Mediastinal and pulmonary masses in children

Differential diagnosis by mediastinal compartments

The spectrum of possible mediastinal pathologies in children directly depends on the specific compartment where the mass is located.

Anterior mediastinum Malignant neoplasms are frequently detected here, primarily lymphoma and leukemia (manifesting as thymic infiltration). Other potential causes include:

• Normal thymus, thymoma, or thymic cyst.
• Lymphadenopathy.
• Teratoma.
• Morgagni hernia.
• Vascular malformations (hemangiomas, lymphangiomas).

Middle mediastinum Pathologies in this compartment are typically congenital in nature. Due to their anatomical proximity to the airways and esophagus, such masses frequently cause compression of these structures. The main variants include:

• Congenital bronchopulmonary foregut malformations (bronchogenic cysts, esophageal duplication).
• Vascular rings.
• Hiatal hernia.
• Lymphadenopathy.

Posterior mediastinum The absolute majority of masses here are neurogenic tumors. Spinal abscesses (staphylococcal or tuberculous), spinal tumors (Ewing sarcoma, PNET), vertebral hematomas, neurenteric cysts, and Bochdalek hernia may also localize in the posterior mediastinum.

Neurogenic tumors of the posterior mediastinum

Neurogenic tumors include neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. The first two occur predominantly in children during the first decade of life, whereas the more benign ganglioneuroma is characteristic of older patients.

Features of thoracic neuroblastoma:

• Accounts for approximately 15% of all neuroblastomas and is characterized by a less malignant course compared to the abdominal form.
• The tumor frequently calcifies (up to 40% of cases on CT) and may extend extradurally into the spinal canal.
• In cases of intraspinal extension, about 50% of children are clinically asymptomatic at the time of diagnosis.
• Radiographs may reveal erosion of the posterior ribs and widening of the intercostal spaces.

MRI rather than CT is preferred for optimal assessment of spinal canal involvement and extradural invasion.

Lung and chest wall tumors

Primary malignant lung tumors in children are extremely rare (0.05 per 100,000). Metastases from extrathoracic primary sites (osteosarcoma, Wilms tumor) are found much more frequently in the pulmonary parenchyma. When performing CT to search for metastases, it is important to scan the child in the prone or lateral position: this allows the lungs to expand and helps differentiate true nodules from gravitational atelectasis in the posterior-basal regions.

Primary lung tumors:

1. Pleuropulmonary blastoma: affects children under 5 years of age. It can be solid, cystic, or mixed. Large tumors may occupy an entire hemithorax, shifting the mediastinum. On imaging, it is difficult to differentiate from congenital pulmonary airway malformation.
2. Bronchogenic carcinoma: occurs in adolescents, behaves extremely aggressively, and often metastasizes before a diagnosis is established.
3. Bronchial adenomas: half of these are carcinoids. Unlike in adults, carcinoid in children rarely causes Cushing syndrome, presenting instead with hemoptysis, wheezing, or atelectasis.

Chest wall tumors: Encountered more frequently than primary lung tumors. These include Ewing sarcoma, PNET, and rhabdomyosarcoma (the most common soft tissue sarcoma). On CT, they appear as heterogeneous solid masses, frequently causing destruction of adjacent ribs. Ultrasound is the imaging modality of choice for initial differentiation between the tumor and a massive pleural effusion.

Diagnostic imaging in cystic fibrosis and immunodeficiencies

Chest radiography is the baseline monitoring modality in cystic fibrosis. Pathological changes evolve with age:

• Infants: lung hyperinflation and areas of atelectasis (small airway disease).
• Older children: bronchial wall thickening and the development of cystic bronchiectasis. The appearance of "mucus plugs" (rounded or tubular dense opacities along the bronchi) is characteristic. Infectious exacerbations present as patchy peribronchial consolidations rather than classic lobar pneumonia.

Children with primary or acquired immunodeficiency (including HIV infection) have an increased susceptibility to severe respiratory infections (Pneumocystis jiroveci, cytomegalovirus, Aspergillus). Since conventional radiography has low sensitivity in early-stage pneumonia, immediate CT is indicated upon any acute clinical deterioration.

Class and exam questions

What else to study on this topic

• Neuroblastoma staging features and the role of PET/CT
• Differential diagnosis of pleuropulmonary blastoma and congenital malformations
• Chest wall rhabdomyosarcoma: imaging protocols
• Opportunistic pneumonias in HIV: characteristic CT patterns
• Bhalla score for assessing cystic fibrosis severity on CT

Other Topics in "Pediatric Diagnostic Radiology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.