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Dentomaxillofacial Radiology (2002) 31, 344 ± 349 2002 Nature Publishing Group. All rights reserved 0250 ± 832X/02 $25.00 www.nature.com/dmfr
RESEARCH
MR imaging of benign and malignant lesions in the buccal space T Kurabayashi*,1, M Ida1, A Tetsumura1, N Ohbayashi1, M Yasumoto2 and T Sasaki1 1
Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University, Japan; 2Department of Radiology, Faculty of Medicine, Tokyo Medical and Dental University, Japan
Objectives: To evaluate MRI characteristics of buccal space lesions and to discuss the sensitivity of MRI in predicting malignancy of those lesions. Methods: Thirty patients with malignant (n=7) or benign (n=23) lesions originating in the buccal space were reviewed retrospectively. MR images were assessed for the margins, internal architecture, signal intensity of lesions and their relation to the surrounding structures. Results: Two cases of soft tissue sarcoma were shown as ill-de®ned masses with in®ltration into adjacent muscles and bone. On the other hand, all tumors of minor salivary gland origin, whether malignant (n=4) or benign (n=2), were well-de®ned and con®ned within the buccal fat pad without in®ltration into surrounding structures. All haemangiomas (n=9) had very high T2-weighted signal intensity. Three out of them contained signal voids on all sequences thought to represent phleboliths, a ®nding strongly suggestive of the diagnosis. In¯ammatory lesions were characterized by the presence of edema in the surrounding fat. When ill-de®ned margins, in®ltration into muscles and bone destruction were used as the criteria for the malignancy, only two out of seven malignant tumors were correctly diagnosed (sensitivity 29%). Conclusions: Although MR imaging was useful in demonstrating the extent of buccal space lesions, its diagnostic value in predicting malignancy was very limited. It was especially true for malignant tumors of minor salivary gland origin, which were typically seen as well-de®ned masses without in®ltration into surrounding structures on MRI. Dentomaxillofacial Radiology (2002) 31, 344 ± 349. doi:10.1038/sj.dmfr.4600723 Keywords: facial neoplasms; mouth neoplasms; magnetic resonance imaging; buccal space Introduction The buccal space is a compartment which constitutes the substance of the cheek. It is anatomically bounded by the buccinator muscle medially, the super®cial layer of the deep cervical fascia and the muscles of facial expression laterally and anteriorly, and the masticator space and the parotid gland posteriorly.1 ± 4 The greater part of the space is ®lled by adipose tissue termed the buccal fat pad. The other contents include the parotid duct, minor salivary glands, accessory parotid lobules, the facial and buccal artery, the facial vein, lymphatic channels and the branches of the facial and mandibular nerve.1 ± 4 Although a variety of lesions are known to occur in this space, their radiological features have not been well covered in the literature. Especially, to our
*Correspondence to: T Kurabayashi, Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8549, Japan. E-mail:
[email protected] Received 2 May 2002; revised 22 July 2002; accepted 30 July 2002
knowledge, MRI on a large series of buccal space lesions has not been reported. The purpose of this study was to evaluate MRI characteristics of lesions originating in the buccal space and to discuss the usefulness of MRI in predicting malignancy of buccal space lesions. Materials and methods Thirty patients with buccal space lesions examined by MRI in our hospital from May 1996 to December 2001 were included in this study. The patients comprised 14 males and 16 females with a mean age of 43.1 years (range 9 ± 69 years). The lesions were divided into 21 tumors, seven malignant and 14 benign, and nine in¯ammatory lesions (Table 1). The histopathological diagnoses were obtained by surgery or biopsy in 25 out of 30 cases. Among the remaining ®ve, the diagnoses of three haemangiomas were established by CT and/or
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Table 1 MR features of buccal space lesions No. of cases Margin
Internal architecture
T1-/T2-weighted signal intensity
2
Well-defined
Homogeneous
2
Well-defined
Heterogeneous
Fibrosarcoma 1 Rhabdomyosarcoma 1 Metastatic LN* 1
Ill-defined Ill-defined Well-defined
Heterogeneous Heterogeneous Homogeneous
Low/Intermediate Low/Very high Intermediate/Intermediate Low/Intermediate ± Very high Low/Low ± Intermediate Low/Intermediate ± High Low/High
1 2
Well-defined (6) Ill-defined (3) Ill-defined Well-defined
Homogeneous (6) Heterogeneous (3) Homogeneous Heterogeneous
1 1
Well-defined Well-defined
Heterogeneous Homogeneous
Low/Very high Low/Intermediate ± Very high Low/High ± Very high High/High
Ill-defined
Heterogeneous
Low/Low ± Very high
Malignant tumors Adenoid cystic carcinoma Acinic cell carcinoma
Benign tumors Haemangioma Lymphangioma Pleomorphic adenoma Neuroma Lipoma
9
Non-neoplastic lesion Inflammation 9
Low/Very high
Infiltration into muscles Other features No No Yes Yes No
Bone destruction Bone destruction
No (6) Yes (3) No No
Containing signal voids (3) Multiple lesions (2)
No No No (5) Yes (4)
Edema within surrounding fat (8) Rim enhancement (2)
*Lymph node metastasis from squamous cell carcinoma of lower alveolar ridge. Figures in parentheses are number of cases
