microcephaly and macrocephaly definition

Microcephaly is a neonatal malformation defined as a head size much smaller compared with other babies of the same age and sex. However, some children with small heads have normal intelligence. The posterior fontanelle should close by age 3 months and anterior fontanelle by 20 months. Disorders such as anencephaly can also result in microcephaly (Figure 8-1). Sometimes detected at birth, microcephaly usually is the result of the brain developing abnormally in the womb or not growing as it should after birth.Microcephaly can be caused by a variety of genetic and environmental factors. Exposure to ionizing radiation during the first two trimesters can result in microcephaly.6,7 It does not appear that exposure to low levels of radiation associated with diagnostic imaging (x-ray, CT, MRI) pose any significant increased risk for the development of microcephaly. Causes of congenital microcephaly include: Prenatal infections: Exposure to the Zika virus, especially in the first trimester of pregnancy, can damage nerve cells in the brain. As in the case of other pathologies or disorders affecting cranial growth, head size is measured through the circumference or Cranial perimeter, the measurement of the contour of the head at the top (Microcephaly, 2016). The genetic form of primary microcephaly can be inherited by either autosomal dominant or autosomal recessive mechanisms. macrocephaly: [ mak″ro-sef´ah-le ] megalocephaly . Paul R. Carney, and James D. Geyer. 156.67.217.215 A definite aetiological diagnosis is important in order to predict the prognosis and offer genetic counselling. Fibrous union of the suture lines occurs by about age 6 months. Microcephaly is a condition that is present at birth in which the baby's head is much smaller than normal for an infant of that age and gender. The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, or from syndromes associated with chromosomal abnormalities. Acronym As opposed to disorders interrupting cerebral development associated with primary microcephaly, secondary microcephaly arises following neuronal injury. Head circumference (HC) two standard deviations (SD) below or above the mean defines microcephaly and macrocephaly, respectively.   •  Privacy Policy Most children with microcephaly also have a small brain and intellectual disability. Terms of Use Medical Definition of Macrocephaly. In some cases, particularly if your child's development is delayed, your doctor may request tests such as a head CT scan or MRI and … The severity of microcephaly … Picture 1 – Comparison of normal head with microcephaly. Microcephaly is rare, generally occurring in anywhere from 1 in 10,000 to 1 in Microcephaly and Macrocephaly Dysmorphic features are common and can include macrocephaly, microcephaly, deep-set eyes, hypotelorism, small palpebral fissures, dysplastic, large, or low-set ears, long face, bitemporal narrowing, high-arched palate, thin upper lip, and scoliosis or mild distal skeletal anomalies, such as … Microcephaly remains a poorly defined condition, and a uniform diagnostic approach is urgently needed. In comparison with children the same age, a child with microcephaly has a smaller head and, on occasion, a smaller brain. Microcephaly definition is - a condition of abnormal smallness of the circumference of the head that is present at birth or develops within the first few years of life and is often associated with developmental delays, impaired cognitive development, poor coordination and … Olusanya BO(1). or less than 10. th. In other cases, a baby can develop microcephaly after birth. Microcephaly is a condition where infants are born with a smaller than average head size. Microcephaly is defined by a head circumference more than two standard deviations below the mean for a given demographic (age, gender, race). The craniobasal bones are ossified by age 8 years. Medical Author: William C. Shiel Jr., MD, FACP, FACR; Macrocephaly: An abnormally large head. They also often have intellectual disability and neurological issues like seizures, problems with muscle stiffness and control, or problems with balance. Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. Microcephaly can happen to a baby while in the womb or within the first few years of life. Olusanya BO(1). It may be pathological or benign, even a familial genetic characteristic. Macrocephaly refers to head enlargement from any cause, including abnormalities of the scalp, cranial bones, and intracranial structures. Craniosynostosis is premature closure of at least one of the cranial bony sutures.9 Primary craniosynostosis is caused by abnormalities of the mesenchymal matrix. Learn more. Microcephaly is a rare nervous system disorder that causes a baby's head to be small and not fully developed. In the amino acid metabolism defects and in diseases with sudden onset of metabolic crisis, microcephaly most commonly results from loss of neuronal tissue. Small head size is an indication of the underlying brain size except in cases of craniosynostosis, or premature closure of the bony sutures. Microcephaly: An abnormally small head due to failure of brain growth.Microcephaly is an ominous sign because it is almost always associated with developmental delay and mental retardation. Microcephaly can be present at birth or it may develop in the first few years of life. Abnormalitiesof Head Size: Microcephaly and Macrocephaly. Fetal exposure to certain chemicals during neuronal induction or cellular migration also increases the risk of microcephaly.   •  Notice Microcephaly, Macrocephaly, Megalencephaly, Developmental delay, Malformation, Syndrome. Macrocephaly is a condition in which the human head is abnormally large; this includes the scalp, the cranial bone, and the contents of the cranium. Microcephaly (from New Latin microcephalia, from Ancient Greek μικρός mikrós "small" and κεφαλή kephalé "head") is a medical condition involving a shorter-than-normal head. Risk factors for macrocephaly. If this combines with poor brain growth, babies with microcephaly can develop developmental disabilities. Microcephaly is a neurological condition that occurs when an infant’s brain doesn’t develop properly, causing a baby’s head to be small. Thirty (6%) did not meet a case definition because of misclassification (e.g., macrocephaly or microphallus), or because both a physician diagnosis and anthropometric information necessary to accurately categorize head circumference percentile were missing. A definite aetiological diagnosis is important in order to predict the prognosis and offer genetic counselling. Microcephaly may be present at birth or it may develop in the first few years of life. ©1996-2021 MedicineNet, Inc. All rights reserved. https://accesspediatrics.mhmedical.com/content.aspx?bookid=459§ionid=41027535. Parents' head sizes also may be measured to determine whether small heads run in the family. The opposite of macrocephaly is microcephaly. found fetal microcephaly could not be reliably diagnosed or excluded on the basis of a single ultrasound examination if the HC was between 2 SD and 5 SD below the mean [2]. Microcephaly Micro = small cephaly = condition of the head. Microcephaly is often congenital, meaning a baby is born with the condition. This div only appears when the trigger link is hovered over. Primary microcephaly occurs because of genetic or environmental factors that produce small brain size (micrencephaly). This site uses cookies to provide, maintain and improve your experience. Macrocephaly can be a normal variant or be a sign of pressure within the growing head during childhood, such as from hydrocephalus. Certain factors increase the risk of microcephaly. Macrocephaly: An abnormally large head. Neonatal-Perinatal Medicine: Specialty Board Review. Most children who have microcephaly experience cognitive delays and other neurological problems. As nouns the difference between microcephaly and microencephaly is that microcephaly is a neurological disorder in which the person affected has an abnormally small head due to a failure of brain growth while microencephaly is (medicine) the condition of having a small brain. Relations have been found between autism, duplications of chromosomes and macrocephaly on one side. The genetic form of primary microcephaly can be inherited by either autosomal dominant or autosomal recessive mechanisms.2 A variety of neuronal migrational disorders—lissencephaly, schizencephaly, agensesis of the corpus callosum, and polymicrogyria—can be associated with microcephaly. Most children with microcephaly also have a small brain and intellectual disability. © 2002 by The McGraw-Hill Companies, Inc. Many factors can impair the growth of the brain, including intrauterine infections (such as rubella, cytomegalovirus, and toxoplasmosis), intrauterine chemical exposure (such as in fetal alcohol … Macrocephaly is defined as a head circumference that is two standard deviations greater than the average based on age, size, and family history. McGraw-Hill Concise Dictionary of Modern Medicine. Cytomegalovirus (CMV), rubella virus, and toxoplasmosis are the most well-known causes of microcephaly, but numerous infections in utero can increase this risk.8. 2 A variety of neuronal migrational disorders—lissencephaly, schizencephaly, agensesis of the corpus callosum, and polymicrogyria—can … Macrocephaly can be a normal variant or be a sign of pressure within the … Microcephaly may be congenital or it may develop in the first few years of life. Full-term newborns with congenital microcephaly and macrocephaly in Southwest Nigeria. It is not a condition in itself, but it may be a symptom of other conditions or complications in the brain. Ants Toi, Gustavo Malinger, in Obstetric Imaging: Fetal Diagnosis and Care (Second Edition), 2018. Head circumference at birth and the association with variables related to maternal health status, gestational age, growth pattern, brain imaging and clinical characteristics were analyzed. Definition An autosomal recessive syndrome characterized by seizures, intellectual disability, hypotonia, scoliosis, macrocephaly, hypertelorism and renal dysfunction. The genetic form of primary microcephaly can be inherited by either autosomal dominant or autosomal recessive mechanisms. microcephaly. The opposite of macrocephaly is microcephaly. A microcephalic individual usually also has a brain of diminished size, though often normal in structure. Other complications can include macrocephaly—fluid on the brain—cerebral hemorrhage caused by birth trauma, brittle teeth, and for some Type IIIs, basilar invagination—the second vertebra moves upward and cuts off the opening in the skull where the spinal cord passes through to the brain, causing dizziness, headache, periods of confusion, numbness, or even death. Microcephaly has been reported in more than 700 genetic syndromes, and macrocephaly in more than 200 genetic syndromes in the Online Mendelian Inheritance in Man (OMIM) database (the more specific clinical term for brain overgrowth, megalencephaly or MEG, is less used in this database). ### What you need to know Fetal microcephaly, a small head circumference in utero or at birth is a rare but important clinical finding that may occur as part of a range of conditions or, rarely, as a normal variant. As nouns the difference between macrocephaly and microcephaly is that macrocephaly is (medicine) a condition in which the head is abnormally large while microcephaly is a neurological disorder in which the person affected has an abnormally small head due to a failure of brain growth. Primary microcephaly occurs because of genetic or environmental factors that produce small brain size (micrencephaly). Dysmorphic features are common and can include macrocephaly, microcephaly, deep-set eyes, hypotelorism, small palpebral fissures, dysplastic, large, or low-set ears, long face, bitemporal narrowing, high-arched palate, thin upper lip, and scoliosis or mild distal skeletal anomalies, such as … Other symptoms and complications include seizures and developmental delays. Causes. Congenital microcephaly and macrocephaly can be primary (without obvious exogenous causes) or acquired (with or without underlying syndromes), although it is not uncommon for the term acquired to be described also as progressive and applied to infants with normal head sizes at birth but with subsequent deceleration of brain growth. Certain chemicals during neuronal induction or cellular migration also increases the risk for microcephaly ) below microcephaly and macrocephaly definition... Poorly defined condition, and a uniform diagnostic approach is urgently needed play a role in causing some cases disorders. 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