Macrocephaly
Encyclopedia
Macrocephaly occurs when the head is abnormally large; this includes the scalp
, the cranial
bone, and the contents of the cranium.
(enlarged brain), hydrocephalus
(water on the brain), cranial hyperostosis
(bone overgrowth), and other conditions. Pathologic macrocephaly is called "syndromic" when it is associated with any other noteworthy condition, and "non-syndromic" otherwise. Pathologic macrocephaly can be caused by congenital anatomic abnormalities, genetic conditions or by environmental events.
Many genetic conditions are associated with macrocephaly, including familial macrocephaly, autism
, PTEN
mutations such as Cowden disease, neurofibromatosis
type 1, and tuberous sclerosis
; overgrowth syndromes such as Sotos syndrome
(cerebral gigantism), Weaver syndrome
, Simpson-Golabi-Behmel syndrome
(Bulldog syndrome), and macrocephaly-capillary malformation
(M-CMTC) syndrome; neuro-cardio-facial-cutaneous syndromes such as Noonan syndrome
, Costello syndrome
, and cardiofaciocutaneous syndrome
; Fragile X syndrome
; leukodystrophies (brain white matter
degeneration) such as Alexander disease
, Canavan disease
, and megalencephalic leukoencephalopathy with subcortical cysts
; and glutaric aciduria type 1 and D-2-hydroxyglutaric aciduria.
In the genetic area relations have been found between autism
, duplications of chromosomes and macrocephaly on one side. On the other side a relation has been found between schizophrenia
, deletions of chromosomes and microcephaly
.
Environmental events associated with macrocephaly include infection, neonatal intraventricular hemorrhage
(bleeding within the infant brain), subdural hematoma
(bleeding beneath the outer lining of the brain), subdural effusion
(collection of fluid beneath the outer lining of the brain), and arachnoid cyst
s (cysts on the brain surface).
s (SD) above the mean. Relative macrocephaly occurs if the measure is less than 2 SD above the mean but is disproportionately above that when ethnicity and stature are considered. In research, cranial height or brain imaging are also used to determine intracranial volume more accurately.
Scalp
The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.-Layers:It is usually described as having five layers, which can conveniently be remembered as a mnemonic:...
, the cranial
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...
bone, and the contents of the cranium.
Causes
Macrocephaly may be pathologic, but many people with an unusually large head are healthy. Pathologic macrocephaly may be due to megalencephalyMegalencephaly
Megalencephaly is a condition in which there is an abnormally large brain. It is usually functioning abnormally. Megalencephaly is, by definition, when the brain weight is greater than average for the age and sex of the infant or child...
(enlarged brain), hydrocephalus
Hydrocephalus
Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
(water on the brain), cranial hyperostosis
Hyperostosis
Hyperostosis is an excessive growth of bone. It may lead to exostosis. It occurs in many musculoskeletal disorders.-See also:* Infantile cortical hyperostosis* SAPHO syndrome* Hyperostosis frontalis interna...
(bone overgrowth), and other conditions. Pathologic macrocephaly is called "syndromic" when it is associated with any other noteworthy condition, and "non-syndromic" otherwise. Pathologic macrocephaly can be caused by congenital anatomic abnormalities, genetic conditions or by environmental events.
Many genetic conditions are associated with macrocephaly, including familial macrocephaly, autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
, PTEN
PTEN (gene)
Phosphatase and tensin homolog is a protein that, in humans, is encoded by the PTEN gene. Mutations of this gene are a step in the development of many cancers....
mutations such as Cowden disease, neurofibromatosis
Neurofibromatosis
Neurofibromatosis is a genetically-inherited disorder in which the nerve tissue grows tumors that may be benign or may cause serious damage by compressing nerves and other tissues...
type 1, and tuberous sclerosis
Tuberous sclerosis
Tuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...
; overgrowth syndromes such as Sotos syndrome
Sotos syndrome
Sotos syndrome is a rare genetic disorder characterized by excessive physical growth during the first 2 to 3 years of life. The disorder may be accompanied by autism mild mental retardation, delayed motor, cognitive, and social development, hypotonia , and speech impairments...
(cerebral gigantism), Weaver syndrome
Weaver syndrome
Weaver syndrome is a congenital disorder associated with rapid growth beginning in the prenatal period, a characteristic facial appearance and certain skeletal features. It was first described by Weaver in 1974....
