Primitive neuroectodermal tumors of the chest wall (Askin tumors): CT and MR findings

The objective of this study was to describe the CT and MR appearances of primitive neuroectodermal tumors of the thoracopulmonary region (Askin tumor), which typically manifest as large tumors involving the chest wall and pleura. This rare malignant neoplasm, seen predominantly in children and young adults, originates in soft tissues of the chest wall, occasionally in bone, or, rarely, in the periphery of the lung.

The study group included two boys and six girls, 7-18 years old, with thoracic primitive neuroectodermal tumors who had had CT and MR studies at presentation. In seven of these patients, the preoperative imaging interpretation was compared with surgical observations.

Seven tumors were large. Unilateral chest wall involvement was seen in all eight patients, pleural involvement in seven, and rib destruction in five. All tumors were heterogeneous on CT scans and T2-weighted MR images, and seven were heterogenous on T1-weighted MR images. The smallest tumor was homogeneous on T1-weighted MR images. Seven tumors had a signal intensity greater than that of skeletal muscle on T1-weighted MR images, and seven showed hemorrhage or necrosis. Invasion of muscle in the chest wall was noted on MR images in seven patients and on CT scans in four patients. CT scans and MR images showed extension of tumor into adjacent lung in four patients but were indeterminate in three patients. One patient had no extension of tumor into adjacent lung. Pulmonary metastases were noted on MR images in one patient and on CT scans in three patients. CT and MR studies correctly showed pleural (n = 6), rib (n = 4), pericardial (n = 1), diaphragmatic (n = 1), and vertebral/spinal cord (n = 1) involvement, confirmed during surgery. CT and MR scans of five patients imaged before surgery were indeterminate for adjacent lung invasion.

The described radiologic features of Askin tumors may be useful in deciding when to include this entity in the differential diagnosis. Areas of hemorrhage and necrosis in the large tumors are responsible for their heterogeneous appearance on CT scans and MR images. CT scans and MR images are complementary for determining the extent of disease. MR imaging is informative for determining invasion of chest wall muscle, whereas CT scanning is preferred for detecting small pulmonary metastases. Neither technique is adequate for predicting invasion of adjacent lung.