1. IMAGING APEAREANCE OF ASKIN TUMORS: ABOUT 5 CASES MA. JELLALI, M. AMOR, A. ZRIG, W. MNARI, M. MAATOUK, W. HARZALLAH, R. SALEM, M. GOLLI. Radiology service, FB Hospital, Monastir, Tunisia. CH18

2. OBJECTIVES  Askin’s tumor is a rare malignant tumor arising from the chest wall. It affects mainly children and young adults.  The aim of this work was to demonstrate the value of imaging in the diagnosis and management of this tumor.

3. MATERIALS AND METHODS  We retrospectively collected five cases of Askin’s tumor of childhood.  All our children underwent chest radiography and chest CT scans, and two patients were also evaluated by thoracic MRI.  Radioguided biopsy for the diagnosis was performed in all cases.

4. RESULTS  The radiographic appearance of these tumors was not specific.  The CT scans can specify the size of the mass, demonstrate their possible intrathoracic invasion and rib erosion.  The MRI can be helpful in the evaluation of the mediastinum and the degree of pleural-based disease along with any extrathoracic extension especially the brachial plexus.

5. A 15-year-old boy patient presented with chest pain. chest radiography showed a opacity posterior parietal of the right basis thoracic Chest CT scan confirms the presence of a parietal mass with costal lysis and contralateral pulmonary metastases

6. A 11-year-old boy patient presented with chest pain. Chest radiography showed a large left apical opacity with lytic lesion in second rib Chest CT scan showed a mass occupant almost all the left pulmonary hemifield. The lytic lesion of the rib moving towards the parietal origin

7. Chest radiograph of a 9 year old girl: right posterior opacity with acute pleural connection CT chest scan showed costal lysis associated with pleural effusion moving towards the parietal origin

8. Chest CT scan: right apical mass with costal and vertebral lysis MRI showed an intracanalar and parietal extension

9. DISCUSSION  Askin tumor is a primitive neuroectodermal tumor located in the thoracopulmonary region.  Most of the tumors arise from the soft tissue of the chest wall. Some tumors have also been found in the lung.  The disease is diagnosed by histologic and immunohistochemical analysis.

10. DISCUSSION  Cytologic smears of the tumor reveal small round malignant cells that contain little cytoplasm and are arranged in rows. The typical feature is the presence of Homer-Wright rosettes with various layers of cells with fibrillary material.  Under immunohistochemical examination, the tumor is positive for several neural markers, such as NSE, CD99, and vimentin.

11. DISCUSSION  The chromosomal translocation t(11;22)(q24;q12) is an additional firm diagnostic criterion.  Conventional radiography usually shows a mass of various size accompanied by calcifications, erosions of the ribs, pleural effusions, and even pneumothorax.  Typical CT findings include a large soft tissue mass based on the signal chest wall with or without ipsilateral pleural effusion and rib destruction.

12. DISCUSSION  Large lesions often have a heterogeneous appearance, representing hemorrhage and necrosis or cystic degeneration. Calcification within the mass and lymphadenopathy are rare.  The mass tends to displace, rather than encase the adjacent organ. Linear and nodular density in the subpleural fat, which may represent local perilymphatic and perineural extension, is an unfavorable prognostic sign.

13. DISCUSSION  After intravenous contrast administration, the tumors demonstrate a heterogeneous appearance with non- enhancing necrotic or cystic areas.  According to the literature, characteristic MRI findings include hyperintensity compared with muscle on T1-weighted imaging and heterogeneously bright signal intensity on T2- weighted imaging representing hemorrhage and necrosis.

14. DISCUSSION  Post-contrast T1-weighted imaging can demonstrate the boundary and parenchyma of the tumor, as well as the blood supply of the mass.  Nevertheless, the radiologic characteristics of Askin tumors are not specific, but imaging can be valuable for evaluating the extent of the tumor, the response to treatment and local recurrences or distant metastases.

15. DISCUSSION  It is also useful for guiding the biopsy route and determining whether the tumor has been completely resected.  MRI is more sensitive in evaluating local invasion by providing true multiplanar imaging and excellent soft tissue differentiation, but CT is better for detecting lung and remote metastases, especially bony detail.

16. CONCLUSION  Askin’s tumor of neuroectodermal origin is a particular form of bone tumors of the chest wall.  It should be considered in the differential diagnosis of any thoracopulmonary mass in childhood and adolescence through appropriate histology and immunohistochemistry of incisional biopsies.  The association with rib lysis comfort the diagnostic.