Ultrasound — MCQs

Ultrasound Indian Medical PG Practice Questions and MCQs

Question 81: What is the investigation of choice for a pregnant lady presenting with an upper abdominal mass?

A. Barium meal
B. MRI (Correct Answer)
C. CT scan
D. DSA

Explanation: **Explanation:** The investigation of choice for a pregnant patient with an upper abdominal mass is **MRI**. **1. Why MRI is the Correct Answer:** In pregnancy, the primary goal is to achieve high diagnostic accuracy while ensuring fetal safety. MRI is the preferred modality because it provides excellent soft-tissue contrast and anatomical detail without the use of ionizing radiation. According to current guidelines, MRI is considered safe during all trimesters of pregnancy. It is particularly superior for characterizing complex masses (e.g., adnexal, hepatic, or pancreatic) when Ultrasound (the initial screening tool) is inconclusive. **2. Why Other Options are Incorrect:** * **CT Scan:** Uses ionizing radiation, which carries risks of teratogenesis and fetal carcinogenesis, especially during the first trimester. It is generally avoided unless it is a life-threatening emergency where MRI is unavailable. * **Barium Meal:** This is a fluoroscopic procedure involving significant radiation exposure to the maternal abdomen and fetus. Furthermore, it only evaluates the lumen of the GI tract and cannot characterize an extrinsic abdominal mass. * **DSA (Digital Subtraction Angiography):** An invasive procedure involving high-dose radiation and iodinated contrast. It is reserved for therapeutic interventions (like embolization), not primary diagnosis. **Clinical Pearls for NEET-PG:** * **First-line investigation** for any abdominal pathology in pregnancy: **Ultrasound (USG)**. * **Investigation of choice (IOC)** if USG is inconclusive: **MRI**. * **Contrast Safety:** Gadolinium (MRI contrast) is generally avoided in pregnancy as it crosses the placenta; however, non-contrast MRI is highly diagnostic. * **Radiation Rule:** The "10-rad rule" suggests that fetal risk is significantly increased only at doses above 100 mGy (10 rads); however, the ALARA (As Low As Reasonably Achievable) principle always favors MRI over CT.

Question 82: On ultrasound, what typically causes dirty shadowing?

A. Air (Correct Answer)
B. Bone
C. Calcification
D. Muscle

Explanation: **Explanation:** In ultrasonography, shadowing occurs when the sound beam encounters a structure with high attenuation or a significant difference in acoustic impedance, preventing the beam from passing through. **1. Why Air is Correct:** Air has a very low acoustic impedance compared to soft tissue, causing nearly 100% reflection of the ultrasound beam at the tissue-gas interface. This results in **"Dirty Shadowing,"** characterized by a greyish, poorly defined shadow containing internal echoes. These echoes are caused by **reverberation artifacts** and **ring-down artifacts** as the sound bounces between the transducer and the gas bubbles or between the bubbles themselves. **2. Why Incorrect Options are Wrong:** * **Bone & Calcification (Options B & C):** These are dense structures that absorb and reflect sound almost entirely. They produce **"Clean Shadowing,"** which is a crisp, well-defined, and completely black (anechoic) area behind the structure because no sound waves penetrate to create internal echoes. * **Muscle (Option D):** Muscle is a soft tissue with intermediate attenuation. It does not typically cause shadowing unless it is heavily calcified or contains foreign bodies. **3. High-Yield NEET-PG Pearls:** * **Clean Shadow:** Seen in Gallstones (Cholelithiasis), Kidney stones (Nephrolithiasis), and mature bone. * **Dirty Shadow:** Seen in Bowel gas, Emphysematous cholecystitis, and Abscesses containing gas-forming organisms. * **Comet-tail Artifact:** A form of reverberation artifact often seen with metallic foreign bodies or adenomyomatosis of the gallbladder. * **Acoustic Enhancement:** The opposite of shadowing; seen behind fluid-filled structures like simple cysts.

Question 83: Nuchal translucency thickness is typically evaluated during which antenatal ultrasound examination?

