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Early View Article: Online published version of an accepted article before publication in the

final form.

Journal Name: Journal of Case Reports and Images in Pathology

Type of Article: Case Report

Title: Retroperitoneal schwannoma of the sciatic nerve: Case report and diagnostic review

Authors: Alberto Bouzón, Ángela Iglesias, Manuel Gómez, Ángel Álvarez, Juan Mosquera

doi: To be assigned

Early view version published: November 10, 2016

How to cite the article: Bouzón A, Iglesias A, Gómez M, Álvarez A, Mosquera J.

Retroperitoneal schwannoma of the sciatic nerve: Case report and diagnostic review.

Journal of Case Reports and Images in Pathology. Forthcoming 2016.

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Manuscript Accepted Early View Article

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TYPE OF ARTICLE: Case Report 1

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TITLE: Retroperitoneal schwannoma of the sciatic nerve: Case report and 3

diagnostic review 4

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AUTHORS: 6

Alberto Bouzón1, 7

Ángela Iglesias2, 8

Manuel Gómez1, 9

Ángel Álvarez3, 10

Juan Mosquera4 11

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AFFILIATIONS: 13

1Department of Surgery, San Rafael Hospital, A Coruña, Spain 14

2Department of Radiology, San Rafael Hospital, A Coruña, Spain 15

3Department of Plastic Surgery, San Rafael Hospital, A Coruña, Spain 16

4Department of Anatomic Pathology, San Rafael Hospital, A Coruña, Spain 17

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CORRESPONDING AUTHOR DETAILS 19

Dr Alberto Bouzón 20

Department of Surgery, San Rafael Hospital, A Coruña, Spain 21

E-mail: dr.alberto@aecirujanos.es 22

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Short Running Title: MRI in diagnosis of Schwannoma of the sciatic nerve 24

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Guarantor of Submission: The corresponding author is the guarantor of 26

submission 27

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Manuscript Accepted Early View Article

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TITLE: Retroperitoneal schwannoma of the sciatic nerve: Case report and 33

diagnostic review 34

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ABSTRACT 36

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Introduction 38

Schwannomas are usually benign tumors arising from Schwann cells of peripheral 39

nerve sheaths. They are rarely located in the retroperitoneum and usually 40

incidentally diagnosed. Sciatic nerve involvement is unusual. 41

42

Case Report 43

We report a case of schwannoma of the right sciatic nerve in a 39-year-old woman 44

with an incidental diagnosis. Magnetic resonance imaging (MRI) showed a 4.5 cm 45

sciatic nerve dependent lesion located in the right pelvic region. Surgical complete 46

resection of the lesion was performed. Final histopathological exam revealed the 47

tumor to be a schwannoma. 48

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Conclusion 50

Schwannoma of the sciatic nerve can cause a pain in the lower limb similar to 51

chronic sciatica. MRI is helpful in the differential diagnosis. Histopathological exam 52

gives definitive diagnosis. 53

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Keywords: Schwannoma, sciatic nerve, MRI 55

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Manuscript Accepted Early View Article

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TITLE: Retroperitoneal schwannoma of the sciatic nerve: Case report and diagnostic 64

review 65

66

INTRODUCTION 67

Schwannomas are rare tumors arising from Schwann cells of peripheral nerve 68

sheaths. They are usually slow-growing benign tumors and rarely undergo malignant 69

transformation. They occur most often in head, neck, posterior mediastinum and 70

limbs. Retroperitoneal schwannomas account for about 2% of all retroperitoneal 71

tumors [1, 2]. An accurate diagnosis at presentation is important to exclude a 72

malignant retroperitoneal tumor. 73

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CASE REPORT 75

We present the case of a 39-year-old woman with a past medical history of chronic 76

sciatica associated to a herniated. A right pelvic mass of 4.5 cm was incidentally 77

diagnosed by ultrasound examination during a gynecological check. 78

Computed tomography (CT) of the pelvis reported the presence of a 4.5 cm nodular 79

lesion, located deep in the right pelvic region (Figure 1). Magnetic resonance 80

