Contributed by Dimitrios N. Kanakis MD, PhD1, Thomas Kamphausen, MD2, Johannes Van de Nes, MD, PhD1
1Institute of Pathology and Neuropathology, Section of Neuropathology, University Hospital Essen, Germany
2Institute of Forensic Medicine, University Hospital Essen, Germany
A 32-year-old male was admitted to the hospital with high fever and diarrhea. The clinical and laboratory investigations showed exsiccosis (dehydration) and highly increased values of liver enzymes. The patient died after three days due to sepsis following bronchopneumonia. In the patient's anamnesis (case history) the occurrence of a subarachnoid hemorrhage, after the rupture of a basilar aneurysm six years ago, as well as the subsequent development of psychiatric symptoms and dementia were reported.
Brain sectioning revealed, apart from macroscopic findings easily identifiable as consequences of the subarachnoid hemorrhage in the past (multiple cortical infarcts, "coiled" basilar aneurysm etc.), three unusual yellowish microlesions in the left and right nucleus ruber (2mm and 4mm in diameter, respectively) and pons (<0.5mm in diameter). Histopathological examination showed that these lesions were of moderate cell density and had clearly defined, but irregularly borders (Figure 1). The Gomori silver stain revealed a well-established network of reticulin fibers surrounding these cells (Figure 2). The lesions consisted of ovoid to elongated cells that were positive for Vimentin, S100-protein (Figure 3) and myelin basic protein (MBP) (Figure 4) but did not react for 2',3'-Cyclic-Nucleotide 3'-Phosphodiesterase (CNP). These cells were intermingled with some lipid-laden macrophages. Within the lesions pre-existing axons seemed to be largely preserved as visualized with an antibody detecting neurofilament protein (NF) (Figure 5). The adjacent brain parenchyma showed reactive astrogliosis. The lesions did not react with antibodies staining for actin, desmin, EMA, synaptophysin, NeuN, Melan A, CD31, p53 or IDH-1. The proliferation index estimated with Ki-67 (MIB-1) was low (approximately 1%). It is worth mentioning that all three lesions were located in the proximity of small stage III infarctions.
The conventional and immunohistochemical staining results of the microlesions were indicative of Schwann cell proliferations. Since such lesions have hardly been observed in the brain parenchyma and to rule out the possibility of multifocal intracerebral schwannomas, we decided to compare the acquired data with those of an intracerebral schwannoma taken from our archive. Histopathological examination of this tumor revealed, in contrast to the microlesions described above, a well-demarcated tumor with regular borders to the adjacent brain parenchyma (compare Figure 6 with Figure 1). Nevertheless, intracerebral schwannoma displayed a similar storiform growth pattern, cytological appearance and abundant presence of reticulin fibers (compare Figure 7 with Figure 2) and it was also positive for S100-protein (compare Figure 8 with Figure 3). However, on the contrary to the microlesions presented here, intracerebral schwannoma did not react at all for MBP (compare Figure 9 with 4) and CNP and further showed a notable though expected absence of neurofilament positive axons within it (compare Figure 10 with Figure 5). According to all previously reported cyto-, histo- and immunohistochemical results of the present lesions the diagnosis of multiple schwannomas could be excluded.