A Late Preterm Neonate With a Small Chest

A late preterm neonate with a small chest.The neonate was admitted to the neonatal intensive care unit. At age 5 minutes, he was placed on continuous positive airway pressure with fraction of inspired oxygen of 0.25 and peak end expiratory pressure of 5 cm H2O. A venous blood gas test was normal with a pH of 7.35, partial pressure of carbon dioxide of 39 mm Hg, partial pressure of oxygen of 60 mm Hg, and bicarbonate level of 23.4 mEq/L. A chest radiograph was obtained (Figure 2). He was started on gavage feedings. Detailed anthropometry and body measurements showed that he had a small chest with normal limb length with findings summarized in Table 1. A skeletal survey was obtained (Figures 3A and B) and genetics was consulted.Asphyxiating thoracic dysplasia (dystrophy)Thoracolaryngopelvic dysplasia (Barnes syndrome)Schneckenbecken dysplasiaFibrochondroplasiaJansen metaphyseal dysplasiaThe skeletal survey (Table 2) demonstrates the following findings: elevated clavicles, hypomineralized bones with cupping of the distal ends of the radii, a bell-shaped thorax, a small and narrow pelvis, bowing of the femurs, and thoracic scoliosis. Because of the potential of having a skeletal dysplasia (SD) associated with airway abnormalities, a laryngoscopy is done that shows no evidence of laryngeal stenosis. The infant’s liver function tests, blood urea nitrogen and creatinine levels, ultrasonogram scans of the head and abdomen, and echocardiography were obtained to rule out systemic associations; these were all found to be normal. Serum calcium, phosphorous, and alkaline phosphorus levels were normal. In consultation with radiology and genetics, a clinical diagnosis of thoracopelvic dysostosis was made.A detailed evaluation of the parents was done, which showed a small pelvis in the mother with a normal thorax. The radiograph of the mother’s pelvis (Figure 3C) showed that the transverse diameter of the inlet, the mediolateral diameter of the midplane, and mediolateral diameter of the outlet were less than 1 unit (ie, 10 cm, normal 15 cm), suggestive of a small pelvis and, given the mother’s height of 141 cm, contributing to cephalopelvic disproportion. The skeletal surveys in the father and sibling were normal.Thoracopelvic dysostosis (variant of Barnes Syndrome)The infant’s respiratory distress was thought to be most likely caused by mild surfactant deficiency. He is weaned off respiratory support at age 3 days and then started to feed orally. The genetics team met with the family and explained the need for genetic confirmation; the family deferred genetic testing initially because of financial constraints. He was discharged home at age 16 days (Figure 1B) at 38 weeks 2 days postmenstrual age with a weight of 2180 g exclusively breastfeeding. He has follow-up with his pediatrician and genetics.SD refers to a group of disorders with abnormalities in the structure and growth of bone and cartilage with an overall prevalence of 2.3 to 7.6 per 10 000 births.1 The major contributing factor to mortality in cases of SD is the degree of thoracic underdevelopment and pulmonary hypoplasia. The extensive involvement of the vertebrae and associated rib anomalies result in thoracic case deformity and improper ventilation.Thoracolaryngopelvic dysplasia, also known as Barnes syndrome, is an SD whereby affected infants have a small thorax with short ribs and a small pelvis with laryngeal stenosis.2 Barnes syndrome has an autosomal dominant pattern of inheritance with 9 cases (3 female adults and 6 infants) reported to date globally and an estimated prevalence of less than 1/1 000 000.2The hallmark feature of Barnes syndrome is a small, rigid bell-shaped chest with short ribs and a small pelvis with a normal height and limb length. Among the 3 women reported,3–5 all underwent cesarean section for cephalo-pelvic disproportion, similar to the mother of our patient. However, in contrast to the reported cases, our patient did not have laryngeal stenosis and did not require prolonged ventilation or tracheostomy, suggesting that this infant probably has a variant of Barnes syndrome (ie, thoracopelvic dysostosis without laryngeal stenosis). Among the previously reported 6 infant cases, all required a tracheostomy in early infancy.3–5 In addition, 1 died in the neonatal period and the other in early adolescence after multiple chest expansion surgeries and numerous hospitalizations for recurrent chest infections.3–5 Long-term data of the remaining 4 infants are not available.The patient in this case required noninvasive support for a short period and remained hemodynamically stable. Because this infant did not have major involvement of the chest and pelvis, relative sparing of the long bones, absence of respiratory infections after discharge, and normal growth, this infant is likely to have a variant of Barnes syndrome that is probably associated with a better quality of life and prognosis than patients with the originally described syndrome. This patient still requires genetic testing to confirm the diagnosis and increase our understanding of the molecular basis of the variation in presentation.The other potential diagnoses considered in this case were ruled out clinically and radiographically. Infants with asphyxiating thoracic dysplasia have bowed extremities with a trident pelvis, polydactyly, short limbs, and associated renal and cardiac malformations in addition to short ribs.6 The absence of rhizomelic shortening of long bones, distinct facial features, and splaying of the end of ribs and spurs arising from the iliac bones makes fibrchondroplasia and Schneckenbecken dysplasia less likely.7 Jansen metaphyseal dysplasia is also of low probability because affected patients have predominant involvement of the long bones, which was not evident in this patient.7A variant of thoracolaryngopelvic dysplasia (Barnes syndrome) should be suspected in neonates with a bell-shaped thorax and maternal-infant dyad having small pelvis and no laryngeal stenosis.SDs without pulmonary hypoplasia and other systemic manifestations are less lethal.A detailed clinical examination and skeletal survey of a neonate with an SD as well as their parents can aid in the clinical-radiological diagnosis.American Board of Pediatrics Neonatal-Perinatal Content SpecificationRecognize the diagnostic implications of single vs multiple anomalies.The authors thank Dr Sangeeta Ravat, Dean, Seth GS Medical College and KEM Hospital, Mumbai, India, for granting permission for publication.