imaging (MRI) showed a dependent right sciatic nerve lesion (Figure 2). The lesion 81

contacted with the anterior surface of the sacrum and medially displaced the right 82

hypogastric artery (Figure 3). 83

A laparotomy to remove the lesion was scheduled. An encapsulated whitish 84

retroperitoneal tumor attached to right sciatic nerve and easily resectable by blunt 85

maneuvers was identified intraoperatively (Figure 4). The gross specimen was a 86

smooth nodular lesion of 5 x 4 cm with soft consistency. The greyish cut surface 87

showed the presence of cystic areas. Microscopic exam revealed a well-88

encapsulated lesion formed by spindle cells with eosinophilic cytoplasma and 89

elongated nuclei without cytologic atypia or pleomorphism arranged in interlacing 90

fascicles (Figure 5 and 6). Immunohistochemical staining showed diffuse positivity of 91

tumor cells for S-100 protein, but was negative for smooth muscle actin (SMA). 92

The patient had pain on the inside of the right foot during the immediate 93

postoperative period. A demyelinating sensory neuropathy of the right posterior tibial 94

nerve was diagnosed by electroneurogram. 95

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DISCUSSION 96

Most retroperitoneal schwannomas are benign, and usually occur in patients 97

between 20 and 50 years [3]. Some studies have reported a higher incidence in 98

women [4, 5]. Sciatic nerve involvement is rare. 99

Pelvic schwannomas are usually diagnosed incidentally, as solitary lesions, although 100

some patients report abdominal pain or chronic sciatica. In case of chronic sciatica 101

with no signs of radicular compression at MRI, the sciatic nerve must be 102

radiologically examined all along its course [6]. Preoperative imaging tests are useful 103

in determining the size, location and relationship of the lesion with neighboring 104

tissues. CT usually reveals a well-circumscribed lesion, with round or oval slight 105

enhancement. Schwannomas are seen as isointense lesions on T1-weighted MRI 106

and hyperintense on T2-weighted MRI. However, many schwannomas may show 107

mix intensity on both T1- and T2-weighted images if they are associated with cystic 108

degeneration, necrosis and (or) haemorrhage within the tumor [7]. Neurofibromas 109

should be considered in the differential diagnosis. An eccentric association with the 110

nerve is suggestive of a schwannoma. 111

The definitive diagnosis of schwannoma is based on histopathologic and 112

immunohistochemical findings [8]. Histologically, they are characterized by 113

alternating areas of high and low cellularity, termed Antoni A and B regions. Mitotic 114

figures are rarely observed. Large tumors often show cystic degeneration. 115

Immunohistochemistry is positive for S-100, neuron specific enolasa and vimentin, 116

but negative for SMA. Schwannomas are easily distinguished from leimyomas or 117

malignant peripheral nerve sheath tumors (NPNSTs). Tumor cells in leiomyomas are 118

negative for S-100, but positive for SMA. NPNSTs have poorly differentiated cells 119

with marked nuclear atypia and frequent mitoses. 120

Surgical treatment represents the only option in symptomatic patients. Management 121

of tumor involves surgical removal by refusing fascicular groups without penetrating 122

them and preserving the continuity of the nerve [9]. Despite the complex location of 123

most of the retroperitoneal tumors, the laparoscopic approach is increasingly used in 124

the management of benign pelvic schwannomas [10]. Schwannomas have a good 125

prognosis and low incidence of recurrence if the removal has been completed. 126

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CONCLUSION 128

Schwannomas of the sciatic nerve can cause pain in the lower limb similar to chronic 129

sciatica. Although these tumors don´t have specific imaging characteristics, 130

radiologic examinations are helpful for achieving a diagnosis. Definitive diagnosis is 131

possible only by histopathologic evaluation after surgical resection of the tumor. 132

