Pleuropulmonary blastoma (PPB) is the most common primary malignant lung tumor of childhood and a rare mesenchymal neoplasm. It typically occurs in children under 5 years. Three types exist: Type I (entirely cystic, <2 years, best prognosis), Type II (cystic + solid, 2-5 years), Type III (entirely solid, >3 years, worst prognosis). PPB has strong association with DICER1 germline mutation — DICER1 syndrome is a familial cancer predisposition syndrome also associated with thyroid carcinoma, ovarian Sertoli-Leydig tumor, cystic nephroma, and other tumors. Type I PPB can be confused with congenital pulmonary airway malformation (CPAM/CCAM) — this distinction is critically important because CPAM is benign while PPB is malignant. On CT, it appears as a cystic (Type I), mixed cystic-solid (Type II), or entirely solid (Type III) lung mass. Treatment is surgical resection + chemotherapy.
Age Range
0-8
Peak Age
3
Gender
Equal
Prevalence
PPB is a malignant tumor originating from primitive mesenchymal cells. The DICER1 gene (14q32) encodes the Dicer enzyme, an endoribonuclease playing a critical role in micro-RNA (miRNA) processing. The Dicer enzyme converts pre-miRNA to mature miRNA — mature miRNAs regulate gene expression at the post-transcriptional level. With DICER1 mutation, miRNA processing is disrupted → gene expression becomes dysregulated → uncontrolled cell proliferation and differentiation defects occur. The three types of PPB reflect disease progression: Type I (cystic) is early stage with a thin layer of primitive mesenchymal cells within cystic structures — hence confusion with CPAM. In Type II, solid component develops — primitive mesenchymal cells proliferate forming solid nodules between cystic structures. In Type III, the tumor becomes entirely solid — aggressive proliferation replaces cystic components. Imaging features reflect this progression. The distinction of PPB's cystic appearance from CPAM is difficult as both appear as multiloculated cystic lesions in the lung. However, in PPB cyst walls may be thicker, solid or mural nodules should raise concern for PPB, and DICER1 mutation family history is a critical clue.
Development of solid component (mural nodule or inter-cystic solid tissue) in a cystic lung lesion previously diagnosed or followed as CPAM strongly suggests malignant transformation to PPB. This change reflects Type I → Type II progression. Increased cyst wall thickness, new solid nodules, or mass size increase on follow-up CT are warning signs. This follow-up is especially critical in families carrying DICER1 mutation.
Type I PPB appears on CT as a multiloculated cystic lung lesion — may be indistinguishable from CPAM (Type 1 or 4). Cysts may be of air or fluid density. Cyst walls may be thin but in PPB, wall thickness is variable and sometimes irregular. Solid component is generally not seen but thin mural nodules are alarming for PPB. The lesion is generally unilateral and confined to one lobe. Pleural effusion is rare in Type I.
Report Sentence
A multiloculated cystic lesion is seen in the left/right lung on CT; thin-section evaluation for CPAM/PPB distinction and DICER1 mutation screening is recommended.
Type II PPB appears on CT as a mass containing both cystic and solid components. Solid components show heterogeneous enhancement. Cystic components may be of air or fluid density. Solid nodules are seen on cyst walls (mural nodules) or between cysts. Mass size is generally larger than Type I. Pleural effusion may accompany. Lymphadenopathy and distant metastasis (brain, bone) should be sought.
Report Sentence
A mass containing both cystic and solid components is seen in the left/right lung on CT; findings are consistent with Type II PPB; brain MRI and bone scintigraphy for staging is recommended.
Type III PPB appears on CT as a large, entirely solid, heterogeneously enhancing lung mass. The mass is generally large (>5-10 cm) and may occupy the entire hemithorax. Necrotic areas appear hypodense. Pleural effusion is common. Mediastinal shift (to contralateral side) is seen. Chest wall invasion and pleural spread may be present. Distant metastasis (brain, bone, liver) should be sought.
Report Sentence
A large, heterogeneously enhancing solid mass occupying the left/right hemithorax is seen on CT with mediastinal shift and pleural effusion; findings are consistent with Type III PPB.
On MRI T2-weighted images, PPB shows different appearances according to type. Type I: T2 hyperintense multiloculated cystic lesion (CPAM-like). Type II: cystic components T2 hyperintense, solid components intermediate signal. Type III: heterogeneous signal — necrotic areas T2 hyperintense, solid tumor intermediate. MRI better evaluates chest wall invasion, diaphragm invasion, and spinal canal extension than CT. Diffusion restriction is seen in solid components on DWI.
Report Sentence
A mass with heterogeneous signal on T2-weighted MRI is seen in the lung with cystic and solid components together; consistent with PPB.
On chest radiograph, PPB shows different appearances according to type. Type I: appears as air-containing cystic lesion (lucent area) — may be indistinguishable from CPAM. Type III: appears as large opaque hemithorax mass — mediastinal shift, pleural effusion, and compression of contralateral lung. Chest radiograph is used for screening but diagnosis is made with CT.
Report Sentence
A large opaque mass is seen in the left/right hemithorax on chest radiograph with mediastinal displacement to the opposite side; CT for further evaluation is recommended.
Criteria
Entirely cystic, <2 years, thin layer of primitive mesenchymal cells within thin cyst walls
Distinct Features
May be confused with CPAM, best prognosis (85-90% survival), surgical resection curative, chemotherapy debated
Criteria
Cystic and solid components together, 2-5 years, aggressive mesenchymal proliferation in solid components
Distinct Features
Intermediate prognosis (60-70% survival), surgery + chemotherapy needed, metastasis risk increases
Criteria
Entirely solid, >3 years, dense primitive mesenchymal proliferation, often rhabdomyoblastic differentiation
Distinct Features
Worst prognosis (40-50% survival), large mass, frequent metastasis (brain, bone), aggressive chemotherapy + surgery needed
Distinguishing Feature
CPAM (CCAM) is benign congenital malformation; PPB is malignant; CPAM has thin regular cyst walls, PPB variable; solid component not expected in CPAM; DICER1 mutation is specific to PPB; growth or solid component development on follow-up suggests PPB
Distinguishing Feature
Childhood lung metastases (Wilms, osteosarcoma) typically appear as multiple bilateral nodules; PPB is generally solitary; primary tumor history is distinguishing
Distinguishing Feature
Mediastinal teratoma contains fat, calcification, and solid component; fat and calcification not expected in PPB; teratoma is generally in anterior mediastinum; PPB is in pulmonary parenchyma
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
3-monthPPB treatment is surgical resection + chemotherapy. In Type I, complete surgical resection (lobectomy) is generally sufficient with excellent prognosis (85-90% survival). In Type II and III, neoadjuvant or adjuvant chemotherapy (IVADo: ifosfamide, vincristine, actinomycin D, doxorubicin) is administered. Follow-up with thorax CT at 3-month intervals is recommended — for local recurrence and metastasis. When DICER1 mutation is detected, genetic counseling is mandatory and family members must be screened. In DICER1 syndrome carriers, thyroid US (annual), ovarian US (annual), and lung CT screening at specified intervals is recommended.
PPB treatment is surgical resection + chemotherapy. Type I (cystic) has the best prognosis (90% survival), Type III (solid) has the worst prognosis (45% survival). DICER1 genetic testing should be performed in all cases and family members. In follow-up of cystic lung lesions, progressive growth or development of solid component should raise concern for PPB.