Sign Up for a Free Account
  • Updated 05.14.2024
  • Released 07.29.1998
  • Expires For CME 05.14.2027

Microcephaly

Introduction

Overview

In this updated article, the author provides insight into the evolving classification of primary microcephaly as gene discovery rapidly progresses, highlights of the role of transcription factors, and details of management in terms of developmental and educational recommendations for affected children.

Key points

• Microcephaly is defined as a head circumference of less than three standard deviations from the population mean for age and gender.

• Microcephaly is a clinical finding that can result from various causes. There are both genetic and nongenetic causes of microcephaly.

• Advances in neuroimaging and genetic testing have value for the diagnosis and prognosis of microcephaly.

• The American Academy of Neurology and Child Neurology Society have published an evidence-based review with recommendations for evaluating a child with microcephaly.

Historical note and terminology

Microcephaly is a descriptive term referring to a cranial vault that is significantly smaller than the standard for the person's age and sex. Microcephaly should be considered a clinical finding rather than a disorder, and it may stem from various causes that lead to the disruption of various stages of brain development. In clinical settings, microcephaly is determined by measuring one's head circumference, which is known to correlate well with cranial volume (13). When the head circumference is smaller than two standard deviations below the mean for the age and sex, microcephaly is present. However, most researchers use head circumference of three standard deviations below the mean as the definition of microcephaly (08; 96; 55).

Microcephaly has been observed and recognized for a long time, but it was not until the late 19th century that it started to attract scientists' attention. Many theories concerning the pathogenesis of microcephaly have been proposed. Some authors viewed microcephaly as a form of atavism, and others thought that it was due to mechanical compression of the fetal brain by contraction of the uterus. Giacomini, in 1885, proposed a classification of microcephaly, which is of historical significance. He divided microcephaly into three categories. The first was named "microcephalia vera," which means "true" microcephaly, in which there is no gross pathological abnormality other than smallness of the brain. Giacomini thought that this condition was due to pure inhibition of brain development. The second category was termed "microcephalia spuria," which refers to "pseudo" microcephaly, in which the pathological process or its residuum is identifiable. The third was "microcephalia combinata," which was thought to be a combination of both inhibitions of developmental and pathological processes. The term "microcephalia vera" is still occasionally used in clinical settings, and refers to patients who have microcephaly with no identifiable gross central nervous system pathology and little or no involvement of the organ systems other than the CNS. Since then, many different classifications and terminologies of microcephaly have emerged. Genetic and nongenetic microcephaly are classified according to etiology. Primary microcephaly is often used synonymously as congenital microcephaly, in which microcephaly is present at the time of birth. In contrast, secondary microcephaly or acquired microcephaly is used when head circumference is normal at birth and subsequently falls to the microcephalic range (62).

The term micrencephaly refers to "small brain," a pathological term. Although the presence of microcephaly usually implies that the brain is small, normal head circumference does not guarantee a normal-sized brain. Hence, microcephaly and micrencephaly are not interchangeable.

This is an article preview.
Start a Free Account
to access the full version.

  • Nearly 3,000 illustrations, including video clips of neurologic disorders.

  • Every article is reviewed by our esteemed Editorial Board for accuracy and currency.

  • Full spectrum of neurology in 1,200 comprehensive articles.

  • Listen to MedLink on the go with Audio versions of each article.

Questions or Comment?

MedLink®, LLC

3525 Del Mar Heights Rd, Ste 304
San Diego, CA 92130-2122

Toll Free (U.S. + Canada): 800-452-2400

US Number: +1-619-640-4660

Support: service@medlink.com

Editor: editor@medlink.com

ISSN: 2831-9125