A 32‐YEAR‐OLD MAN WITH A FOURTH VENTRICULAR MASS

CLINICAL HISTORY

A 32‐year‐old man was admitted to the neurosurgery department due to progressive dizziness and weakness of the feet for a month. An MRI revealed a well‐demarcated mass measuring 60 × 35 × 25 mm, obstructing the fourth ventricle with dilatation of the lateral ventricles, third ventricle and the aqueduct. The lesion showed contrast enhancement with heterogeneous low signal intensity on T1WI (Figure 1) and mixed heterogeneous low and iso‐signal intensity on T2WI (Figure 2). Several foci of cystic change were noted. A gross total resection was performed.

Figure 1.

Figure 2.

NEUROPATHOLOGICAL FINDINGS

Microscopically, the tumor was composed of pleomorphic cells with eosinophilic cytoplasm, irregular nuclear contours, and small nucleoli. In addition, there were large areas with cells that showed a signet‐ring appearance, with large vacuoles in their cytoplasm and the nuclei pushed to the periphery of the cell membrane, assuming a crescent shape (3, 4). Both types of tumor cells exhibited a perivascular arrangement and some of them even had long fibrillary cytoplasmic processes condensed about the stromal vessel in a fashion similar to the perivascular pseudorosette of a cellular ependymoma (Figure 5). Eosinophilic granular bodies were frequent, but Rosenthal fibers were absent (Figure 6). Microvascular proliferation, necrosis, and mitotic figures were not identified.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Both types of tumor cells showed strong positive staining with GFAP (Figure 7) and S‐100 protein, being diffuse in the cytoplasm of the eosinophilic cells and in the rim of the signet‐ring cells. Immunostains for EMA, synaptophysin, and neurofilament were negative. The Ki‐67/MIB‐1 labeling index was less than 10%.

Figure 7.

Ultrastructurally, the neoplastic cells were elongated in shape and had a peripheral, deeply indented nucleus. The cytoplasm was filled with abundant intermediate filaments (Figure 8). However, in the signet‐ring cells, large lipid droplets are observed within the cytoplasm (Figure 9) as well as few condensed intermediate filaments in the periphery. All of the tumor cells were surrounded by a continuous basal lamina. Neither dense core granules nor synaptic structures were found. Ependymal features such as microvilli, cilia or intercellular junctions were not identified.

Figure 8.

Figure 9.

DIAGNOSIS

Intraventricular astrocytoma with extensive lipidization (lipoastrocytoma).

DISCUSSION

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Lipidization is an unusual phenomenon in primary neuroectodermal tumors. Lipidization of the tumor cells can give rise to a xanthomatous appearance (7), or as adipocytic change, in which the lipid vacuoles in the cytoplasm are few and large, as exemplified by cerebellar liponeurocytoma (2), medulloblastoma (3), ependymoma 8, 9 and low grade astrocytoma 4, 6, 10.The presence of adipocyte‐like cells in an astrocytoma is rare and only four cases were reported in the literature 4, 6, 10 and the term “lipoastrocytoma” has been proposed (4). Our case is the first report of a cerebellar lipoastrocytoma.

Our case also has a perivascular arrangement of the tumor cells not previously described. All other defining features of ependymal differentiation are absent in our case. Lipidization and pseudorosette formation has been reported in a liponeurocytoma (5). However, that tumor had immunoreactivity for neuroendocrine markers and ultrastructural findings of dense core granules.

The pathogenesis of lipomatous change in neuroectodermal tumors is unclear. The proposed mechanisms include a disturbance in cellular metabolism (8), a divergent differentiation of precursor cells with capacity for differentiation into astrocytic and fat cells (1), or a true adipose metaplasia.

The prognostic significance of lipomatous changes in an astrocytoma is yet to be established. Previously reported lipoastrocytomas have been indolent 4, 6, 10 and our case appears to be similar. In conclusion, we have presented an unusual case of a lipoastrocytoma in a young adult. Immunohistochemical and ultrastructural studies are helpful aids in differentiating astrocytoma with extensive lipidization from other neuroectodermal tumors exhibiting lipomatous change as well as providing evidence of glial degeneration exhibited as lipidization.

ABSTRACT

Lipoastrocytomas are rare and only four cases have been reported previously. Our case is in the fourth ventricle of a 32 year‐old man. Many areas showed tumor cells with a signet‐ring appearance and focally formed perivascular arrangements. Eosinophilic granular bodies were frequent. There was strong positive immunoreactivity to GFAP and S‐100 protein, even in those vacuolated tumor cells. The proliferation index was less than 10%. Ultrastructural studies showed that the signet‐ring cells had large lipid droplets as well as intermediate filaments. Ultrastructural features characteristic of ependymomas were not seen. These findings confirm that the vacuoles were lipid droplets in astrocytic tumor cells. The features noted are suggestive of a probable better prognosis in this variant of low‐grade astrocytoma.