Cloverleaf skull

Cloverleaf skull


A cloverleaf configuration of the skull consists of trilobed protrusion of the skull with broadening of the temporal region and face. The skull protrusion is separated from focal bulges by furrows. Often the sagittal, coronal, and lambdoid sutures show premature synostosis, although other combinations of sutural involvement are possible, including coronal, lambdoid, and metopic closure, or sagittal and squamosal closure. Increased thickening of occipital bone squama prevents lengthening of the skull, producing the typical shape. Occasionally, atypical or unilateral sutural involvement may produce an asymmetric bulging of the calvarium. One individual has been described where cloverleaf skull occurred in the absence of craniosynostosis. In this latter case there was lissencephaly and hypoplasia of several cranial bones, allowing eventration of the brain and surrounding tissues into a trilobed configuration. The eyes usually protrude; occipital encephaloceles can occur, and hydrocephaly is common. 85% of individuals with cloverleaf skull will have other anomalies, and the pattern is often consistent with a syndrome diagnosis or specific genetic mutations. The skull develops from mesenchyme, with the portion surrounding the brain termed the neurocranium. The neurocranium consists of a cartilaginous portion (chondrocranium) and a membranous portion. The chondrocranium is the cartilaginous base of the skull, which develops by fusion of several cartilages. The membranous neurocranium ossifies to form the cranial vault, the bones of which are separated by connective tissue membranes known as sutures. Six fibrous areas, the fontanelles, are also present. The five major sutures are the frontal, or metopic, sagittal, coronal, lambdoid and squamosal. The sutures allow for moulding to occur during the delivery process, and enlargement to accommodate normal brain growth. When the cranial bones fuse prematurely there is decreased growth potential. Bone deposition occurs abnormally, with the majority being directed away from the fused bony plate. In turn, perimeter sutures adjacent to the prematurely fused suture compensate in growth to a greater extent than sutures distant to the fused area. The primary cause of synostosis may be a defect at the cranial base at the site of initial attachment of the dura; other studies suggest a vascular defect causing deficient osteoclasia. A recent morphologic, radiographic and histologic analysis of an 18 week fetus with cloverleaf skull suggests the calvarium may be the primary focus of abnormal events, with the cranial base involved as a secondary event. Cloverleaf skull historically has been classified into three groups: type 1, in which cloverleaf skull coexists with thanatophoric dysplasia; type 2, in which cloverleaf skull is associated with less severe skeletal lesions such as joint ankylosis and subluxation of the radial heads; and type 3, where the skull anomaly is isolated, and the prognosis is much improved.


The cloverleaf deformity of the fetal head is best appreciated in coronal section, occipito-mental view, through the temporal lobes. The trilobed appearance may also be viewed in transverse section. Diagnosis is feasible from 22 weeks gestation. The skull abnormality may be accompanied by hydrocephaly, orbital proptosis, hypertelorism, high forehead, frontal bossing, lowset ears, short limbs, and polyhydramnios. Three-dimensional visualisation of the skull based on volumetric ultrasonographic image data offers the possibility of revealing the structural coherence of the sutures and fontanelles in the fetal skull more clearly. This technique allows imaging of coronal, lambdoidal and squamosal sutures, anterior, posterior, mastoid and sphenoid fontanelles. 3D reconstruction may clarify the true magnitude of the defect and occasionally allow a diagnosis not possible with 2D or non-reconstructed 3D.

Differential Diagnosis

Most encephaloceles are located in the occipital area. An underlying bony defect is the rule, but may be difficult to demonstrate when small. The mass is seen to derive from, and move with, the fetal head. It may be cystic, solid or a combination. Calvarial thinning or partial absence in the presence of cloverleaf skull may render the distinction from encephalocele difficult. Cystic hygroma is a cystic mass resulting from jugular lymphatic obstruction. It is seen as a single or multiloculated fluid-filled cavity, usually in the posterior nuchal region. It lacks a solid component. Internal septation is common.

Sonographic Features

A trilobed appearance of the skull, with bulging over the temporal lobes and the anterior fontanelle

Associated facial features include high and prominent forehead, protuberant and wide spaced eyes, lowset ears, and frontal bossing

Associated skeletal findings include disproportionate short limbs, polydactyly and syndactyly

Hydrocephaly is common

Polyhydramnios may be found

Associated Syndromes

  • Amniotic band
  • Antley-Bixler
  • Apert
  • Campomelic dysplasia
  • Carpenter
  • Chromosomal abnormality
  • Crouzon
  • Pfeiffer
  • Thanatophoric dysplasia


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