A 3-year-old female has a 2-week history of fever, bifrontal headache, lethargy, and vomiting. She has perioral cyanosis and dyspnea since infancy. She has a 10-minute focal tonic-clonic seizure. She is obtunded, temperature 100.8°F, pulse 118, BP 96/70 mm Hg. Perioral cyanosis is noted at rest, with a harsh pansystolic murmur along the left sternal border. Bilateral papilledema and right-sided weakness with hyperreflexia and extensor plantar reflex are present. The most likely cause of hemiparesis is

Correct Answer: D

Rationale: A brain abscess best explains this scenario. The childs congenital heart defect (likely tetralogy of Fallot, given cyanosis and murmur) predisposto paradoxical emboli, seeding a brain abscess. Fever, headache, lethargy, vomiting, and focal seizure over 2 weeks, plus papilledema and focal neurologic signs (hemiparesis, hyperreflexia, Babinski), suggest an intracranial mass with infection. Abscessare common in cyanotic heart disease due to right-to-left shunting. Moyamoya causischemia, not fever or papilledema acutely. Brain tumor grows slowly, lacking fever. Intracranial hemorrhage is acute, not subacute with infection signs. Methemoglobinemia (original D) causcyanosis but not focal neurology or abscess. Abscesss fit with infection, mass effect, and cardiac history makes D the correct answer.

Correct Answer: D

Rationale: The anterior fontanel closat 18 months on average, per pediatric norms (e.g., Nelson Textbook). It rangfrom 9-24 months, but 18 months is the mean, reflecting cranial suture fusion. Earlier closure (A-C, 12-16 months) occurs in some, while 22 months is late. This milestone tracks brain growth; premature closure may signal craniosynostosis. Longitudinal data confirm 18 months as typical, making D the correct answer, balancing variability and standard development.

Correct Answer: B

Rationale: Folate supplementation 1 month before conception reducneural tube defect (NTD) incidence by 50-70%, per CDC, supporting neurulation by day 28 post-conception. Starting at 12 weeks is too late; neurulation is complete. Avoiding STDs prevents infections, not NTDs. Chromosomal screening identifitrisomies, not NTDs. Preconception folatpreventive timing, per public health data, make B the correct answer.

Correct Answer: D

Rationale: Migraine (ICHD-3) requirrecurrent headachwith featurlike abdominal pain , nausea/emesis , throbbing quality , unilateral location (D in original), relief with sleep , or aura . Absent family history is not a diagnostic criterion; family history supports diagnosis but isnt required. Its exclusion from core features, per migraine definitions, makes D the exception and correct answer.

Correct Answer: C

Rationale: Post-varicella cerebellar ataxia is a common, self-limited complication in children, onset days after chickenpox, causing acute ataxia with normal cognition. Encephalitis involvfever and altered mentation. Thrombosis causfocal deficits. Demyelination (e.g., ADEM) is rarer, often post-vaccination. Chorea involvmovements, not ataxia. Cerebellar ataxias viral link makes C the correct answer.