Abstract
A 13 year-old boy, previously diagnosed as having Neurofibromatosis Type 1 (NF1) but otherwise healthy, was referred to our Department for headache, vomiting, ataxia and VI-VII left cranial nerve palsy. Emergency head CT scan was performed, immediately followed by contrast-enhanced MR scan with Echo-Planar (EPI) water diffusibility study. A large ovalar mass lesion was evident in the left cerebellar hemisphere, hyperdense on CT, hypointense in T2-weighted images, isointense to grey matter in FLAIR and T1-weighted images, with clear mass effect on the surrounding structures, but only mild peripheral contrast-enhancement in the anterior part of the mass, these features resembling those of a desmoplastic medulloblastoma. However, the EPI Diffusion-weighted images (DWI) and corresponding Apparent Diffusion Coefficient (ADC) maps consistently showed increased water diffusivity, a pattern not compatible with the dense cell-packing typical of medulloblastomas.
The pathological analysis of the surgical specimen indeed showed focal neoplastic cell clusters interspersed in a diffusely altered cerebellar cortex. Neoplastic cells exhibited large eosinophilic cytoplasma, hyperchromatic and multinucleolated nuclei, and frequent mitoses, a pattern indicative of anaplastic astrocytoma.
The case presented supports the evidence that NF1 is associated with increased risk of developing several different neoplasms, beside the well-known pilocytic astrocytomas of the optic pathway. As these neoplasms may exhibit misleading imaging features at CT or “conventional” MRI study, the assessment of water diffusivity may provide useful data for reaching a correct pre-operative diagnosis, since it reflects the histological architecture of the neoplastic tissue.
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