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Imaging findings of benign peripheral nerve sheath tumor in jaw
Vol. 116 No. 3 September 2013
Imaging findings of benign peripheral nerve sheath tumor in jaw Akiko Imaizumi, DDS, PhD,a Sayaka Kodama, DDS,b Junichiro Sakamoto, DDS, PhD,a Yoshinori Sasaki, DDS,b Mika Otonari-Yamamoto, DDS, PhD,c Ami Kuribayashi, DDS, PhD,d Tohru Kurabayashi, DDS, PhD,e and Tsukasa Sano, DDS, PhDf Tokyo Dental College, Chiba, Japan and Graduate School, Tokyo Medical and Dental University, Tokyo, Japan
Objective. The aim of this study was to investigate the imaging characteristics of peripheral nerve sheath tumors (PNSTs) in the jaw. Study design. Imaging studies of 6 patients were retrospectively reviewed. Conventional radiography, computed tomography, and magnetic resonance imaging were performed in all patients. Results. A fusiform lesion continuous with the nerve was observed in 2 cases, with the tumor arising within the inferior alveolar canal. In the other 4 cases, with the tumor arising outside the canal, the tumor had protruded and eroded into the bone. Protrusion was also present in 1 of the 2 cases, with the tumor arising within the canal. A target or fascicular sign was observed each in 1 case. Conclusions. A fusiform lesion continuous with the nerve and a target or fascicular sign was only present in a few cases. The PNSTs, however, showed a tendency to protrude into the bone. (Oral Surg Oral Med Oral Pathol Oral Radiol 2013;116:369-376)
Benign peripheral nerve sheath tumor (PNST) is divided into 2 groups: schwannoma and neurofibroma. Approximately half of PNSTs occur in the head and neck region. An intraoral origin, however, is unusual.1 The most common site where they occur in the oral cavity is the tongue, whereas other sites include the buccal mucosa, palate, floor of the mouth, gingiva, and lip.2-5 Although extremely rare, PNSTs can also arise in the jaw,2,4 in which case the most frequently affected site is the posterior mandible where the inferior alveolar nerve courses through.6 Clinically, PNSTs generally arise in young patients with a female predilection.6-9 Swelling is the most common symptom, and pain or paresthesia may be present.6-9 Although several reports have described PNSTs arising in the jaw, their imaging features, including those at computed tomography (CT) or magnetic resonance imaging (MRI), remain to be characterized in detail.10-13 Preoperative diagnosis of PNST is important, particularly if adequate information is to be provided to the patient regarding intraoperative risk of nerve damage.
This indicates the need for radiologists to be fully familiar with the imaging characteristics of PNSTs. The purpose of this study was to investigate the imaging characteristics of PNSTs arising in the jaw.
MATERIALS AND METHODS Patients This retrospective study protocol was approved by our Institutional Review Board (No. 362). We retrospectively reviewed imaging studies of 6 patients with PNSTs of the jaw (Table I). The patients comprised 5 men and 1 woman with a mean age of 36 years (range 19-66 years). The histopathologic diagnosis was schwannoma in 4 cases (including 1 case of ancient schwannoma) and neurofibroma in 2 cases. Although 1 case of neurofibroma (case 6) was associated with neurofibromatosis, there was no other lesion in the head and neck region. The site of the tumor was the maxilla in 1 case and the mandible in 5 cases. Of the 5 mandibular lesions, 2 were schwannomas originating within the inferior alveolar canal.
a
Assistant Professor, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. b Graduate Student, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. c Lecturer, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. d Assistant Professor, Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University. e Professor and Chairman, Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University. f Professor and Chairman, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. Received for publication Oct 26, 2012; returned for revision Feb 10, 2013; accepted for publication Jun 12, 2013. Ó 2013 Elsevier Inc. All rights reserved. 2212-4403/$ - see front matter http://dx.doi.org/10.1016/j.oooo.2013.06.010
Imaging Conventional radiography (periapical or panoramic), CT, and MRI were performed in all patients. Periapical radiographs were obtained using Xspot-TW (Asahi Roentgen Ind. Co., Ltd., Kyoto, Japan) operated at 60 kV
Statement of Clinical Relevance In this article, we report the imaging findings of benign peripheral nerve sheath tumor in the jaw, which may be helpful for oral and maxillofacial radiologists in clinical practice. 369
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Table I. Summary of 6 patients with peripheral nerve sheath tumor of the jaw Imaging findings Conventional radiography, CT, MRI
CT
MRI
Shape of lesion Tumor site
Histopathologic diagnosis
Fusiform shape
Protrusion
Schwannoma
þ
Schwannoma
þ
þ
þ
þ
No.
Age/sex
1
34/M
2
66/M
3
33/M
Mandible (Inferior alveolar canal) Mandible (Inferior alveolar canal) Maxilla
4
19/F
Mandible
Schwannoma (Ancient schwannoma) Schwannoma
5
38/M
Mandible
Neurofibroma
þ
6
24/M
Mandible
Neurofibroma (Neurofibromatosis)
þ
Signal intensity Density Homogeneous Low NA* Heterogeneous Low-intermediate Heterogeneous Low-intermediate Heterogeneous Low-intermediate Heterogeneous Low-intermediate
Contrast enhancement NA Heterogeneous NA NA NA Heterogeneous
T1WI
T2WI
Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate
Heterogeneous High Heterogeneous High Heterogeneous Low-high Homogeneous High Homogeneous High Heterogeneous High
Contrast enhancement
Target sign
Fascicular sign
Homogeneous
þ
Heterogeneous
þ
Peripheral
Homogeneous
Peripheral
NA
NA, not available; T1WI, T1-weighted image; T2WI, T2-weighted image. *Precontrast CT images were not obtained.
