ABPath Pediatric Pathology cheat sheet

Neural tube closes by day 26-28 (anterior) and day 28 (posterior); folate supplementation reduces recurrence risk.

Heart begins beating ~day 22; cardiac septation completes by week 8, so teratogen exposure peaks in weeks 3-8.

Limb buds appear week 4, digit separation by week 8; thalidomide-sensitive window is days 24-36.

Palate fuses weeks 6-10; cleft palate alone has a later teratogenic window than cleft lip.

Renal system: pronephros, mesonephros, metanephros; ureteric bud induces metanephric blastema (weeks 5-8).

Birth weight triples by 1 year, quadruples by 2 years; length increases ~50% by 1 year.

Cranial sutures close by ~2 years (fontanelles), allowing brain growth to ~80% adult size by age 2.

Maternal IgG crosses placenta via FcRn, mainly after 32 weeks; IgM does not cross.

RhD alloimmunization requires fetomaternal hemorrhage; risk rises with delivery, abruption, amniocentesis, and trauma.

Kleihauer-Betke or flow cytometry quantifies fetomaternal hemorrhage; one full dose of RhIG covers ~30 mL whole blood.

Maternal diabetes: hyperglycemia drives fetal hyperinsulinemia, macrosomia, and delayed surfactant maturation.

Maternal PKU with poor control causes microcephaly, intellectual disability, and congenital heart disease.

TORCH infections cause IUGR, hydrops, and calcifications; timing of exposure determines phenotype severity.

Maternal smoking and cocaine increase risk of abruption, IUGR, and preterm birth.

Placenta previa: implantation over or near internal os; painless third-trimester bleeding.

Placental abruption: premature separation; painful bleeding, retroplacental hematoma, fetal distress.

Placenta accreta spectrum: abnormal trophoblast invasion; increta into myometrium, percreta through serosa.

Oligohydramnios: amniotic fluid index <5 cm; associated with renal agenesis, obstruction, and Potter sequence.

Polyhydramnios: AFI >24 cm; associated with esophageal atresia, anencephaly, and diabetes.

Single umbilical artery: associated with renal and cardiac anomalies; examine placenta for velamentous cord insertion.

Chorioamnionitis: maternal fever, fetal tachycardia, and neutrophilic infiltrate in membranes (staging by Blanc).

Stillbirth: fetal death ≥20 weeks; causes include placental insufficiency, infection, cord accident, and anomalies.

Maceration: skin slippage and reddening indicate death ≥12-24 hours before delivery; degree estimates timing.

Hydrops fetalis: immune (Rh) vs non-immune (cardiac, aneuploidy, parvovirus, alpha-thalassemia).

Perinatal asphyxia: HIE with hypoxic-ischemic injury to basal ganglia and watershed cortex.

Meconium aspiration syndrome: thick meconium, respiratory distress, and air trapping; risk of persistent pulmonary hypertension.

NEC in preterm infants: ischemic and infectious; pneumatosis intestinalis is a radiographic hallmark.

Iatrogenic: catheter-related thrombosis, TPN cholestasis, and retinopathy of prematurity from oxygen therapy.

VACTERL: vertebral, anal, cardiac, tracheoesophageal, renal, and limb anomalies; requires ≥3 features.

CHARGE: coloboma, heart defects, choanal atresia, retardation, genital, ear anomalies; CHD7 mutation.

Potter sequence: renal agenesis → oligohydramnios → pulmonary hypoplasia, limb deformities, and flat facies.

Pierre Robin sequence: micrognathia, glossoptosis, and cleft palate; may be isolated or syndromic.

Down syndrome (T21): endocardial cushion defects, duodenal atresia, and Hirschsprung disease.

Turner syndrome (45,X): coarctation, bicuspid aortic valve, cystic hygroma, and horseshoe kidney.

DiGeorge (22q11.2): conotruncal cardiac defects, thymic hypoplasia, and hypocalcemia.

Phenylketonuria: PAH deficiency; untreated causes intellectual disability, musty odor, and fair skin.

Galactosemia: GALT deficiency; jaundice, hepatomegaly, cataracts, and E. coli sepsis; avoid galactose.

MCAD deficiency: fatty acid oxidation defect; hypoketotic hypoglycemia and sudden death with fasting.

Urea cycle defects: hyperammonemia with respiratory alkalosis; treat with nitrogen scavengers.

