Introduction

Primary pulmonary neoplasms are uncommon in children. One such tumor, pleuropulmonary blastoma (PPB), is very rare, highly aggressive and malignant, and originates from either the lungs or pleura. It contains both mesenchymal and benign epithelial elements that resemble fetal lung, and occurs mainly in children aged less than five years. (₁)

Report of the case

A 16-month-old male baby was referred to our department for evaluation of encysted pleural effusion on a chest radiogram. The baby presented with a picture of pneumonia with pleural effusion. He received medical treatment for 2 weeks with clinical improvement but the abnormal chest x-ray showed no change. A thoracentesis was performed and removed about 150 ml of serous fluid which was culture negative. CT scan showed a large cystic mass occupying most of the right side of the chest (Figure 1).

Figure 1

Figure 1: CT scan chest mediastinal window showing a large tumor mass occupying most of the right side of the chest; the mass is mainly cystic with some solid areas.

We undertook a right thoracotomy and found a large cystic mass measuring about 20x12x5 cm arising from the right lower lobe and invading the chest wall (Figure 2).

Figure 2

Figure 2: Photography of the tumor as seen through right posterolateral thoracostomy.

There was no hilar or mediastinal lymph nodes; freeing the mass from the chest wall by extra pleural dissection was successful and right lower lobectomy was completed. The resected tumor was cystic with associated solid parts of fleshy, gray white masses. Histologically the solid portion consisted of nests of primitive round to oval blastomatous cells separated by delicate fibrous tissue septa with areas of rhabdomyosarcomatous differentiation and gliomatous neural element with neurofibrillary background; foci of dystrophic calcification and cystic changes were seen and the resection margins were free. These findings correspond to a type II PPB. Postoperative course was uneventful. The baby is doing well 4 months after surgery and he now is under chemotherapy.

Discussion

Pleuropulmonary blastoma is an aggressive tumor accounting for less than 1% of all primary malignant lung tumors in the paediatric population (₂). Manivel and associates coined the term PPB to describe a specific subtype of pulmonary blastoma on the basis of its exclusive clinical presentation in childhood and its pathologic features of variable anatomic location, primitive embryonic-like blastema and stroma, absence of a carcinomatous component, and potential for sarcomatous differentiation (₃) .

Denher and associates classified PPB into three groups: type 1 with purely cystic tumors, type 3 with predominantly solid tumors, and type 2 as an intermediate type (₄). A progression from type I to type III over time may occur (₅). The histologic appearance is variable - the tumor is characterised by primitive blastema and a malignant mesenchymal stroma often showing multidirectional differentiation as rhabdomyosarcomatous (as in our case), chondrosarcomatous or liposarcomatous. The cystic component is lined by benign metaplastic epithelium (₆). Vargas et al. demonstrated with cytogenetic analysis that the polysomy of chromosome 8 is a constant feature of pleuropulmonary blastoma and the clonal proliferation in pleuropulmonary blastoma is restricted to the malignant mesenchymal elements, supporting the notion that the epithelial components are non-neoplastic. (₇) This neoplasm occurs not only in lung, but it may arise from mediastinum, diaphragm and/or pleura. This has raised the possibility that PPB might originate from the splanchnopleural or somatopleural mesoderm. Common metastatic sites include the brain, bone, lymph nodes, liver, pancreas, kidney, and adrenal glands(₈).

PPB may be associated with cystic pulmonary lesions, which may be evident at the time of diagnosis or predate the appearance of the tumor, there are contradictory reports about the value of prophylactic resection of the pulmonary cysts in protecting patients from developing PPB (₉).

The occurrence of PPB appears to herald a constitutional and heritable predisposition to dysplastic or neoplastic disease in approximately 25% of cases. Associated conditions include PPB, medulloblastoma, malignant germ cell tumor, thyroid neoplasia, and others. Thus, All patients with PPB and their families should be investigated carefully (₂).

The baby like most reported cases presented with a picture of pulmonary infection and respiratory difficulty. The tumor has no characteristic findings on imaging studies, but it should be considered in the differential diagnosis of other benign cystic lung lesions on imaging studies (₆).

As complete tumor ablation is essential to prevent local recurrence and allow any chance of survival, the main goal of therapy should be radical surgery, followed by chemotherapy. Because the response to chemotherapy is poor, some authors suggest that chemotherapy should be given with local radiotherapy in the majority of patients (₁₀).

The prognosis for these patients is grave Types II and III PPBs are clearly aggressive malignancies with projected overall survival of 62% at 2 yrs and 42% at 5 yrs, even after multimodality therapy. Patients with pleural, mediastinal or Extrapulmonary involvement at the time of diagnosis have worse prognosis than those without such involvement (₆,₁₀)