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Year : 2011  |  Volume : 54  |  Issue : 3  |  Page : 629-631
Rosenthal fibers and eosinophilic granular bodies in an acoustic schwannoma

Department of Pathology, GB Pant Hospital, New Delhi, India

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Date of Web Publication20-Sep-2011

How to cite this article:
Singh G, Tatke M. Rosenthal fibers and eosinophilic granular bodies in an acoustic schwannoma. Indian J Pathol Microbiol 2011;54:629-31

How to cite this URL:
Singh G, Tatke M. Rosenthal fibers and eosinophilic granular bodies in an acoustic schwannoma. Indian J Pathol Microbiol [serial online] 2011 [cited 2020 Dec 2];54:629-31. Available from: https://www.ijpmonline.org/text.asp?2011/54/3/629/85123

The patient is a 50-year-old male who presented with diminished hearing and tinnitus for the past 8 months. His magnetic resonance (MR) imaging showed a homogenously enhancing, well-circumscribed retroclival mass in the cerebellopontine angle, measuring 3.6 × 2.8 × 3 cm [Figure 1]. The mass was not pushing into the neighboring parenchyma of the pons or the cerebellum. The tumor at surgery was soft, suckable with a well-defined plane of cleavage, and it had both solid and cystic components. The operative diagnosis was epidermoid cyst or metastatic tumor.
Figure 1: Post-gadolinium enhanced T1-weighted MRI sagitial section displaying a homogenously enhancing, well-circumscribed retroclival mass in the cerebellopontine angle

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The mass was completely excised and sent for histopathologic examination in 10% neutral buffered formalin. It was processed in whole, and paraffin-embedded sections were stained with hematoxylin and eosin (H and E), Gordon and Sweets reticulin and Masson's trichrome. Microscopic examination of H and E stained sections revealed a classical schwannoma with a biphasic growth pattern. Both Antoni A and Antoni B areas were seen with many Verocay bodies. Hyalinized blood vessels, collections of foamy macrophages and hemosiderin laden macrophages were noted focally. The tumor was reticulin rich.

Interestingly, all of the sections showed variable number of Rosenthal fibers (RFs), mostly in Antoni B areas and occasionally in close relation to a Verocay body [Figure 2]a-c. The RFs had the classical morphology of these structures-elongated, wormiform homogenous, hyaline and eosinophilic [Figure 2]d. On Masson's trichrome stain, they were highlighted red. In addition, one section showed eosinophilic granular bodies (EGBs). These structures were not only localized to peripheral portions of the tumor but were also seen evenly distributed through out the tumor.
Figure 2: (a) Scanner view showing numerous Rosenthal fi bers in a classical schwannoma. Note the nuclear palisading and Verocay body formation (arrows) (H and E, ×40); (b) low-power view showing the Rosenthal fibers in close relation to a Verocay body (H and E, ×100); (c, d) classical "wormiform" Rosenthal fibers with scattered eosinophilic granular bodies (H and E, ×200 and ×400); (e) GFAP immunoreactivity in Antoni B areas, Verocay bodies were negative for GFAP (×40); (f) GFAP immunostain highlighting the Rosenthal fibers (×200)

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Immunostaining was performed with S 100 (RTU-S 100 p, Rabbit polyclonal, Novocastro, Novocastra, Newcastle upon Tyne, UK) and glial fibrillary acidic protein (GFAP) (Polyclonal Rabbit Anti-cow, DAKO cytomation Glostrup, Denmark) using the peroxidase antiperoxidase method withpositivecontrols. Immunohistochemical analysis showed strong and diffuse nuclear and cytoplasmic immunoreactivity for S 100. In addition, patchy GFAP immmunoreactivity was noted predominantly in the central part of the tumor, more in the Antoni B areas [Figure 2]e. The RFs and EGBs were also highlighted by GFAP [Figure 2]f. The Antoni A areas and Verocay bodies did not show GFAP reactivity.

