Ultrasound — MCQs

Ultrasound Indian Medical PG Practice Questions and MCQs

Question 151: A pseudogestational sac seen on ultrasonography is suspicious of what condition?

A. Missed abortion
B. Incomplete abortion
C. Ectopic pregnancy (Correct Answer)
D. Complete abortion

Explanation: ### Explanation **Correct Answer: C. Ectopic pregnancy** A **pseudogestational sac** is a common sonographic pitfall in the diagnosis of early pregnancy. It represents an intra-uterine fluid collection (blood or secretions) surrounded by a single layer of decidua, mimicking a true gestational sac. * **Why it indicates Ectopic Pregnancy:** In an ectopic pregnancy, high levels of hCG stimulate the uterine lining, causing a decidual reaction. This can lead to the accumulation of fluid or blood in the endometrial cavity. Unlike a true gestational sac, a pseudogestational sac is **centrally located** (not eccentric), lacks a **yolk sac**, and does not show the **"Double Decidual Sign"** (the two concentric rings representing the decidua capsularis and decidua parietalis). Its presence in a patient with a positive pregnancy test and no visible intrauterine pregnancy should immediately raise suspicion for an ectopic pregnancy. **Analysis of Incorrect Options:** * **A, B, & D (Missed, Incomplete, and Complete Abortion):** These are forms of intrauterine pregnancies (IUP). While they may show an irregular sac or retained products of conception, they are preceded by a true gestational sac. A pseudogestational sac is specifically a "false" sac associated with an extrauterine (ectopic) pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Double Decidual Sign:** The most reliable sign of a true early IUP (usually seen at 5.5–6 weeks). * **Yolk Sac:** Its presence definitively confirms an IUP and rules out a pseudogestational sac. * **Location:** A true gestational sac is typically **eccentric** (embedded in the endometrium), whereas a pseudogestational sac is **central** (within the uterine cavity). * **Discriminatory Zone:** If the serum β-hCG is >1,500–2,000 mIU/mL and no IUP is seen on TVS, ectopic pregnancy must be excluded.

Question 152: What is the primary purpose of a fetal ultrasound performed at 18-20 weeks of gestation?

A. To detect fetal abnormalities (Correct Answer)
B. To determine the sex of the fetus
C. To estimate amniotic fluid volume
D. To determine fetal maturity

Explanation: **Explanation:** The ultrasound performed at **18–20 weeks** of gestation is commonly known as the **Anomaly Scan** (Level II Ultrasound) or the Mid-trimester Morphology Scan. **1. Why Option A is Correct:** By 18–20 weeks, fetal organogenesis is complete, and the fetus is large enough for detailed anatomical visualization. This is the "gold standard" window to screen for structural malformations such as neural tube defects (e.g., anencephaly, spina bifida), cardiac anomalies, cleft lip/palate, and renal agenesis. It also allows for the identification of "soft markers" (e.g., nuchal fold thickness, echogenic intracardiac focus) that may suggest underlying chromosomal trisomies. **2. Why Other Options are Incorrect:** * **Option B:** While fetal sex can be determined at this stage, it is **not** the primary medical indication for the scan. Furthermore, in India, disclosing the sex of the fetus is illegal under the **PCPNDT Act**. * **Option C:** Amniotic fluid volume (AFI) is assessed during this scan, but it is a secondary observation. Primary assessment of AFI is more critical in the third trimester to monitor placental insufficiency or fetal distress. * **Option D:** Fetal maturity is best determined by the **Crown-Rump Length (CRL)** in the first trimester (7–13 weeks). By the second trimester, biological variation increases, making ultrasound less accurate for dating. **High-Yield Clinical Pearls for NEET-PG:** * **Best time for Nuchal Translucency (NT) scan:** 11–13+6 weeks (First-trimester screening). * **Best time for Anomaly scan:** 18–20 weeks. * **Most sensitive parameter for dating in 2nd trimester:** Biparietal Diameter (BPD) and Head Circumference (HC). * **Rule of Thumb:** The earlier the ultrasound, the more accurate the gestational age estimation.

