Macrocephaly

General

Macrocephaly means increased size of the head.

OFC >2 two SD above the mean for a given age, sex, and gestation (i.e. ≥ 97th percentile).

Macrocrania

by convention refers to a head circumference> 98th percentile.

Not to be confused with macroencephaly

Assessment should start when

A single OFC measurement is abnormal

When serial measurements reveal progressive enlargement (i.e. crossing of one or more major percentile lines [e.g. 10th, 25th, 50th, 75th, 90th] between health supervision visits),

There is an increase in OFC of > 2 cm/month (for infants aged 0-6 months)

Aetiological classification

By frequency

In a paediatric practice the 3 most common aetiologies in decreasing order of frequency:

Familial (parents have big heads)

Aka: benign familial megalencephaly
The most common type of anatomic megalencephaly
Children are born with large heads and normal body size, and during infancy OFC increases to greater than the 90th percentile, typically 2-4 cm above, but parallel to, the 98th percentile;
head growth velocity slows to a normal rate by approximately 6 months of age.
In children with a normal neurologic examination, normal development, no clinical features suggestive of a specific syndrome, and no family history of abnormal neurologic or developmental problems, familial megalencephaly can be confirmed by measuring the patient’s parents’ head circumferences and by using Weaver curves.

If the child’s OFC falls within the normal ranges as estimated using the Weaver curves, radiologic evaluation is not necessary.

Benign subdural fluid collections of infancy
Hydrocephalus.

By contents

Increased CSF

With normal or mildly enlarged ventricles

Arachnoid cyst

AKA subependymal or subarachnoid cyst
A duplication of the ependyma or arachnoid layer filled with CSF. Usually reach maximal size by 1 month of age and do not enlarge further.
Treatment is required in ≈ 30% due to rapid enlargement or growth beyond first month.
Cyst may be shunted or fenestrated.
Prognosis with true arachnoid cyst is generally good (unlike porencephalic cyst) if no increased ICP or progressive macrocephaly during 1st year of life

“external hydrocephalus”: prominent subarachnoid spaces and basal cisterns; see External hydrocephalus (AKA benign external hydrocephalus)

“craniocerebral disproportion”

Benign enlargement of subarachnoid spaces

With ventricular enlargement

(Hydrostatic) hydrocephalus (HCP)

Communicating
Obstructive

Hydranencephaly (p.305)

Constitutional ventriculomegaly:

ventricular enlargement of no known aetiology with normal neurologic function

Hydrocephalus ex vacuo:

loss of cerebral tissue (more often associated with microcephaly, e.g. with TORCH infections)

Vein of Galen aneurysms

Increased brain (Macroencephaly)

Anatomic (increased cells):

Familial Macroencephaly (commonest)

parents also have large heads, the brains eventually “catch up”

Neurocutaneous syndromes:

Usually due to increased volume of brain tissue (Macroencephaly)
Seen especially in

Common

neurofibromatosis
congenital hypermelanosis

Less common

tuberous sclerosis
Sturge-Weber

Rare

Hemimegalencephaly syndrome

Autistic spectrum disorders

Achondroplasia

Cerebral gigantism (Sotos syndrome)

Fragile X syndrome

Cowden syndrome

Gorlin syndrome

Metabolic (deposition of substances in brain tissue):

Leukodystrophies

Canavan disease
Neurometabolic diseases: (lysosomal disease)

usually due to deposition of metabolic substances in the brain.
Seen in

Tay-Sachs gangliosidosis,
Krabbe disease
Metachromatic leukodystrophy

Idiopathic

Increased blood

Haemorrhage (extradural, subdural, parenchymal, intraventricular)

subdural fluid

hematoma
hygroma
effusion benign and symptomatic
benign subdural collections of infancy (p.939)
Cerebral edema: some consider this to be a form of pseudotumor cerebri

Toxic: e.g. lead encephalopathy (from chronic lead poisoning)
Endocrine: hypoparathyroidism, galactosemia, hypophosphatasia, hypervitaminosis A, adrenal insufficiency

Arteriovenous malformation

especially vein of Galen “aneurysm”
Auscultate for cranial bruit. With vein of Galen aneurysms, macrocephaly may be due to HCP from obstruction of the Sylvian aqueduct. With other malformations, macrocrania may be due to increased pressure in venous system without HCP

Increased bone

Thalassaemia (marrow expansion)

Primary bone disorders

Skull dysplasia: e.g. osteopetrosis

“gigantism syndromes”

Soto’s syndrome:

associated with advanced bone age on X-ray, and multiple dysplastic features of face, skin, and bones

Exomphalomacroglossia-gigantism (EMG) syndrome: Consist of

hypoglycemia (from abnormalities in islets of Langerhans),
large birth weight,
large umbilicus or umbilical hernia
macroglossia

Achondroplastic dwarf:

cranial structures are enlarged but the skull base is small, giving rise to a prominent forehead and an OFC≥97th percentile for age, hypoplasia of midface, and stenosis at foramen magnum.
Head growth follows different curve than normal (OFC ≥ 97th percentile for age is not unusual and does not necessitate shunting)

Intracranial mass

Cyst

Abscess

Brain tumors without hydrocephalus:

brain tumors are rare in infancy, and most cause obstructive HCP.
Tumors that occasionally present without HCP include astrocytomas.
May also be seen in the rare diencephalic syndrome, see tumor of anterior hypothalamus