A. First trimester
B. Prenatal screening
C. Second trimester (Correct Answer)
D. Third trimester

Explanation: **Explanation:** The evaluation of **Nuchal Translucency (NT)** is a critical component of the **First Trimester Screening** (Option A). However, based on the specific options provided and the context of standard antenatal protocols, the question refers to the timing of the examination. * **Correct Answer (A/First Trimester):** NT is the sonographic appearance of a collection of fluid under the skin behind the fetal neck. It is measured strictly between **11 weeks and 13 weeks 6 days** of gestation (CRL 45–84 mm). An increased NT thickness is associated with chromosomal abnormalities (most commonly Trisomy 21), structural heart defects, and other genetic syndromes. * **Why Option C (Second Trimester) is technically incorrect for NT:** In the second trimester (18–22 weeks), the equivalent marker is called **Nuchal Fold (NF)** thickness. While NT disappears after 14 weeks, an increased Nuchal Fold (>6 mm) is a soft marker for Down syndrome during the second-trimester anomaly scan. *(Note: If the provided key insists on "Second Trimester," it likely confuses NT with Nuchal Fold; however, in standard medical literature, NT is strictly a first-trimester marker.)* **Incorrect Options:** * **Prenatal screening (B):** This is a broad category of testing, not a specific ultrasound examination period. * **Third trimester (D):** Scans at this stage focus on fetal growth, liquor volume, and placental position; NT/NF are no longer valid markers here. **High-Yield Clinical Pearls for NEET-PG:** * **NT Cut-off:** Generally considered abnormal if **>3.0 mm** or above the 95th percentile for CRL. * **Nuchal Fold (NF):** Measured in the second trimester; abnormal if **>6 mm**. * **Combined Screening:** Includes NT measurement + Serum PAPP-A + Free β-hCG. * **Nasal Bone:** Absence of the nasal bone during the NT scan further increases the risk for Trisomy 21.

Question 84: Which of the following is an oral contrast agent?

A. Sonavist
B. Levovist
C. Sono Rx (Correct Answer)
D. Echogen

Explanation: **Explanation:** In ultrasound imaging, the presence of gas in the stomach and bowel loops often creates acoustic shadowing and artifacts, which obscure the visualization of deep-seated abdominal organs like the pancreas. **Sono Rx** is a specialized **oral ultrasound contrast agent** designed to overcome this. It is a cellulose-based (simethicone-coated cellulose) suspension that, when ingested, displaces bowel gas and provides a uniform "acoustic window," allowing for better visualization of the retroperitoneum. **Analysis of Options:** * **Sono Rx (Correct):** It is the only agent listed specifically administered **orally** to improve transabdominal ultrasound imaging by reducing gas interference. * **Levovist:** This is a first-generation **intravenous (IV)** contrast agent consisting of galactose microparticles. It is used primarily for echocardiography and Doppler enhancement. * **Sonavist:** This is an **intravenous** contrast agent composed of air-filled cyanoacrylate polymer microbubbles, used for liver and vascular imaging. * **Echogen:** This is an **intravenous** emulsion of dodecafluoropentane which forms microbubbles upon injection; it is used for myocardial opacification. **High-Yield Pearls for NEET-PG:** * **Mechanism:** Most US contrast agents are **microbubbles** (stabilized by lipid or protein shells) that have high acoustic impedance, causing strong reflections. * **Generations:** * *1st Gen:* Levovist (Galactose-based). * *2nd Gen:* SonoVue (Sulfur hexafluoride) – widely used for characterizing liver lesions (e.g., Hemangioma vs. HCC). * **Clinical Use:** Contrast-enhanced ultrasound (CEUS) is excellent for patients with renal failure where CT/MRI contrast is contraindicated.

Question 85: Which is the best parameter by ultrasound to assess fetal maturity?

A. Crown rump length at 16 weeks
B. Head circumference at 36 weeks
C. Biparietal diameter at 12 weeks (Correct Answer)
D. Femur length at 12 weeks

Explanation: **Explanation:** The assessment of fetal maturity (gestational age) via ultrasound relies on the principle that biological variability increases as pregnancy progresses. Therefore, measurements taken earlier in pregnancy are significantly more accurate than those taken in the third trimester. **Why Biparietal Diameter (BPD) at 12 weeks is correct:** The **Biparietal Diameter (BPD)** is most accurate when measured between **12 and 20 weeks** of gestation. At 12 weeks, the margin of error is approximately **± 3–5 days**. While Crown-Rump Length (CRL) is the single most accurate parameter overall (when measured between 7–12 weeks), BPD becomes the gold standard once the fetus starts to curl, making CRL difficult to measure accurately. At 12 weeks, BPD provides a highly reproducible and precise estimate of fetal age. **Analysis of Incorrect Options:** * **A. Crown-Rump Length (CRL) at 16 weeks:** CRL is only valid up to **12 weeks**. Beyond this, the fetus undergoes "fetal curling," making linear measurement inaccurate. * **B. Head Circumference (HC) at 36 weeks:** In the third trimester, biological variation and intrauterine crowding significantly reduce accuracy. The margin of error at 36 weeks can be as high as **± 3 weeks**. * **D. Femur Length (FL) at 12 weeks:** While FL is a standard parameter, it is generally used after 14 weeks. At 12 weeks, the BPD is technically easier to visualize and more standardized for dating. **High-Yield Clinical Pearls for NEET-PG:** * **Most accurate overall:** CRL in the 1st trimester (7–12 weeks) with an error of ± 3–5 days. * **Best parameter in 2nd trimester:** BPD (up to 20 weeks). * **Best parameter for Fetal Growth/IUGR:** Abdominal Circumference (AC). * **Best parameter for Weight Estimation:** AC is the most sensitive, but a combination of BPD, HC, AC, and FL is typically used (Hadlock's formula).