   Discussion Top

RFs represent degenerated intermediate filaments of astrocytes. It is suggested that RF formation is a two-stage process, starting with excessive accumulation of GFAP within astrocytic processes followed by their gradual alteration into electron-dense amorphous material under the influence of some unknown metabolic or other factors. [1] They are immunoreactive for ab crystallin and ubiquitin. EGBs are acidophilic globules of lysosomal origin, immunoreactive for a1 antitrypsin, a1 antichymotrypsin, ubiquitin and ab crystalline, and commonly seen in association with RFs. These structures are seen in pilocytic astrocytomas and also commonly in the gliotic tissues surrounding craniopharyngiomas and cerebellar hemangioblastomas, which is evidence of the slow growing and expansive nature of these tumors.

This is only the second case of RFs and EGBs reported in a classic schwannoma after that described by Brown and Rushing [2] in 1997. In their observations, the authors identified numerous RFs and occasional EGBs in the center of the tumor, evenly distributed in Antoni A and Antoni B areas and often associated with Verocay bodies. Similar to the present case, their patient was also a middle-aged male with a cerebellopontine angle tumor.

The origin of RFs and EGBs in schwannomas can be attributed to degenerated aberrant GFAP filaments. There is abundant literature on GFAP immunoreactivity in schwannomas which has been noted in 11.3-78% [3],[4],[5] of cases in different series. Interestingly, GFAP reactivity is found to be more in centrally placed schwannomas compared to peripheral ones. Within the centrally placed schwannomas, in the study by Stanton et al., [3] 6/15 acoustic schwannomas (40%) were GFAP positive and 2/2 intracerebral schwannomas were GFAP positive. Based on epitopes, the GFAP of the intracerebral form was the same as astrocytic GFAP; however, the GFAP of the cranial nerve form consistently differed by a single epitope (C9). The authors hypothesized that the GFAP reactivity in intracerebral forms is due to entrapment of surrounding astrocytes or protein uptake by the adjacent schwann cells. Another hypothesis put forward was that the medial central segment of the eighth nerve is composed of glial tissue which is the source of GFAP reactivity in acoustic schwannomas. [5]

In the present tumor, the diffuse and strong immunoreactivity for S 100 along with its reticulin-rich nature confirmed the diagnosis of schwannoma. Aberrant GFAP reactivity was noted in the Antoni B areas. The areas with RFs and EGBs were in close relation to the Verocay bodies and showed S 100 reactivity in addition to the aberrant GFAP reactivity, thus indicating that the structures were in the schwannian areas and did not just represent peripheral entrapped gliotic tissue.

This unusual and interesting morphological feature in an acoustic schwannoma cautions to the fact that all cellular spindled cell tumors in the posterior fossa with RFs and EGBs are not pilocytic astrocytomas.

   References Top

1.Dinda AK, Sarkar C, Roy S. Rosenthal fibres: an immunohistochemical, ultrastructural and immunoelectron microscopic study. Acta Neuropathologica 1990;79:456-60.  Back to cited text no. 1
2.Brown DF, Rushing EJ. Rosenthal fibres and eosinophilic granular bodies in a classic acoustic schwannoma. Arch Pathol lab Med 1997;121:1207- 9.  Back to cited text no. 2
3.Stanton C, Perentes E, Collins VP, Rubinstein LJ. GFA protein reactivity in nerve sheath tumors: A polyvalent and monoclonal antibody study. J Neuropathol Exp Neurol 1987;46:634-43.  Back to cited text no. 3
4.Fanburg- Smith JC, Majidi M, Miettinen M. Keratin expression in schwannoma: A study of 115 retroperitoneal and 22 peripheral schwannomas. Mod Pathol 2006;19:115-21.  Back to cited text no. 4
5.Kasantikul V, Palmer JO, Netsky MG, Glasscock ME 3 rd , Hays JW. Glioma of the acoustic nerve. Arch Otolaryngol 1980;106:456-9.  Back to cited text no. 5

Correspondence Address:
Medha Tatke
Department of Pathology, 3rd Floor, Academic Block, GB Pant Hospital, Bahadur Shah Jafar Marg, New Delhi - 110 002
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.85123

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