Neonatal Para-Cardiac Cystic Lesions: The Differential Diagnosis

congenital and non-congenital conditions. respiratory and atypical to chest CT. CT studies were performed on one of the following scanners: A second-generation dual source CT system (Siemens Somatom Flash, Siemens Erlangen, Germany), with two x-ray tubes and two detectors settled at an angular offset of 95°. A Somaton Sensation 64 (Siemens Medical Solutions, Erlangen, Germany). In both the systems we used a tube current modulation (CARE Dose) with kVp: 70-80 and ref. mAs: 70. Images were reconstructed with a slice thickness of 1 mm. Kernel/Algorithm: B30, B60. With the dual source, Sinogram-Affirmed Iterative Reconstruction (SAFIRE) filter, strength of 1, was employed. None of the children required sedation for CT examinations. We did not inject contrast media because it was considered superfluous. The cases reported for the differential diagnosis studied by CT were performed with the same systems. Cross sectional imaging by MRI was obtained by a 1.5 T MRI scanner (Achieva Intera; Philips Systems, The Netherlands) The single CT Abstract Mediastinal localized air collection in a newborn can be caused by a congenital cystic mass or by pneumomediastinum resulting from pulmonary assisted ventilation for underlying lung disease. Three newborns with respiratory distress and atypical chest X ray signs have been submitted to chest CT.


Case 1
A male was born at 38th week of pregnancy by a regular

Case 2
A female was born at 39 th week of pregnancy by a regular vaginal delivery. Her body weight was 3100 g. Prenatal US was normal. At two days old, she presented clinical signs of respiratory depression who required supplemental oxygen. Chest X-ray showed a wide radiolucent area over the mediastinum (Figure 2). Chest CT was performed the same day. A large multiloculated mass was detected in the anterior mediastinum, with the thymus compressed upwards.
There was evidence of pneumothorax without signs of PIE ( Figure   2). A drainage was positioned and the case was completely resolved.

Case 3
A male born at 30 th week of pregnancy, of 1100-g, developed respiratory distress after delivery and chest X-ray showed the signs of a Respiratory Distress Syndrome (RDS). The baby was intubated. During the second day of life, a typical PIE was detected, on the third day of life a large retro cardiac air collection was identified. The lucency was on the midline ( Figure 3). CT was performed to localize the large air collection that appeared oblong, well circumscribed, and crossing the midline. There was shift of the mediastinal structures anteriorly. The air-filled mass was interpreted either an infra-azygous pneumomediastinum or an air collection in the pulmonary ligament [5]. Over the following week, the extra ventilatory air collections is gradually resorbed: the large midline gas collection became smaller and didn't shift laterally suggesting an infra azygous pneumomediastinum [6]. During the subsequent week, the median gas collection has shrunk but it not shifting sideways ( Figure 3).

Discussion
The reported incidence of pneumomediastinum is 4−25 per 10,000 live births [1]. Spontaneous pneumomediastinum in otherwise healthy newborns is relatively rare (case 1,2). Our patients (cases 1 and 2) had a pneumomediastinum without prior assisted ventilation or eventful labor [1,7]. One possible justification for the extemporaneous occurrence of a pneumomediastinum may be the vigorous inspiration at birth, causing alveolar over inflation and breach. Our cases also showed a tendency to loculate locally even if in case 2 a pneumothorax was concomitant unlike in literature. Quattromani [8] described a fascia around the great vessels and the trachea, which, at the hilus, is endless with the pericardium and with the fascia of the pulmonary vessels. This is the connection of the lungs to the mediastinum. The fascia creates the thymic capsule and interlobular septa of the thymus. Probably the air spreads along the thymic connective septa, forming a multiloculated pseudo-cystic mass. About the case 3, the infraazygous region is a latent space in the retrocardiac mediastinum. However, mediastinal bronchogenic cysts are located near the carina between the trachea and the esophagus and, therefore, obstruction of the main bronchi resulting in respiratory distress is a common complication [13] Lymphatic cystic malformations ( Figure 7) appear as single or multiloculated fluid-filled cavities [14]. They can occur everywhere but are only rarely found within the mediastinum between the anterior chest wall and the right heart. In this location, they can be confused with a pericardial cyst. True thymic cysts (Figure 8) are typically lined by squamous epithelium, they are filled with fluid and not multiloculated [15,16].
Multiloculated cysts are acquired (postinfectious, autoimmune conditions, etc.). Anterior meningocele (Figure 9) is usually located in the right posterior chest and associated with vertebral anomalies. Mediastinal compression is common [12]. CPAM are usually diagnosed prenatally (Figure 10). At birth, there is a variable amount of air/fluid in the lesion [13,1718]. PIE (Figure11) is characterized on CT by broncho-vascular bundles in the center of air-filled cysts [3]. Even the diaphragmatic hernias (Figure12) are diagnosed in uterus.

Conclusion
Neonatal para-cardiac cystic lesions are a diagnostic challenge because to make a differential diagnosis is not always easy, knowledge of prenatal diagnosis is critical as well as the history of birth.