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Microcephaly & Macrocephaly

ByPeter Korček

Primary prerequisite for the diagnosis of microcephaly/macrocephaly is the proper horizontal head circumference (HC) measurement (frontal-occipital circumference):

  • supine position
  • glabella – opisthocranion as anchor points
  • normocephaly (32-38 cm for a term newborn) => refer to percentile graphs for your hospital, region or country
  • percentile graphs for preterm population (Fenton graphs)
  • sexual dimorphism at birth (1 cm)

Head circumference at birth is usually proportional to birth length in appropriate-for-gestational-age newborns. For asymmetrical IUGR (intrauterine growth restriction) infants, head circumference and length at birth is usually normal, as compared to their lower birth weight.

Microcephaly = head circumference < 3.percentile in the corresponding percentile growth charts for the specific patient (gestational and postnatal age, sex)

Macrocephaly = head circumference > 97.percentile (see above)

Etiology

Etiology – General

  • measurement errors (make sure to measure anthropometric parameters precisely and if needed, perform serial measurements)
  • false positive measurements (transient changes to the body area – breech delivery; instrumental delivery; head molding during birth; caput succedaneum; cephalhematoma)

Etiology – Macrocephaly

  • hereditary / familiar
  • hydrocephalus = abnormal accumulation of cerebrospinal fluid in the intracranial space
    • congenital (CNS malformations – stenosis of the Sylvian aqueduct; Chiari syndromes; Dandy-Walker syndrome; vascular malformations) – congenital hydrocephalus is often diagnosed prenatally (15-18 weeks of gestation)
    • acquired (post-hemorrhagic; post-infectious)
  • achondroplasia
  • inherited metabolic disorders (Alexander disease; infantile form of Krabbe disease; glutaric acidemia/aciduria I)
  • genetic syndromes (neurofibromatosis von Recklinghausen I; Silver-Russell; Sotos; Sturge-Weber-Krabbe)
  • scaphocephaly (premature fusion of the sagittal suture)

Etiology – Microcephaly

  • hereditary / familiar
  • congenital infection (TORCH – cytomegalovirus; herpetic viruses; rubella; varicella; toxoplasmosis)
  • teratogens (alcohol – fetal alcohol syndrome; radiation before 15 weeks of gestation; phenytoin (anti-epileptic drug) – fetal hydantoin syndrome)
  • congenital CNS anomalies (lissencephaly; cranial encephalocele/meningocele)
  • numeric chromosomal abnormalities (Patau – trisomy 13; Edwards – trisomy 18; Down – trisomy 21)
  • genetic syndromes (Bloom; Dubowitz; Nijmegen breakage syndrome; Prader-Willi; Rubinstein-Taybi; Seckel; Smith-Lemli-Opitz)
  • other causes (maternal hyperphenylalaninemia; complex craniosynostosis)
  • intrauterine hypoxic-ischemic insult

Diagnosis

Clinical signs

  • Proper and serial head circumference measurement (see above) – rate of growth of HC > + 1.25 cm/week can be abnormal
  • Features of deviation from the normal development (facial dysmorphism, other anomalies)
  • Medical history (pregnancy; medication; extended family – anthropometric measurements in family)

Laboratory findings

  • Biochemistry and hematology
    • inflammatory markers (CRP, procalcitonin, interleukin-6)
    • full blood count
    • biochemistry (urea, creatinine, liver function tests; ammonia; blood gas; phenylalanine in mother
    • inherited metabolic disorders (blood + urine + cerebrospinal fluid)
  • Serology (IgM, IgG – blood + cerebrospinal fluid)
  • PCR – DNA (TORCH – blood + urine + cerebrospinal fluid)
  • Genetics (karyotype; micro-array; prenatal diagnosis can be done also from amniotic fluid or chorionic villi)
  • Cerebrospinal fluid (biochemistry, cytology, culture, serology)

Imaging

  • Cranial ultrasound (prenatal, postnatal)
  • MRI (prenatal, postnatal)
  • X-ray of skull
  • Ophthalmology (fundus – chorioretinitis with TORCH infection – CMV, Toxoplasma)

Therapy

Surgery

  • Craniosynostosis (remodelling to ensure optimal brain growth and to optimise neurocranium shape)
    • indicated and performed between 4-6 months of age
  • Hydrocephalus (derivation of cerebrospinal fluid)
    • temporary (external reservoir = Ommaya reservoir)
    • permanent (internal reservoir = ventriculoperitoneal (VP) shunt)

References

① Leibovitz Z, Lerman-Sagie T. Diagnostic approach to fetal microcephaly. Eur J Paediatr Neurol. 2018;22(6):935-943. doi:10.1016/j.ejpn.2018.06.002

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