Antenatal sonographic diagnosis of thanatophoric dysplasia: a report of three cases and a review of the literature with special emphasis on the differential diagnosis

Anatomical Considerations of Embryology and Development of the Musculoskeletal System: Basic Notions for Musculoskeletal Radiologists

The musculoskeletal (MSK) system begins to form in the third week of intrauterine development. Multiple genes are involved in the complex different processes to form the skeleton, muscles and joints. The embryonic period, from the third to the eighth week of development, is critical for normal development and therefore the time when most structural defects are induced. Many of these defects have a genetic origin, but environmental factors may also play a very important role. This review summarizes the embryology of the different components of the MSK system and their configuration as an organ-system, analyzes the clinical implications resulting from failures in the process of organogenesis, and describes the first approach to diagnosis of skeletal abnormalities using prenatal ultrasound.

Prenatal Diagnosis of Skeletal Dysplasia and Review of the Literature

Introduction

Obstetric ultrasonography is routinely used to screen for fetal anomalies. Thanatophoric dysplasia (TD) is one of the common though rare lethal skeletal dysplasia, detected during routine ultrasound scan. TD is caused by a mutation in FGFR3 gene. Characteristic features include shortening of limbs, macrocephaly and platyspondyly. In our local setting, it is common to miss the diagnosis in the early scans due to lack of expertise of the sonographers. To the best of our knowledge, this is the first publication from Ghana. Case Presentation. We present the case of a 33-year-old woman who was referred to the facility on account of ultrasound scan report suggestive of thanatophoric dysplasia type 1 at 34 weeks of a female baby. The diagnosis was not made despite the mother being a regular antenatal attendant, until a fifth scan done at 34 weeks reported features suggestive of thanatophoric dysplasia. The ultrasound scan features included a biparietal diameter of 37weeks, femur length—24weeks, narrowed thoracic cage with hypoplastic lungs and short ribs. The liquor volume was increased with amniotic fluid index (AFI) of 38.4 cm. The femur, tibia, fibula, humerus, ulna, and radius were shortened (micromelia). The diagnosis of thanatophoric dysplasia type 1 was confirmed on autopsy.

Conclusion

This report was aimed to highlight the potential contribution of ultrasound scan in the diagnosis of thanatophoric dysplasia in our setting.

Comparative X-ray morphometry of prenatal osteogenesis imperfecta type 2 and thanatophoric dysplasia: a contribution to prenatal differential diagnosis

OBJECTIVE

The purpose of the paper was to assess the morphometric parameters to improve the specificity of the ultrasound (US) signs for the early differential diagnosis between two lethal dysplasias, as thanatophoric dysplasia (TD) and osteogenesis imperfecta type 2 (OI-2).

METHOD

The diaphyseal length and the bowed shape of long bones associated with vertebral body dimension assessment were investigated in a group of 14 pregnancy terminations carried out in the time period 2007-2013. The definitive diagnosis was established after pregnancy termination by means of skeletal standardized X-rays, histopathology and gene analysis.

RESULTS

TD and OI-2 long bones were significantly shorter than controls. No significant differences were observed between the two dysplasias. The bowing angle was higher in OI-2; a true angulation or eventually axial displacement was present only in the latter. Furthermore, they did not show any evidence of vertebral collapse. The thanatophoric dysplasia presented less bowed long bones, and never true angulation. The spine was steadily characterized by flattened anterior vertebral bodies.

CONCLUSION

Long bone shortening is not a sufficient and accurate sign for early sonographic differential diagnosis between TD and OI-2. Angled diaphysis, axial diaphyseal displacement and a conserved vertebral body height in the prenatal period support the diagnosis of osteogenesis imperfecta type 2, while moderately regular bowed diaphysis associated with platyspondyly that of thanatophoric dysplasia.

Evaluating skeletal dysplasias on prenatal ultrasound: an emphasis on predicting lethality

Lethal skeletal dysplasias can be diagnosed by prenatal ultrasound (US) using several sonographic parameters. Degree of femoral shortening, lung volumes, femur length to abdominal circumference ratio, and chest circumference to abdominal circumference ratio are the most sensitive and specific predictors. Although there are more than 450 different skeletal dysplasias, only a few are lethal in the perinatal period. We review current fetal US literature and present an updated algorithmic approach to first establish lethality and, second, evaluate for hallmark sonographic features to help determine a specific diagnosis.

Temporal lobe dysplasia: a characteristic sonographic finding in thanatophoric dysplasia

OBJECTIVE

To determine the incidence of temporal lobe dysplasia (TLD) detected on prenatal ultrasound in thanatophoric dysplasia (TD) over an 11-year period in a tertiary referral center.