Question 153: Early diastolic notching of the uterine artery disappears by which week of gestation?

A. 20 weeks
B. 21 weeks
C. 22 weeks (Correct Answer)
D. 24 weeks

Explanation: **Explanation:** The correct answer is **22 weeks**. **Underlying Medical Concept:** In a non-pregnant state, the uterine artery is a high-resistance vessel characterized by an **early diastolic notch**. During a normal pregnancy, trophoblastic invasion of the spiral arteries occurs in two waves (at 8–10 weeks and 16–18 weeks). This process converts the uterine circulation from a high-resistance to a low-resistance, high-flow system to ensure adequate placental perfusion. As resistance falls, the diastolic flow increases, and the early diastolic notch typically disappears by **22–24 weeks** of gestation. Persistence of this notch beyond 24 weeks is a significant predictor of placental insufficiency. **Analysis of Options:** * **A & B (20 & 21 weeks):** While the transition begins earlier, the physiological remodeling is often incomplete at this stage. Using these weeks as a cutoff would result in a high false-positive rate for predicting complications. * **C (22 weeks):** This is the standard clinical benchmark. By the end of the 22nd week, the notch should ideally disappear in a healthy pregnancy. * **D (24 weeks):** While some sources mention 24 weeks as the absolute upper limit, **22 weeks** is the most frequently tested "milestone" week for the disappearance of the notch in competitive exams like NEET-PG. **High-Yield Clinical Pearls for NEET-PG:** * **Persistence of the notch:** If the notch persists beyond 24 weeks, it indicates a high risk for **Preeclampsia** and **Intrauterine Growth Restriction (IUGR)**. * **Best time for screening:** Uterine artery Doppler screening for preeclampsia is ideally performed between **11–14 weeks** (PI) and **20–24 weeks** (Notching). * **Reversed End-Diastolic Flow (REDF):** In the umbilical artery, this is a critical sign of fetal distress and often an indication for urgent delivery.

Question 154: USG is/are based on which of the following principles?

A. Piezoelectric effect (Correct Answer)
B. Diamagnetic effect
C. Paramagnetic effect
D. Ferromagnetic effect

Explanation: **Explanation:** **1. Why Piezoelectric Effect is Correct:** The cornerstone of Ultrasound (USG) imaging is the **Piezoelectric Effect**, discovered by Pierre and Jacques Curie. * **The Process:** USG transducers contain piezoelectric crystals (most commonly **Lead Zirconate Titanate - PZT**). When an electric current is applied, these crystals vibrate and convert electrical energy into mechanical sound waves (**Reverse Piezoelectric Effect**). * **Image Formation:** These sound waves travel through tissues and reflect back to the transducer. The crystals then convert these returning mechanical echoes back into electrical signals (**Piezoelectric Effect**), which the computer processes into an image. **2. Why Other Options are Incorrect:** * **Diamagnetic, Paramagnetic, and Ferromagnetic effects** refer to the magnetic properties of substances and their behavior within an external magnetic field. These principles are fundamental to **Magnetic Resonance Imaging (MRI)**, not Ultrasound. * *Paramagnetic* substances (like Gadolinium) are used as MRI contrast agents. * *Ferromagnetic* substances (like iron) are strongly attracted to magnets and pose safety risks in the MRI suite. **3. Clinical Pearls for NEET-PG:** * **Transducer Material:** Synthetic ceramic **PZT** is the most common; however, newer CMUT (Capacitive Micromachined Ultrasonic Transducers) technology is emerging. * **Frequency vs. Resolution:** High-frequency probes (7.5–15 MHz) provide high resolution but low penetration (used for small parts/superficial structures). Low-frequency probes (2.5–5 MHz) provide deep penetration but lower resolution (used for abdominal scans). * **A-Mode vs. B-Mode:** **A-mode** (Amplitude) is used in ophthalmology for axial length; **B-mode** (Brightness) is the standard 2D grayscale imaging used in clinical practice. * **M-Mode:** Used for moving structures, primarily in fetal heart rate monitoring and echocardiography.

