description
microcephaly is a clinical syndrome where the head circumference (taken at the level of the transthalamic plane) is below normal. if three standard deviations below the mean is used as the threshold for diagnosis, the incidence is 0.1 per cent.
diagnosis
difficulties exist in the prenatal diagnosis of microcephaly. the utility of head measurements alone is limited, as these can be markedly biased by factors such as incorrect dating or intrauterine growth restriction. furthermore, the natural history of microcephaly is largely unknown. some authors have suggested a progressive intrauterine development of the lesion, rendering early diagnosis impossible in some cases. microcephalic heads have a sloping forehead which can be seen on ultrasound. the lateral ventricles may be enlarged due to cortical atrophy. when gross abnormalities exist within the fetal head, and the fetal head measurement is more than three standard deviations (sd) below the mean, the likelihood of true microcephaly and mental retardation is great. however, when the measurements are between 1-3 sd below the norm, with no intracranial abnormalities, there is reasonable hope that these fetuses will develop normally. microcephaly may be found without associated malformations and may be genetic (eg. phenylketonuria, methylmalonic acidemia) or environmental (radiation, viral infection, alcohol, fetal hydantoin syndrome). where there are associated malformations, genetic causes include trisomies (21, 13, 18) as well as 22, 4p-, 5p-, 18p-, and 18q- syndromes, in addition to a number of single gene defects such as lissencephaly, meckel-gruber, menkes, smith-lemli-opitz and roberts syndromes. it is therefore suggested that if microcephaly (with or without associated malformations) is suspected karyotyping should be recommended. because of the association with moderate to severe mental retardation in over 60 per cent of infants with a head circumferences below 3 sd, the prognosis is necessarily guarded.
differential diagnosis
in its severe form microcephaly may be very difficult to differentiate from anencephaly, but appreciation of an intact calvarium will enable the correct diagnosis in the presence of abnormal intracranial anatomy, the diagnosis of aprosencephaly should be considered.
sonographic features
head circumference 3 sd below mean for gestational age.
exclude incorrect dates and intrauterine growth restriction.
usually best diagnosed by serial scans in the second half of pregnancy.
severe cases may be difficult to differentiate from anencephaly but prognosis in both is hopeless.
associated syndromes
- 3-hydroxyisobutyric aciduria
- ablepharon-macrostomia
- absent abdominal muscles-microphthalmia
- acanthosis nigricans-short stature
- achalasia-adrenocortical insufficiency-alacrima
- achalasia
- adducted thumbs
- adrenal hypoplasia-growth hormone deficiency-skeletal anomalies
- albinism-digital anomalies
- alcohol
- alopecia-congenital seizures
- alopecia-keratosis follicularis-dwarfism
- alopecia-mental retardation
- alopecia-shawl scrotum
- alopecia-skeletal anomalies
- aminopterin-like
- angelman
- anophthalmia-postnatal growth failure
- armendares
- arthrogryposis
- asphyxiating thoracic dysplasia variant
- asymmetric crying facies
- athetosis-deafness-pachygyria
- bartsocas-papas
- bavinck
- bawle-horton
- benzodiazepine
- blepharophimosis-microcephaly
- bowen-conradi
- brachy/camptodactyly-short stature
- brachydactyly a2-diabetes
- brachydactyly-nail dysplasia
- burton
- býrjeson-forssman-lehmann
- calcified cerebral white matter
- canescence-joint laxity
- cantu
- cerebro-oculo-facio-skeletal
- cervical vertebral fusion-short stature
- choanal stenosis-short stature
- chondrodysplasia-joint dislocations
- chorioretinal dysplasia
- chromosome abnormalities
- chromosome instability
- chromosome mosaic variegated aneuploidy
- cleft lip/palate-congenital megacolon
- cleft mandible-athetosis
- coffin-siris
- cofs-osteopetrosis
- cohen
- congenital heart defects-skeletal changes
- congenital heart defects-unusual facies
- cortada
- craniosynostosis-coloboma-split hand
- craniosynostosis-limb reduction-clefting
- crouzon
- cutaneous hypo- and hyperpigmentation-spastic paraparesis
- cutis laxa (male lethal)
- de barsy
- de lange
- deafness-male pseudohermaphroditism
- distal aphalangia
- dolicospondylic dysplasia
- drayer
- dubowitz
- dwarfism
- epiphyseal dysplasia-retinitis pigmentosa
- facial anomalies
- familial microcephaly
- fanconi pancytopenia
- feingold
- filippi
- fundoscopic anomalies without retardation
- german
- goldblatt
- gombo