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Fig. 1. Case 1: A 34-year-old man with schwannoma in the left mandible (inferior alveolar canal). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion expands the left inferior alveolar canal in a fusiform shape. CT image demonstrates a fusiform lesion continuous with the inferior alveolar canal in the left mandible. MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hyperintensity on T2-weighted image, and homogeneous enhancement on contrast-enhanced T1-weighted image. On T2-weighted image, signal intensity of the central area of a lesion is lower than that of the peripheral area, representing the target sign.
and 6 mA. Panoramic radiographs were obtained using Hyper-XF (Asahi Roentgen Ind. Co., Ltd.) or Super Veraviewepocs (Morita Corp., Kyoto, Japan) operated at 70 kV and 6 mA. CT was performed using Somatom Plus 4 (Siemens Medical Systems, Erlangen, Germany) or Somatom Sensation 64 (Siemens Medical Systems) operated at 120 kV and 130 mA. Axial images of 3-5 mm thickness were obtained with both soft tissue and bone algorithms. Multiplanar reconstructed images were also obtained. Intravenous contrast agent was administered in 2 patients. MRI was performed using a 1.5-T unit (Magnetom Vision; Siemens Medical Systems, Erlangen, Germany or Magnetom Symphony Maestro Class; Siemens Medical Systems) with a head and neck coil. T1weighted spin-echo (repetition time (TR) 500-700 ms, echo time (TE) 10-15 ms) and T2-weighted fast spinecho images (TR 3000-5000 ms, TE 80-110 ms, echo train length 7-19) with fat saturation were obtained in the axial, coronal, and sagittal planes. In 5 patients, axial, coronal, and sagittal postcontrast T1-weighted spin-echo images (TR 500-700 ms, TE 10-15 ms) with fat saturation were also obtained. All magnetic resonance (MR) images were obtained with a 3-5-mm section thickness and a 0.3-1.0-mm intersection gap. Evaluation of images Two oral radiologists reviewed the images. The shape of the lesion was evaluated on conventional radiographs,
CT, and MR images. On the CT images, the density of the lesion was also evaluated. On the MR images, the signal intensity of the lesion and the presence of target or fascicular signs were also determined. Target and fascicular signs are characteristic MRI findings in PNSTs.14 The target sign appears as a hypointense central area surrounded by a hyperintense area on T2-weighted images. The fascicular sign manifests as multiple small hypointense foci within a hyperintense lesion on T2weighted images.
RESULTS Images of the 6 patients are shown in Figures 1-6, and their imaging findings are summarized in Table I. Shape of lesion A fusiform lesion continuous with the nerve was observed in 2 cases, with the tumor arising within the inferior alveolar canal (cases 1 and 2) (Figures 1 and 2). In the other 4 cases, although no continuity with the nerve was apparent, the tumor had protruded and eroded into the bone (cases 3-6) (Figures 3-6). This protrusion was also observed in case 2, with the tumor arising within the canal (Figure 2). Density on CT images and signal intensity on MR images On CT images, the lesion was heterogeneously hypo to isodense compared with the muscles in 4 cases
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Fig. 2. Case 2: A 66-year-old man with schwannoma in the right mandible (inferior alveolar canal). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Oblique sagittal MR image (contrast-enhanced T1-weighted image with fat saturation). (D) Coronal MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrastenhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates partially ill-defined radiolucent lesion in the right mandible. Lesion expands the right inferior alveolar canal in a fusiform shape. Lesion protrudes and erodes into the bone in a superior direction (arrows). CT and oblique sagittal MR images demonstrate a fusiform lesion continuous with the inferior alveolar canal in the right mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hyperintensity on T2-weighted image, and heterogeneous enhancement on contrast-enhanced T1-weighted image. On T2-weighted image, there are multiple small hypointense foci within hyperintense lesion, representing the fascicular sign.
Fig. 3. Case 3: A 33-year-old man with ancient schwannoma in the left maxilla. (A) Axial CT images (left: bone algorithm; right: soft tissue algorithm). (B) Sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). On CT images, lesion protrudes and erodes into the bone in an anterior direction (arrows). Lesion shows heterogeneous hypo to isodensity compared with muscles. MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hypo to hyperintensity on T2-weighted image, and peripheral enhancement on contrast-enhanced T1-weighted image.
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Fig. 4. Case 4: A 19-year-old woman with schwannoma in the left mandible. (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, homogeneous hyperintensity on T2-weighted image, and homogeneous enhancement on contrast-enhanced T1-weighted image.
(Figure 3), and homogeneously hypodense in 1 case. Contrast enhancement was heterogeneous in both cases. On T1-weighted images, the lesion was homogeneously isointense compared with the muscles in all 6 cases (Figures 1-6). On T2-weighted images, the lesion was heterogeneously hyperintense in 3 cases (Figures 1, 2, and 6), homogeneously hyperintense in 2 cases (Figures 4 and 5), and heterogeneously hypo to hyperintense in 1 case with ancient schwannoma (Figure 3). Contrast enhancement was homogeneous in 2 cases (Figures 1 and 4), and heterogeneous in 1 case (Figure 2). In the other 2 cases, contrast enhancement was observed only peripherally (Figures 3 and 5). Target and fascicular signs A target or fascicular sign was present each in 1 case. Both were tumors originating within the inferior alveolar canal (cases 1 and 2) (Figures 1 and 2).