Question 155: In transvaginal ultrasound, what is the earliest detection of the gestational sac?

A. 21 days after ovulation
B. 21 days after implantation
C. 28 days post ovulation
D. 14 days after ovulation (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right:** In a typical 28-day menstrual cycle, ovulation occurs on Day 14. If fertilization occurs, the blastocyst implants approximately 6–7 days later. The gestational sac (the first sonographic evidence of pregnancy) becomes visible on **Transvaginal Sonography (TVS)** when it reaches a diameter of 2–3 mm. This typically occurs at **4 weeks of gestational age** (calculated from the Last Menstrual Period). Since gestational age starts 14 days before ovulation, 4 weeks of gestation is equivalent to **14 days post-ovulation**. **2. Analysis of Incorrect Options:** * **Option A (21 days after ovulation):** This corresponds to 5 weeks of gestation. By this time, the yolk sac is usually visible, and the gestational sac is well-established. * **Option B (21 days after implantation):** This would be approximately 27–28 days post-ovulation (nearly 6 weeks gestation), at which point a fetal pole with cardiac activity is often visible. * **Option C (28 days post-ovulation):** This is 6 weeks of gestation. At this stage, the embryo is clearly visible, and TVS should definitely show a heartbeat. **3. High-Yield Clinical Pearls for NEET-PG:** * **Order of Appearance (TVS):** Gestational Sac (4 weeks) → Yolk Sac (5 weeks) → Embryo/Heartbeat (6 weeks). * **Discriminatory Zone:** The level of serum β-hCG at which a gestational sac should be visible. For TVS, it is **1,500–2,000 mIU/ml**; for Transabdominal Sonography (TAS), it is **3,000–3,500 mIU/ml**. * **Double Decidual Sign:** A classic ultrasound feature of an early intrauterine pregnancy, helping distinguish it from a pseudogestational sac seen in ectopic pregnancies. * **Mean Sac Diameter (MSD):** If the MSD is >25 mm on TVS and no embryo is seen, it indicates a failed pregnancy (Anembryonic gestation).

Question 156: Minimal ascites can be best detected by which imaging modality?

A. Ultrasound (USG) (Correct Answer)
B. Plain X-ray abdomen
C. MRI
D. CT scan

Explanation: **Explanation:** **Ultrasound (USG)** is the gold standard and most sensitive modality for the detection of minimal ascites. It can detect as little as **5–10 mL** of peritoneal fluid. The primary reason for its superiority is its ability to demonstrate anechoic (black) fluid collections in dependent areas, such as the **Pouch of Douglas** (in females), the retrovesical space (in males), or **Morison’s pouch** (hepatorenal recess), which is the most dependent part of the upper abdomen in a supine patient. **Analysis of Incorrect Options:** * **Plain X-ray Abdomen:** This is the least sensitive method. Ascites only becomes visible on a radiograph when at least **500–1000 mL** of fluid has accumulated. Signs include "ground-glass" appearance and bulging of the flanks. * **CT Scan:** While highly accurate and capable of detecting small amounts of fluid (~30–50 mL), it is not the "best" initial choice due to ionizing radiation, higher cost, and lower bedside accessibility compared to USG. * **MRI:** Though sensitive, it is never used as a primary screening tool for ascites due to its cost, duration, and lack of portability. **High-Yield Clinical Pearls for NEET-PG:** * **Most sensitive site for ascites (Supine):** Morison’s Pouch. * **First site of fluid accumulation (Upright):** Pouch of Douglas. * **FAST (Focused Assessment with Sonography for Trauma):** Uses USG to detect hemoperitoneum in trauma; it specifically looks at Morison’s pouch, the splenorenal recess, the pelvis, and the pericardium. * **Clinical Detection:** Shifting dullness requires ~500 mL of fluid, while a fluid thrill requires ~1500–2000 mL.

