Pediatrics

Genetics — RB1 Gene and Knudson's Two-Hit Hypothesis

Clinical Presentation — Leukocoria and its Differential Diagnosis

Leukocoria (abnormal white pupillary reflex) is the most common presenting sign. Differential diagnosis:

• Congenital cataract
• Persistent Fetal Vasculature (formerly PHPV)
• Coats disease
• Retinopathy of prematurity (Section 1, Q8)
• Ocular toxocariasis

International Classification of Intraocular Retinoblastoma (ICIR/IIRC)

Groups A–E (increasing severity) — guides eye-preserving vs enucleation decision; Group E generally requires enucleation.

Eye-Preserving Therapies

Indications

Donor Selection — HLA Typing

Guided by HLA matching, in descending order of typical preference:

1. Matched sibling donor — traditional gold standard, best outcomes
2. Matched unrelated donor — via international registries, generally somewhat inferior to sibling
3. Umbilical cord blood — rapid availability, greater HLA mismatch tolerance, but smaller stem cell dose
4. Haploidentical (half-matched) donor — typically a parent; near-universal availability; modern post-transplant cyclophosphamide-based techniques have substantially improved outcomes

Conditioning Regimens

Serve dual purposes: myeloablation (eliminate diseased marrow) and immunosuppression (prevent graft rejection). Reduced-intensity required for Fanconi anemia (Q123). Autologous HSCT avoids GVHD entirely but lacks graft-versus-tumor effect.

Graft-versus-Host Disease (GVHD)

Prevention: calcineurin inhibitor-based prophylaxis; post-transplant cyclophosphamide (especially haploidentical transplant).

Classification and Distinctive Pediatric Distribution Pattern

Red Flag Signs of Raised Intracranial Pressure

• Early morning headache (improves through the day)
• Vomiting (especially without other GI symptoms; relieves headache)
• Papilledema on fundoscopy
• Cranial nerve palsies (especially VI nerve — a “false localizing sign” given its long intracranial course)
• Ataxia/gait disturbance (reflecting posterior fossa predominance)
• In infants: increasing head circumference, bulging anterior fontanelle

Any combination warrants prompt neuroimaging — general raised ICP recognition/management principles (Section 2, Q29) apply equally here.

AHA Guidelines — Complete Kawasaki Disease

Diagnosed based on fever for ≥5 days combined with at least 4 of the following 5 principal clinical features:

Incomplete Kawasaki Disease

In a child with fever ≥5 days and only 2–3 principal criteria (particularly relevant in infants, who carry disproportionately elevated coronary complication risk), the AHA algorithm incorporates:

• Supplemental laboratory criteria — elevated CRP/ESR plus supportive findings: anemia, thrombocytosis after day 7, hypoalbuminemia, elevated ALT, leukocytosis, sterile pyuria
• Echocardiographic findings — coronary artery abnormalities are themselves sufficient supportive evidence to diagnose incomplete KD and initiate treatment

Echocardiographic Screening for Coronary Artery Aneurysms

Coronary findings are graded using standardized z-score-based (body-surface-area-adjusted) classification: no involvement → small → medium → large/giant aneurysm — directly determining follow-up intensity and antithrombotic strategy.

IVIG Resistance and Escalation Therapy

Standard initial treatment: IVIG 2 g/kg single infusion + aspirin.

1. Second dose of IVIG (2 g/kg) — first escalation step for IVIG-resistant disease
2. Methylprednisolone/corticosteroids — escalation step, or upfront in high-risk children (validated risk-scoring systems)
3. Infliximab (anti-TNF-alpha) — for refractory disease despite IVIG + steroid escalation

Long-Term Management

Stratified by aneurysm size: low-dose aspirin alone for small aneurysms → combined antiplatelet + anticoagulant therapy for large/giant aneurysms (elevated thrombosis risk), with periodic cardiology follow-up, stress testing, and consideration of interventional/surgical revascularization for significant coronary stenosis.

Anatomical Components — The Classic Tetrad

1. Ventricular Septal Defect (VSD) — typically large, non-restrictive, perimembranous
2. Right Ventricular Outflow Tract (RVOT) obstruction (pulmonary stenosis) — the primary determinant of clinical severity/cyanosis, ranging from mild infundibular narrowing to complete pulmonary atresia
3. Overriding aorta — aortic root positioned overriding the VSD, receiving flow from both ventricles
4. Right ventricular hypertrophy — secondary, compensatory (not a primary defect)

Pathophysiology

Degree of RVOT obstruction determines shunt direction/magnitude across the VSD — more severe obstruction → greater right-to-left shunting → desaturated blood enters systemic circulation → cyanosis.

