Contrast enhanced MR imaging of postoperative medulloblastoma in childhood: emphasis on meningeal enhancement

To differentiate the postoperative changes from the recurrence of tumor and to evaluate MR imaging of early postoperative leptomeningeal seeding in medulloblastoma, We have retrospectively analysed 34 cases of MR images of 17 patients who were confirmed as medulloblastoma by histopathology. Noncontrast and postcontrast T1 weighted MR images were obtained in all patients. In 11 patients follow-up MR was done more than once (average: 1.5 times) and average interval of MR imaging was 6 months. The timing of 34 MR images was as follow: 6 case within 2 months, 9 cases between 2 months and 1 year, 19 cases more than 1 year after surgery respectively. MR images within 2 month after surgery revealed contrast enhancement at operation site and adjacent meninges, hemorrhage, residual tumor. In patients who had no evidence of tumor recurrence, these early postoperative changes were markedly decreased within 6 month after surgery. MR images obtained more than 1 year after surgery showed no abnormal contrast enhancement or mild focal dural enhancement at operation site. Diffuse moderate dural enhancement was noted in one patient who had the history of post-surgical subdural hemorrhage. In six patients with tumor recurrences which were detected from as early as 9 months to 6 years after surgery, the findings of recurrence included leptomeningeal enhancement of brain stem and cerebellar surface at early stage, variable sized enhancing leptomeningeal nodules, linear or irregular sulcus obliterating enhancing lesions, enhancing mass at primary or metastatic site. We have concluded that leptomeningeal enhancement detected after 6 months of surgery is an important MR finding suggesting the possibility of tumor recurrence. Small nodular and linear enhancement of leptomeninges at brainstem or cerebellar surface is considered as the early manifestation of intracranial tumor seeding