Question 86: What causes an acoustic shadow in ultrasound imaging?

A. Artifact
B. Absorption
C. Reflection (Correct Answer)
D. Refraction

Explanation: ### Explanation **Correct Answer: C. Reflection** **Why Reflection is Correct:** Acoustic shadowing occurs when an ultrasound beam encounters a structure with high **acoustic impedance** (such as a gallstone or bone). Because the difference in impedance between the structure and the surrounding soft tissue is so vast, the majority of the sound waves are **reflected** back to the transducer. Since very few sound waves can penetrate through the object to reach deeper tissues, a signal-void area (black/anechoic zone) is created behind the object. This is known as "clean" shadowing. **Analysis of Incorrect Options:** * **A. Artifact:** While acoustic shadowing is technically a type of *acoustic artifact*, the question asks for the **physical cause**. Reflection is the mechanism that generates this specific artifact. * **B. Absorption:** While some energy is lost to heat (absorption), it is not the primary cause of the distinct shadow seen behind dense calcifications. Absorption is more relevant to tissue heating and attenuation in soft tissues. * **D. Refraction:** This refers to the bending of the ultrasound beam at an interface. Refraction causes "edge shadows" (narrow shadows at the margins of curved structures like the gallbladder or kidney), but not the dense central shadow of a stone. **High-Yield Clinical Pearls for NEET-PG:** * **Clean Shadowing:** Produced by calcified structures (e.g., gallstones, kidney stones, bone). It indicates high reflection. * **Dirty Shadowing:** Produced by **gas/air** (e.g., bowel gas, emphysematous cholecystitis). It is caused by multiple internal reflections (reverberation) and appears greyish/hazy. * **Acoustic Enhancement:** The opposite of shadowing; it occurs behind fluid-filled structures (like cysts) because fluid attenuates sound less than surrounding tissue, making deeper structures appear brighter.

Question 87: Fetal sex can be detected by ultrasound at which gestational age?

A. 14 weeks (Correct Answer)
B. 16 weeks
C. 18 weeks
D. 20 weeks

Explanation: **Explanation:** The determination of fetal sex via ultrasound relies on the visualization of the external genitalia. While the genital tubercle begins to differentiate earlier, the **14th week of gestation** is considered the earliest reliable time for sex determination with high accuracy (approaching 100% in optimal conditions). * **Why 14 weeks is correct:** By the end of the first trimester (12–13 weeks), the "sagittal sign" or the angle of the genital tubercle can suggest gender, but it is prone to error. By **14 weeks**, the morphological development of the penis/scrotum in males and the labia in females is sufficiently distinct for a definitive diagnosis using high-resolution transabdominal or transvaginal probes. * **Why other options are incorrect:** * **16, 18, and 20 weeks:** While fetal sex is easily and routinely identified during these periods (especially during the 18–20 week anomaly scan), these options are incorrect because the question asks for the *earliest* gestational age at which detection is possible. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Square Sign":** In the second trimester, the male genitalia often appear as a "mural" or "square" shape, while the female genitalia show the **"Hamburger Sign"** (representing the three lines of the labia). 2. **PCPNDT Act:** In India, performing or communicating fetal sex determination is a **punishable offense** under the Pre-Conception and Pre-Natal Diagnostic Techniques Act. 3. **Genital Tubercle Angle:** At 11–13 weeks, a tubercle angle >30° relative to the spine suggests a male, while an angle <10° or parallel to the spine suggests a female.

Question 88: Scrotal calcifications in fetal sonography may be seen in which of the following conditions?

