A comparative study of embedded nerve tissue in six NF2-associated schwannomas and 17 nonassociated NF2 schwannomas

ELSEVIER

Neoplasm

A COMPARATIVE

STUDY OF EMBEDDED NERVE TISSUE IN SIX NF2-ASSOCIATED SCHWANNOMAS AND 17 NONASSOCIATED NF2 SCHWANNOMAS

Yasuhiro Hamada, M.D.,*t Toru Iwaki, M.D.,* Masashi Fukui, M.D.,t and Jun Tateishi, M.D.* Depautments of *Neuropathology and TNeurosurgery, Neurological Institute, Faculty of Medicine, Kyushu University, Fukuoka, Japan

Hamada Y, Iwaki T, Fukui embedded nerve tissue and 17 nonassociated 1997;48:395-400.

M, Tateishi J. A comparative study of in six NFZ-associated schwannomas NF2 schwannomas. Surg Neurol

KEY WORDS

Schwannoma,embeddednerve, neurofilament, myelin basic protein, neurofibromatosis2.

BACKGROUND

Neurofibromatosis-2 (NF2) is an autosomal dominant disorder in which patients typically show bilateral acoustic tumors, and they are usually diagnosed histopathologitally as schwannomas. The nerve of origin of a schwannoma is often demonstrated on the periphery along the capsule but not penetrating the substance of the tumor. However, there is a possibility that NF2 schwannomas and solitary schwannomas differ from participation in nerve components. METHODS

In this study, the authors noted the relationship between the tumor and the original nerves. To detect whether there were embedded nerves in the tumor, immunohistologic staining using neurofilament and myelin basic protein antibodies was performed on 6 NF2 schwannomas and 17 non-NF2 schwannomas. RESULTS

Four of five NF2 schwannomashad embeddednerves and one of four, which was considered to be the early stage of the tumor occurrence, remarkably embedded original nerves. On the other hand, embedded nerves were not seen in non-NF2 schwannomas. CONCLUSIONS

The authors concluded that the NF2 schwannomastend have original nerves embedded in the tumor substance, which may be based on the difference of the motility of tumor cells, and the authors believe that it is difficult to remove NF2 schwannomaswhile preserving the original nerve. 0 1997by Elsevier Science Inc.

Address reprint requests to: Dr. Yasuhiro Hamada. Department ropathology, Neurological Institute, Faculty of Medicine, Kyushu sity 60, Fukuoka 81262, Japan. Received December 8, 1995; accepted September 26, 1996. 0 1997 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010

of NeuUniver-

S

chwannoma is one of the truly encapsulated neoplasms, and the nerve of origin of the tumor is often demonstrated in periphery, flattened along the capsule but not penetrating the substance of the tumor [1,12-141. Therefore, it is thought that the nerve of origin can be preserved when removing such a tumor. On the other hand, neurofibroma can be solitary or multiple, and the latter form represents the most important component of neurofibromatosis-1 (NFl) [2]. The diffuse involvement of the nerves in neurofibromas is common, and may mean that it is impossible to preserve the nerves when performing a complete resection. Neurofibromatosis-2 (NF2) is an autosomal dominant disorder in which patients are predisposed to neoplastic lesions such as schwannomas, meningiomas, and gliomas [7,8,10,11,18]. Such patients typically show bilateral acoustic tumors, and these tumors are usually diagnosed as schwannomas histopathologically. However, there is a possibility that NF2 schwannomas and solitary schwannomas differ from each other in terms of the involvement of various nerve components. In this study, NF2 tumors and non-NF2 tumors diagnosed as schwannomas using H.E. staining were immunostained to identify nerve fibers using antibodies against neurofilament protein and myelin basic protein, in order to investigate the relationship between these tumors and their embedded nerve fibers, particu-

larly concerning

NF2 tumor

genesis. 0090-3019/97/$17.00 PII SOO90-3019(96)00487-9

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Clinical and Histologic Features of NF2 and non-NF2 Tumors

