DOI:10.2214/AJR.04.1388
AJR 2005; 185:1342-1346
© American Roentgen Ray Society
MDCT Diagnosis of the Child with Posterior Plagiocephaly
Raymond W. Sze1,
Richard A. Hopper2,
Victor Ghioni1,
Joseph S. Gruss2,
Richard G. Ellenbogen3,
Darcy King4,
Anne V. Hing4 and
Michael L. Cunningham4
1 Department of Radiology, University of Washington, 4800 Sand Point Way NE, PO
Box 5371/CH-69, Seattle, WA 98105-0371.
2 Department of Plastic Surgery, University of Washington, Seattle, WA
98105-0371.
3 Department of Neurosurgery, University of Washington, Seattle, WA
98105-0371.
4 Children's Craniofacial Center, Children's Hospital and Regional Medical
Center, Seattle, WA 98105.
Received September 1, 2004;
accepted after revision November 29, 2004.
Address correspondence to R. W. Sze
(raymond.sze{at}seattlechildrens.org).
Abstract
OBJECTIVE. In this article, we review the normal anatomy and
development of the posterior skull base and describe distinguishing imaging
features of the two most common causes of posterior plagiocephaly: posterior
deformational plagiocephaly and unilateral lambdoid synostosis. We also
describe three unusual cases of posterior plagiocephaly, including asymmetric
premature fusion of the anterior and posterior intraoccipital synchondroses,
with diagnoses enabled by volume-reformatted MDCT.
CONCLUSION. Three-dimensional reformatted MDCT enables accurate
diagnosis of common and rare causes of posterior plagiocephaly in
children.
Introduction
Posterior plagiocephaly, or asymmetric posterior head shape, is a common
presentation in pediatric patients. Distinguishing unilateral lambdoid
synostosis, which requires complex surgery, from posterior deformational
plagiocephaly, which responds well to conservative management, is critical. A
craniofacial specialist can make the diagnosis in most patients by clinical
examination; however, in unusual cases or in patients with a high likelihood
of having unilateral lambdoid synostosis, CT with volume reformation is the
next diagnostic step [1].
Recent advances in imaging resolution using MDCT technology enable detection
of skull base synchondrosis fusions and mendosal suture abnormalities that
also result in or modify posterior plagiocephaly. In this pictorial essay, we
review the normal anatomy and development of the posterior skull base.
Distinguishing features of unilateral lambdoid synostosis versus posterior
deformational plagiocephaly are illustrated followed by visualization of three
unusual abnormalities of the occipital bone sutures and synchondroses that
cause posterior plagiocephaly. Accurate diagnosis and treatment rest on
optimal acquisition and interpretation of axial and volumetric CT data from
the pediatric skull.
Posterior Plagiocephaly Controversies
Although diagnostic considerations in the infant with posterior
plagiocephaly have long centered on posterior deformational plagiocephaly
versus unilateral lambdoid synostosis, the incidence, clinical findings, and
imaging criteria have been extremely controversial until recently
[1,
2]. It is now accepted that
lambdoid synostosis requires true osseous fusion and cannot be functionally
fused. True lambdoid fusion occurs in only 2-3% of patients with posterior
plagiocephaly, not 15-20% as incorrectly stated in previous literature
[1]. The skull morphology of
children with posterior deformational plagiocephaly versus unilateral lambdoid
synostosis imaged with 3D CT is different, not similar
[1]. Imaging signs
misinterpreted as representing unilateral lambdoid synostosis include
perisutural sclerosis, thickening of the adjacent inner table, and an
end-to-end morphology of the suture
[3]. Contributing to the
sixfold increase in craniofacial center referrals for posterior plagiocephaly
was the 1992 American Academy of Pediatrics recommendation that sleeping
infants be placed on their back to reduce the risk of sudden infant death
syndrome [4].
Occipital Bone Anatomy and Development
The occipital bone comprises the Kerckring ossicle and basioccipital,
supraoccipital, interparietal, and paired exoccipital portions (Figs.
