fetal calvarium** is complete and clearly visible on ultrasound. Before this period, the lack of mineralization in a normal fetus can mimic the absence of the skull, leading to false positives. At 14 weeks, the classic "Frog-eye appearance" (Mickey Mouse sign) due to prominent orbits and absence of the forehead is most reliably identified. **Analysis of Incorrect Options:** * **6 weeks (A):** At this stage, only the gestational sac and yolk sac are typically visible. Organogenesis is still in the very early stages. * **8 weeks (B):** The rhombencephalon (a normal cystic space in the hindbrain) is visible at this stage, but the skull vault has not yet begun significant mineralization. * **10 weeks (C):** Although the choroid plexus is visible, the calvarium is not sufficiently ossified to distinguish between normal development and acrania/anencephaly with certainty. **High-Yield Clinical Pearls for NEET-PG:** * **Mickey Mouse Sign / Frog-eye Sign:** Pathognomonic ultrasound appearance of anencephaly in the coronal plane. * **Sequence:** It usually starts as **Exencephaly** (exposed brain tissue) which progresses to **Anencephaly** due to mechanical trauma and chemical erosion by amniotic fluid (Angiomatous stroma). * **Associated Finding:** **Polyhydramnios** is common in the second/third trimester because the fetus lacks the swallowing reflex. * **Biochemical Marker:** Elevated **Alpha-fetoprotein (AFP)** in maternal serum and amniotic fluid. * **Prevention:** 400 mcg/day of Folic acid (4 mg/day for high-risk) started pre-conceptionally.

Question 95: What is Doppler ultrasonography used for in twin pregnancies?

A. Twin to twin transfusion
B. Conjoined twins
C. Diagnosis of twins
D. All of the above (Correct Answer)

Explanation: **Explanation:** Doppler ultrasonography is a versatile tool in the management of multiple gestations, used for both diagnostic confirmation and hemodynamic monitoring. 1. **Twin-to-Twin Transfusion Syndrome (TTTS):** This is the most critical application. Doppler is used to assess the umbilical artery, ductus venosus, and middle cerebral artery (MCA) to monitor fetal distress and hemodynamic imbalance between the donor and recipient twins in monochorionic pregnancies. 2. **Conjoined Twins:** While B-mode ultrasound identifies the physical connection, Doppler is essential to evaluate shared vascular structures (e.g., shared hearts or hepatic vessels). This is crucial for surgical planning and determining viability. 3. **Diagnosis of Twins:** Color Doppler can be used early in pregnancy to identify separate fetal heartbeats and confirm the presence of multiple viable embryos, especially when B-mode imaging is ambiguous. **Why "All of the Above" is correct:** While Doppler is most famously associated with TTTS, its utility spans the entire spectrum of twin management—from initial confirmation of life to the complex anatomical assessment of conjoined twins. **High-Yield Clinical Pearls for NEET-PG:** * **TTTS Staging:** The **Quintero Staging System** uses Doppler findings (absent or reversed end-diastolic flow) to categorize the severity of TTTS. * **Twin Anemia Polycythemia Sequence (TAPS):** Diagnosed primarily using **MCA-PSV** (Peak Systolic Velocity) Doppler to detect discordant hemoglobin levels. * **TRAP Sequence:** Doppler is used to identify the "pump twin" and the retrograde flow in the "acardiac twin." * **Lambda vs. T-sign:** Remember that these are B-mode findings for chorionicity, but Doppler confirms the vascularity within the intervening membrane.

Question 96: Parallel shotgun appearance on Ultrasound is seen in which of the following conditions?