CASE AGE No. SEX NF 1 2 3

z 6 7 8

9 10 11 12 13 14 15 16 17 18

19 20 21 22 23 24

18F 42M 44M 21F 11M 13F 53M 41M 35M 60M 63F 48M 56F 67F 58F 47M 45F 60F 47F 45F 28F 44M 38M 22M

NF2 NF2 NF2 NF2 NF2 NF2 NFl

SITEOF TUMOR Rt. acoustic Rt. acoustic Rt. acoustic

Lt. acoustic Rt. C, root Lt. trochlear n. Lt. acoustic Rt. acoustic Lt. acoustic Lt. acoustic Lt. acoustic Rt. acoustic Rt. acoustic Rt. acoustic Lt. acoustic Rt. acoustic Rt. acoustic Rt. acoustic Lt. acoustic Lt. juglar Rt. Th,, root Rt. Th, root Rt. C, root Rt. C, root

**8TH CRANIALNERVEOF EMBEDDED ACOUS~CS~H~ANNOMA *SIZE OF NERVE OPERATIVE POSTOPERATIVE TUMOR(MM) HISTOLOGY TISSUE FINDINGS STATE 60 35 30 7 30 3 50 35 32 30 30 25 25 25 20 15 15 12 12 40 25 15 10 20

schwannoma schwannoma schwannoma schwannoma schwannoma

schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma

schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma schwannoma

schwannoma neurofibroma

t + + + + ++ ++

*The size of the tumor indicates the maximum diameter of the tumor. **Operative findings of acoustic schwannomas. Compressed; 8th nerve could be identified on the surface involved in the tumor. Preserved: 8th nerve was anatomically preserved. Disrupted; 8th nerve was disrupted.

CASESANDMATERIALS NF2 CASES (CASES 1-6) Five patients received surgical treatment for CNS schwannomas from September 1983 to February 1995 in the Department of Neurosurgery, Kyushu University. Four cases (cases l-4) had bilateral acoustic tumors and the 8th nerve could not be grossly identified in three (cases l-3) of the four cases at operation. The tumors of three cases (cases l-3) were removed including the 8th nerves, since the original nerves were strongly involved in the tumors. In case 4, the tumor, whose diameter was about 7 mm, was partially biopsied from the internal acoustic meatus for the purpose of decompression of the cochlear nerve. Case 5 had a firstdegree relative with NF2, in addition to a right C, root tumor that was revealed by magnetic resonance imaging @IRI). At operation, an original nerve of the tumor was observed to penetrate into the tumor, and the operators believed it to be a neurofibroma. Case 6 had a left acoustic schwannoma, a left cerebellopontine angle meningioma, a

Involved Involved Involved Involved

Disrupted Disrupted -

Compressed Compressed Compressed Compressed Compressed

Disrupted Disrupted Disrupted Disrupted Preserved Disrupted Disrupted

Involved Compressed Compressed Compressed Compressed Compressed Compressed Compressed

of the tumor.

Disrupted Preserved

Preserved Disrupted

Preserved

Involved;

Preserved Preserved Preserved

8th nerve

was

left oculomotor nerve schwannoma, and a left trochlear nerve schwannoma. In case 6, partial removal of the meningioma was performed. The left trochlear nerve was partially swollen like a neurofibroma and a small trochlear nerve tumor (3 mm in diameter) was totally resected including the original nerve. We histologically examined the trochlear nerve tumor (Table 1). All six cases were diagnosed as NF2 according to clinical criteria [8]. NON-NF2 CASES (CASES 7-23) Seventeen patients received surgical treatment for solitary CNS schwannomas from November 1992January 1995 in the Department of Neurosurgery, Kyushu University. Thirteen tumors were clinically diagnosed as acoustic schwannomas, one was diagnosed as a jugular foramen schwannoma extending to the internal acoustic meatus, and three were diagnosed as spinal nerve root schwannomas (Table 1). At operation, the original 8th nerve could be identified in 12 of 13 acoustic schwannomas. In some acoustic schwannomas, the original nerve was thought to be the vestibular nerve, but it was

Embedded Nerve Tissue

difficult to discriminate whether the origin was the superior or the inferior vestibular nerve. The 8th nerve was usually found on the surface of the tumor, not penetrating into the tumor substance, and it was also anatomically preserved in six of 13 acoustic schwannomas. NEUROFIBROMA CASE (CASE 24) One neurofibroma was examined in order to compare with schwannomas. Case 23 had a right Cz root neurofibroma of NFl. The original nerve was observed to penetrate into the tumor, which was totally resected including the nerve (Table 1).