DISCUSSION We have reported the imaging findings in 6 cases of PNSTs arising in the jaw. In 2 of these cases, the PNST originated within the inferior alveolar canal, whereas in the other 4 cases, it originated outside the canal. All tumors were surgically resected. The nerve of origin was intraoperatively confirmed to be the inferior alveolar nerve in the 2 cases with the tumor arising within the canal, but could not be identified in the other
4 cases. Clinically, PNSTs can occur at any age but generally arise in young patients.6-9 There is a female predilection.6-8 Swelling is the most common symptom, and pain or paresthesia may be present.6-9,13,15 However, some patients have no symptom.8 In this study, swelling was observed in 2 patients, pain in 2 patients, both swelling and pain in 1 patient, and no symptom in 1 patient. A fusiform lesion continuous with the nerve is considered as a strong indicator of a diagnosis of PNST.14,16-18 In this study, fusiform lesions continuous with the nerve were only observed in 2 cases, with the tumor arising within the inferior alveolar canal (cases 1 and 2). Although the other 4 lesions arising outside the canal did not show this characteristic, they did show protrusion and erosion into the bone (cases 3-6). Protrusion and erosion was also observed in 1 of the cases in which the tumor had arisen within the canal (case 2). This imaging finding appears to indicate growth of the tumor along the intraosseous nerve. In this study, the tumor had protruded into the interdental septa in all 5 cases in which protrusion was present. This suggests that the tumor had developed along the gingival rami arising from the superior or inferior alveolar nerve. The gingival rami run through the interdental septa and innervate the gingiva and periodontal ligament. On conventional radiographs, PNSTs arising within the inferior alveolar canal expand the canal in
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Fig. 5. Case 5: A 38-year-old man with neurofibroma in the left mandible. (A) Periapical radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrastenhanced T1-weighted image with fat saturation). Periapical radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, homogeneous hyperintensity on T2-weighted image, and peripheral enhancement on contrast-enhanced T1-weighted image.
a fusiform shape and enlarge the foramen if they reach either the mandibular or mental foramen.7-9,19 These imaging findings suggest a neural origin. In this study, the tumors arising within the canal had expanded the canal in a fusiform shape, and the diagnosis of PNST was not difficult. On the other hand, it has been reported that tumors arising outside the canal appear as a well- or ill-defined, uni or multilocular radiolucency.6-8 This radiographic appearance is nonspecific, and the diagnosis of PNST on conventional radiographs is difficult. However, as protrusion can be demonstrated on conventional radiographs, it may be useful in the diagnosis of PNST. To the best of our knowledge, CT and MRI findings have only been reported in 5 cases of benign PNST in the jaw.10-13 CT and MRI findings of PNSTs in the soft tissue have been reported in more detail than those of PNSTs in the jaw. In the soft tissue, a PNST shows hypo to isodensity compared with the muscles, and homogeneous or heterogeneous contrast enhancement on CT images.14,16-21,25-31 The signal intensity of the lesion is homogeneously isointense compared with the muscles on T1-weighted images and homogeneously or heterogeneously hyperintense on T2-weighted images.22-24
On contrast-enhanced MR images, homogeneous, heterogeneous, peripheral, or central contrast enhancement is seen.14,16,17-21,25-31 It is known that, with increase in size, a schwannoma tends to undergo degenerative change, and its internal appearance becomes heterogeneous.14,16,17,19,20,28-31 A long-standing lesion showing marked degenerative change is referred to as an ancient schwannoma. In this study, the case of ancient schwannoma showed considerably heterogeneous density and signal intensity. The density on CT images and signal intensity on MR images in the present study were consistent with those in previous studies, but nonspecific. Target and fascicular signs are known as characteristic MRI findings in PNSTs.14 In this study, the target or fascicular sign was only observed each in 1 case and both were schwannomas arising within the inferior alveolar canal (cases 1 and 2). The target sign appears as a central hypointense area surrounded by a hyperintense area on T2-weighted images. Histopathologically, the peripheral area corresponds to hypocellular myxoid tissue, and the central area to hypercellular fibrous tissue.14,32 It has been reported that the target sign is present in 25%-52% of benign PNSTs, but it is less
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Fig. 6. Case 6: A 24-year-old man with neurofibroma in the left mandible (associated with neurofibromatosis). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; right: T2-weighted image with fat saturation). Panoramic radiograph demonstrates partially ill-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image and heterogeneous hyperintensity on T2-weighted image (arrows). As tumor is accompanied by inflammation, surrounding bone marrow shows hypointensity on T1-weighted image and hyperintensity on T2-weighted image.
