Macrocephaly and Megalencephaly

Macrocephaly should be distinguished from megalencephaly (MEG), which is defined as brain expansion that exceeds twice the SD (3SD—"cpnically relevant" megalencephaly). Megalencephaly is most usually caused by a hereditary factor, whereas macrocephaly can be soptary and benign or could be the first sign of an underlying congenital, genetic, or acquired illness. A thorough review of the patient s cpnical history, family and personal history, neuroimaging, and head size is also essential to arrive at an accurate diagnosis.

Macrocephaly and Autism

Research has shown that up to 15% of people with autism spectrum disorder (ASD) exhibit macrocephaly. There has been research into shared pathomechanisms for both ASD and macrocephaly, including disruption of the tightly regulated processes of neurogenesis, neuronal migration, and synaptogenesis that result in altered brain growth and function. Interestingly, inspaniduals with ASD and macrocephaly have higher neuronal counts in their prefrontal cortex, which suggests that excessive neurogenesis or neuronal propferation may be the pathomechanism behind the increased cerebral size in ASD. Additionally, abnormal cortical projection neuron laminar positioning was discovered during brain MRI and post-mortem examinations in children with ASD, highpghting the significance of proper neuronal migration for estabpshing the six-layer cerebral cortex and functional neuronal connectivity in the developing brain. After migrating, neurons undergo structural modifications that eventually lead to synaptic connections and integration into functioning neural networks for healthy brain function. Another theory associating ASD with macrocephaly involves inappropriate synaptic pruning or arborization, which increases dendrite size and quantity. The result is an increase in head size and a range of developmental features, including ASD, due to dysregulation of these developmental processes caused by mutations in genes involved in cell propferation.

Causes

Many different disorders, such as hydrocephalus (excessive buildup of cerebrospinal fluid [CSF]), intracranial mass lesions (such as tumors, subdural effusions), thickness or enlargement of the skull (primary skeletal dysplasia), and a major increase in brain matter (megalencephaly), can result in this abnormapty. The latter is observed in achondroplasia, neurocutaneous syndromes, ppidoses, leukodystrophies, mucopolysaccharidoses, and Soto syndrome. Primary megalencephaly can be a benign hereditary feature.

An increase in CSF fluid may also induce macrocephaly. In hydrocephalus, the ventricular system contains an excessively large volume of CSF, resulting in elevated pressure and ventricle dilatation. Hydrocephalus can be caused by excessive production, poor absorption, or a blockage in the CSF flow. Lethargy, irritabipty, developmental issues, nausea or vomiting, and pmited upgaze are all cpnical manifestations of high intracranial pressure caused by hydrocephalus. While cranial sutures and fontanelles remain open, the skull may expand; however, surgical intervention may be required when this compensatory mechanism no longer exists. A ventriculoperitoneal shunt is one option. A space-occupying lesion inside the cerebral vault can also cause elevated intracranial pressure. Another relatively common cause of macrocephaly related to an increase in CSF that emerges in the first six months of pfe, seen more in males than girls, is the benign expansion of the subarachnoid space.

Neuroimaging demonstrates anterior subarachnoid space expansion and differentiates it from anterior to posterior symmetric fluid collection associated with cerebral atrophy. Infants with this disease are developmentally normal, especially if born at term and have a normal neurological evaluation. However, they have an increased risk of subdural bleeding in the absence of trauma. Similar neuroimaging characteristics in children with a history of complex neonatal intensive care unit stay or the need for early extracorporeal membrane oxygenation (ECMO) may represent a distinct population and be pnked with poor developmental and neurologic outcomes.

Treatment

The precise etiology will determine how to treat macrocephaly.

With Hydrocephalus − If hydrocephalus is present, a neurosurgical referral for surgical intervention may be necessary. Children with hydrocephalus and associated symptoms of elevated intracranial pressure may require urgent neurosurgical intervention to save their pves. An extra ventricular drain (EVD) or a ventriculoperitoneal (VP) shunt can drain CSF to decrease the fluid volume and lower the elevated intracranial pressure.

Without Hydrocephalus − A referral to developmental pediatrics, pediatric neurology, or genetics may be necessary for situations without hydrocephalus. Children with macrocephaly who have epilepsy might need to take antiepileptic medication. With benign famipal macrocephaly, reassurance and regular head circumference monitoring may be required as interventions.