- grix
- halal
- hallerman- streiff
- hall-riggs
- hepatic cirrhosis-unusual facies
- herpes
- hirschsprung-cleft palate
- hirschsprung-iris coloboma
- hmc
- holmes
- hunter-mcalpine
- hurst
- hutteroth
- hydantoin embryopathy
- hypogonadism-short stature
- hypogonadism-short stature-obesity
- hypoplastic right heart
- immunodeficiency-chromosome instability
- immunodeficiency-malformations
- immunodeficiency-normal intelligence
- intermittent hyperpnea-wide mouth
- intestinal atresia-ocular anomalies
- intracranial calcification
- ives
- johanson-blizzard
- jorgenson
- juberg-hayward
- kaufman
- kawashima
- kbg
- kelly
- kraus-rupert
- langer-giedion
- lenz microphthalmia
- leprechaunism
- lindstrom: iugr-dwarfism
- macroepiphyses-wrinkled skin
- madokoro
- marfanoid habitus
- marion-mayers
- martsolf
- maternal hyperthermia
- maternal phenylketonuria
- megalocornea
- mental retardation-osteosclerosis
- methylmercury
- microbrachycephaly-eye anomalies-clefting
- microcephaly-cardiomyopathy
- microcephaly-cubitus valgus
- microcephaly-deafness
- microcephaly-grey matter heterotopia
- microcephaly-lymphedema (benign)
- microcephaly-lymphedema (mental retardation)
- microcephaly-normal intelligence
- microcephaly-normal intelligence-oligodontia
- microcephaly-osteodysplastic dysplasia
- microcephaly-radio-ulnar synostosis
- micromelic short stature-knee subluxation
- microphthalmia
- microphthalmia-retinal folds
- multiple pterygium-lethal
- mulvihill-smith
- mutchinick
- myhre
- neonatal axonal dystrophy
- neonatal infantile spasms
- nephrotic syndrome-infantile spasms
- norman-urich
- obesity-short stature (x-linked)
- oculo-palato-cerebral dysplasia
- osteogenesis imperfecta-cataracts
- osteoporosis-pseudoglioma
- oto-facial-digital ii
- palant
- partington
- pilodentoungular dysplasia
- pilotto
- pitt-rogers-danks
- poland anomaly
- polysyndactyly-ptosis
- prader-willi
- preaxial polydactyly-clefting
- premature aging-short stature
- premaxillary agenesis-midline cleft
- primordial dwarfism-cataracts
- proptosis-pierre robin
- pseudoprogeria/hallerman-streiff
- pterygia-short stature
- radial microbrain
- reardon
- renpenning
- retinal detachment-acral anomalies
- rhizomelic chondrodysplasia punctata
- richieri-costa
- roberts-sc phocomelia
- rubinstein-taybi
- ruvalcaba
- salinas
- saul
- say
- seckel
- seckel like- premature senility
- seckel-like- ataxia-endocrinopathy
- seckel-like- majoor-krakauer
- seckel-like- osteodysplastic
- seckel-like- osteodysplastic types i & iii
- short stature-skin pigment anomalies
- smith-fineman-myers
- smith-lemli-opitz
- sparse hair-seizures
- stimmler
- sutherland
- tapetoretinal degeneration
- theile
- toluene
- toriello
- trichothiodystrophy-icthyosis
- trigonocephaly-hypospadias
- trigonocephaly-short stature-developmental delay
- trimethadione
- urbach
- velo-cardio-facial
- ventricular extrasystole-hyperpigmentation
- vitamin a
- vohwinkel
- weaver williams
- wiedemann: fibrolipomatoid hamartoma
- wiedemann: retardation-unusual facies
- wiedemann: thumb anomaly-short stature
- wiedemann: unusual facies-anal atresia
- winter
- wrinkly skin
- xeroderma pigmentosum
- x-linked-unusual facies-callosal agenesis
- yunis-varon
- zerres
- zollino
references
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lehman cd, nyberg da, winter tc, kapur rp, resta rb, luthy da trisomy 13 syndrome: prenatal us findings in review of 33 cases radiology 194: 217-222
persutte wh, kurczynski tw, chaudhuri k, lenke rr, woldenberg l, brinker ra prenatal diagnosis of autosomal dominant microcephaly and postnatal evaluation with magnetic resonance imaging prenat diagn 10: 631-42
goldstein i, reece ea, pilu g, oíconnor tz, lockwood cj, hobbins jc sonographic assessment of the fetal frontal lobe: a potential tool for prenatal diagnosis of microcephaly am j obstet gynecol 158: 1057-1062
chervenak fa, rosenberg j, brightman rc, chitkara u, jeanty p a prospective study of the accuracy of ultrasound in predicting fetal microcephaly obstet gynecol 69: 908-910
siebert jr, warkany j, lemire rj atelencephalic microcephaly in a 21-week human fetus teratology 34: 9-19
chervenak fa, jeanty p, cantraine f, chitkara u, venus i, berkowitz rl, hobbins jc the diagnosis of fetal microcephaly am j obstet gynecol 149: 512-517
kurtz ab, wapner rj, rubin cs, cole-beuglet, ross rd, goldberg bb ultrasound criteria for in utero diagnosis of microcephaly j clin ultrasound 8: 11-16
rees ae, bates a, clarke h cerebellar hypoplasia in the second trimester associated with microcephaly at birth ultra in obstet & gynec 5: 206-208