Diagnosis of initial resection: Low grade astrocytoma with comment (some areas of this tumor exhibit features of a primitive polar spongioblastoma; the prognostic significance of these features are uncertain).
Diagnosis of recurrence: Pilocytic astrocytoma
Sections of the first resection of this tumor exhibited numerous fragments which had a striking histologic pattern that has been described in primitive polar spongioblastomas, however, other fragments showed a low grade astrocytoma most consistent with a pilocytic astrocytoma. There was no mitotic activity. We interpreted the palisading as an unusual pattern of a pilocytic astrocytoma. Because primitive polar spongioblastomas may be aggressive, however, we cautioned the clinicians to follow this patient closely.
The second resection, 18 months later, consisted almost entirely of a pilocytic astrocytoma, with only rare fragments containing some palisading cells.
Primitive polar spongioblastomas are an extremely rare tumor most often occurring in the first decade of life (1,2). They have been described in the cerebral hemispheres, but are more commonly located in the posterior fossa or the upper spinal cord. The distinctive morphology of the tumor consists of compact rows of oval nuclei separated by paucicellular zones filled with parallel arrays of fibers. In some cases, the nuclei are hyperchromatic and mitotic activity may be present. The delicate processes between the cell columns are only rarely immunoreactive for S-100 or GFAP. Ultrastructural studies have sometimes shown evidence of neuronal differentiation (2) and some have argued that these tumors are an embryonal tumor recapitulating an early stage of glial embryogenesis. Adding to the confusion is that the term "spongioblastoma" has in the past been used to refer to both pilocytic astrocytoma and glioblastoma multifore (2).
Primitive polar spongioblastomas are a disputed pathologic entity (3) primarily because in rare cases a similar histologic pattern can be seen in other tumors such as pilocytic astrocytomas, oligodendrogliomas, medulloblastomas, central neurocytomas, ependymomas and cerebellar astrocytomas (2,3). The W.H.O. classification places primitive polar spongioblastomas in the category of "Tumors of Uncertain Origin" (2). These tumors may have a clinically aggressive course including spinal metastases (4), however, in other cases they have a more indolent nature. It could be argued that in the latter cases, these tumors were actually a variant of pilocytic astrocytomas as in our example. In cases in which all of the tumor tissue has the distinctive histologic pattern and there is evidence of mitotic activity, it may be best to alert the clinicians to the malignant potential of the tumor by using the term "primitive polar spongioblastoma."
Contributed by Ronald Hamilton, M.D.