A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 36-year-old man is brought to the emergency department for right upper quadrant abdominal pain that began 3 days ago. The pain is nonradiating and has no alleviating or exacerbating factors. He denies any nausea or vomiting. He immigrated from Mexico 6 months ago and currently works at a pet shop. He has been healthy except for 1 week of bloody diarrhea 5 months ago. He is 182 cm (5 ft 11 in) tall and weighs 120 kg (264 lb); BMI is 36 kg/m2. His temperature is 101.8°F (38.8°C), pulse is 85/min, respirations are 14/min, and blood pressure is 120/75 mm Hg. Lungs are clear to auscultation. He has tenderness to palpation in the right upper quadrant. Laboratory studies show:
Hemoglobin 11.7 g/dL3
Leukocyte Count 14,000/mm
Segmented neutrophils 74%
Eosinophils 2%
Lymphocytes 17%
Monocytes 7%
Platelet count 140,000/mm3
Serum
Na+ 139 mEq/L
Cl- 101 mEq/L
K+ 4.4 mEq/L
HCO3- 25 mEq/L
Urea nitrogen 8 mg/dL
Creatinine 1.6 mg/dL
Total bilirubin 0.4 mg/dL
AST 76 U/L
ALT 80 U/L
Alkaline phosphatase 103 U/L
Ultrasonography of the abdomen shows a 4-cm round, hypoechoic lesion in the right lobe of the liver with low-level internal echoes. Which of the following is the most likely diagnosis?"
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A
AmebiasisCorrect. Amebic liver abscess from E. histolytica fits: young Mexican immigrant, prior bloody diarrhea, solitary right-lobe hypoechoic lesion. Treated with metronidazole plus a luminal agent.
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B
Hepatic hydatid cystIncorrect. Hepatic hydatid cyst (Echinococcus) would show a well-defined cyst with daughter cysts or eggshell calcification on imaging, and exposure history is dogs and sheep — not a pet shop in Mexico.
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C
Pyogenic liver abscessIncorrect. Pyogenic liver abscesses are typically multiple, occur in older patients with biliary or portal source, and tend to be polymicrobial — the demographics and prior amebic dysentery here favor amebiasis.
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D
Hepatocellular carcinomaIncorrect. Hepatocellular carcinoma occurs in cirrhotic or hepatitis B/C carriers, presents over months with weight loss and elevated AFP, and would not produce fever with a hypoechoic cystic-appearing lesion.
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E
Hepatic adenomaIncorrect. Hepatic adenoma is a benign vascular tumor typically seen in young women on oral contraceptives or with anabolic-steroid exposure; it does not present with fever, leukocytosis, or prior dysentery.
↑ Tap an answer to reveal the reasoning
Answer: A. A young Mexican immigrant with a recent history of bloody diarrhea now presenting with fever, RUQ pain, elevated transaminases, and a solitary hypoechoic right-lobe liver lesion has amebic liver abscess from Entamoeba histolytica. The classic sequence is colonic infection (which may have caused the prior bloody diarrhea) followed weeks to months later by hematogenous spread via the portal vein to the right lobe of the liver, where trophozoites produce the so-called "anchovy paste" sterile abscess.
Ultrasound typically shows a single hypoechoic lesion with low-level internal echoes in the right hepatic lobe, exactly as described. Diagnosis is confirmed by serology (E. histolytica IgG, highly sensitive in extraintestinal disease) rather than aspiration, because aspirate is acellular (no neutrophils because trophozoites lyse them) and trophozoites are usually only at the wall. Treatment is metronidazole or tinidazole followed by a luminal agent (paromomycin or iodoquinol) to clear intestinal carriage.
Distinguish from pyogenic abscess (usually multiple, older patients, biliary or portal source, often polymicrobial with E. coli or Klebsiella) and from hydatid cyst (eggshell calcifications, daughter cysts, exposure to dogs/sheep) — neither fits the demographic and prior dysentery.
**Why each option:**
**A.** Amebic liver abscess from E. histolytica fits: young Mexican immigrant, prior bloody diarrhea, solitary right-lobe hypoechoic lesion. Treated with metronidazole plus a luminal agent.
**B.** Hepatic hydatid cyst (Echinococcus) would show a well-defined cyst with daughter cysts or eggshell calcification on imaging, and exposure history is dogs and sheep — not a pet shop in Mexico.
**C.** Pyogenic liver abscesses are typically multiple, occur in older patients with biliary or portal source, and tend to be polymicrobial — the demographics and prior amebic dysentery here favor amebiasis.
**D.** Hepatocellular carcinoma occurs in cirrhotic or hepatitis B/C carriers, presents over months with weight loss and elevated AFP, and would not produce fever with a hypoechoic cystic-appearing lesion.