1A and
1B). Six sutures or
synchondroses join the occipital bone portions or form margins with the
neighboring petrous and mastoid portions of the temporal bone and sphenoid
body. These include the Kerckring ossicle-supraoccipital synchondrosis,
anterior intraoccipital synchondrosis, posterior intraoccipital synchondrosis,
mendosal sutures, spheno-occipital synchondrosis, petrooccipital
synchondrosis, and occipitomastoid synchondrosis (Figs.
1A and
1B). The mendosal sutures
represent the junctions between membranous and endochondral origins of the
occipital bone (Figs. 1A and
1B). The pattern and timing of
skull base synchondroses fusion were established with CT
[5]. The Kerckring ossicle
fuses with the supraoccipital portion within the first month of life. Both the
anterior intraoccipital synchondrosis and posterior intraoccipital
synchondrosis begin fusing when infants are approximately 1-2 years old. The
posterior intraoccipital synchondrosis fusion proceeds medial to lateral and
is usually complete in children 4-7 years old. The anterior intraoccipital
synchondrosis fusion pattern is more complex but is usually complete in
children 7-10 years old. Both the occipitomastoid and petrooccipital
synchondroses complete fusion by the late teens.
View larger version (129K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1A —Endocranial skull base views show basioccipital (B), paired
exoccipital (E), supraoccipital (S), and interparietal (I) portions of
occipital bone. Surrounding synchondroses include spheno-occipital (small
solid arrows), anterior intraoccipital (large solid arrow),
posterior intraoccipital (solid arrowhead), petrooccipital (open
arrowheads), and occipitomastoid (open arrows). Mendosal sutures
(small solid arrowheads) mark junction between membranous and
endocranial portions of occipital bone. Image shows portions of occipital bone
and surrounding synchondroses in 3-week-old boy. k = Kerckring ossicle.
|
|
View larger version (128K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1B —Endocranial skull base views show basioccipital (B), paired
exoccipital (E), supraoccipital (S), and interparietal (I) portions of
occipital bone. Surrounding synchondroses include spheno-occipital (small
solid arrows), anterior intraoccipital (large solid arrow),
posterior intraoccipital (solid arrowhead), petrooccipital (open
arrowheads), and occipitomastoid (open arrows). Mendosal sutures
(small solid arrowheads) mark junction between membranous and
endocranial portions of occipital bone. Image shows portions of occipital
bone, fusion of mendosal sutures, and narrowing but preserved patency of
multiple skull base synchondroses in 10-month-old girl.
|
|
View larger version (107K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B —10-month-old boy with posterior deformational plagiocephaly.
Vertex view of volume reformation shows parallelogram shape of skull with
parallel relationship between frontal and posterior convexities.
|
|
View larger version (116K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C —10-month-old boy with posterior deformational plagiocephaly.
Endocranial skull base view shows no deviation in anterior skull base axis
line (bisecting cribriform plate) and posterior skull base axis (connecting
basion and opisthion).
|
|
View larger version (68K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D —10-month-old boy with posterior deformational plagiocephaly.
Axial CT scan shows asymmetric flattening of right posterior skull but patency
of bilateral lambdoid sutures. Note that perisutural thickening
(arrowhead) is not sign of suture fusion.
|
|
View larger version (119K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3A —3-month-old boy with left unilateral lambdoid synostosis.
Posterior view of volume reformation shows left lambdoid suture fusion and
ipsilateral skull base tilt. Also note parallelogram shape on this posterior
view due to ipsilateral occipitomastoid bossing and contralateral parietal
bulge.
|
|
View larger version (113K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3B —3-month-old boy with left unilateral lambdoid synostosis.
Vertex view of volume reformation shows characteristic trapezoid shape with
convergence of frontal and posterior convexities toward side of left lambdoid
fusion.
|
|
View larger version (123K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3C —3-month-old boy with left unilateral lambdoid synostosis.
Endocranial skull base view shows significant deviation of intersecting
anterior cranial fossa and posterior cranial fossa axis lines, with posterior
fossa twisted toward side of left lambdoid fusion.
|
|
View larger version (69K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3D —3-month-old boy with left unilateral lambdoid synostosis.