commonly present in tumors with degenerative change or malignant PNSTs.14,18,27,33,34 The fascicular sign manifests as multiple small hypointense foci within a hyperintense lesion on T2-weighted images. This appearance corresponds to the fascicular bundles seen pathologically in neurogenic tumors, particularly in more differentiated benign PNSTs. It has been reported that the fascicular sign is present in 35%-54% of benign PNSTs.14,18,20,27 In this study, the target and fascicular signs were not as frequently observed as in previous studies on PNSTs in the soft tissue. These signs were absent in the tumor with marked degenerative change (case 3) and the small tumors restricted to the alveolar bone (cases 4-6). We did not distinguish between schwannoma and neurofibroma in this study. Most neurofibromas are solitary, but approximately 10% are associated with neurofibromatosis. If neurofibroma is associated with neurofibromatosis, there is a markedly increased risk of malignant transformation.6,16,20,32 In this study, 1 case was associated with neurofibromatosis (case 6). Jee et al. investigated whether MRI allowed discrimination between schwannomas and neurofibromas and reported that, although MRI findings were helpful for differentiation, definitive differentiation was impossible.27
In conclusion, a fusiform lesion continuous with the nerve and a target or fascicular sign was observed in only a few cases. Moreover, the density on CT images and signal intensity on MR images were nonspecific. On the other hand, there was a tendency for protrusion into the bone. This imaging finding appears to indicate the growth of the tumor along the intraosseous nerve. We would like to thank Associate Professor Jeremy Williams, Tokyo Dental College, for his assistance with the English of this manuscript. REFERENCES 1. Das Gupta TK, Brasfield RD, Strong EW, Hajdu SI. Benign solitary schwannomas (neurilemomas). Cancer. 1969;24:355-366. 2. Wright BA, Jackson D. Neural tumors of the oral cavity. A review of the spectrum of benign and malignant oral tumors of the oral cavity and jaws. Oral Surg Oral Med Oral Pathol. 1980;49: 509-522. 3. Hatziotis JC, Asprides H. Neurilemoma (schwannoma) of the oral cavity. Oral Surg Oral Med Oral Pathol. 1967;24:510-526. 4. Chen SY, Miller AS. Neurofibroma and schwannoma of the oral cavity. A clinical and ultrastructural study. Oral Surg Oral Med Oral Pathol. 1979;47:522-528. 5. Cherrick HM, Eversole LR. Benign neural sheath neoplasm of the oral cavity. Report of thirty-seven cases. Oral Surg Oral Med Oral Pathol. 1971;32:900-909.
ORAL AND MAXILLOFACIAL RADIOLOGY 376 Imaizumi et al. 6. Ellis GL, Abrams AM, Melrose RJ. Intraosseous benign neural sheath neoplasms of the jaws. Report of seven new cases and review of the literature. Oral Surg Oral Med Oral Pathol. 1977;44:731-743. 7. Polak M, Polak G, Brocheriou C, Vigneul J. Solitary neurofibroma of the mandible: case report and review of the literature. J Oral Maxillofac Surg. 1989;47:65-68. 8. Chi AC, Carey J, Muller S. Intraosseous schwannoma of the mandible: a case report and review of the literature. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003;96:54-65. 9. White SC, Pharoah MJ. Benign tumors of the jaws. In: White SC, Pharoah MJ, eds. Oral Radiology: Principles and Interpretation. 6th ed. St. Louis: Mosby; 2009:366-404. 10. Nakasato T, Katoh K, Ehara S, et al. Intraosseous neurilemmoma of the mandible. AJNR Am J Neuroradiol. 2000;21:1945-1947. 11. Minowa K, Sakakibara N, Yoshikawa K, et al. CT and MRI findings of intraosseous schwannoma of the mandible: a case report. Dentomaxillofac Radiol. 2007;36:113-116. 12. Park YK, Kim YW, Yang MH, Kim EJ, Ryu DM. Neurilemmoma of the mandible. Skeletal Radiol. 1999;28:536-539. 13. Che Z, Nam W, Park WS, et al. Intraosseous nerve sheath tumors in the jaws. Yonsei Med J. 2006;47:264-270. 14. Murphey MD, Smith WS, Smith SE, Kransdorf MJ, Temple HT. From the archives of the AFIP. Imaging of musculoskeletal neurogenic tumors: radiologicepathologic correlation. Radiographics. 1999;19:1253-1280. 15. Zainab H, Kale AD, Hallikerimath S. Intraosseous schwannoma of the mandible. J Oral Maxillofac Pathol. 2012;16:294-296. 16. Lin J, Martel W. Cross-sectional imaging of peripheral nerve sheath tumors: characteristic signs on CT, MR imaging, and sonography. AJR Am J Roentgenol. 2001;176:75-82. 17. Pilavaki M, Chourmouzi D, Kiziridou A, Skordalaki A, Zarampoukas T, Drevelengas A. Imaging of peripheral nerve sheath tumors with pathologic correlation: pictorial review. Eur J Radiol. 2004;52:229-239. 18. Li CS, Huang GS, Wu HD, et al. Differentiation of soft tissue benign and malignant peripheral nerve sheath tumors with magnetic resonance imaging. Clin Imaging. 2008;32:121-127. 19. Curé JK. Schwannoma, V3 (MS). In: Harnsberger HR, ed. Diagnostic Imaging. Head and Neck. Salt Lake City: Amirsys Inc; 2004:III-6-16. 20. Sakai O, ed. Head and Neck Imaging Cases. New York: The McGraw-Hill Companies, Inc; 2011:537-644, 745-822. 21. Yamazaki H, Kaneko A, Ota Y, Tsukinoki K. Schwannoma of the mental nerve: usefulness of preoperative imaging: a case report.