METHODS

An 11-year retrospective review of perinatal autopsies from 2002 to 2013 was performed to identify cases of TD. The ultrasound images and corresponding reports of all TD cases were examined for the presence of TLD. The same set of images subsequently underwent a retrospective review by a perinatal radiologist with knowledge of the features of TLD to determine whether they could be identified.

RESULTS

Thirty-one cases of TD underwent perinatal autopsy, and prenatal ultrasound imaging was available for review in 24 (77%). Mean gestational age at diagnosis of TD was 21.3 (range, 18-36) weeks. TLD was identified and reported in 6/24 (25%) cases; all six cases occurred after 2007. Retrospective interpretation of the ultrasound images identified features of TLD in 10 additional cases. In total, 16/24 (67%) cases displayed sonographic evidence of TLD. Temporal trends showed that TLD features were present in 50% (5/10) of all TD cases between 2002 and 2006 and in 79% (11/14) of those detected between 2007 and 2013.

CONCLUSIONS

At present, the detection rate of TLD by ultrasound is low but may be increased by modified brain images that enhance visualization of the temporal lobes. Prenatal identification of TLD may help in the prenatal diagnosis of TD and thus provide more accurate prenatal counseling and guide molecular investigations to confirm the specific diagnosis of TD.

Thanatophoric dysplasia. Correlation among bone X-ray morphometry, histopathology, and gene analysis

OBJECTIVE

Documentation through X-ray morphometry and histology of the steady phenotype expressed by FGFR3 gene mutation and interpolation of mechanical factors on spine and long bones dysmorphism.

MATERIALS AND METHODS

Long bones and spine of eight thanatophoric dysplasia and three age-matched controls without skeletal dysplasia were studied after pregnancy termination between the 18th and the 22nd week with X-ray morphometry, histology, and molecular analysis. Statistical analysis with comparison between TD cases and controls and intraobserver/interobserver variation were applied to X-ray morphometric data.

RESULTS

Generalized shortening of long bones was observed in TD. A variable distribution of axial deformities was correlated with chondrocyte proliferation inhibition, defective seriate cell columns organization, and final formation of the primary metaphyseal trabeculae. The periosteal longitudinal growth was not equally inhibited, so that decoupling with the cartilage growth pattern produced the typical lateral spurs around the metaphyseal growth plates. In spine, platyspondyly was due to a reduced height of the vertebral body anterior ossification center, while its enlargement in the transversal plane was not restricted. The peculiar radiographic and histopathological features of TD bones support the hypothesis of interpolation of mechanical factors with FGFR3 gene mutations.

CONCLUSIONS

The correlated observations of X-ray morphometry, histopathology, and gene analysis prompted the following diagnostic workup for TD: (1) prenatal sonography suspicion of skeletal dysplasia; (2) post-mortem X-ray morphometry for provisional diagnosis; (3) confirmation by genetic tests (hot-spot exons 7, 10, 15, and 19 analysis with 80-90% sensibility); (4) in negative cases if histopathology confirms TD diagnosis, research of rare mutations through sequential analysis of FGFR3 gene.

Thanatophoric dysplasia in a dichorionic twin confirmed by genetic analysis at the early second trimester: A case report and literature review

Thanatophoric dysplasia (TD) is caused by mutation of the gene that encodes fibroblast growth factor 3 (FGFR3). Owing to the poor prognosis for TD, prenatal diagnosis is critical to optimal perinatal management. We report here a case of TD in twin pregnancy, which was prenatally diagnosed by DNA analysis following amniocentesis at 15 weeks, and was managed by selective fetal termination. Prenatal ultrasonography and molecular analysis to detect TD-specific mutations enable accurate diagnosis of FGFR3-related TD in utero and appropriate obstetrical management at early gestation during twin pregnancy.

Molecular Analysis of a Case of Thanatophoric Dysplasia Reveals Two de novo FGFR3 Missense Mutations located in cis

OBJECTIVES

Thanatophoric dysplasia (TD) is the most common form of lethal skeletal dysplasia. It is primarily an autosomal dominant disorder and is characterised by macrocephaly, a narrow thorax, short ribs, brachydactyly, and hypotonia. In addition to these core phenotypic features, TD type I involves micromelia with bowed femurs, while TD type II is characterised by micromelia with straight femurs and a moderate to severe clover-leaf deformity of the skull. Mutations in the FGFR3 gene are responsible for all cases of TD reported to date. The objective of the study here was to delineate further the mutational spectrum responsible for TD.

METHODS

Conventional polymerase chain reaction (PCR), allele-specific PCR, and sequence analysis were used to identify FGFR3 gene mutations in a fetus with a lethal skeletal dysplasia consistent with TD, which was detected during a routine antenatal ultrasound examination.

RESULTS

In this report we describe the identification of two de novo missense mutations in cis in the FGFR3 gene (p.Asn540Lys and p.Val555Met) in a fetus displaying phenotypic features consistent with TD.

