In patients with nephrotic syndrome, there would be transudative pleural effusion secondary to raised hydrostatic pressure or reduced capillary oncotic pressure.

Unilateral hemithorax opacification has few differential diagnosis in pediatrics age group:

1. Pulmonary agenesis/hypoplasia: Ipsilateral mediastinal shift with contralateral hyperinflation. Usually neonatal presentation.

2. Congenital diaphragmatic hernia: Few cystic lucencies can be identified in the affected side. The diaphragm would not be sharply defined. Usually neonatal presentation.

3. Foreign body aspiration: If the affected lung is collapsed, it would appear opaque with ipsilateral mediastinal pull seen. Please note that clinical history is very important.

4. Large volume pleural effusion: Positive meniscus sign sometimes. There would be mediastinal shift towards contralateral side. However there can be ipsilateral mediastinal shift, if there is significant collapse. 

6. Malignant lesions: examples are malignant germ cell tumors, Askins tumor, pleuropulmonary blastoma etc.

7. Childhood pneumonectomy: The affected side would show mediastinal shift(due to volume loss),
 post surgical changes in the ribs and surgical clips.