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Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2004;97: 122-126. López-Carriches C, Baca-Pérez-Bryan R, Montalvo-Montero S. Schwannoma located in the palate: clinical case and literature review. Med Oral Patol Oral Cir Bucal. 2009;14:e465-e468. Asaumi J, Konouchi H, Kishi K. Schwannoma of the upper lip: ultrasound, CT, and MRI findings. J Oral Maxillofac Surg. 2000;58:1173-1175. Kami Y, Chikui T, Okamura K, et al. Imaging findings of neurogenic tumours in the head and neck region. Dentomaxillofac Radiol. 2012;41:18-23. Iida S, Aikawa T, Kishino M, et al. Spheric mass beneath the alar base: MR images of nasolabial cyst and schwannoma. AJNR Am J Neuroradiol. 2006;27:1826-1829. Shimizu K, Iwai H, Ikeda K, Sakaida N, Sawada S. Intraparotid facial nerve schwannoma: a report of five cases and an analysis of MR imaging results. AJNR Am J Neuroradiol. 2005;26: 1328-1330. Jee WH, Oh SN, McCauley T, et al. Extraaxial neurofibromas versus neurilemmomas: discrimination with MRI. AJR Am J Roentgenol. 2004;183:629-633. Gomez-Brouchet A, Delisle MB, Cognard C, et al. Vestibular schwannomas: correlations between magnetic resonance imaging and histopathologic appearance. Otol Neurotol. 2001;22:79-86. Wakoh M, Yonezu H, Otonari T, et al. Two cases of schwannoma with marked cystic changes. Dentomaxillofac Radiol. 2005;34: 44-50. Kawakami R, Kaneko T, Kadoya M, et al. Schwannoma in the sublingual space. Dentomaxillofac Radiol. 2004;33:259-261. Isobe K, Shimizu T, Akahane T, Kato H. Imaging of ancient schwannoma. AJR Am J Roentgenol. 2004;183:331-336. Banks KP. The target sign: extremity. Radiology. 2005;234:899-900. Shimose S, Sugita T, Kubo T, et al. Major-nerve schwannomas versus intramuscular schwannomas. Acta Radiol. 2007;48:672-677. Varma DG, Moulopoulos A, Sara AS, et al. MR imaging of extracranial nerve sheath tumors. J Comput Assist Tomogr. 1992;16:448-453.
Reprint requests: Akiko Imaizumi, DDS, PhD Department of Oral and Maxillofacial Radiology Tokyo Dental College, Masago 1-2-2 Mihama-ku, Chiba 261-8502, Japan [email protected]
Imaging findings of benign peripheral nerve sheath tumor in jaw Akiko Imaizumi, DDS, PhD,a Sayaka Kodama, DDS,b Junichiro Sakamoto, DDS, PhD,a Yoshinori Sasaki, DDS,b Mika Otonari-Yamamoto, DDS, PhD,c Ami Kuribayashi, DDS, PhD,d Tohru Kurabayashi, DDS, PhD,e and Tsukasa Sano, DDS, PhDf Tokyo Dental College, Chiba, Japan and Graduate School, Tokyo Medical and Dental University, Tokyo, Japan
Objective. The aim of this study was to investigate the imaging characteristics of peripheral nerve sheath tumors (PNSTs) in the jaw. Study design. Imaging studies of 6 patients were retrospectively reviewed. Conventional radiography, computed tomography, and magnetic resonance imaging were performed in all patients. Results. A fusiform lesion continuous with the nerve was observed in 2 cases, with the tumor arising within the inferior alveolar canal. In the other 4 cases, with the tumor arising outside the canal, the tumor had protruded and eroded into the bone. Protrusion was also present in 1 of the 2 cases, with the tumor arising within the canal. A target or fascicular sign was observed each in 1 case. Conclusions. A fusiform lesion continuous with the nerve and a target or fascicular sign was only present in a few cases. The PNSTs, however, showed a tendency to protrude into the bone. (Oral Surg Oral Med Oral Pathol Oral Radiol 2013;116:369-376)
Benign peripheral nerve sheath tumor (PNST) is divided into 2 groups: schwannoma and neurofibroma. Approximately half of PNSTs occur in the head and neck region. An intraoral origin, however, is unusual.1 The most common site where they occur in the oral cavity is the tongue, whereas other sites include the buccal mucosa, palate, floor of the mouth, gingiva, and lip.2-5 Although extremely rare, PNSTs can also arise in the jaw,2,4 in which case the most frequently affected site is the posterior mandible where the inferior alveolar nerve courses through.6 Clinically, PNSTs generally arise in young patients with a female predilection.6-9 Swelling is the most common symptom, and pain or paresthesia may be present.6-9 Although several reports have described PNSTs arising in the jaw, their imaging features, including those at computed tomography (CT) or magnetic resonance imaging (MRI), remain to be characterized in detail.10-13 Preoperative diagnosis of PNST is important, particularly if adequate information is to be provided to the patient regarding intraoperative risk of nerve damage.
This indicates the need for radiologists to be fully familiar with the imaging characteristics of PNSTs. The purpose of this study was to investigate the imaging characteristics of PNSTs arising in the jaw.