CONCLUSION

This is the second description of a case of TD occurring as a result of double missense FGFR3 gene mutations, suggesting that the spectrum of mutations involved in the pathogenesis of TD may be broader than previously recognised.

Otolaryngologic manifestations of skeletal dysplasias in children

This article reviews some of the otolaryngologic manifestations of skeletal dysplasias. Achondroplasia is discussed most comprehensively. Skeletal dysplasias are bone and cartilage disorders that disrupt the development of the long bones, craniofacial skeleton, and vertebral column, with the most notable characteristic being short stature. Children with skeletal dysplasias have various medical problems. These children often develop head and neck manifestations of their disorders. Hearing loss, middle ear disease, and respiratory difficulties are seen in these children. Otolaryngologists must be knowledgeable about these disorders to diagnose, treat, and appropriately refer children with skeletal dysplasias.

Diagnosis and counseling of thanatophoric dysplasia with four-dimensional ultrasound

Thanatophoric dysplasia is a severe skeletal disorder with estimated frequency of 0.2-0.5 per 10,000 births. Affected infants die shortly after birth. The diagnosis of thanatophoric dysplasia can be made by two-dimensional ultrasound but the perception of these images is very difficult for the patients. The use of four-dimensional real time ultrasound gives the physician the possibility to discuss and counsel the patients with images that are more understandable to the general public.

Rapid detection of common mutations of the FGFR3 gene causing thanatophoric dysplasia type I: two case reports

Thanatophoric dysplasia (TD) is a relatively common lethal skeletal dysplasia. These malformations result from the mutations in fibroblast growth factor receptor 3 (FGFR3) gene, which is located on the short arm of chromosome 4. Accurate diagnosis of fetal TD is important for patient counseling and to plan the management. A definite diagnosis can be established by molecular genetic analysis to find out the abnormal mutations in the FGFR3 gene. We reported on two cases of TD type I found by prenatal ultrasound and confirmed by molecular analysis of FGFR3 gene using high-resolution melting analysis.

Filho RL, Rosa RFM, Maia CR, Graziadio C, Paskulin GA. Diagnóstico pré-natal de displasia tanatofórica: papel do ultrassom fetal

OBJETIVO: Relatar o caso de um paciente com displasia tanatofórica, uma forma autossômica dominante e letal de nanismo, diagnosticado ainda no período pré-natal, e revisar a literatura, discutindo os principais diagnósticos diferenciais e ressaltando a importância do ultrassom fetal na identificação de fetos portadores dessa displasia. DESCRIÇÃO DO CASO: O paciente é o segundo filho de pais jovens sem história familiar de doenças genéticas. O ultrassom fetal realizado com 35 semanas de gestação mostrou polidrâmnio, proeminência frontal e desproporção entre crânio e tronco, com hipoplasia torácica e encurtamento dos ossos longos, compatível com o diagnóstico de displasia tanatofórica. Ao nascimento, a criança era pequena e possuía hipotonia, macrocefalia, fontanelas amplas, hipoplasia de face média, olhos protrusos, hemangioma plano no nariz e pálpebras, nariz em sela, micrognatia, pescoço e tórax curtos e encurtamento importante de braços, antebraços, coxas e pernas. A avaliação radiográfica mostrou crânio com grande diâmetro transverso, tórax com costelas curtas e corpos vertebrais reduzidos, importante encurtamento e deformidade dos ossos longos dos membros superiores e inferiores (os fêmures eram curvos) e hipoplasia da bacia. Esses achados confirmaram o diagnóstico pré-natal de displasia tanatofórica. O paciente evoluiu para o óbito poucos dias após o nascimento devido à insuficiência respiratória. COMENTÁRIOS: A ultrassonografia fetal é um método não invasivo capaz de diagnosticar inúmeras displasias ósseas, incluindo a tanatofórica. A importância do diagnóstico intra-útero reside no fato de que auxilia no diagnóstico diferencial, e permite o aconselhamento genético à família.

Congenital abnormalities of the musculoskeletal system: Perinatal evaluation and long-term outcome

Many musculoskeletal malformations can be detected by prenatal US. Whether isolated or part of a syndrome, these anomalies can have a significant impact on the entire life of the individual. Nonfatal conditions may be subtle and become more recognizable in the second and third trimester. After delivery, radiography helps confirm the diagnosis. US, CT, and MRI all have a role in imaging the primary abnormality, the follow-up effects of treatment, and in monitoring for potential complications that may develop over time. Three-dimensional imaging has an increasing role, in US, CT, and MRI, both in the prenatal and postnatal periods.

Reference values for fetal limb biometry at 10-14 weeks of gestation

OBJECTIVES

To calculate reference ranges for fetal limb measurements obtained by transabdominal ultrasound at 10-14 weeks of gestation.