METHODS The 24 original specimens were fixed in formaldehyde and embedded in paraffin. The sections were routinely stained with hematoxylin and eosin, and with Bodian’s stain. Immunohistochemical staining was performed using an indirect immunoperoxidase technique [S], and the sections were lightly counterstained with hematoxylin. The primary antibodies used were: (1) rabbit polyclonal antibovine S-100 protein antibody (DAKO, Denmark, diluted 1:SOO); (2) mouse monoclonal antihuman neurofilament protein antibody 2Fll (DAKO, diluted l:lOO), which reacts with 200 kDa and 70 kDa components of the three major polypeptide subunits (70 kDa, 160 kDa, and 200 kDa); (3) rabbit polyclonal antihuman 160 kDa neurofilament antibody [17] (diluted 1:300); and (4) rabbit polyclonal antihuman myelin basic protein (MBP) antibody (DAKO, diluted 1:lOO). Schwannoma cells were stained with S-100 protein antibody. In addition, the nerves were identified using neurofilament protein antibody that reflected the existence of axons and MBP antibody that reflected the existence of myelin.

RESULTS In cases of acoustic schwannomas with diameters more than 30 mm, the preservation of the 8th nerve was difficult. In acoustic schwannomas of NF2 (cases l-3), the 8th nerves could not be grossly identified; however, the original nerves could be grossly identified in most non-NF2 acoustic schwannomas (cases 7-19) at operation (Table 1). Twenty-three tumors (cases l-23) were histologically diagnosed as schwannomas using hematoxylin and eosin staining. The tumors with NF2 were all diagnosed as schwannomas. In one of the NF2 schwannomas (case 5) a growth pattern in which

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nearly completely circumscribed round or oval lobules were present within the tumor was identified (Figure lA,B). This feature is often recognized in NF2 schwannomas as “grapelike” appearance [ 8,10,19]. Myelinated nerves could be identified with H.E. staining in two (cases 4 and 6) of six NF2 schwannomas (Figure 2A). Immunohistologically, filamentous positive findings against neurofilament antibodies were recognized in the specimens of cases 4 and 6 (Figure 2B), and there was no remarkable difference in the immunostaining between the use of polyclonal neurofilament antibody and monoclonal neurofilament antibody (clone 2Fll). In addition, myelinated sheaths were recognized in the same cases using MBP antibody (Figure 2C). Since the regions of these positive findings did not include apparent nuclei and they partially showed positive against MBP antibody, we considered that the original peripheral nerves were thus embedded in the tumor tissue [ 3,4,6,7,18,20]. Nerve fibers were occasionally seen in the specimens from cases 2,3, and 5 in a similar fashion. In the specimen of case 5, nerve fibers were recognized in the periphery of tumor lobules (Figure 1C). In case 1, however, only a few nerve fibers could not be seen in the specimen. On the other hand, an immunohistochemical analysis using neurofilament antibodies showed negative findings in 16 of 17 non-NF2 schwannomas. One of the non-NF2 schwannomas (case 11) included nerve tissue because the vestibular nerve was resected with the tumor at surgery (Figure 3). The cochlear nerve, however, could be preserved. This case was therefore, considered not to have any “embedded nerves,” since nerve fibers were located in the periphery of the tumor and were flattened along the capsule. A case of neurofibroma (case 24) was immunostained as a control in order to identify nerve fibers. It was strongly positive for neurofilament antibodies and MBP antibody. These findings were therefore considered to show embedded original peripheral nerves in the tumor tissue.

DISCUSSION Schwannomas contain no nerve fibers within their mass, but myelinated and unmyelinated axons of the nerve of origin can be found compressed beneath the perineural capsule of the tumors [ 1,9,13, 14,161. On the other hand, there are some histologic differences between NF2 schwannomas and nonNF2 schwannomas according to Sobel et al. [19]. They reported that NF2 schwannomas had more Verocay bodies, foci of cellularity, and lobular

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Photomicrographs showing a lobular “grape-like” pattern of the specimen from case 5, NF2 patient. (A) Circumscribed round lobules are present (H&E X 10); (B) it is difficult to recognize nerve fibers in H.E. staining X 25; (C) nerve fibers are occasionally seen in the periphery of the tumor lobules (arrows). Antineurofilament antibody (2Fll) X 25.