MATERIALS AND METHODS Patients This retrospective study protocol was approved by our Institutional Review Board (No. 362). We retrospectively reviewed imaging studies of 6 patients with PNSTs of the jaw (Table I). The patients comprised 5 men and 1 woman with a mean age of 36 years (range 19-66 years). The histopathologic diagnosis was schwannoma in 4 cases (including 1 case of ancient schwannoma) and neurofibroma in 2 cases. Although 1 case of neurofibroma (case 6) was associated with neurofibromatosis, there was no other lesion in the head and neck region. The site of the tumor was the maxilla in 1 case and the mandible in 5 cases. Of the 5 mandibular lesions, 2 were schwannomas originating within the inferior alveolar canal.
a
Assistant Professor, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. b Graduate Student, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. c Lecturer, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. d Assistant Professor, Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University. e Professor and Chairman, Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University. f Professor and Chairman, Department of Oral and Maxillofacial Radiology, Tokyo Dental College. Received for publication Oct 26, 2012; returned for revision Feb 10, 2013; accepted for publication Jun 12, 2013. Ó 2013 Elsevier Inc. All rights reserved. 2212-4403/$ - see front matter http://dx.doi.org/10.1016/j.oooo.2013.06.010
Imaging Conventional radiography (periapical or panoramic), CT, and MRI were performed in all patients. Periapical radiographs were obtained using Xspot-TW (Asahi Roentgen Ind. Co., Ltd., Kyoto, Japan) operated at 60 kV
Statement of Clinical Relevance In this article, we report the imaging findings of benign peripheral nerve sheath tumor in the jaw, which may be helpful for oral and maxillofacial radiologists in clinical practice. 369
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Table I. Summary of 6 patients with peripheral nerve sheath tumor of the jaw Imaging findings Conventional radiography, CT, MRI
CT
MRI
Shape of lesion Tumor site
Histopathologic diagnosis
Fusiform shape
Protrusion
Schwannoma
þ
Schwannoma
þ
þ
þ
þ
No.
Age/sex
1
34/M
2
66/M
3
33/M
Mandible (Inferior alveolar canal) Mandible (Inferior alveolar canal) Maxilla
4
19/F
Mandible
Schwannoma (Ancient schwannoma) Schwannoma
5
38/M
Mandible
Neurofibroma
þ
6
24/M
Mandible
Neurofibroma (Neurofibromatosis)
þ
Signal intensity Density Homogeneous Low NA* Heterogeneous Low-intermediate Heterogeneous Low-intermediate Heterogeneous Low-intermediate Heterogeneous Low-intermediate
Contrast enhancement NA Heterogeneous NA NA NA Heterogeneous
T1WI
T2WI
Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate Homogeneous Intermediate
Heterogeneous High Heterogeneous High Heterogeneous Low-high Homogeneous High Homogeneous High Heterogeneous High
Contrast enhancement
Target sign
Fascicular sign
Homogeneous
þ
Heterogeneous
þ
Peripheral
Homogeneous
Peripheral
NA
NA, not available; T1WI, T1-weighted image; T2WI, T2-weighted image. *Precontrast CT images were not obtained.
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Fig. 1. Case 1: A 34-year-old man with schwannoma in the left mandible (inferior alveolar canal). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion expands the left inferior alveolar canal in a fusiform shape. CT image demonstrates a fusiform lesion continuous with the inferior alveolar canal in the left mandible. MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hyperintensity on T2-weighted image, and homogeneous enhancement on contrast-enhanced T1-weighted image. On T2-weighted image, signal intensity of the central area of a lesion is lower than that of the peripheral area, representing the target sign.
and 6 mA. Panoramic radiographs were obtained using Hyper-XF (Asahi Roentgen Ind. Co., Ltd.) or Super Veraviewepocs (Morita Corp., Kyoto, Japan) operated at 70 kV and 6 mA. CT was performed using Somatom Plus 4 (Siemens Medical Systems, Erlangen, Germany) or Somatom Sensation 64 (Siemens Medical Systems) operated at 120 kV and 130 mA. Axial images of 3-5 mm thickness were obtained with both soft tissue and bone algorithms. Multiplanar reconstructed images were also obtained. Intravenous contrast agent was administered in 2 patients. MRI was performed using a 1.5-T unit (Magnetom Vision; Siemens Medical Systems, Erlangen, Germany or Magnetom Symphony Maestro Class; Siemens Medical Systems) with a head and neck coil. T1weighted spin-echo (repetition time (TR) 500-700 ms, echo time (TE) 10-15 ms) and T2-weighted fast spinecho images (TR 3000-5000 ms, TE 80-110 ms, echo train length 7-19) with fat saturation were obtained in the axial, coronal, and sagittal planes. In 5 patients, axial, coronal, and sagittal postcontrast T1-weighted spin-echo images (TR 500-700 ms, TE 10-15 ms) with fat saturation were also obtained. All magnetic resonance (MR) images were obtained with a 3-5-mm section thickness and a 0.3-1.0-mm intersection gap. Evaluation of images Two oral radiologists reviewed the images. The shape of the lesion was evaluated on conventional radiographs,
CT, and MR images. On the CT images, the density of the lesion was also evaluated. On the MR images, the signal intensity of the lesion and the presence of target or fascicular signs were also determined. Target and fascicular signs are characteristic MRI findings in PNSTs.14 The target sign appears as a hypointense central area surrounded by a hyperintense area on T2-weighted images. The fascicular sign manifests as multiple small hypointense foci within a hyperintense lesion on T2weighted images.
