PMC3620447_01
a MRI, 3DFSPGRT1 sequence, sagittal plane. The tumor is localized in the brainstem and is extremely expanding and deforming its structure. Noteworthy is severe compression of the fourth ventricle, but evidently between the tumor and lumen of the fourth ventricle, there remains a thin, uninterrupted strip of brain tissue (arrow). b MRI, DGRET1 with contrast, axial plane. Contrast enhancement within the tumor is conspicuously insignificant. c MRI, frFSET2, coronal plane. The tumor appears as a very well delineated expansive process, with heterogeneous signal, containing some fluid-filled areas at the level of fourth ventricle and medial part of left cerebellar hemisphere, which has atrophied. The tumor molds and compresses the brainstem and obliterates the fourth ventricle. Supratentorially, there are features of hydrocephalus with transudate of CSF into surrounding brain tissue. d Macroscopic cross section of the tumor at the level of the cerebellum. Noteworthy is the very distinct border between the tumor and apparently untouched but evidently severely displaced and compressed cerebellar tissue. e Characteristic mixture of neuropil-like paucicellular zones with quite uniformly scattered cellular "densities" consisting of small undifferentiated cells. Both within densities and also directly within neuropil zones, one could discern rosettes which are quite characteristic for this tumor, H&E, objective magnification x10. f A close-up view of rosettes. Some with empty core but delicately contoured with pinkish line, and some with homogenous featureless core (arrow), H&E, objective magnification x40
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Fig1
Computer tomography (CT) and magnetic resonance imaging (MRI) revealed an enormous tumor (44 x 35 x 45 mm in CT and 35 x 36 x 32 mm in MRI) in the brainstem, mostly in the left pons and medulla oblongata (Fig. 1a, b). T1 with narrowing of the fourth ventricle (Fig. 1b). There were no features of supratentorial hydrocephalus in spite of evidence of elevated pressure in the posterior fossa. The state of the child was unstable and the risk of its marked worsening due to operation was high. Repeated MRI revealed enlargement of the tumor (52 x 50 x 54 mm) and supratentorial hydrocephalus due to compression of the cerebral aqueduct with transudation (Fig. 1c). The tumor distorted the whole brainstem and cerebellum, pushing aside and compressing the fourth ventricle, but definitely not originating from it (Fig. 1d). This confirmed the previous MRI findings of a primary brainstem tumor (Fig. 1a). Microscopic pictures represented a very conspicuous pattern with relatively paucicellular neuropil-like background with numerous and rather evenly distributed cellular densities populated with small undifferentiated cells (Fig. 1e). Rosettes formed another characteristic element of the tumor (Fig. 1f). The rosettes had an "empty," homogenous core, but frequently with a delicate eosinophilic contouring reminiscent of ependymoblastic rosettes, though somewhat more delicate than those occurring in typical ependymoblastoma (Fig. 1e, f).
a The more cellular zones (asterisk), in contrary to neuropil background, are rather negative for synaptophysin, objective magnification x20. b All rosettes were negative for synaptophysin. Apart from the rosettes, strongly synaptophysin-positive cells with prominent processes resembling astrocytes rather than neurons were noted, objective magnification x40. c Both rosettes and almost all cells within cellular "densities" are strongly immunopositive for vimentin, objective magnification x40. d Rosettes are negative for S100. However, between the rosettes there are S-100 positive cells with marked processes, objective magnification x20. e Some mature looking synaptophysin-positive neurons (arrowheads) are scattered within neuropil, objective magnification x40. f Proliferating activity as evidenced by immunopositivity to Ki67 was marked within rosettes and also around vessels (not shown in this picture), objective magnification x40
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Fig2
Neuropil zones, in contrast to the cellular zones, showed immunopositivity to synaptophysin (Fig. 2a). Both in cellular zones and neuropil zones, there were scattered characteristic rosettes, totally negative to synaptophysin (Fig. 2b) but strongly positive to vimentin (Fig. 2c). The rosettes were also weakly positive for glial fibrillary acidic protein (GFAP) and for S100 protein (Fig. 2d). Moreover, outside of the rosettes, synaptophysin-positive mature neuron-like cells were noted (Fig. 2b), and some were even strongly positive for synaptophysin, in spite of resembling astrocytes (Fig. 2e). Ki-67 expression was high but limited to rosettes (Fig. 2f) and cellular zones especially around the vessels.