133

CONFLICT OF INTEREST 134

Authors report no conflict of interest. 135

136

AUTHOR´S CONTRIBUTIONS 137

A.B., M.G., A.A., 138

Studied and participated on patient´s surgical treatment. 139

140

A.I. 141

Studied on patients´s radiological diagnosis 142

143

J.M 144

Prepared the pathological specimen and studied on pathological diagnosis. 145

146

All authors contributed to conception, design and acquisition of data presented in this 147

paper. 148

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A.B. and M.G 150

Participated in the final approval of the version to be published 151

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REFERENCES 153

1. Takatera H, Takiuchi H, Namiki M, Takaha M, Ohnishi S and Sonoda T. 154

Retroperitoneal schwannoma. Urology. 1986; 28:529-31 155

2. Borghese M, Corigliano N, Gabriele R, Antoniozzi A, Izzo L, Barbaro M,et al. 156

Benign schwannoma of the pelvic retroperitoneum. Report of a case and 157

review of the literature. G Chir. 2000;21:232–8 158

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3. Song JY, Kim SY, Park EG, Kim CJ, Kim do G, Lee HK et al. Schwannoma in 159

the retroperitoneum. J Obstet Gynaecol Res. 2007;33:371-5 160

4. Hughes MJ, Thomas JM, Fisher C and Moskovic EC. Imaging features of 161

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schwannoma. ANZ J Surg. 2007;77:237-40 164

6. Omezzine SJ, Zaara B, Ben Ali M, Abid F, Sassi N, and Hamza HA. A rare 165

cause of non discal sciatica: schwannoma of the sciatic nerve. Orthop 166

Traumatol Surg Res. 2009;95:543-6 167

7. Hayasaka K, Tanaka Y, Soeda S, Huppert P, Claussen CD. MR findings in 168

primary retroperitoneal schwannoma. Acta Radiol. 1999;40:78-82 169

8. Yoshino T and Yoneda K. Laparoscopic resection of a retroperitoneal ancient 170

schwannoma: A case report and review of the literature. Anticancer Res. 171

2008;28:2889-91 172

9. Thiebot J, Laissy JR, Delangre T, Biga N, Liotard A. Benign solitary 173

neurinomas of the sciatic popliteal nerves CT study. Neuroradiology. 174

1991;33:186-8 175

10. Okuyama T, Tagaya N, Saito K, Takahashi S, Shibusawa H, and Oya M. 176

Laparascopic resection of a retroperitoneal pelvic schwannoma. J Surg Case 177

Rep. 2014; pii:rtj122 178

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FIGURE LEGENDS 180

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Figure 1: Contrast enhanced CT scan coronal image: a well-defined hypodense 182

mass within the right hemi-pelvis is noted (arrow). 183

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Figure 2: MRI T2-weighted sagittal image (Fast Spin Echo): well-circumscribed 185

fusiform dependent sciatic nerve mass (arrow).MRI showing an isointense mass with 186

a hyperintense center and a thin hypointense capsule. 187

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Figure 3: MRI T1-weighted axial image: a well-defined hypointense mass (arrow) 189

adjacent to the hypogastric vessels (arrow) is noted. 190

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Figure 4: Macroscopic image: well-encapsulated, whitish and oval lesion. 191

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Figure 5: Microscopic image: Hematoxylin and eosin staining revealed spindle cell 193

proliferation with a palisading pattern. 194

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FIGURES 196

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Figure 1: Contrast enhanced CT scan coronal image: a well-defined hypodense 200

mass within the right hemi-pelvis is noted (arrow). 201

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Figure 2: MRI T2-weighted sagittal image (Fast Spin Echo): well-circumscribed 208

fusiform dependent sciatic nerve mass (arrow).MRI showing an isointense mass with 209

a hyperintense center and a thin hypointense capsule. 210

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Figure 3: MRI T1-weighted axial image: a well-defined hypointense mass (arrow) 226

adjacent to the hypogastric vessels (arrow) is noted. 227

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Figure 4: Macroscopic image: well-encapsulated, whitish and oval lesion. 231

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Figure 5: Microscopic image: Hematoxylin and eosin staining revealed spindle cell 235

proliferation with a palisading pattern (magnification, x10) 236

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Figure 6: Microscopic image: Hematoxylin and eosin staining revealed a well-240

encapsulated lesion without mitoses or atypia (magnification, x4) 241