RESULTS Images of the 6 patients are shown in Figures 1-6, and their imaging findings are summarized in Table I. Shape of lesion A fusiform lesion continuous with the nerve was observed in 2 cases, with the tumor arising within the inferior alveolar canal (cases 1 and 2) (Figures 1 and 2). In the other 4 cases, although no continuity with the nerve was apparent, the tumor had protruded and eroded into the bone (cases 3-6) (Figures 3-6). This protrusion was also observed in case 2, with the tumor arising within the canal (Figure 2). Density on CT images and signal intensity on MR images On CT images, the lesion was heterogeneously hypo to isodense compared with the muscles in 4 cases
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Fig. 2. Case 2: A 66-year-old man with schwannoma in the right mandible (inferior alveolar canal). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Oblique sagittal MR image (contrast-enhanced T1-weighted image with fat saturation). (D) Coronal MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrastenhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates partially ill-defined radiolucent lesion in the right mandible. Lesion expands the right inferior alveolar canal in a fusiform shape. Lesion protrudes and erodes into the bone in a superior direction (arrows). CT and oblique sagittal MR images demonstrate a fusiform lesion continuous with the inferior alveolar canal in the right mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hyperintensity on T2-weighted image, and heterogeneous enhancement on contrast-enhanced T1-weighted image. On T2-weighted image, there are multiple small hypointense foci within hyperintense lesion, representing the fascicular sign.
Fig. 3. Case 3: A 33-year-old man with ancient schwannoma in the left maxilla. (A) Axial CT images (left: bone algorithm; right: soft tissue algorithm). (B) Sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). On CT images, lesion protrudes and erodes into the bone in an anterior direction (arrows). Lesion shows heterogeneous hypo to isodensity compared with muscles. MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, heterogeneous hypo to hyperintensity on T2-weighted image, and peripheral enhancement on contrast-enhanced T1-weighted image.
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Fig. 4. Case 4: A 19-year-old woman with schwannoma in the left mandible. (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrast-enhanced T1-weighted image with fat saturation). Panoramic radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, homogeneous hyperintensity on T2-weighted image, and homogeneous enhancement on contrast-enhanced T1-weighted image.
(Figure 3), and homogeneously hypodense in 1 case. Contrast enhancement was heterogeneous in both cases. On T1-weighted images, the lesion was homogeneously isointense compared with the muscles in all 6 cases (Figures 1-6). On T2-weighted images, the lesion was heterogeneously hyperintense in 3 cases (Figures 1, 2, and 6), homogeneously hyperintense in 2 cases (Figures 4 and 5), and heterogeneously hypo to hyperintense in 1 case with ancient schwannoma (Figure 3). Contrast enhancement was homogeneous in 2 cases (Figures 1 and 4), and heterogeneous in 1 case (Figure 2). In the other 2 cases, contrast enhancement was observed only peripherally (Figures 3 and 5). Target and fascicular signs A target or fascicular sign was present each in 1 case. Both were tumors originating within the inferior alveolar canal (cases 1 and 2) (Figures 1 and 2).
DISCUSSION We have reported the imaging findings in 6 cases of PNSTs arising in the jaw. In 2 of these cases, the PNST originated within the inferior alveolar canal, whereas in the other 4 cases, it originated outside the canal. All tumors were surgically resected. The nerve of origin was intraoperatively confirmed to be the inferior alveolar nerve in the 2 cases with the tumor arising within the canal, but could not be identified in the other
4 cases. Clinically, PNSTs can occur at any age but generally arise in young patients.6-9 There is a female predilection.6-8 Swelling is the most common symptom, and pain or paresthesia may be present.6-9,13,15 However, some patients have no symptom.8 In this study, swelling was observed in 2 patients, pain in 2 patients, both swelling and pain in 1 patient, and no symptom in 1 patient. A fusiform lesion continuous with the nerve is considered as a strong indicator of a diagnosis of PNST.14,16-18 In this study, fusiform lesions continuous with the nerve were only observed in 2 cases, with the tumor arising within the inferior alveolar canal (cases 1 and 2). Although the other 4 lesions arising outside the canal did not show this characteristic, they did show protrusion and erosion into the bone (cases 3-6). Protrusion and erosion was also observed in 1 of the cases in which the tumor had arisen within the canal (case 2). This imaging finding appears to indicate growth of the tumor along the intraosseous nerve. In this study, the tumor had protruded into the interdental septa in all 5 cases in which protrusion was present. This suggests that the tumor had developed along the gingival rami arising from the superior or inferior alveolar nerve. The gingival rami run through the interdental septa and innervate the gingiva and periodontal ligament. On conventional radiographs, PNSTs arising within the inferior alveolar canal expand the canal in
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Fig. 5. Case 5: A 38-year-old man with neurofibroma in the left mandible. (A) Periapical radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; center: T2-weighted image with fat saturation; right: contrastenhanced T1-weighted image with fat saturation). Periapical radiograph demonstrates a well-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image, homogeneous hyperintensity on T2-weighted image, and peripheral enhancement on contrast-enhanced T1-weighted image.
