Pleuropulmonary blastoma

Pleuropulmonary blastomas (PPB) are a rare, variably aggressive, childhood primary intrathoracic malignancy. In up to 25% of cases, the mass can be extrapulmonary with attachment to the parietal pleura. 

Epidemiology

PPB is encountered in childhood, mostly in the first years of life (90% in those between 0-2 years old). 

Associations

PPBs are associated with type 4 CPAM.  

PPB is associated with PPB family tumour and dysplasia syndrome in 33% of cases. Many of these patients have a mutation of the DICER-1 gene. In 10% of cases, patient with PPB may also present with multilocular cystic nephroma, and, very rarely, Wilms tumour ^7-9.

Pathology

PPB comprises both mesenchymal and epithelial components resembling fetal lung. Bilateral occurrence is very rare.

Classification

This classification is a continuum from the less malignant to the most malignant lesion:

• cystic: type I (prenatal and 10 months old), 14%
• mixed: type II (mean age 34 months), 48%
• solid: type III (mean age 44 months), 38%

Type 1 PPBs are impossible to differentiate from types 1 and 4 CPAM. Thus, it must be included in the differential diagnosis, particularly if the patient is known for another type of blastoma, as 25% of PPB appear in families with history of blastomas.

PPBs are usually right-sided, pleurally-based, without chest wall invasion and without calcifications. It can sometimes present with pneumothorax. Types II and III PPBs are associated with CNS and bone metastases.

Radiographic features

Often late presentation at radiographic diagnosis. Unilateral lung whiteout on plain film with mediastinal shift to opposite side. Usually there are no adjacent rib erosions or calcifications.

Ultrasound

A poor imaging modality for this diagnosis. Non-specific and may show a large region of consolidation without sonographic air bronchograms ³.

CT

Usually seen as a large mass in the thorax with mixed solid-cystic heterogeneous low attenuation, pleural effusion (not dominant abnomality), contralateral mediastinal shift, and lack of chest wall invasion ^3,4.

Treatment and prognosis

Type I tumours have a good prognosis. Complete surgical resection is often the treatment of choice, as it is with CPAM. Tumours larger than 5 cm just like type 1 and 2 PPB carry a worse prognosis ²_.

Differential diagnosis

General imaging differential considerations include:

• intrathoracic soft tissue sarcoma
• PNET of thorax
• large bronchogenic cyst/lung cyst (for type I)
• FLIT (fetal(fetal lung interstitial tumour)¹⁰
• types 1 and 4 CPAMs: for type 1 PPB

See also

• sarcomatoid carcinoma of the lungs