Changes mimicking new leptomeningeal disease after intensity-modulated radiotherapy for medulloblastoma

Abstract

Purpose: Acute and late changes in magnetic resonance imaging of the pediatric brain have been described after radiotherapy (RT). We report the post-RT neuroimaging changes in the posterior fossa after intensity-modulated RT (IMRT) in children with medulloblastoma and contrast them with those of leptomeningeal disease.

Methods and materials: We performed a retrospective review of 53 consecutive children with medulloblastoma who were treated with craniospinal RT followed by IMRT to the posterior fossa and chemotherapy between 1997 and 2006.

Results: After IMRT to the posterior fossa, 8 (15%) of 53 patients developed increased fluid-attenuated inversion-recovery signal changes in the brainstem or cerebellum and patchy, multifocal, nodular contrast enhancement at a median of 6 months. The enhancement superficially resembled leptomeningeal disease. However, the enhancement resolved without intervention at a median of 6 months later. The accompanying fluid-attenuated inversion-recovery signal changes occasionally preceded the enhancement, were often parenchymal in location, and resolved or persisted to a lesser degree. All 8 patients with transient magnetic resonance imaging changes in the posterior fossa were alive at last follow-up. In contrast, leptomeningeal disease occurred in 8 (15%) of our 53 patients at a median of 19.5 months after IMRT completion. Of these 8 patients, 7 demonstrated initial nodular enhancement outside the conformal field, and 7 patients died.

Conclusion: Magnetic resonance imaging changes can occur in the posterior fossa of children treated with IMRT for medulloblastoma. In our experience, these transient changes occur at a characteristic time and location after RT, allowing them to be distinguished from leptomeningeal disease.

Fig. 1

Intensity-modulated radiotherapy map for Patient 8. Example of dose heterogeneity and conformality of radiation dose to avoid normal structures.

Fig. 2

Magnetic resonance imaging scans of Patient 8. (a) Axial, fluid-attenuated inversion-recovery image demonstrating new, increased, nodular signal along periphery of right inferior cerebellar hemisphere at 4 months after intensity-modulated radiotherapy (IMRT). (b) Axial postcontrast T₁-weighted image demonstrating avid nodular enhancement approximately 5.5 months after IMRT. (c) Abnormal fluid-attenuated inversion-recovery signal and enhancement had resolved at 12.5 months after IMRT.

Fig. 3

Magnetic resonance imaging scans of Patient 12 with leptomeningeal disease. (a) Axial fluid-attenuated inversion-recovery images demonstrating linear and nodular increased signal confined to superior cerebellar sulci. (b) Postcontrast T₁-weighted images demonstrating linear enhancement in sulci.

Fig. 4

Magnetic resonance imaging scans of Patient 4. (a) Axial fluid-attenuated inversion-recovery images demonstrating patchy fluid-attenuated inversion-recovery signal in right cerebellar parenchyma and left pons at 5.5 months after intensity-modulated radiotherapy. (b) Axial T₁-weighted images with avid patchy and nodular enhancement in same locations and at same time point. (c) Abnormal fluid-attenuated inversion-recovery signal changes have persisted and enhancement has resolved at 24.5 months after intensity-modulated radiotherapy.