Abstract
DWI reportedly accurately differentiates pediatric posterior fossa tumors, but anecdotal experience suggests limitations. In 3 years, medulloblastoma and JPA were differentiated by DWI alone in 23/26 cases (88%). Ependymoma (n = 5) could not be reliably differentiated from medulloblastoma or JPA. A trend toward increased diffusion restriction in higher grade tumors (1/14 grade I, 7%; 9/12 grade IV, 75%) had too much overlap to predict the grade of individual cases. The overlap in ADC between tumor types appeared partly due to technical factors (in small, heterogeneous, calcific, or hemorrhagic tumors) but also likely reflected true histologic variability, given that our 3 overlap cases included a desmoplastic medulloblastoma, an anaplastic ependymoma, and a JPA with restricted diffusion in its nodule. Simple structural features (macrocystic tumor, location off midline) aided in distinguishing JPA from the other tumors in these cases.
Highlights
CLINICAL REPORTSUMMARY: DWI reportedly accurately differentiates pediatric posterior fossa tumors, but anecdotal experience suggests limitations
JPAs had significantly higher ADCmin than either ependymomas or medulloblastomas, but ADC values overlapped among the 3 tumor types
We confirmed that DWI is the single most useful sequence for differentiating pediatric posterior fossa tumors and that as expected, diffusion restriction is rare in grade 1 tumors and common in grade 4 tumors
Summary
SUMMARY: DWI reportedly accurately differentiates pediatric posterior fossa tumors, but anecdotal experience suggests limitations. In 3 years, medulloblastoma and JPA were differentiated by DWI alone in 23/26 cases (88%). Ependymoma (n ϭ 5) could not be reliably differentiated from medulloblastoma or JPA. A trend toward increased diffusion restriction in higher grade tumors (1/14 grade I, 7%; 9/12 grade IV, 75%) had too much overlap to predict the grade of individual cases. The overlap in ADC between tumor types appeared partly due to technical factors (in small, heterogeneous, calcific, or hemorrhagic tumors) and likely reflected true histologic variability, given that our 3 overlap cases included a desmoplastic medulloblastoma, an anaplastic ependymoma, and a JPA with restricted diffusion in its nodule. Simple structural features (macrocystic tumor, location off midline) aided in distinguishing JPA from the other tumors in these cases. ABBREVIATIONS: ADC ϭ apparent diffusion coefficient; ADCmean ϭ mean value of ADC; ADCmin ϭ minimum value of ADC; DWI ϭ diffusion-weighted imaging; FLAIR ϭ fluid-attenuated inversion recovery; JPA ϭ juvenile pilocytic astrocytoma; WHO ϭ World Health Organization
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