A. Portal hypertension
B. Biliary ascariasis
C. Obstructive jaundice (Correct Answer)
D. Sclerosing cholangitis

Explanation: **Explanation:** The **"Shotgun Sign"** (also known as the "Double-Channel Sign") is a classic ultrasonographic finding in **Obstructive Jaundice**. Under normal physiological conditions, the intrahepatic bile ducts are too small to be visualized on a routine ultrasound. However, when there is a distal obstruction (e.g., choledocholithiasis or periampullary carcinoma), the bile ducts dilate. On ultrasound, the dilated intrahepatic bile duct runs parallel to the adjacent portal vein branch. Since both tubes are fluid-filled and approximately equal in diameter, they resemble the twin barrels of a double-barreled shotgun. **Analysis of Options:** * **Obstructive Jaundice (Correct):** Obstruction leads to proximal dilatation of the biliary tree. The dilated duct (anterior) and the portal vein (posterior) create the parallel shotgun appearance. * **Portal Hypertension:** This typically presents with a dilated portal vein, splenomegaly, and portosystemic collaterals. It does not cause biliary dilatation unless there is associated portal cavernoma formation (portal biliopathy), which is not the primary cause of this sign. * **Biliary Ascariasis:** This is characterized by a "linear echogenic structure" (the worm) within the bile duct, often showing a "tube-within-a-tube" or "strip" appearance, rather than a simple parallel shotgun sign. * **Sclerosing Cholangitis:** This condition usually presents with irregular, "beaded" appearances of the bile ducts due to alternating segments of strictures and focal dilatations, rather than uniform parallel dilatation. **High-Yield Clinical Pearls for NEET-PG:** * **Flash Sign:** Using Color Doppler can help differentiate the two "barrels"; the portal vein will show flow, while the dilated bile duct will not. * **Stellate Pattern:** In severe cases, multiple dilated ducts converging toward the porta hepatis create a "star-shaped" or stellate configuration. * **Duct Size:** An intrahepatic bile duct is considered dilated if it is >2 mm or more than 40% of the diameter of the adjacent portal vein.

Question 97: Anencephaly is best diagnosed using which of the following methods?

A. Maternal serum alpha-fetoprotein
B. Amniotic fluid alpha-fetoprotein
C. Ultrasound (USG) (Correct Answer)
D. X-ray

Explanation: **Explanation:** **Anencephaly** is a lethal neural tube defect (NTD) characterized by the absence of the cranial vault (acrania) and the cerebral hemispheres. **Why Ultrasound (USG) is the Correct Answer:** Ultrasound is the **gold standard and investigation of choice** for diagnosing anencephaly. It can reliably detect the condition as early as the late first trimester (11–14 weeks). The classic sonographic findings include the **"Frog-eye appearance"** (Mickey Mouse sign) due to prominent orbits and the absence of the calvarium above the level of the orbits. USG is preferred because it is non-invasive, provides real-time visualization, and has nearly 100% sensitivity for this condition after the first trimester. **Analysis of Incorrect Options:** * **Maternal Serum Alpha-Fetoprotein (MSAFP):** While MSAFP is a screening tool for NTDs (levels are elevated), it is not diagnostic. High levels require confirmation via ultrasound. * **Amniotic Fluid Alpha-Fetoprotein (AFAFP):** This is an invasive procedure (amniocentesis). While it shows elevated AFP and Acetylcholinesterase, it is rarely used for diagnosis today because USG provides a definitive diagnosis non-invasively. * **X-ray:** Historically used to show the absence of the skull vault, but it is now obsolete due to radiation risks to the fetus and the superior resolution of USG. **Clinical Pearls for NEET-PG:** * **Earliest Diagnosis:** Can be suspected at 10-14 weeks (Acrania-Anencephaly sequence). * **Associated Finding:** **Polyhydramnios** is common in the second trimester because the fetus lacks the swallowing reflex. * **Key Sign:** "Frog-eye" or "Mickey Mouse" appearance on coronal/axial views. * **Screening:** Elevated MSAFP (>2.5 MoM) is the first step in screening for open NTDs.

Question 98: What is the earliest detectable congenital malformation by ultrasound?

A. Anencephaly (Correct Answer)
B. Spina bifida
C. Meningocele
D. Cystic hygroma

Explanation: **Explanation:** **Anencephaly** is the correct answer because it is a major neural tube defect characterized by the absence of the cranial vault and cerebral hemispheres. It can be reliably detected as early as **11 to 14 weeks** of gestation (late first trimester) during the routine nuchal translucency scan. The diagnosis is based on the **"Mickey Mouse sign"** (the appearance of prominent orbits without a surrounding calvarium) or the **"Frog-eye sign"** in the coronal view. Since the skull vault normally ossifies by 10–11 weeks, its absence is the earliest structural malformation visible on ultrasound. **Analysis of Incorrect Options:** * **Spina Bifida:** While it can sometimes be suspected in the late first trimester via indirect signs (like intracranial translucency), a definitive diagnosis usually requires a mid-trimester (18–22 weeks) anomaly scan to visualize the vertebral arch defect and secondary brain signs (Lemon/Banana signs). * **Meningocele:** Similar to spina bifida, this protrusion of meninges is typically diagnosed during the second-trimester anatomy survey when the fetal spine and skull are more developed. * **Cystic Hygroma:** Although it can be seen in the first trimester (associated with Turner syndrome), it is technically a lymphatic malformation/fluid collection rather than a primary structural "congenital malformation" of an organ system that predates the detection of anencephaly. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Sign:** Absence of the "calvarial echo." * **AFP Levels:** Anencephaly is associated with markedly **elevated Maternal Serum Alpha-Fetoprotein (MSAFP)**. * **Polyhydramnios:** Often occurs in the second/third trimester due to the fetus's inability to swallow amniotic fluid. * **Prevention:** Periconceptional **Folic Acid (400 mcg/day)** reduces the risk of neural tube defects by 70%.

