New MRI concepts for the diagnosis of Parotid tumors

Transcription

1 New MRI concepts for the diagnosis of Parotid tumors Poster No.: C-1331 Congress: ECR 2012 Type: Educational Exhibit Authors: F. Guerra Gutierrez, F. Baudraxler, V. Suárez-Vega, J. A. Gómez Patiño, C. Sánchez Almaraz, J. Fernández Cuadrado; Madrid/ES Keywords: MR-Diffusion/Perfusion, MR, Salivary glands, Head and neck, Biopsy, Decision analysis, Education, Neoplasia DOI: /ecr2012/C-1331 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 35

2 Learning objectives Anatomic review Usufulness of the different radiological techniques in parotid lesions Diffusion and perfusion utility in parotid tumor characterization Page 2 of 35

3 Background Preoperative characterization of parotid gland tumors is of crucial interest as unnecessary surgery can be avoided when/if benign tumors are detected. Sonography remains an accessible and affordable diagnostic imaging technique but with serious inconvenience. It is a useful tool to determine with certainty whether a lesion is intra- or extraglandular (Fig 1a and 1b), but it fails to clearly identify the deep lobe lesions, or to differentiate between benign and malignant lesions (Fig 2a, 2b and 2c). The main indication of the ultrasound remains to direct fine-needle aspiration which has been so far the crucial preoperative diagnostic technique. Computed tomography (CT) is a widely used imaging technique, mainly because access to Magnetic Resonance (MR) imaging is often limited. The disadvantages of CT are radiation, worse definition than ultrasound or MR imaging for small lesions and that it cannot differentiate between benign and malignant lesions. On the other hand, CT can correctly detect the deep lobe lesions which allows a correct pre-operative planning of surgical access. The diagnostic accuracy of Positron Emission Tomography- Computed Tomography ( PET-CT) for these lesions is limited because the PET tracer can be purchased from both benign and malignant lesions (Fig 3). Unlike CT, conventional MRI allows tissue characterization (Fig 4a and 4b), can define the involvement of neighboring structures and can detect perineural invasion. It has been observed that up to 25% of untreated pleomorphic adenomas showed malignant degeneration, whereas Warthin tumors presented this degeneration in less than 1%. According to the World Health Organization histological classification of 2005, malignant tumors derived from salivary gland pleomorphic adenomas ( also called malignant mixed tumors ) can be subclassified into three types: 1) carcinoma ex pleomorphic adenoma, 2) carcinosarcoma 3) metastazing pleomorphic adenoma. Most of the malignant mixed tumors derived from old pleomorphic adenomas. The surgical planning elected by surgeon for salivary gland tumors depends on its location and its histology. Deep lobe afectation (Fig 5) is of great chirurgic implication, because a posterior gland aproach is needed in orden to preserve facial nerve. Malignant tumors require a total parotidectomy or lobectomy with possible facial nerve resection, which can lead to significant morbidity. Page 3 of 35

4 The advantages of static MRI are both, the absence of radiation and good preoperative anatomic assessment (Fig 6), primarily to assess the tumor extension into the deep lobe of the parotid gland and perineural extension. The introduction of MR contrast-enhanced dynamic studies (Fig 7) and apparent diffusion coefficient (ADC) maps allow a high diagnostic accuracy to distinguish between different parotid gland tumor types. Page 4 of 35

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16 Imaging findings OR Procedure details Most common features of parotid tumors on MRI: * Pleomorphic Adenoma About 80% of all benign parotid tumors are pleomorphic adenomas. Pleomorphic adenomas, also known as mixed tumors, occur most often in middle-age women. All pleomorphic adenomas are well-defined tumors in imaging. On MRI ( Fig 8a and 8b), pleomorphic adenomas present with a low signal on SE T1 weighted images and show high signal intensity on SE T2 weighted sequences. Another feature of many pleomorphic adenomas is the lobulated shape and a complete capsule which is dark on T2 weighted sequences. Pleomorphic adenomas may contain calcifications and present cystic degeneration. As calcifications are rarely seen in other parotid tumors, the presence of calcification suggests pleomorphic adenoma. Small tumors present a homogenous signal intensity, whereas internal inhomogeneities are found in growing tumors. After intravenous contrast pleomorphic adenomas show a late enhancement in either CT or MRI ( Fig 9). Pleomorphic adenomas have to be removed surgically because about 15-20% of them become highly malignant tumors. Less then 1% of these tumors are multicentric. Radiologically monomorphic adenomas resemble pleomorphic adenomas, althoug they are more common in the submandibular glands. * Warthin tumor Also known as cystadenolymphoma. The tumor most often is located in the parotid gland and it is the most common multiple and bilateral tumor of the parotid gland. Malignant changes seem to be extremely rare. On MRI ( Fig 10a and 10b) Warthin tumors may show a varying signal pattern on T1 and T2 weighted images. The signal intensity is often very heterogenous. Almost 30% of these tumors present cystic areas. Warthin tumors are usually small tumors (less than 4cm). Page 16 of 35