Pathophysiology of Hypercyanotic (“Tet”) Spells

Acute worsening of right-to-left shunting triggered by:

Acute Emergency Management — Stepwise Sequence

1. Knee-to-chest positioning (infants) or squatting (older children) — ↑ SVR by mechanically compressing femoral arteries/↑ afterload → reduces R-to-L shunt gradient — single most important first step
2. Calm the child — minimizes catecholamine-driven infundibular spasm
3. Oxygen — limited benefit (fixed anatomical shunt) but reasonable, low-risk adjunct
4. Morphine — sedation + direct relaxant effect on infundibular musculature
5. IV fluid bolus — ↑ preload/circulating volume, improves forward flow across obstructed RVOT
6. Phenylephrine (pure alpha-agonist) — pharmacologically ↑ SVR
7. Beta-blockade (propranolol/esmolol) — directly reduces dynamic infundibular spasm
8. General anesthesia and emergency surgery — final escalation for refractory spells

Palliative Shunts and Definitive Repair

Hemodynamics — Size and Pulmonary Vascular Resistance (PVR)

Development of Pulmonary Arterial Hypertension and Eisenmenger Physiology

Chronic exposure to elevated flow/pressure → progressive pulmonary vascular remodeling: initially reversible functional changes → if uncorrected, irreversible structural changes (medial hypertrophy, intimal fibrosis, plexiform lesions) → rising PVR.

Once PVR approaches/exceeds SVR, shunt direction reverses (right-to-left or bidirectional) — this fixed pulmonary hypertension + shunt reversal + cyanosis = Eisenmenger syndrome.

Indications for Intervention versus Medical Management

Medical management (diuretics, heart-failure-directed therapy) may bridge infants awaiting surgery or optimize clinical status pre-operatively.

Clinical Presentation — An Age-Dependent Spectrum

Imaging

Echocardiography — first-line, visualizes the coarcted segment and associated abnormalities (bicuspid aortic valve is the most common association; severe cases may show hypoplastic left heart structures). CT/MR angiography — detailed anatomical characterization for surgical/interventional planning or complex/older cases.

Prostaglandin E1 (PGE1) Infusion — The Critical Emergency Intervention

PGE1 side effects requiring monitoring: apnea (careful respiratory monitoring, often prophylactic intubation readiness during transport), fever, peripheral vasodilation/hypotension.

Surgical and Catheter-Based Interventions

Pathophysiology — The “Parallel Circulation” Problem

In d-TGA, the aorta arises from the RV and the pulmonary artery arises from the LV (ventriculoarterial discordance), creating two parallel circulations instead of the normal serial arrangement:

Neonatal Presentation

Severe cyanosis from birth, often with relatively preserved respiratory effort initially. Severity/timing of cyanosis depends on natural intercirculatory mixing (foramen ovale, VSD if present, ductus arteriosus). Most severe/earliest cyanosis in “simple” TGA (intact ventricular septum).

Balloon Atrial Septostomy (Rashkind Procedure)

Emergency, life-saving palliative catheter intervention for inadequate intercirculatory mixing despite PGE1: a balloon-tipped catheter is advanced across the foramen ovale into the LA, then rapidly withdrawn while inflated, tearing/enlarging the atrial septal opening — creating a larger, non-restrictive interatrial communication and dramatically improving mixing.

Adjunctive PGE1 Infusion

Maintains ductal patency as an additional mixing site — may be sufficient alone in some cases without septostomy, if ductal-level mixing is adequate.

Arterial Switch Operation (Jatene Procedure)

Definitive, curative repair: transects and switches the aorta and pulmonary artery to their correct ventricular origins, plus coronary artery transfer/reimplantation to the neo-aortic root — the most technically challenging step given small neonatal coronary caliber.

Diagnostic ECG Features of SVT (vs. Sinus Tachycardia)

Management — Stepwise Algorithm

1. Vagal maneuvers — ice pack/cold stimulus to face in infants (diving reflex); Valsalva or carotid sinus massage in older children
2. Adenosine — rapid IV push + immediate rapid saline flush (very short half-life); transiently blocks AV nodal conduction — diagnostic and therapeutic
3. Synchronized cardioversion — for hemodynamically unstable SVT, or stable SVT refractory to adenosine
4. Chronic prophylaxis — antiarrhythmic medication or catheter ablation (potentially curative) for recurrent, symptomatic episodes

Congenital Complete Heart Block

Distinct from acquired conduction disease — most commonly due to transplacental transfer of maternal anti-Ro/SSA and anti-La/SSB antibodies (mothers with, or later found to have, SLE or Sjögren syndrome). Causes immune-mediated injury to the fetal conduction system → complete (third-degree) AV block, identified antenatally (fetal bradycardia on echo) or at birth.

Pathology of Chronic RHD

Cumulative valvular consequence of recurrent (or occasionally single severe) rheumatic carditis episodes — progressive fibrosis, thickening, calcification, and fusion of valve leaflets and subvalvular apparatus (chordae tendineae, papillary muscles). The mitral valve is most commonly/severely affected, followed by the aortic valve. Early disease favors regurgitation; advanced disease favors stenosis.

Clinical Evaluation of Mitral Regurgitation and Stenosis

Echocardiographic Scoring

Standardized scoring (leaflet mobility, thickening, calcification, subvalvular involvement) grades severity and assesses suitability for balloon mitral valvuloplasty (preferred for pliable, minimally calcified valves) versus surgical valve replacement (greater long-term complications given young patient age — lifelong anticoagulation, valve degeneration).

Secondary Penicillin Prophylaxis Guidelines