a fusiform shape and enlarge the foramen if they reach either the mandibular or mental foramen.7-9,19 These imaging findings suggest a neural origin. In this study, the tumors arising within the canal had expanded the canal in a fusiform shape, and the diagnosis of PNST was not difficult. On the other hand, it has been reported that tumors arising outside the canal appear as a well- or ill-defined, uni or multilocular radiolucency.6-8 This radiographic appearance is nonspecific, and the diagnosis of PNST on conventional radiographs is difficult. However, as protrusion can be demonstrated on conventional radiographs, it may be useful in the diagnosis of PNST. To the best of our knowledge, CT and MRI findings have only been reported in 5 cases of benign PNST in the jaw.10-13 CT and MRI findings of PNSTs in the soft tissue have been reported in more detail than those of PNSTs in the jaw. In the soft tissue, a PNST shows hypo to isodensity compared with the muscles, and homogeneous or heterogeneous contrast enhancement on CT images.14,16-21,25-31 The signal intensity of the lesion is homogeneously isointense compared with the muscles on T1-weighted images and homogeneously or heterogeneously hyperintense on T2-weighted images.22-24
On contrast-enhanced MR images, homogeneous, heterogeneous, peripheral, or central contrast enhancement is seen.14,16,17-21,25-31 It is known that, with increase in size, a schwannoma tends to undergo degenerative change, and its internal appearance becomes heterogeneous.14,16,17,19,20,28-31 A long-standing lesion showing marked degenerative change is referred to as an ancient schwannoma. In this study, the case of ancient schwannoma showed considerably heterogeneous density and signal intensity. The density on CT images and signal intensity on MR images in the present study were consistent with those in previous studies, but nonspecific. Target and fascicular signs are known as characteristic MRI findings in PNSTs.14 In this study, the target or fascicular sign was only observed each in 1 case and both were schwannomas arising within the inferior alveolar canal (cases 1 and 2). The target sign appears as a central hypointense area surrounded by a hyperintense area on T2-weighted images. Histopathologically, the peripheral area corresponds to hypocellular myxoid tissue, and the central area to hypercellular fibrous tissue.14,32 It has been reported that the target sign is present in 25%-52% of benign PNSTs, but it is less
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Fig. 6. Case 6: A 24-year-old man with neurofibroma in the left mandible (associated with neurofibromatosis). (A) Panoramic radiograph. (B) Oblique sagittal CT image (bone algorithm). (C) Axial MR images (left: T1-weighted image; right: T2-weighted image with fat saturation). Panoramic radiograph demonstrates partially ill-defined radiolucent lesion in the left mandible. Lesion protrudes and erodes into the bone in the superior direction (arrows). CT image demonstrates a lesion protruding and eroding into the bone in the superior direction (arrows). MR images demonstrate a lesion with homogeneous isointensity compared with muscles on T1-weighted image and heterogeneous hyperintensity on T2-weighted image (arrows). As tumor is accompanied by inflammation, surrounding bone marrow shows hypointensity on T1-weighted image and hyperintensity on T2-weighted image.
commonly present in tumors with degenerative change or malignant PNSTs.14,18,27,33,34 The fascicular sign manifests as multiple small hypointense foci within a hyperintense lesion on T2-weighted images. This appearance corresponds to the fascicular bundles seen pathologically in neurogenic tumors, particularly in more differentiated benign PNSTs. It has been reported that the fascicular sign is present in 35%-54% of benign PNSTs.14,18,20,27 In this study, the target and fascicular signs were not as frequently observed as in previous studies on PNSTs in the soft tissue. These signs were absent in the tumor with marked degenerative change (case 3) and the small tumors restricted to the alveolar bone (cases 4-6). We did not distinguish between schwannoma and neurofibroma in this study. Most neurofibromas are solitary, but approximately 10% are associated with neurofibromatosis. If neurofibroma is associated with neurofibromatosis, there is a markedly increased risk of malignant transformation.6,16,20,32 In this study, 1 case was associated with neurofibromatosis (case 6). Jee et al. investigated whether MRI allowed discrimination between schwannomas and neurofibromas and reported that, although MRI findings were helpful for differentiation, definitive differentiation was impossible.27
In conclusion, a fusiform lesion continuous with the nerve and a target or fascicular sign was observed in only a few cases. Moreover, the density on CT images and signal intensity on MR images were nonspecific. On the other hand, there was a tendency for protrusion into the bone. This imaging finding appears to indicate the growth of the tumor along the intraosseous nerve. We would like to thank Associate Professor Jeremy Williams, Tokyo Dental College, for his assistance with the English of this manuscript. REFERENCES 1. Das Gupta TK, Brasfield RD, Strong EW, Hajdu SI. Benign solitary schwannomas (neurilemomas). Cancer. 1969;24:355-366. 2. Wright BA, Jackson D. Neural tumors of the oral cavity. A review of the spectrum of benign and malignant oral tumors of the oral cavity and jaws. Oral Surg Oral Med Oral Pathol. 1980;49: 509-522. 3. Hatziotis JC, Asprides H. Neurilemoma (schwannoma) of the oral cavity. Oral Surg Oral Med Oral Pathol. 1967;24:510-526. 4. Chen SY, Miller AS. Neurofibroma and schwannoma of the oral cavity. A clinical and ultrastructural study. Oral Surg Oral Med Oral Pathol. 1979;47:522-528. 5. Cherrick HM, Eversole LR. Benign neural sheath neoplasm of the oral cavity. Report of thirty-seven cases. Oral Surg Oral Med Oral Pathol. 1971;32:900-909.
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Reprint requests: Akiko Imaizumi, DDS, PhD Department of Oral and Maxillofacial Radiology Tokyo Dental College, Masago 1-2-2 Mihama-ku, Chiba 261-8502, Japan [email protected]