, Simpson-Golabi-Behmel syndrome
Simpson-Golabi-Behmel syndrome
Simpson–Golabi–Behmel syndrome , also called Bulldog syndrome, Sara Agers syndrome, Golabi–Rosen syndrome, Simpson dysmorphia syndrome or X-linked dysplasia gigantism syndrome , is a rare inherited congenital disorder with widely variable expression, causing craniofacial and other abnormalities.It...
(Bulldog syndrome), and macrocephaly-capillary malformation
Macrocephaly-capillary malformation
Macrocephaly-capillary malformation is a multiple malformation syndrome causing abnormal body and head overgrowth and cutaneous, vascular, neurologic, and limb abnormalities. The disorder is assumed to have a genetic basis, but the precise genetic cause for M-CM is unknown and diagnosis is...
(M-CMTC) syndrome; neuro-cardio-facial-cutaneous syndromes such as Noonan syndrome
Noonan syndrome
Noonan Syndrome is a relatively common autosomal dominant congenital disorder considered to be a type of dwarfism, that affects both males and females equally. It used to be referred to as the male version of Turner's syndrome ; however, the genetic causes of Noonan syndrome and Turner syndrome...
, Costello syndrome
Costello syndrome
Costello syndrome, also called faciocutaneoskeletal syndrome or FCS syndrome, is a rare genetic disorder that affects many parts of the body. It is characterized by delayed development and mental retardation, distinctive facial features, unusually flexible joints, and loose folds of extra skin,...
, and cardiofaciocutaneous syndrome
Cardiofaciocutaneous syndrome
Cardiofaciocutaneous Syndrome is an extremely rare and serious genetic disorder.It is characterized by the following:*Distinctive facial appearance*Unusually sparse, brittle, curly scalp hair...
; Fragile X syndrome
Fragile X syndrome
Fragile X syndrome , Martin–Bell syndrome, or Escalante's syndrome , is a genetic syndrome that is the most commonly known single-gene cause of autism and the most common inherited cause of intellectual disability...
; leukodystrophies (brain white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
degeneration) such as Alexander disease
Alexander disease
Alexander disease is a slowly progressing and fatal neurodegenerative disease. It is a very rare disorder which results from a genetic mutation and mostly affects infants and children, causing developmental delay and changes in physical characteristics....
, Canavan disease
Canavan disease
Canavan disease, also called Canavan-Van Bogaert-Bertrand disease, aspartoacylase deficiency or aminoacylase 2 deficiency, is an autosomal recessive degenerative disorder that causes progressive damage to nerve cells in the brain. Canavan disease is also one of the most common degenerative...
, and megalencephalic leukoencephalopathy with subcortical cysts
Megalencephalic leukoencephalopathy with subcortical cysts
Megalencephalic leukoencephalopathy with subcortical cysts is a form of hereditary CNS demyelinating disease. It belongs to a group of disorders called leukodystrophies.It is associated with MLC1.-External links:...
; and glutaric aciduria type 1 and D-2-hydroxyglutaric aciduria.
In the genetic area relations have been found between autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
, duplications of chromosomes and macrocephaly on one side. On the other side a relation has been found between schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
, deletions of chromosomes and microcephaly
Microcephaly
Microcephaly is a neurodevelopmental disorder in which the circumference of the head is more than two standard deviations smaller than average for the person's age and sex. Microcephaly may be congenital or it may develop in the first few years of life...
.
Environmental events associated with macrocephaly include infection, neonatal intraventricular hemorrhage
Intraventricular hemorrhage
An intraventricular hemorrhage , often abbreviated "IVH," is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space...
(bleeding within the infant brain), subdural hematoma
Subdural hematoma
A subdural hematoma or subdural haematoma , also known as a subdural haemorrhage , is a type of haematoma, a form of traumatic brain injury. Blood gathers within the outermost meningeal layer, between the dura mater, which adheres to the skull, and the arachnoid mater, which envelops the brain...
(bleeding beneath the outer lining of the brain), subdural effusion
Subdural effusion
Subdural effusion refers to an effusion in the subdural space, usually of cerebrospinal fluid.It is sometimes treated with surgery....
(collection of fluid beneath the outer lining of the brain), and arachnoid cyst
Arachnoid cyst
Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord...
s (cysts on the brain surface).
Diagnosis
Macrocephaly is customarily diagnosed if head circumference is greater than 2 standard deviationStandard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
s (SD) above the mean. Relative macrocephaly occurs if the measure is less than 2 SD above the mean but is disproportionately above that when ethnicity and stature are considered. In research, cranial height or brain imaging are also used to determine intracranial volume more accurately.