Question 157: Which of the following is NOT a typical ultrasound finding of Polycystic Ovary Syndrome (PCOS)?

A. Presence of 12 or more follicles measuring 2-9 mm in diameter in each ovary, and/or increased ovarian volume (>10 mL)
B. Ovarian volume of 10 cc or less (Correct Answer)
C. Peripheral distribution of small follicles, often described as a 'string of pearls' or 'necklace sign'
D. Increased ovarian stromal echogenicity or stromal volume

Explanation: **Explanation:** The diagnosis of Polycystic Ovary Syndrome (PCOS) on ultrasound is primarily based on the **Rotterdam Criteria**. According to these criteria, an ovary is considered polycystic if it exhibits an **increased ovarian volume of >10 mL** (calculated using the formula: $0.5 \times \text{length} \times \text{width} \times \text{thickness}$). Therefore, **Option B** is the correct answer because an ovarian volume of 10 cc or less is a normal finding and does not meet the diagnostic threshold for PCOS. **Analysis of Incorrect Options:** * **Option A:** This is a classic diagnostic criterion. The presence of **12 or more follicles** (measuring 2–9 mm) in either ovary is a hallmark of PCOS. Note: Newer guidelines (ASRM/ESHRE) using high-frequency transducers have increased this threshold to $\geq 20$ follicles, but 12 remains the standard for NEET-PG. * **Option C:** The **'String of Pearls'** or **'Necklace sign'** refers to the characteristic peripheral arrangement of follicles around a dense central stroma, a classic sonographic description of PCOS. * **Option D:** **Increased stromal echogenicity** and volume are subjective but highly specific findings in PCOS, resulting from the hypertrophy of theca cells. **High-Yield Clinical Pearls for NEET-PG:** * **Rotterdam Criteria (2 out of 3):** 1. Clinical/biochemical hyperandrogenism, 2. Ovulatory dysfunction (Oligo/Anovulation), 3. Polycystic ovaries on USG. * **Golden Rule:** If a dominant follicle (>10 mm) or a corpus luteum is present, the scan should be repeated during the next cycle to avoid false positives. * **LH:FSH Ratio:** Typically increased (>2:1 or 3:1) in PCOS patients.

Question 158: Harmonic imaging is related to which of the following imaging modalities?

A. Sonography (Correct Answer)
B. Digital radiography
C. MRCP
D. Nuclear imaging

Explanation: **Explanation:** **Tissue Harmonic Imaging (THI)** is a specialized ultrasound technique based on the principle of non-linear propagation of sound waves through tissues. When an ultrasound pulse travels, it undergoes distortion, generating frequencies that are integer multiples of the original (fundamental) frequency. The ultrasound machine filters out the fundamental frequency and processes only these "harmonics" (usually the second harmonic) to create an image. **Why Sonography is correct:** In sonography, THI significantly improves image quality by: * **Reducing artifacts:** It minimizes side-lobe artifacts and reverberations (e.g., "sludge" in the gallbladder). * **Improving resolution:** It provides better lateral resolution and improved contrast-to-noise ratios, making it easier to visualize small lesions or cysts in technically difficult patients (e.g., obese patients). **Why other options are incorrect:** * **Digital Radiography:** Uses X-rays and digital detectors; it does not utilize wave harmonics. * **MRCP (Magnetic Resonance Cholangiopancreatography):** Uses MRI sequences (T2-weighted) based on proton spin and relaxation times, not acoustic harmonics. * **Nuclear Imaging:** Relies on the detection of gamma rays emitted from radiopharmaceuticals injected into the body. **High-Yield Clinical Pearls for NEET-PG:** * **Contrast-Enhanced Ultrasound (CEUS):** Uses microbubble contrast agents which are highly non-linear, making harmonic imaging essential for visualizing blood flow and tumor vascularity. * **Key Advantage:** THI is particularly useful for clearing "pseudo-sludge" in the gallbladder and improving the visualization of the endocardial border in echocardiography. * **Trade-off:** While THI improves resolution, it may result in a slight loss of penetration depth compared to fundamental imaging.