METHODS

Six hundred and six normal fetuses were examined transabdominally in a cross-sectional study by a single observer. The crown-rump length of the fetuses ranged from 31 to 78 mm. Measurement of the length of the humerus, ulna, femur, tibia and foot was attempted from the longest section of each structure. To assess intraobserver repeatability, three sets of repeated measurements were obtained in 26 fetuses.

RESULTS

An appropriate ultrasound measurement was obtained in a percentage of cases ranging from 93.2% to 97.9%. A significant correlation was found between crown-rump length measurements and humerus length (r = 0.74, P < 0.001), ulna length (r = 0.70, P < 0.001), femur length (r = 0.77, P < 0.001), tibia length (r = 0.69, P < 0.001) and foot length (r = 0.58, P < 0.001). Crown-rump length-specific reference ranges for each measurement were calculated with the method of scaled absolute residuals. The study of intraobserver variability showed coefficients of variation ranging from 7.9 to 10.0% and intraclass correlation coefficients ranging from 0.89 to 0.94.

CONCLUSIONS

Fetal limb size is strongly correlated with crown-rump length. Despite a significant biological variability of the measurements, the availability of reference ranges could be of help in the early diagnosis of fetal skeletal dysplasias.

Prenatal diagnosis and genetic analysis of type I and type II thanatophoric dysplasia

Thanatophoric dysplasia (TD) is one of the most common neonatal lethal skeletal dysplasias. Prenatal sonographic and molecular genetic diagnoses of three cases of TD type I (TD1) and one case of TD type II (TD2) are presented here. Two fetuses of TD1 were characterized by polyhydramnios, macrocephaly, short limbs, a narrow thoracic cage and curved short femora, but without a cloverleaf skull at 27 and 31 weeks' gestation, respectively. The third fetus with TD1 was, however, not associated with macrocephaly, polyhydramnios, chest narrowing and severe femoral bowing on prenatal ultrasound at 18 weeks' gestation. The TD2 fetus was characterized by polyhydramnios, short limbs, a narrow thoracic cage, straight short femora, hydrocephalus and a cloverleaf skull at 24 weeks' gestation. Three-dimensional ultrasound was able to enhance the visualization of thickened, redundant skin folds and craniofacial and limb deformities associated with TD. Molecular analysis of the fibroblast growth factor receptor 3 (FGFR3) gene by restriction enzyme digestion analysis and direct sequencing using cultured amniotic fluid cells or cord blood cells revealed a missense mutation of 742C-->T (Arg248Cys) in all cases with TD1 and a missense mutation of 1948A-->G (Lys650Glu) in the case with TD2. The present report shows that adjunctive applications of molecular genetic analysis of the FGFR3 gene and three-dimensional ultrasound are useful for prenatal diagnosis of TD.

Sonographic and molecular diagnosis of thanatophoric dysplasia type I at 18 weeks of gestation

Thanatophoric dysplasia is the most common type of lethal skeletal dysplasia. It can usually be diagnosed with ultrasound, but differential diagnosis with other osteochondrodysplasias is not always possible. Mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have been demonstrated to cause two distinct subtypes of the disorder. We describe a case of thanatophoric dysplasia type I diagnosed at 18 weeks of gestation by ultrasonography. Genomic DNA obtained by chorionic villus sampling showed a C to G substitution at position 746 in the FGFR3 gene, resulting in a Ser249Cys substitution already known to be associated with type I disease. Implications for perinatal management are discussed.

Prenatal diagnosis of thanatophoric dysplasia by mutational analysis of the fibroblast growth factor receptor 3 gene and a proposed correction of previously published PCR results

Thanatophoric dysplasia (TD) is the most frequent form of neonatal lethal skeletal dysplasia. Recently. mutations in the fibroblast growth factor receptor 3 (FGFR3) gene that cause two subtypes of this disorder, type I (TDI) and type II (TDII), have been identified. This discovery has now made it possible to make a definite diagnosis of TD by molecular methods. To date, prenatal diagnosis of TD has been accomplished by ultrasonography in the second trimester. However, it is not always possible to distinguish TD fetuses it utero from the other osteochondrodysplasias by ultrasonography or radiography. We report on the prenatal diagnosis of a TD fetus, showing severe shortness of limbs and polyhydramnios, by identification of a mutation in the FGFR3 gene. Genomic DNA was isolated from the amniotic fluid and then subjected to PCR amplification. The common TDI mutation, C-->T transition at nucleotide 742 in the FGFR3 gene, was identified using restriction enzyme analysis. This information was critical in obstetric management decisions later in pregnancy. However, although the mutation responsible for TDI was detected previously, we noticed some inconsistencies in the published PCR results and have proposed a correction.