Axial CT scan shows bone fusion of left lambdoid suture. Right lambdoid suture
(arrowhead) is patent. Note that end-to-end morphology of suture is
not sign of suture fusion.
|
|
MDCT Craniofacial Scanning Technique
Our 16-MDCT craniofacial scanning protocol is 0.5-mm collimation, 16 slices
every half second, and 90 or 150 mAs for children below or above 1 year old,
respectively. We include the upper cervical spine through the vertex;
acquisition time is 15-20 sec. This protocol results in 0.5-mm isotropic
voxels subsequently postprocessed on a workstation (Vitrea, Vital Images). In
addition to a standard filming protocol of the skull without and with the
calvarium removed, the workstation enables interactive segmentation and
magnification of the data.
Unilateral Lambdoid Synostosis Versus Posterior Deformational Plagiocephaly
On axial images and volume reformations, detection of an area of osseous
fusion of the lambdoid suture is diagnostic of lambdoid synostosis. A short
segment fusion, however, can be missed on axial views. Importantly,
perisutural ridging and an end-to-end morphology are not signs of suture
fusion (Figs. 2A,
2B,
2C,
2D,
3A,
3B,
3C, and
3D). On volume reformations,
several discriminators become evident
[1]. On the posterior view, the
posterior deformational plagiocephaly skull has a flat skull base and
normal-appearing head shape, and the unilateral lambdoid synostosis skull has
an ipsilateral downward cant of the skull base and a parallelogram head shape
(Figs. 2A,
2B,
2C,
2D,
3A,
3B,
3C, and
3D). On the vertex view, the
posterior deformational plagiocephaly skull has a parallelogram shape, and the
unilateral lambdoid synostosis has a trapezoid shape (Figs.
2A,
2B,
2C,
2D,
3A,
3B,
3C, and
3D). Finally, on the
endocranial skull base view, the posterior deformational plagiocephaly skull
has no significant distortion of the anteroposterior axis of the skull base,
whereas the unilateral lambdoid synostosis skull base shows a distinct
ipsilateral deviation of the posterior fossa (Figs.
2A,
2B,
2C,
2D,
3A,
3B,
3C, and
3D). This is best assessed by
drawing an anterior skull base axis (bisecting the cribriform plate) and a
posterior skull base axis (from the basion to opisthion); the posterior
deformational plagiocephaly skull will have minimal if any deviation of these
intersecting lines (mean ± SD, 2.3° ± 1.3°), whereas the
unilateral lambdoid synostosis skull will show substantial deviation (mean
± SD, 13.7° ± 5.6°)
[6]. A mental trick for
anticipating the skull changes of lambdoid fusion is to think of the abnormal
suture as a "black hole" drawing the surrounding structures toward
it, thus leading to the ipsilateral skull base cant, "twisting" of
the posterior fossa, and trapezoidal distortion of the calvarium.
View larger version (119K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4A —3-month-old boy with right lambdoid fusion modified by
prominent communicating mendosal sutures. Posterior volume reformation shows
fusion of lateral half of right lambdoid suture (open arrow) and
prominent mendosal sutures (solid arrows) meeting in midline, giving
impression of duplicated lambdoid suture. Skull base cant expected from
unilateral lambdoid synostosis has been minimized by patent mendosal
sutures.
|
|
View larger version (128K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4B —3-month-old boy with right lambdoid fusion modified by
prominent communicating mendosal sutures. Right posterior oblique view of
volume reformation shows fusion of lateral right lambdoid and prominent bulge
over right mendosal suture.
|
|
View larger version (121K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4C —3-month-old boy with right lambdoid fusion modified by
prominent communicating mendosal sutures. Endocranial skull base view shows
bulge over patent right mendosal suture and only minimal deviation of
relationship between anterior and posterior skull base axis lines.
|
|
View larger version (119K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5A —6-month-old girl with premature fusion of posterior
intraoccipital synchondrosis. Posterior view of volume reformation shows
prominent left inferior skull base cant not associated with lambdoid suture
fusion.
|
|
View larger version (133K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5B —6-month-old girl with premature fusion of posterior
intraoccipital synchondrosis. Endocranial skull base view shows leftward
deviation of posterior skull base axis lines. Right posterior intraoccipital
synchondrosis is prematurely fused and not visible. Normal, patent left
posterior intraoccipital synchondrosis (arrowhead) is well seen.
|
|
View larger version (68K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5C —6-month-old girl with premature fusion of posterior
intraoccipital synchondrosis. Axial CT image shows how difficult this
diagnosis would be to make without volumetric endocranial skull base views.
