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Small Round Cell Tumor of the Lung in Children

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Dr Sameer Raniga, Dr Pranav Sharma, Dr Salil Sharma, Dr Chintan Shah, Dr Prakash A Vohra, Dr Vijay Vaidya    12 December 2017

KEYWORDS

Lung, small round cell tumor, chest radiographs with a thoracic mass malignant

Assistant Professor

Resident

Professor and Head

Assistant Professor

Dept. of Radiology

SSG Hospital and Medical College, Vadodara

Address for Corespondance

Dr Sameer Raniga

81, Shantinagar Society, Tarsali Road, Vadodara – 390 009, Gujarat

Large malignant thoracic tumors in children may arise from the chest wall, pleura, lung parenchyma or mediastinum and may be primary or secondary. If the site of origin of the intrathoracic tumor can be determined, the differential diagnosis may be based on the location of the tumor, age of the patient and distinguishing imaging features.

The purpose of this report is to illustrate imaging findings of small round cell tumor of the chest that presented as a large intrathoracic mass on the initial chest radiograph.

CASE REPORT

An 8-year-old boy presented with a 7 months history of cough, dull pain over the chest wall and exertional dyspnea. The laboratory investigations were within normal limits except for mild anemia (hemoglobin-10.5 g/dL). Clinical examination did not reveal any significant finding. Pulmonary function tests showed a mild restrictive picture. The chest radiographs revealed a sharply circumscribed solitary parenchymal mass in the left upper and midzone (Fig. 1). Pre- and post-contrast chest computed tomography (CT) showed heterogeneously minimally enhancing large solid parenchymal mass lesion with necrotic areas within (Fig. 2). The mass was seen abutting the mediastinum with ill-defined fat planes and the chest wall; however, there was no definitive evidence of the invasion of ribs or vertebrae. Abdominal involvement was not present. Intraoperatively, a part of the mass had invaded the chest wall and could not be completely resected. No involvement of the ribs or vertebrae was however seen. Microscopic examination showed the lesion to be composed of multiple small round cells. Diagnosis of small round cell tumor of chest was suggested. Postoperative radiographs and CT showed residual tumor near the apex of the lung with intercostal drainage tube in situ (Figs. 3 and 4).

DISCUSSION

The majority of mediastinal and chest wall tumors in children are malignant. Lung lesions are usually benign, unless a known extrapulmonary tumor suggests pulmonary metastases.1 The small round cell tumors of the childhood that cause large intrathoracic masses include Ewing’s sarcoma, rhabdomyosarcoma, primitive neuroectodermal tumors (PNET)/Askin tumor, lymphoma, neuroblastoma and other soft tissue sarcomas.2,3 Large primary malignant tumors are rare and include pulmonary rhabdomyosarcoma, leiomyosarcoma and pleural mesothelioma. Mesenchymal sarcomas, rhabdomyosarcomas and pulmonary blastomas may arise from pre-existing cystic lung lesions or from mesenchymal cystic  hamartomas.4,5

Desmoplastic small round cell tumor (DSRCT) is a rare malignant neoplasm of adolescent males.6 Most previously reported cases involved the peritoneum or tunica vaginalis, suggesting a histogenetic relationship to the mesothelium.7

On initial chest radiographs, these masses usually appear as an opaque hemithorax or an obvious large opaque mass.8 Imaging features include large heterogeneous mass on CT scans and magnetic resonance imaging (MRI) images because of hemorrhage and or necrosis in the mass.9 Calcification is unusual. Early imaging clues that suggest the site of origin as the chest wall include recognition of subtle or obvious bony destruction of the ribs or vertebrae on plain films or on CT scans or bone scintigraphy or detection of soft tissue extension into the chest wall on CT scans or MRI images.10

The identification of some tumors is difficult, since some of them may mimic pulmonary inflammation. The first diagnostic tool is chest radiography. After that, a CT with contrast medium should be performed, if possible a multislice-CT. Identification of mediastinal structures is best with MRI.11 The most common diseases that mimic large pulmonary masses are large consolidating pneumonias, pseudotumors or large abscesses, findings on CT scans suggesting the possibility of an inflammatory or infectious origin of the mass include: (1) visualization of the mass on both sides of fissure containing pleural fluid; (2) multiple loculated rim enhancing pleural fluid collections; (3) low attenuation nodes with or without rim enhancement and (4) the presence of abnormal air collections not seen on plain films.12

In children, secondary malignant metastatic lung and pleural lesions such as osteogenic sarcoma or Ewing’s sarcoma have rarely been reported to become massive and usually the primary lesion is already known.

Neuroblastoma, another small round cell tumor of the childhood usually occurs in the posterior mediastinum in paraspinal location, shows presence of calcification; thinning, splaying and erosion of the posterior ribs; neural foraminal enlargement and intraforaminal or intraspinal extension. These tumors show expression of Mic2 protein and t(11;22)(q24;q12) translocation. The tumor cells are positive for periodic acid-Schiff, neuron-specific enolase and vimentin, but negative for Leu7, chromogranin A and pro-gastrin-releasing peptide and are negative for leukocyte common antigen, S-100 protein, pankeratin, chromogranin A and desmin.13,14

Operation, combination chemotherapy or radiotherapy has been selected for treatment but none is satisfactory.15 Image-guided intensity-modulated radiotherapy is an option in the treatment of pelvic DSRCT and may permit escalation of conventional radiotherapy doses and could have a favorable impact on local control of disease.16

CONCLUSION

Desmoplastic small round cell tumor is an aggressive malignant neoplasm that occurs in adolescents and young adults with a 5-year survival of less than 15%. Imaging features include large heterogeneous mass on CT scans and magnetic resonance imaging (MRI) images because of hemorrhage and or necrosis in the mass. The purpose of this report is to illustrate imaging findings of small round cell tumor of the chest that presented as a large intrathoracic mass on the initial chest radiograph.

REFERENCES

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