plain radiographs, which con®rmed the presence of phleboliths, and those of two in¯ammatory lesions by clinical follow-up. The presence of buccal space lesions were clinically apparent in all cases because they could easily be palpated just under the buccal mucosa or the skin of the cheek. MRI was performed on a 1.5 T unit (Magnetom Vision, Siemens Medical Systems, Erlangen, Germany) with a head and neck coil. T1-weighted spin-echo images were obtained in axial and/or coronal planes using parameters of 500 ± 650/14 (TR/TE ms) in all patients. T2-weighted fast spin-echo images (3000 ± 5000/90 ms) were obtained in axial and coronal planes, with fat suppression in 20 cases (two sarcomas, two acinic cell carcinomas, an adenoid cystic carcinoma, a lymph node metastasis from squamous cell carcinoma, four haemangiomas, a lymphangioma, a pleomorphic adenoma, a neuroma, a lipoma and six in¯ammatory lesions) and without fat suppression in ten cases. In 14 out of 30 cases (a ®brosarcoma, an adenoid cystic carcinoma, an acinic cell carcinoma, a lymph node metastasis from squamous cell carcinoma, four haemangiomas, a pleomorphic adenoma and ®ve in¯ammatory lesions), Gd-DTPA enhanced T1-weighted images with fat suppression were also obtained. All images had a 2566192 matrix and 3 ± 5 mm sections with a 0.3 ± 1.0 mm interslice gap: superior and inferior presaturation pulses were applied for axial imaging. The margins, internal architecture, signal intensity of the lesions and their relation to the surrounding structures were interpreted by two oral and maxillofacial radiologists who were blind to the histopathological ®ndings. When initial disagreement existed, a ®nal diagnosis was reached by forced consensus. Signal intensity was compared with that of normal structures on both T1- and T2- weighted images and classi®ed as
low (isointense with muscle), intermediate (higher than muscle, lower than fat), high (isointense with fat) and very high (higher than fat). Results The thirty lesions were all clearly demonstrated on MRI. And their appearance summarized in Table 1. Two cases of soft tissue sarcoma were shown as illde®ned masses with in®ltration into the surrounding muscles, i.e. the masticatory and buccinator muscles, and bone (Figure 1). On the other hand, all salivary gland tumors, whether malignant (n=4) or benign (n=2), were well-de®ned masses con®ned within the buccal fat pad and adjacent to the outer surface of the buccinator muscle (Figures 2 and 3). Signal intensity of these tumors was non-speci®c and dierent even among those of the same histopathological type. All haemangiomas were characterized by very high T2weighted signal intensity, higher than that of fat and similar to that of cerebrospinal ¯uid. Although six out of nine haemangiomas were well-de®ned, the remaining three were ill-de®ned masses with in®ltration into the masticatory muscles. The latter all had characteristic features of signal voids, thought to represent phleboliths and/or a multilobular structure (Figure 4). A lipoma was isointense with fat on both of T1- and T2weighted images (Figure 5). Nine in¯ammatory lesions were all shown as ill-de®ned masses with or without in®ltration into the buccinator muscle. All of those lesions but one were characterized by the presence of edema in the surrounding fat, that is, hypointense signal on T1-weighted images with a striated pattern, hyperintense signal on fat-suppressed T2-weighted images (Figure 6). Dentomaxillofacial Radiology
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a
a
b
b
Figure 1 Rhabdomyosarcoma in a 27-year-old woman T2-weighted axial image with fat suppression (a) and coronal image without fat suppression (b) revealed an ill-de®ned, heterogeneous mass in the left buccal space. The mass shows in®ltration into the mandible (a) and the masticatory and buccinator muscles (b), strongly suggestive of malignancy
Out of 14 cases in which Gd-DTPA was administered, two in¯ammatory lesions showed rim enhancement on postcontrast T1-weighted images, both of which were con®rmed to be abscess at biopsy (Figure 6). The remaining twelve (four malignant tumors, ®ve benign tumors and three in¯ammatory lesions) showed homogeneous or slightly inhomogeneous enhancement, showing no ¯uid collection. Using any single image feature of ill-de®ned margins, in®ltration into muscle or bone destruction on MRI as the criteria for the malignancy of the buccal space, the sensitivity was 29% (2/7) and the speci®city was 43% (10/23). Discussion The type of tumor arising in a particular compartment depends on the type of tissue generally found there. Dentomaxillofacial Radiology
c
Figure 2 Adenoid cystic carcinoma in a 47-year-old woman T1weighted image (a), T2-weighted image without fat suppression (b), and Gd-DTPA enhanced T1-weighted image with fat suppression (c) revealed a well-de®ned, homogeneous mass con®ned within the left buccal fat pad, mimicking a benign tumor
Thus, the dierential diagnosis of a buccal space lesion includes a tumor originating from glandular, vascular, lymphatic, connective, muscular, ductal and neural
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a
a
b
b
c
Figure 3 Pleomorphic adenoma in a 54-year-old man T1-weighted image (a), T2-weighted image with fat suppression (b), and GdDTPA enhanced T1-weighted image with fat suppression (c) revealed a well-de®ned, heterogeneous mass con®ned within the left buccal fat pad