Question 99: What is the most accurate method for estimating gestational age using ultrasonography?

A. Head circumference
B. Abdominal circumference
C. Biparietal diameter
D. Crown-rump length (Correct Answer)

Explanation: **Explanation:** The **Crown-Rump Length (CRL)** is the most accurate parameter for estimating gestational age (GA) in the first trimester (specifically between 7 and 13 weeks). During this period, fetal growth is rapid and biological variation is minimal because growth is largely unaffected by external factors like placental insufficiency or genetic growth potential. The margin of error for CRL is only **±3 to 5 days**. **Analysis of Options:** * **Crown-Rump Length (CRL):** Correct. It is the gold standard for dating. Once the CRL exceeds 84 mm (approx. 14 weeks), its accuracy decreases, and second-trimester parameters must be used. * **Biparietal Diameter (BPD):** This is the most accurate parameter in the **second trimester** (up to 20 weeks), with an error margin of ±7 to 10 days. However, it is less accurate than CRL. * **Head Circumference (HC):** While a reliable predictor of GA in the second trimester and less affected by head shape (dolichocephaly/brachycephaly) than BPD, it still lacks the precision of first-trimester CRL. * **Abdominal Circumference (AC):** This is the **least accurate** parameter for dating as it is highly sensitive to fetal nutrition and growth restriction (IUGR). Its primary role is assessing fetal weight and growth rather than GA. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Sign of Pregnancy on USG:** Gestational Sac (seen at ~4.5–5 weeks). * **First Fetal Structure Visualized:** Yolk Sac (seen at ~5 weeks; confirms intrauterine pregnancy). * **Rule of Thumb:** If there is a discrepancy between LMP and USG dating, the **earliest ultrasound** (CRL) is always considered the most reliable for establishing the EDD. * **Mean Sac Diameter (MSD):** Used if the embryo is not yet visible; however, CRL is superior once the fetal pole appears.

Question 100: The diagnostic feature of congenital diaphragmatic hernia on prenatal ultrasonography is:

A. A cyst behind the left atrium
B. Mediastinal shift with normal heart axis
C. Peristalsis in the thoracic cavity (Correct Answer)
D. Abnormally large abdominal circumference

Explanation: **Explanation:** Congenital Diaphragmatic Hernia (CDH) occurs due to the failure of the pleuroperitoneal membranes to fuse, most commonly on the left side (Bochdalek hernia). This allows abdominal viscera to herniate into the thoracic cavity. **Why Option C is correct:** The presence of **peristalsis in the thoracic cavity** is the most specific and pathognomonic sign of CDH on prenatal ultrasound. It directly visualizes the movement of bowel loops within the chest, confirming that abdominal contents have displaced into the thorax. **Analysis of Incorrect Options:** * **Option A:** While a fluid-filled stomach (which may look like a cyst) is often seen behind the left atrium, it is not as definitive as active peristalsis. Furthermore, the stomach is usually displaced **laterally** rather than directly behind the atrium. * **Option B:** CDH typically causes a significant **mediastinal shift** toward the contralateral side, but the **heart axis is usually abnormal** (levocardia or dextrocardia) due to compression by the herniated mass. * **Option D:** In CDH, the abdominal circumference is **abnormally small (scaphoid abdomen)** because the abdominal organs have migrated into the chest. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Left side (85%), through the **Foramen of Bochdalek** (Posterolateral). * **Key USG findings:** Herniated bowel/stomach in the chest, mediastinal shift, and **polyhydramnios** (due to esophageal compression). * **Prognostic indicator:** The **Lung-to-Head Ratio (LHR)** is used to predict pulmonary hypoplasia and postnatal survival. * **Associated Malformation:** Pulmonary hypoplasia and persistent pulmonary hypertension are the primary causes of postnatal mortality.

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Ultrasound — MCQs

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