Severe combined immunodeficiency: absent T cells; presents with failure to thrive and opportunistic infections.

Chronic granulomatous disease: NADPH oxidase defect; recurrent catalase-positive infections and granulomas.

Wiskott-Aldrich: eczema, thrombocytopenia, and immunodeficiency; X-linked, WAS gene mutation.

Congenital CMV: periventricular calcifications, microcephaly, sensorineural hearing loss, and petechiae.

Congenital toxoplasmosis: diffuse intracranial calcifications, hydrocephalus, and chorioretinitis.

Congenital rubella: cataracts, deafness, and patent ductus arteriosus (classic triad).

Parvovirus B19: causes hydrops fetalis via aplastic crisis and myocarditis.

Neonatal HSV: vesicles, encephalitis, and disseminated disease; highest risk with primary maternal infection.

Group B Streptococcus: leading cause of neonatal sepsis and meningitis; intrapartum prophylaxis reduces risk.

Listeria monocytogenes: neonatal sepsis and meningitis; associated with maternal foodborne exposure.

Neuroblastoma: N-myc amplification, elevated urinary catecholamines, and bone marrow metastases.

Wilms tumor: WT1 mutation; associated with WAGR, Denys-Drash, and Beckwith-Wiedemann syndromes.

Retinoblastoma: RB1 biallelic inactivation; leukocoria and calcification on imaging.

Hepatoblastoma: elevated AFP; associated with Beckwith-Wiedemann and familial adenomatous polyposis.

Rhabdomyosarcoma: alveolar (PAX3/7-FOXO1 fusion) vs embryonal subtypes; pediatric soft tissue tumor.

Medulloblastoma: cerebellar tumor; WNT, SHH, group 3, and group 4 molecular subgroups.

Langerhans cell histiocytosis: CD1a and langerin positive; Birbeck granules on electron microscopy.

Flow cytometry: CD45 for leukocytes; surface markers identify lineage and clonality.

FISH: detects translocations and amplifications (e.g., N-myc, EWSR1) on interphase cells.

Karyotype: detects numerical and structural abnormalities; requires dividing cells.

PCR and sequencing: detect point mutations and small insertions/deletions with high sensitivity.

IHC markers: desmin and myogenin for muscle; CD99 for Ewing sarcoma; synaptophysin for neuroendocrine.

Cytogenetics: t(11;22) EWSR1-FLI1 in Ewing sarcoma; t(2;13) PAX3-FOXO1 in alveolar rhabdomyosarcoma.

Microarray (CMA): detects copy-number variants; first-tier test for developmental delay and autism.

Neonatal reference intervals differ from adults; age-specific ranges are required for interpretation.

Newborn screening: heel-stick dried blood spot; detects PKU, hypothyroidism, CAH, and hemoglobinopathies.

Physiologic anemia of infancy: nadir hemoglobin ~9-11 g/dL at 8-12 weeks.

Fetal hemoglobin (HbF) predominates at birth; switches to HbA over the first 6 months.

Blood banking: neonates have passive maternal IgG; crossmatch may be omitted for first transfusion in some protocols.

Microbiology: neonatal sepsis workup includes blood, CSF, and urine cultures; GBS and E. coli most common.

Genomic pathology: trio exome sequencing for undiagnosed developmental disorders.

Pediatric autopsy: external exam, radiographs, organ weights vs normative charts, and histology.

Sudden infant death syndrome: diagnosis of exclusion; requires scene investigation and complete autopsy.

Shaken baby syndrome: subdural hematoma, retinal hemorrhages, and encephalopathy.

Perinatal autopsy: examine placenta and cord; document gestational age and maceration.

Forensic: chain of custody and photographic documentation are required for legal admissibility.

Postmortem changes: livor, rigor, and algor mortis help estimate time since death.

Cause vs manner of death: manner categories are natural, accident, homicide, suicide, and undetermined.

CLIA: laboratory certification; proficiency testing required for regulated analytes.

Quality control: daily controls for quantitative assays; Westgard rules detect systematic and random error.

CAP accreditation: inspections and proficiency testing; peer comparison for performance.

Turnaround time: monitor from order to result; critical values require documented notification.

Lean/Six Sigma: reduce waste and variation; sigma metrics assess process capability.

Biosafety: BSL-2 for most clinical specimens; BSL-3 for TB and certain agents.

Documentation: corrective action and root cause analysis for deviations and adverse events.