17 * Hemangioma Hemangiomas are the most common benign tumor in children. About 40% of them are noted shortly after birth and most of them present spontaneous regression by adolescence. On MRI, hemangiomas show high signal intensity on T2 weighted images ( Fig 11). * Mucoepidermoid carcinoma Mucoepidermoid carcinoma is the most common malignant neoplasm of the parotid gland. They represent 30% of all tumors occurring in salivary glands and 60% of them occur in the parotid gland. Conventional MRI cannot differentiate between pleomorfic adenomas and Warthin tumors, because they can present a capsule and can be welldelineated. High grade tumors as well as less differentiated mucoepidermoid carcinoma show low signal intensity on T2 weighted images. Low grade tumors are hyperintense on T2 weighted images. * Adenoid cystic carcinoma Adenoid cystic carcinoma is the second most common malignant neoplasm of the salivary gland and is known for its tendency to spread perineurally ( 50-60% of all cases). Diffusion Diffusion occurs as a result of the constant movement of water molecules inside the cell and inside the interstitium. Diffusion-weighted MR imaging can provide useful information about parotid gland pathology Parotid glands possess low ADCs values ( 0,8x10 mm /sec) because of the protenaceous contents and the amount of adipose tissue. Diseases like chronic sialoadenitis of the parotid gland or Sjögren s syndrome lead to changes in ADC. The glands with sialoadenitis and Sjögren s syndrome are characterized by progressive acinar destruction which leads to increased ADCs (Fig 12). Studies showed that diffusion imaging has no utility in differentiating between benign and malignant lesions (Fig 13), although pleomorfic adenomas present hypocellular areas Page 17 of 35

18 -3 with high ADCs values. In our experience, lesions with ADC values higher than 1,8x10 2 mm /sec resulted in pleomorphic adenomas (Fig 14). Perfusion On conventional MRI malignant neoplasm of the salivary gland show the following features: irregular tumor margin, signal intensity heterogeneity, low signal intensity on T2 weighted images and tumor infiltration into surrounding tissue. Dynamic contrast-enhanced MR imaging of the parotid gland is very useful because in addition to assessing whether or not the lesion enhance, and see how far it extends, it also allows to assess which areas most enhance and which uptake curve it presents. Yabuuchi et al valuated all different parotid tumors by using dynamic contrast-enhanced MRI. They described 4 time-intensity curve ( TIC) patterns: * type A (Fig 15): time to maximal enhancement was more than 120 seconds after contrast-administration ( persistent) * type B (Fig 16): time to peak was 120 seconds or less with high washout ratio ( - >30%) ( washout) * type C (Fig 17): time to peak was 120 seconds or less with low washout ratio (<30%) ( plateau) * type D: ( flat) Using this classification only the type A TIC pattern is characteristic of pleomorphic adenoma. Warthin tumors as well as carcinomas can show the type B washout TIC pattern. Type C plateau TIC pattern can be found in pleomorphic adenomas or malignant lesions. Lesions which show type D TIC pattern are usually benign. Given these characteristics, poses the same dilemma with diffusion-weighted MR imaging that it cannot differentiate benign from malignant lesions completely. Yabuuchi et al showed that the sum of the TIC patterns and ADC values significantly increase the differentiation between benign and malignant parotid tumors ( Table 1). Page 18 of 35

19 Fig. 24 References: Felix et al. 30th SERAM Congress. Coruña Type A TIC pattern is seen almost exclusively in benign pleomorphic adenoma. Type D curves are considered benign. In type B curves to differentiate between benign and malignant, the appropriate cut-off value is 1. Lesions with values of 1x10 lesions mm /sec or more are considered malignant In the type C curves the cutoff would be 1,4x10 mm /sec. Lesions with values of 1,4x10 2 mm /sec or more are considered benign. Page 19 of 35

20 Images for this section: Fig. 12 Page 20 of 35

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33 Conclusion MRI is the best radiological technique for the characterization of parotid lesions Add ADC values to perfusion curves improves significantly preoperative diagnosis of parotid tumors Page 33 of 35

34 Personal Information Page 34 of 35

35 References Yabuuchi H, Fukuya T, Tajima T, Hachitanda Y, Tomita K, Koga M. Salivary gland tumors: diagnostica value of gadolinium-enhanced dynamic MR imaging with histopathologic correlation. Radiology Feb;226(2): Erratum in: Radiology Jun;227(3):909. Yabuuchi H, Matsuo Y, Kamitani T, Setoguchi T, Okafuji T, Soeda H, et al. Parotid gland tumors: can addition of diffusion-weighted MR imaging to dynamic contrastenhanced imaging improve diagnostic accuracy in characterization? Radiology Dec;249(3): Ikeda M, Motoori K, Hanazawa T, Nagai Y, Yamamoto S, Ueda T, Funatsu H, Ito H. Warthin tumor of the parotid gland: diagnostic value of MR imaging with histopathologic correlation. AJNR Am J Neuroradiol Aug;25(7): Eida S, Sumi M, Sakihama N, Takahashi H, Nakamura T. Apparent diffusion coefficient mapping of salivary gland tumors: prediction of the benignancy and malignancy. AJNR Am J Neuroradiol Jan;28(1): Page 35 of 35