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Three‐dimensional computed tomography of fetal spondylothoracic dysostosis at 23 weeks' gestation

Spondylothoracic dysostosis (STD) is an extremely rare, life-threatening skeletal dysplasia characterized radiologically by abnormal segmentation of all vertebral segments, shortening of the spine, and rib fusions bilaterally resulting in a ‘fan-like’ appearance of the rib cage. Clinically, it is characterized by a short and rigid neck, short thorax, and a restricted thoracic cavity with severe thoracic insufficiency. Scoliosis is infrequent but hernias and urinary tract abnormalities occur with regularity. The prognosis for children born with STD is poor. Prenatal diagnosis by twodimensional (2-D) and three-dimensional (3-D) ultrasound of the fetus is possible,but a narrow shortened thorax is nonspecific and the condition varies phenotypically. Thus, occasionally, more information than can be collected by ultrasound alone may be necessary to establish a prenatal image-dependent diagnosis. Three-dimensional computed tomography (CT) reconstruction has been used for diagnosing fetal skeletal dysplasias, but to our knowledge, no living second-trimester fetus has been diagnosed with STD using 3-D CT technology. We present a case of STD in a low-risk patient suspected at 23weeks gestation through 2-D ultrasound findings and confirmed by spiral CT with 3-D reconstruction. Early diagnosis allowed an orderly multidisplinary approach to counseling and preparation for birth. A 21-year-old Puerto Rican gravida 1 of a nonconsanguineous union presented at 23weeks for an abnormally small fetal thorax on ultrasound. The patient and her partner lacked any family history of skeletal dysplasia. Abdominal CT was performed with a 256 slice scanner (SOMATOM Definition Flash, Siemens, Germany) with standard parameters: 120 kV, 134mAs, collimation 128mm 0.6mm. A 3-D image of the fetal skeleton was rendered using a surface shading display method. The CT images provided further detail on the fetal anomalies including thoracic and lumbosacral hemivertebrae, hypoplastic cervical vertebral bodies, fusion of mid-thoracic vertebral bodies with symmetrical bilateral posterior costal fusion (Figure 1). Additionally, the medial portion of the ribs clustered at the thoracic spine was notably fanning outward laterally with straight ribs (crab-like) (Figure 1). The findings were consistent with STD. The patient was offered all methods of management including pregnancy termination and invasive diagnostic testing but declined and elected to continue the pregnancy despite a poor prognosis. Multispecialty consultations were obtained in preparation for birth. The patient had developed severe polyhydramnios and, at 38weeks, underwent cesarean section obtaining a 3556-gram female infant with Apgar scores of 5 and 8 at 1 and 5min. The infant was intubated at birth and was described as having macrocephly, short extremities, short neck, small chest, and short umbilical cord. The postnatal radiographic findings showed segmentation and formation defects throughout the spine along with the posterior costal fusion and fanning of the ribs (Figure 2). The clinical and radiological findings were consistent with STD. Molecular genetic testing for mesoderm posterior 2 gene (MESP2), the only gene known to be associated with STD, was ordered but not performed secondary to lab error. Molecular genetic testing for the most common gene loci affected in spondylocostal dysostisis (SCD) type Jarcho–Levin, DLL3, was negative. On discharge from the hospital, the mother was given an order for the MESP2 testing to be performed as an outpatient, but the test was never obtained. After an extended Neonatal Intensive Care Unit stay, the infant has survived to greater than 1 year of life requiring 24-h nursing care on positive pressure ventilation via tracheostomy and with a gastronomy tube for nourishment.