A 16‐YEAR‐OLD MALE WITH A CEREBELLAR MASS

CLINICAL HISTORY

A 16‐year‐old right‐handed male presented to an emergency room after suffering mild head trauma from a fall onto his head while intoxicated with alcohol. Physical examination revealed a healthy, inebriated male with no focal neurological deficit. The mother reported that her son had experienced excessive fatigue over the last three months. The patient's past medical, surgical and family history were all noncontributory.

MRI revealed a 3.1 × 3.9 × 3.4 cm solid, heterogeneous, midline posterior fossa lesion with a 2.6 × 4 × 4.5 cm posterior cystic component. The solid lesion extended into the proximal portion of the right foramina of Luschka and appeared isointense on T1 and T2 imaging, while the cystic component remained hypointense and hyperintense on T1 and T2, respectively. The solid component showed moderate, heterogeneous enhancement (1, 2). The cyst wall did not enhance. There was minimal signal on the FLAIR sequence in the surrounding tissue. MRI of the total spine revealed no evidence of metastatic disease.

Figure 1.

Figure 2.

A suboccipital craniotomy revealed a large cyst filled with clear yellow fluid surrounded by a translucent membrane. The solid component was grey and gelatinous with ill defined margins and was adherent to the floor of the fourth ventricle. There were numerous vascular pedicles feeding the lesion that caused significant bleeding. A gross total resection was obtained.

PATHOLOGY

Cytologic preparation of the intraoperative material showed abundant plump pleomorphic cells and inter‐mixed small lymphocytes. The pleomorphic population had ample glassy eosinophilic cytoplasm and showed occasional multinucleation. Cytoplasmic processes were suggested but were not a prominent feature. Nuclei were hyperchromatic, and some showed intranuclear inclusions secondary to cytoplasmic invagination (Figure 3). On H&E stained permanent sections, the large bizarre tumor cells were arranged in compact sheets punctuated by small lymphocytes (4, 5). An infiltrating component resembling diffuse astrocytoma could be found in areas (Figure 6). Rosenthal fibers were particularly abundant in the areas of infiltrating glioma (Figure 7). Only a scarce mitotic figure was found. Necrosis was absent. Intratumoral vessels were thin walled without proliferation of endothelium, and some showed perivascular CD3‐positive T cells (Figure 8). Reticulin fibers between individual cells were focally abundant (Figure 9). Glial fibrillary acidic protein (GFAP; figure 10) and vimentin were strongly expressed in many cells, while synaptophysin and neurofilament protein were not. Ki‐67 showed a very low proliferation index.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

DIAGNOSIS

Cerebellar pleomorphic xanthoastrocytoma

DISCUSSION

A differential diagnosis based on imaging alone would include juvenile pilocytic astrocytoma (JPA), a common cerebellar tumor in the pediatric population, and ependymoma, given the lesion's association with the fourth ventricle. Expanding the radiologic differential to include other lesions of the cyst/mural nodule variety would include ganglioglioma, hemangioblastoma and pleomorphic xanthoastrocytoma (PXA). The features described above lead one to the diagnosis of a cerebellar PXA.

PXA was first recognized as a distinct type of astrocytoma by Kepes, et al, in 1979 (6). Most patients are adolescents or young adults who present with seizures. Though typically regarded as superficial meningocerebral neoplasms, PXAs have occurred in the cerebellum, as in this case, and other unusual locations such as spinal cord 3, 7 and retina (8). Sixteen cases of cerebellar PXA, including the present case, have been described in the literature, six of which showed combined features of PXA and ganglioglioma and two others with oligodendroglioma (2). Of the previously reported cases of cerebellar PXA, most have occurred in adults, and the range of age at diagnosis was 3 months to 68 years (2). Of the cases of cerebellar PXA with clinical follow‐up, only two had poor outcomes with patient death 17.5 months and 3 years after presentation, and both tumors had oligodendroglial components (2). While conventional PXA is a WHO grade II lesion, findings such as necrosis and/ or greater that 5 mitotic figures per 10 high power fields are generally regarded as anaplastic features (5). A study of 71 predominately supratentorial PXAs confirmed the overall favorable prognosis of PXA and showed that extent of resection and mitotic index were the main predictors of recurrence free survival and overall survival (1). Genetic changes associated with infiltrating gliomas are rare to absent in cerebral PXAs according to one study (4). To our knowledge, there are no studies addressing prognostic markers or molecular features specific for cerebellar PXA. This case stresses the importance of including PXA in the differential diagnosis of a cerebellar lesion.

ABSTRACT

A 16‐year‐old male presented to an emergency room after falling on his head while inebriated. The patient had only a history of recent fatigue and demonstrated no focal neurological deficit. MRI revealed a cystic and solid, enhancing midline cerebellar lesion. A suboccipital craniotomy was performed. Histologically, the mass showed large bizarre cells arranged in sheets with admixed small lymphocytes. The pleomorphic population had ample glassy eosinophilic cytoplasm and intranuclear inclusions. An infiltrating component resembling diffuse astrocytoma could be found in areas. Rosenthal fibers were particularly abundant in the areas of infiltrating glioma. Mitotic activity was very low, and necrosis was absent. Reticulin fibers between individual cells were focally abundant. Glial fibrillary acidic protein and vimentin were strongly expressed in many cells, while synaptophysin and neurofilament protein were not. Ki‐67 showed a very low proliferation index. The pathologic diagnosis was pleomorphic xanthoastrocytoma (PXA) of the cerebellum. PXA is a diagnosis typically regarded as a superficial meningocerebral neoplasm. This case is one of sixteen cerebellar PXAs reported in the literature.