tissues.1,3,5 Among them, a minor salivary gland tumor and a haemangioma are known to be more common lesions.4,6 In our series, these two types of tumor
Figure 4 (a) Haemangioma in a 43-year-old woman and (b) haemangioma in a 47-year-old woman. T2-weighted images without (a) and with fat suppression (b) revealed two cases of haemangioma which appeared as a solitary, well-de®ned mass in (a), but in contrast as multiple masses with in®ltrative margins in (b). A signal void thought to represent a phlebolith is also seen in (b) with an arrow
accounted for 71% (15/21) of all the tumors. Metastatic lymph nodes, i.e. metastasis to the buccal lymph node from squamous cell carcinoma of the face, may be also more common lesion in such institutions as large cancer centers,4 although we encountered only one case in this series. In¯ammatory lesions originating in this space are also common7,8 from odontogenic infections. Less commonly, they may result from infections of buccal lymph nodes or minor salivary glands.7 Although there have been some reports of buccal space lesions,4,6,9 their MRI characteristics have not been well covered except by Tart et al,4 who evaluated MRI of six cases of buccal space lesions, plus a few case reports.10 ± 12 MRI clearly demonstrated the extent of the lesion in all cases because of its excellent soft tissue contrast. Although ours was not a comparative study, we believe that MRI is superior to CT in delineating the margins of the lesion with respect to muscle, which borders Dentomaxillofacial Radiology
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a
a
b
b
Figure 5 Lipoma in a 64-year-old-man T1-weighted image (a) and T2-weighted image with fat suppression (b) revealed a well-de®ned mass in the right buccal space showing isointensity with fat
most of the buccal space. T2-weighted images with fat suppression revealed the margins of the lesion more clearly than those without fat suppression. However, there was only a small number of lesions with MR imaging characteristics enough to allow speci®c diagnosis. Among malignant tumors, four cases of minor salivary gland origin were all shown as wellde®ned, non-speci®c masses con®ned within the buccal fat pad. They could not be dierentiated from benign tumors, leading to low sensitivity of MRI (29%) in predicting malignancy. It is well-known the diagnostic value of MRI is limited in dierentiating between benign and malignant tumors of the major salivary glands.13,14 Especially, a salivary gland carcinoma of small size is likely to have a sharp margin, mimicking a benign tumor.15 In our series, malignant tumors of minor salivary glands were less than 20 mm in the maximum diameter in all cases but one. A buccal space tumor can be clinically detected in its smaller size because it is easily palpated just under the buccal mucosa or the skin of the cheek.16 This may indicate that predicting malignancy is more dicult for tumors Dentomaxillofacial Radiology
c
Figure 6 In¯ammatory lesion (abscess) in a 33-year-old-man T1weighted image (a) and T2-weighted image with fat suppression (b) revealed an ill-de®ned mass in the left buccal space. The mass shows a rim enhancement in Gd-DTPA enhanced T1-weighted image with fat suppression (c). Surrounding fat shows hypointense signal in (a) arrows, hyperintense signal in (b) and moderate contrast enhancement in (c)
of minor salivary glands in the buccal space compared with those of the major salivary glands. Although
MRI of buccal space T Kurabayashi et al
dynamic MR study may be useful in tissue characterization of these tumors,17,18 there is still controversy regarding the value of the technique.19 On the other hand, two cases of sarcoma in this study were shown as ill-de®ned masses with in®ltration into adjacent muscles and bone, strongly suggestive of malignancy. Although metastatic squamous cell carcinoma to the buccal lymph node was shown as a non-speci®c mass, the diagnosis was not dicult because the primary tumor was clinically apparent. A considerable number of benign lesions in our study had ill-de®ned margins, however most of them presented characteristic MR features, which provided important clues to the dierential diagnosis. Among them, three haemangiomas with very high T2-weighted signal intensity and signal voids thought to represent phleboliths were considered distinguishable from other
lesions on the basis of MRI. In¯ammatory lesions, either cellulitis or abscess, were characterized by the presence of edema in the surrounding fat. Although such a feature was speci®c to in¯ammatory lesions in our series and considered helpful in dierentiating from malignant tumors, it is not reliable enough to obviate biopsy because similar features can be found in malignant tumors with infection20 or signi®cant lymphatic channel obstruction.21 In conclusion, MRI was useful in demonstrating the extent of the buccal space lesions and their relation to the surrounding structures. However, its diagnostic value in predicting malignancy of buccal space lesions was limited. It was especially true for malignant tumors of minor salivary gland origin, which were typically seen as well-de®ned masses without in®ltration into surrounding structures on MRI.
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