Hamada et al

Photomicrographs showing Antoni A area of the qisadingspecimen from case 6, NF2 patient. (A) Nuclear palis present, and original nerves (arrowheads) are embedded in the tumor (H&E x25); (B) nerve fibers are remarkably seen to intervene among the tumor cells. Antineurofilament antibody (2Fll) X25; (C) myelin sheaths of nerves are present (arrowheads). Antimyelin basic protein X25.

Embedded Nerve Tissue

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A photomicrograph showing the margin of the tuEf mor (T) derived from the vestibular nerve (N). No embedded nerve is seen in the tumor substance (case 10). Antineurofilament

antibody (2Fll)

x25.

“grape-like” growth patterns while non-NF2 schwannomas had more hyalinized vessels, hemosiderin deposits, and recent or old thrombi. In addition, Ogawa et al. reported that the growth rate of NF2 schwannoma was higher than that of non-NF2 schwannoma [15]. To our knowledge, however, small NF2 schwannomas that are considered to represent an early stage of the tumor occurrence have not been histologically examined to determine whether any original nerves are embedded in the substance of the tumor, although Jaaskelainen et al. reported that the embedding of nerve fibers was more frequent in NF2 at the interface between the facial nerve and the large acoustic schwannoma [6]. With regard to our cases, the original nerve could usually be preserved in cases where the tumor size is less than 15 mm, but seldom preserved in cases where the tumor size is more than 30 mm because of the difficulty of operation (Table 1). On the other hand, the NF2 schwannomas of cases 4 and 6, whose diameters were about 7 mm and 3 mm, respectively, were quite small and were therefore, considered to be at a relatively early stage of tumor occurrence. The microscopic tissue preparation of these specimens showed the tumor to be composed of interlacing neoplastic cells in bundles with many intervening nerve fibers (Figure 2). This finding means that there was no possibility of preserving the original nerve when removing the tumor. In addition, this finding also means that the original nerve fibers could be embedded in the tumor at the beginning of the tumor occurrence. This feature

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was considered to be an unusual finding for aschwannoma, and would normally be recognized in a nurofibroma rather than in a schwannoma. In a schwannoma, the original nerve tends to be deflected over the whole surface of the mass when the tumor is small, and the original nerve is not contained in the substance of the tumor in general. These cases (cases 4 and 6) however, demonstrated embedded nerves in the tumor. On the other hand, some nerve fibers were recognized in the tumors of cases 2 and 3, since it is considered that the embedded nerve fibers were scattered over a wide area of the tumor whose diameter was about 30 mm and therefore, was much larger than those of cases 4 and 6. The tumor of case 1, whose diameter was about 60 mm, was quite large, and few embedded nerve fibers were observed in this specimen because the nerve fibers were widely dispersed in the whole of the tumor. No embedded nerve fibers, however, could be found in any of the non-NF2 schwannomas, compared with NF2 schwannomas. The operative finding that the original nerves were identified in most of the non-NF2 schwannomas supports this fact. These results may indicate that it is difficult to remove such tumors while preserving the original nerve in either case where a tumor is small or in cases where a partial removal is performed. Some studies have previously pointed out that there are some histologic differences between NF2 and nonNF2 schwannomas [19], while, in addition, the frequency of embedded nerve fibers that exist at the interface between the tumor and the nerve was also different in NF2 and non-NF2 schwannomas [6]. In this study, it appeared that nerve fibers spread over not only the interface between the nerve and the tumor but also the whole of the tumor in NF2. In addition, the tendency of NF2 schwannomas to have original nerves embedded in the tumor substance may be due to differences in the tumor genesis or tumor motility. REFERENCES 1. Burger P, Scheithauer B. Tumors of the peripheral nerve sheath tumor. 1993;l333343 Washington D.C.: Armed Forces Institute of Pathology. 2. von Deimling A, Krone W, Menon A. Neuroflbromatosis type 1: pathology, clinical features and molecular genetics. Brain Pathology 1995;5:153-62. 3. Forton G, Moeneclaey L, Declau F, Marquet J. The involvement of the cochlear nerve in neurinomas of the eighth cranial nerve. Arch Otorhinolaryngol1989; 246:156-60. 4. Gould VE, Moll R, Moll I, Lee I, Schwechheimer K, Franke WW. The intermediate filament complex of the spectrum of nerve sheath neoplasms. Lab Invest 1986;55:463-74.