A. Testicular torsion
B. Hydrocele
C. Meconium ileus (Correct Answer)
D. All of the above

Explanation: **Explanation:** The presence of scrotal calcifications in fetal sonography is a classic diagnostic marker for **Meconium Peritonitis**, which is frequently associated with **Meconium Ileus** (often secondary to Cystic Fibrosis). **1. Why Meconium Ileus is correct:** In cases of meconium ileus, bowel perforation can occur in utero. This leads to the leakage of sterile meconium into the peritoneal cavity, causing a chemical inflammatory response known as meconium peritonitis. Because the **tunica vaginalis** is an extension of the peritoneum (via the patent processus vaginalis), the meconium can migrate into the scrotal sac. Over time, these deposits undergo calcification, appearing as highly echogenic foci with or without shadowing on fetal ultrasound. **2. Why other options are incorrect:** * **Testicular Torsion:** While torsion can occur in utero (extravaginal torsion), it typically presents as an enlarged, heterogenous, or hydrocele-associated testis. Calcification is an extremely rare, late-stage finding and is not a characteristic prenatal sonographic feature. * **Hydrocele:** A simple fetal hydrocele is a common, benign finding representing fluid in the scrotum. It appears anechoic (black) and does not contain calcifications unless associated with underlying pathology like peritonitis. **High-Yield Clinical Pearls for NEET-PG:** * **Meconium Peritonitis Triad:** Ascites, peritoneal calcifications, and polyhydramnios. * **Scrotal Pearl:** A term used for benign, post-natal extratesticular calcifications, but in a **fetus**, scrotal calcification is a "red flag" for healed or active meconium peritonitis. * **Cystic Fibrosis Link:** Approximately 15-20% of infants with meconium ileus have Cystic Fibrosis; if fetal scrotal calcifications are seen, genetic screening is often recommended.

Question 89: What is the smallest size of gallstone that can be confidently diagnosed using ultrasonography?

A. 1.5 mm (Correct Answer)
B. 3 mm
C. 5 mm
D. 10 mm

Explanation: **Explanation:** Ultrasonography (USG) is the gold standard for diagnosing cholelithiasis due to its high sensitivity (up to 95%) and specificity. The correct answer is **1.5 mm** because modern high-frequency transducers (5–10 MHz) have excellent axial resolution, allowing for the detection of very small, echogenic foci within the gallbladder lumen. * **Why 1.5 mm is correct:** A gallstone is characterized by an echogenic focus that moves with gravity and typically casts a posterior acoustic shadow. While shadowing is more consistently seen in stones >3 mm, a stone as small as 1.5 mm can be confidently identified if it is highly reflective and the focal zone of the transducer is correctly positioned. * **Why other options are incorrect:** * **3 mm:** While this is often cited as the threshold where **posterior acoustic shadowing** becomes reliably visible, it is not the minimum size for detection. * **5 mm and 10 mm:** These are significantly larger than the technical limit of modern USG. These sizes are more relevant when considering surgical indications (e.g., polyps >10 mm) rather than diagnostic limits. **High-Yield Clinical Pearls for NEET-PG:** * **WES Triad:** Wall-Echo-Shadow (WES) sign is seen when the gallbladder is completely filled with stones. * **Acoustic Shadowing:** Occurs because stones reflect/absorb sound waves. To enhance a shadow from a small stone, use a **higher frequency transducer** and ensure the stone is in the **focal zone**. * **Sludge:** Low-level echoes that do not shadow but move slowly with change in position (precursor to stone formation). * **False Positives:** Polyps (do not move/shadow) and Porcelain Gallbladder (calcified wall).

Question 90: Congenital anomalies that can be identified by USG are all except:

A. Hydrops fetalis
B. Esophageal atresia
C. Anencephaly
D. Cystic hygroma (Correct Answer)

Explanation: **Explanation:** The question asks which anomaly **cannot** be identified by ultrasound. However, there is a technical discrepancy in the provided options: **Cystic hygroma, Anencephaly, and Hydrops fetalis are all classic ultrasound diagnoses.** The most likely intended answer for an "except" question in this context is **Esophageal atresia**, as it is notoriously difficult to diagnose directly via USG. 1. **Why Esophageal Atresia (Option B) is the likely intended answer:** Esophageal atresia (EA) cannot be visualized directly on ultrasound because the esophagus is a collapsed structure. Diagnosis is usually **indirect**, suggested by the presence of polyhydramnios and a "small or absent stomach bubble." However, in 90% of cases (Type C), a tracheoesophageal fistula allows fluid into the stomach, making the USG appear normal. Thus, EA is the most challenging to identify. 2. **Analysis of other options:** * **Anencephaly (Option C):** This is the easiest to diagnose. It can be detected as early as 10–12 weeks. Key signs include the "Frog-eye appearance" due to the absence of the cranial vault and brain tissue. * **Cystic Hygroma (Option D):** This is a fluid-filled sac resulting from lymphatic malformation, typically found in the neck. It is easily identified on USG as a multiloculated cystic mass with internal septations. * **Hydrops Fetalis (Option A):** Diagnosed by seeing fluid accumulation in at least two fetal compartments (e.g., ascites, pleural effusion, pericardial effusion, or skin edema) on USG. **NEET-PG High-Yield Pearls:** * **Best time for Level II Anomaly Scan:** 18–20 weeks. * **Anencephaly:** Most common neural tube defect; associated with increased Alpha-fetoprotein (AFP). * **Cystic Hygroma:** Strongly associated with **Turner Syndrome (45, XO)** and Trisomy 21. * **Lemon Sign & Banana Sign:** USG markers for Spina Bifida (Chiari II malformation).

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Ultrasound — MCQs

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