Cerebellar oligodendroglioma with bone marrow metastasis.
Prior to the dissemination to the bone marrow, the tumor was diagnosed as Oligodendroglioma WHO grade II, with 1p/19q codeletion, consistent with the genetically favorable variant of oligodendroglioma. However, the increased proliferative index was considered worrisome for the possibility of early anaplastic transformation and a comment suggesting close clinical follow-up was made. FISH studies were also attempted in the bone marrow core biopsy, but were non-informative, likely due to poor DNA preservation after specimen decalcification.
Oligodendrogliomas are diffusely infiltrating gliomas of unknown histogenesis with uniformly rounded nuclei that most closely resemble non-neoplastic oligodendrocytes. They virtually always arise in the cerebral hemispheres, with most involving both neocortex and underlying white matter. In contrast, location in the cerebellum, brainstem, or spinal cord is so exceptional that the diagnosis often engenders appropriate skepticism. To date, less than 30 cases of primary infratentorial oligodendrogliomas have been published, with the vast majority reported prior to the genetic era and the diagnosis often based on little more than the presence of round nuclei with clear haloes. In general, these cases have been inadequately documented by current standards and would most likely be diagnosed as other entities today, including pilocytic astrocytoma, clear cell ependymoma, extraventricular neurocytoma, cerebellar liponeurocytoma, and rosette forming glioneuronal tumor. For instance, Westergaard et al. reported 2 posterior fossa examples out of 96 oligodendrogliomas, but there was essentially no proof provided for this diagnosis6. A more recent Korean series by Lee et al. reported a remarkable 6 of 149 oligodendrogliomas presenting in the posterior fossa3. Unfortunately, this study was focused on radiology issues and provided minimal pathology data with no genetic confirmation. We are aware of only one case report of a cerebellar oligodendroglioma examining 1p and 19q status by fluorescence in situ hybridization (FISH) and it was negative for deletions5. A careful examination suggests that rosette-forming glioneuronal tumor might have been another consideration based on the perivascular neuropil-like material shown in Fig. 1F4. Lastly, based on personal experience, one of the authors (AP) has received many consultation cases where the diagnosis of cerebellar oligodendroglioma was initially considered in the differential. With the exception of the current case, none showed a 1p/19q codeletion pattern by FISH and they were all eventually diagnosed as other entities. Herein, we report a highly unusual example of genetically confirmed primary oligodendroglioma of the cerebellum with associated CSF, bone marrow, and lung metastases. To our knowledge, this represents the first well supported case of cerebellar oligodendroglioma in the literature. Given its rarity however, it remains unclear whether the unusually aggressive clinical behavior encountered in our patient is typical of oligodendrogliomas in this location.