400

Hamada et al

Surg Neurol 1997;48:395-400

5. Iwaki T, Kume-Iwaki A, Goldman JE. Cellular distribution of cwB-crystallin in non-lentricular tissues. J Histochem Cystochem 1990;38:31-39. 6. Jlaskellinen J, Paetau A, Pyykkii I, Blomstedt G, Palva T, Troupp H. Interface between the facial nerve and large acoustic neurinomas-immunohistochemical study of the cleavage plane in NF2 and non-NF2 cases. J Neurosurgery 1994;80:541-7. 7. Kawahara E, Oda Y, Ooi A, Katsuda S, Nakanishi I, Umeda S. Expression of glial fibrillary acidic protein (GFAP) in peripheral nerve sheath tumors. Am J Surg Path01 1988;12:115-20. 8. Louis D, Ramesh V, Gusella J. Neuropathology and molecular genetics of neurofibromatosis 2 and related tumors. Brain Pathology 1995;5:163-72. 9. Luetje C, Whittaker C, Callaway L, Veraga G. Histological acoustic tumor involvement of the VlIth nerve and multicentric origin in the VIIth nerve. Laryngoscope 1983;93:1133-9. 2 (bilateral 10. Martuza R, Eldrige R. Neurofibromatosis acoustic neurofibromatosis) [review]. N Engl J Med 1988;318:684-88. 11. Martuza R, Ojemann R. Bilateral acoustic neuromas: clinical aspects, pathogenesis, and treatment. Neurosurgery 1982;10:1-12. 12. National Institutes of Health. National Institutes of Health Consensus Development Conference, Neurofibromatosis Conference Statement. Arch Neurol 1988;

451575-g.

13. Neely J, Britton B and Greenberg S. Microscopic characteristics of the acoustic tumor in relationship of its nerve origin. Laryngoscope 1976;86:984-91. 14. Neely J. Gross and microscopic anatomy of the eighth cranial nerve in relationship to the solitary schwannoma. Laryngoscope 1981;91:1512-31. 15. Ogawa K, Kanzaki J, Ogawa S, Yamamoto M, Ikeda S, Shiobara R. The growth rate of acoustic neuromas. Acta Otolaryngol Suppl 1991;487:157-63. 16. Rosai J. Soft tissues 1-1547-1633. St. Louis: The C. V. Mosby Company, 1989. 17. Sawa H, Takeshita I, Kuramitsu M, Mannoji H, Machi T, Fukui M, Kitamura K. Neuronal and glial proteins in medulloblastomas: immunohistochemical study. Anticancer Res 1986;6:905-9. 18. Seizinger B, Rouleau G, Ozelius L, Lane A, P. St.

George-Hyslop P, Huson S, Gusella J, Martuza R. Common pathogenetic mechanism for three tumor types in bilateral acoustic neurofibromatosis. Science 1987; 236:317-g. 19. Sobel R, Wang Y. Vestibular (acoustic) schwannomas: histologic features in neurofibromatosis 2 and in unilateral cases. J Neuropathol Exp Neurol 1993;52:10613. 20. Yao D-L, Komoly S, Zhang Q-L, Webster H. Myelinated axons demonstrated in the CNS and PNS by antineurofilament immunoreactivity and 1~x01 fast blue counterstaining. Brain Pathology 1994;4:97-100.

COMMENTARY

This is a most careful histologic study that confirms the usual difference between acoustic (vestibular) schwannomas of NF2 and the solitary acoustics. However, in my own experience, there have been neural fibers within a number of the solitary acoustics, as well as in virtually all of those in NF2. In the solitary acoustics, this has been most frequent in the very large tumors, over 4 cm, and those arising from the inferior vestibular nerve rather than the commonly seen superior vestibular. Some of these large tumors have even extended subpially, requiring removal of brain stem pia for complete resection. I agree that hearing preservation is less frequently achieved in NF2, but I believe that this is most often due to multifascicular origin in these lesions. While resection of some facial fascicles will still permit good facial function, partial resection of auditory fascicles has regularly caused total hearing loss in my patients. Leonard

I. Malis,

M.D.

Neurosurgeon New York, New York