Patent left intraoccipital synchondrosis (arrowheads) is seen for
only very short segments because it is in plane with axial slices.
|
|
View larger version (68K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5D —6-month-old girl with premature fusion of posterior
intraoccipital synchondrosis. Axial CT image does show right posterior
intraoccipital synchondrosis is fused; however, this can be determined only by
directed interrogation of its expected course in posterior skull base
(arrowhead).
|
|
View larger version (113K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6B —3-year-old girl with premature fusion of anterior
intraoccipital synchondrosis. Endocranial skull base view shows leftward
deviation of posterior skull base axis lines and subtle fusion of anterior
intraoccipital synchondrosis (arrow).
|
|
View larger version (121K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6C —3-year-old girl with premature fusion of anterior
intraoccipital synchondrosis. Magnified inferior view of occipital bone shows
partial fusion of left anterior intraoccipital synchondrosis (open
arrow) and patent right anterior intraoccipital synchondrosis (solid
arrow).
|
|
View larger version (72K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6D —3-year-old girl with premature fusion of anterior
intraoccipital synchondrosis. Axial CT image confirms premature fusion of most
medial aspect of left anterior intraoccipital synchondrosis with cortical
thickening (open arrow). Normal right anterior intraoccipital
synchondrosis (solid arrow) is widely patent.
|
|
Unusual Causes of Posterior Plagiocephaly
Since the installation of an 16-MDCT scanner at our institution and
modification of our protocols 1 year ago, we have encountered three unusual
cases of posterior plagiocephaly. The first child had partial fusion of the
right lambdoid suture with modification of the characteristic skull and skull
base changes due to unusual prominence and midline continuation of the
mendosal sutures (Figs. 4A,
4B, and
4C). The ipsilateral skull
base cant and posterior fossa distortion were attenuated, and the most
prominent feature of the skull was a marked ipsilateral bulge centered on the
mendosal suture.
We also have encountered two patients each with premature fusion of the
posterior intraoccipital synchondrosis or anterior intraoccipital
synchondrosis. The patients had patent lambdoid sutures, but they had skull
base and calvarial changes typical for unilateral lambdoid synostosis (Figs.
5A,
5B,
5C,
5D,
6A,
6B,
6C, and
6D). The ability to
interrogate the skull base in three dimensions was critical to making the
final diagnosis.
We are not aware of previous descriptions of these abnormalities, and it
seems unlikely they would make their first appearance after we obtained access
to improved imaging technology. We therefore suggest that MDCT and volumetric
postprocessing technology finally have reached a point at which previously
occult causes of posterior plagiocephaly are now detectable, necessitating a
broadening of the differential diagnosis considerations in the infant or child
presenting with abnormal posterior head shape.
References
- Huang MHS, Gruss JS, Clarren SK, et al. The differential diagnosis
of posterior plagiocephaly: true lambdoid synostosis versus positional
molding. Plast Reconstr Surg 1996;98
: 765-774[Medline]
- Fernbach SK. Craniosynostosis 1998: concepts and controversies.
Pediatr Radiol 1998;28
: 722-728[CrossRef][Medline]
- Rollins N, Sklar F. Factitious lambdoid perisutural sclerosis: does
the "sticky suture" exist? Pediatr Radiol1996; 26:356
-358[CrossRef][Medline]
- [No authors listed]. American Academy of Pediatrics AAP Task Force
on Infant Positioning and SIDS: positioning and SIDS.
Pediatrics 1992;89
(1 Pt 1): 1120-1126; Erratum
in Pediatrics 1992; 90(2 Pt 1):264[Abstract/Free Full Text]
- Madeline LA, Elster AD. Suture closure in the human chondrocranium:
CT assessment. Radiology 1995;195
: 747-756[Abstract/Free Full Text]
- Lo L, Marsh JL, Pilgram TK, et al. Plagiocephaly: differential
diagnosis based on endocranial morphology. Plast Reconstr
Surg 1996; 97:282
-291[Medline]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Abstract
Introduction