Question 159: What is the preferred non-invasive imaging modality for screening carotid artery stenosis?

A. Ultrasound (USG)
B. Computed Tomography (CT)
C. Magnetic Resonance Imaging (MRI)
D. Doppler Ultrasound (Correct Answer)

Explanation: **Explanation:** **Doppler Ultrasound** is the preferred non-invasive screening modality for carotid artery stenosis because it provides both anatomical and functional data. It combines high-resolution B-mode imaging (to visualize plaque morphology) with spectral Doppler (to measure blood flow velocities). According to the NASCET criteria, peak systolic velocity (PSV) is the primary parameter used to grade the severity of stenosis. It is cost-effective, portable, and lacks ionizing radiation or nephrotoxic contrast. **Why other options are incorrect:** * **Ultrasound (USG):** While B-mode ultrasound visualizes the vessel wall and plaque, it cannot assess the hemodynamic significance (flow velocity) of the stenosis. "Doppler" is the specific functional component required for diagnosis. * **Computed Tomography (CT):** CT Angiography (CTA) is highly accurate for surgical planning but is not used for *screening* due to radiation exposure and the need for iodinated contrast. * **Magnetic Resonance Imaging (MRI):** MR Angiography (MRA) is excellent for visualizing the carotids but is expensive, time-consuming, and less accessible than Doppler, making it unsuitable for initial screening. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** Digital Subtraction Angiography (DSA) remains the gold standard but is invasive. * **Key Parameter:** A **Peak Systolic Velocity (PSV) >230 cm/s** typically correlates with >70% stenosis. * **Plaque Characterization:** Ultrasound is superior for identifying "vulnerable plaques" (hypoechoic/ulcerated), which carry a higher risk of embolic stroke. * **ICA/CCA Ratio:** A ratio >4.0 is highly suggestive of significant internal carotid artery stenosis.

Question 160: What is seen earliest on ultrasonography?

A. Yolk sac (Correct Answer)
B. Fetal heart
C. Chorion
D. Placenta

Explanation: **Explanation:** In the chronological progression of early pregnancy as visualized by transvaginal sonography (TVS), structures appear in a predictable sequence. Understanding this timeline is crucial for NEET-PG. **1. Why Yolk Sac is correct:** The **Yolk Sac** is the first structure to appear within the gestational sac. It typically becomes visible via TVS at approximately **5 to 5.5 weeks** of gestation (when the Mean Sac Diameter is about 8 mm). Its presence confirms an intrauterine pregnancy and excludes a pseudogestational sac. **2. Why the other options are incorrect:** * **Fetal Heart:** Cardiac activity is usually detected at **6 to 6.5 weeks** (when the Crown-Rump Length is ≥7 mm). It appears after the yolk sac and the fetal pole. * **Chorion:** While the chorionic cavity forms early, the "Chorion" as a distinct, mature anatomical entity or the fusion of membranes occurs later. The gestational sac itself is the chorionic cavity, but the yolk sac is the first *internal* structure identified. * **Placenta:** The definitive placenta begins to take shape around **9–10 weeks** and is clearly visualized by the end of the first trimester (12 weeks), making it the latest structure among the choices. **Clinical Pearls for NEET-PG:** * **Sequence of appearance (TVS):** Gestational Sac (4.5–5 weeks) → Yolk Sac (5–5.5 weeks) → Fetal Pole/Embryo (5.5–6 weeks) → Cardiac Activity (6–6.5 weeks). * **Double Decidual Sign:** The earliest sign of intrauterine pregnancy before the yolk sac appears. * **Discriminatory Zone:** The hCG level at which a gestational sac should be visible (TVS: 1,500–2,000 mIU/mL; TAS: 6,500 mIU/mL). * **Yolk Sac Size:** A diameter >6 mm or an irregular shape is often associated with a poor pregnancy prognosis.

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Ultrasound — MCQs

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