Journal of Perinatology (2012) 32, 476–478
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IMAGING CASE REPORT
Thanatophoric dysplasia, type I
TE Herman and MJ Siegel
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO, USA
Journal of Perinatology (2012) 32, 476–478; doi:10.1038/jp.2011.108
Case presentation
A 20-year-old woman (gravid 4, para 2-0-1) in the 18th week of
pregnancy attended a baby shower where there was a sonographic
baby picture boutique. The images seen at that sonogram
suggested that the female fetus had short-limb dwarfism. The
mother was referred to the obstetrical sonography group for further
evaluation. Sonography performed at approximately 23 weeks
gestation again demonstrated marked short-limb dwarfism, and it
was believed that this was a lethal chondrodysplasia. However, the
mother wanted to confirm this diagnosis before delivery. Therefore,
a low-dose computed tomography (CT) scan of the fetus and
maternal pelvis was performed on a Siemens Somatom Definition
AS (Munich, Germany) at settings of 100 kV and 36 mA
(Figures 1–3), at 26 weeks gestation. Subsequently, at 28 weeks
with the pregnancy complicated by progressive polyhydramnios, the
mother developed premature labor. Labor was allowed to progress
and a stillborn infant was delivered. Post delivery skeletal survey
(Figure 4) was obtained.
condition, uniformly lethal in the perinatal period. TD is the most
common of the platyspondylic lethal skeletal dysplasias (PLSDs). It
is divided into type 1 with a normal skull confirmation, as in this
case, and type 2 with a clover-leaf skull (kleeblatschadel).5 Both
TD1 and TD2 are due to mutations in the fibroblast growth factor
receptor 3 gene (FGFR3). There is a single known mutation
accounting for cases of TD2 and approximately 12 missense
mutations accounting for cases of TD1.6 There are two additional
types of PLSD, the Sandiego type and the Torrance–Luton type.
The Sandiego PLSD is a slightly milder disease than TD but is
associated with mutations in the FGFR3 gene. Torrance–Luton is
a milder disease, sometimes associated with long-term survival,
and due to a mutation in the type II collage gene (COL2A1).7,8
The characteristic radiographic findings of all forms of PLSD
are marked platyspondyly. In TD, the vertebral bodies and posterior
elements in the lumbar region, viewed on frontal radiographs,
have a ‘n’ or inverted ‘u’ appearance. Characteristically the
midportion of the vertebral body may be slightly flatter than the
anterior and posterior portions, unlike Sandiego and Torrance–
Luton type, which are more wafer-like throughout and do not have
an inverted ‘u’ appearance usually. The skull is essentially normal
Denouement and discussion
The use of low-dose CT scan to confirm the diagnosis of lethal
chondrodysplasia has been recently described.1 This procedure
allows better definition of the skeleton than both sonography and
maternal pelvic magnetic resonance imaging. The American
College of Radiology’s reference dose for radiation is CT dose index
volume (CTDIvol). In our very obese patient, the CTDIvol was
13.9 mGy. The CT dose index volume is roughly equal to the fetal
dose in this patient.2,3 The American College of Radiology’s CT
accreditation reference CTDIvol in abdominal CT is 25 mGy, which
corresponds to an embryo dose of B35 mGy in a 70-kg patient.
Thus, our fetal dose was within acceptable limits. This value is
below the reported dose threshold for the induction of
teratogenesis.4
The fetal CT and the post natal images both demonstrate
thanatophoric dysplasia (TD), type 1, an autosomal dominant
Correspondence: Dr TE Herman, Mallinckrodt Institute of Radiology, Washington University
School of Medicine, 510 South Kings highway Boulevard, St Louis, MO 63110, USA.
E-mail: [email protected]
Received 5 July 2011; accepted 15 July 2011
Figure 1 Transaxial computed tomography (CT) image of the maternal pelvis
acquired with low-dose acquisition. The fetal skeletal within the pelvis of the obese
patient is not well seen.
Thanatophoric dysplasia
TE Herman and MJ Siegel
477
Figure 2 Sagittal 3-D fetal reconstruction from the axial views. Straight white
arrows indicate the markedly flattened or platyspondylic lumbar vertebral bodies.
Open arrows points to the curved, shortened femoral bilaterally. 3-D
reconstructions allow better definition of the skeleton than axial images.
Figure 3 Coronal reconstructed fetal skeleton. The relatively normal skull
configuration is seen without a clover-leaf shape. Short limbs (open arrows), short
thin ribs and thin clavicles (straight arrows) are seen.
in appearance in TD1, except for frontal bossing, but has a cloverleaf configuration in TD2. In both types, there is usually mid- and
upper-face hypoplasia. In TD, the clavicles and ribs are thin, and
the scapula slightly hypoplastic. The sacrosciatic notches are
narrowed, and the acetabular roofs are flat. Secondary ossification
centers may develop in the ischia and ilia in both TD and Sandiego
type PLSD.6 Markedly shortened limbs are present, which in TD1
have a characteristic bowed appearance resembling a telephone
receiver, with a medial metaphyseal spur.5 In TD2 and Sandiego
and Torrance–Luton PLSD the femurs are straighter. The fibula in
TD is usually markedly shorter than the tibia. The findings in this
patient were characteristic of TD1, with a grossly normal wellossified skull, with mid-face hypoplasia and frontal bossing,
marked platyspondyly with lumbar inverted ‘u’ pattern, deformity
of the femurs with a telephone receiver configuration and
markedly shortened fibulae (Figures 3 and 4).
Journal of Perinatology
Thanatophoric dysplasia
TE Herman and MJ Siegel
478
from respiratory insufficiency. Rare long-term survivors, even to
adulthood, have been described, especially among patients with
Torrance–Luton-type PLSD.7
Conflict of interest
The authors declare no conflict of interest.
References
Figure 4 (a) Frontal and (b) Lateral post mortem radiographs of the
stillborn infant. The frontal radiograph demonstrates the lumbar inverted ‘u’
appearance of the vertebral body and posterior elements. The lateral radiograph
demonstrates the marked platyspondyly slightly more significant in the mid
portion of the vertebral body (straight arrows). Curved arrow on the lateral
radiograph demonstrates the frontal bossing, accentuated by mid-face hypoplasia.
Polyhydramnios usually develops in the second and third
trimesters. Death usually occurs within hours or days after delivery
Journal of Perinatology
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