Primary intracranial solitary leptomeningeal astrocytoma (WHO grade 3).
Primary intracranial solitary leptomeningeal astrocytoma (PLA) is very rare; it usually arises in the leptomeninges of the brain or spinal cord with no involvement of intraparenchymal tissue. PLA represent nests of glial tissue separated from the bulk of the CNS, which remain trapped in the leptomeningeal sheets, during embryogenesis, following an aberrant migration [1,4]. This form of astrocytoma differs from the more common secondary leptomeningeal astrocytoma, which refers to secondary spread from an intra-axial glioma. PLA can present in two ways: a diffuse form that is macroscopically similar to meningitis, and a localized solitary form, that mimics other, more common, extra-axial lesions, namely meningiomas.
Cooper and Kernohan criteria for a diagnosis of PLA are as follows: no attachment of meningeal tumor to the brain, no evidence of neoplasia within the brain, presence of leptomeningeal encapsulation around the tumour. All three criteria were satisfied in this case.
Concurrent adjacent meninigoma and astrocytoma has been described , but a retrospective analysis of the removed piece failed to detect any meningiomatous component of the lesion.
Fifteen cases of PLA are reported in the literature ; the rarity of this pathological entity make this diagnosis a challenge on a neuroradiological basis. Notwithstanding, this challenge is of great importance since the diagnosis of astrocytoma versus meningioma implicates a notable difference both in prognosis and therapy. Retrospective neuroradiological analysis of this case failed to detect any findings to help in the differential diagnosis, thus confirming the fundamental role of the neuropathologist even in what can appear to be straightforward radiological diagnoses.
Contributed by Eytan Raz, Manila Antonelli, Angelo Pichierri, Arturo Consoli, Felice Giangaspero, Marco Fiorelli