Intracranial and Calvarial Disorders

Summary

This chapter explores those conditions that cause abnormal head shape or head size in the newborn infant. The underlying causes, clinical presentation, diagnosis, and available interventions will be presented.

Examination of the Head

Abnormalities are first identified by observation of the general shape and texture of the head and scalp. Palpation of neurocutaneous lesions are noted. The anterior fontanelle, demarking the junction of the frontal and parietal bones at the intersection of the metopic, coronal, and sagittal sutures, should always be palpated. It is usually soft, flat, and pulsatile with the heartbeat. The anterior fontanelle may be tense or full when a child is crying, but sustained bulging of the fontanelle may be indicative of a pathologic process associated with elevated intracranial pressure. It usually closes by 18 months of age, although some recent studies have shown that it can take up to 24 months to fully close (mean 16.3 months for boys and 18.8 months for girls). The posterior fontanelle is smaller and denotes the junction of the parietal and occipital bones at the intersection of the sagittal and lambdoid sutures. It usually closes by 3 months. Palpation for abnormal splaying or overlap of the cranial sutures, measured in millimeters, should also be recorded.

Head circumference measurement should be recorded with each examination, as it is a gauge of intracranial volume. The occipitofrontal circumference (OFC) is obtained with a tape measure firmly pressed against the scalp to include the occiput at or just above the external occipital protuberance (inion) and the forehead just above the glabella. Gestation age-adjusted measurements should be made on growth charts for preterm infants. Normal head growth occurs at approximately 2 cm per month in the first 3 months, 1 cm per month the next 3 months, and then 0.5 cm per month for the next 6 months.

The Neonate

Neurulation and Cleavage

An in-depth review of craniofacial development is beyond the scope of this chapter; however, there are well-studied defects in embryogenesis that lead to abnormally shaped heads in the neonate. Microcephaly, or a small head, is a primary manifestation of embryologic and congenital abnormalities resulting in a small brain ( Fig. 57.1 ). Briefly, the embryologic process begins with primary neurulation between days 17 and 27 of gestation. Errors in neurulation and neural tube closure lead to dysraphic malformations. The most devastating of all neural tube defects is anencephaly ( Fig. 57.2 ). This fatal condition results from failure of the anterior neuropore to close, and leads to an absent cranial vault.

Abnormal cleavage, which is the normal separation of the embryonic forebrain to form paired telencephalic hemispheres by day 33 of gestation, can lead to conditions such as holoprosencephaly. Varying degrees of holoprosencephaly exist, with the most complete form being alobar holoprosencephaly and lesser forms termed semilobar and lobar ( Fig. 57.3 ). Associated median facial defects can range from a single midline eye to orbital hypotelorism, nose flattening, cleft lip and palate, or trigonocephaly.

Migration

Neuronal migration is the radial and tangential process by which the cerebrum is formed. Progenitor cells migrate from the ventricular zone and basal forebrain to create the cortex. There is cortical disruption when this migration does not occur normally, and conditions like schizencephaly (cleft in the hemisphere) ( Fig. 57.4 ), lissencephaly (“smooth brain”) ( Fig. 57.5 ), or polymicrogyria occur ( Fig. 57.6 ). The hallmark features include gyral anomalies. Midline structures are also often involved, such as failure of the corpus callosum to form completely or agenesis of the corpus callosum ( Fig. 57.7 ). The septum pellucidum can also be absent. External features can lead to abnormally shaped heads ( Fig. 57.8 ). Abnormal migration can also lead to syndromes of neuronal heterotopias, such as Aicardi syndrome characterized by microcephaly.

Neural crest cells, first formed in a zone between the neural plate and the ectoderm, also play a major role in the formation of the fetal skull and face. Errors in that process, including in the migration of neural crest cells, lead to improperly formed face and heads. Examples include Waardenburg syndrome and craniofrontal dysplasia.