1. MAGNETIC RESONANCE IMAGING OF PAROTID GLAND TUMORS (eP-144)
ZHE GUAN, MS*; MOHANNAD IBRAHIM, MD*; MICHAEL ADIX, MD†; MATTHEW SPECTOR, MD*; ASHOK SRINIVASAN, MBBS* *UNIVERSITY OF MICHIGAN, ANN ARBOR, MI †ALTA VISTA RADIOLOGY, PARADISE VALLEY, AZ

2. Disclosures
The authors have no conflicts of interest to disclose.

3. Introduction
Identification of parotid gland tumors as benign or malignant is important for determining surgical management
Benign lesions may be managed by local excision or superficial parotidectomy
Malignant lesions require total parotidectomy with greater risk of nerve injury
Clinical evaluation is generally not helpful for distinguishing benign and malignant
Imaging studies are used in preoperative planning and may detect findings that suggest whether a lesion is benign or malignant
MRI offers greater diagnostic content and detail of the soft tissue compartments
We review our experience with a consecutive series of 65 parotid tumor patients

4. Purpose
To evaluate the MRI features that can be helpful in distinguishing benign and malignant parotid tumors

5. Methods HIPAA compliant IRB approved study
Retrospective review of all pathology proven benign and malignant parotid tumors in adults with preoperative MRI available from June 2013 to April 2015
Metastatic tumors and scans with limited exam were excluded
MRIs evaluated for signal intensity, presence of contrast enhancement, ill-defined margins, deep lobe involvement, and perineural spread
DWIs evaluated when available for mean apparent diffusion coefficient
Radiologist blinded to diagnosis and asked to predict if benign or malignant
Contingency table testing and logistic regression modeling performed with SAS

6. Results 65 patients: 38 benign, 27 malignant
Mean age 56.1, sex ratio 1:1.17
DWI available for 48 patients (73.8%): 30 benign (78.9%), 18 malignant (66.7%)
Restricted diffusion defined as ≤ 1.18 based on ROC curve
Age, sex, T1 and T2 signal intensity, ill-defined margins, deep lobe involvement, perineural invasion, and ADC were associated with malignancy
Age and ADC were independently associated with increased odds of malignancy
Radiologist prediction was correct for 39 patients (60.0%): 23 benign (60.5%), 16 malignant (59.3%)

7. Pathologic Diagnosis of Tumors
Benign (38)
Malignant (27)
Pleomorphic adenoma (30)
Acinic cell carcinoma (8)
Warthin tumor (3)
Salivary duct carcinoma (5)
Oncocytoma (2)
Adenoid cystic carcinoma (4)
Lymphoepithelial cyst (1)
Mucoepidermoid carcinoma (3)
Neurofibroma (1)
Squamous cell carcinoma (3)
Lipoma (1)
Adenocarcinoma (2)
Marginal zone lymphoma (1)
Synovial sarcoma (1)

8. Patient and MRI Characteristics
Benign
Malignant
p value
Age (years)
52.6 ± 16.7
61.0 ± 16.1
0.0473
≥ 70
7 (18.4%)
12 (44.4%)
0.0230*
Female sex
24 (63.2%)
11 (40.7%)
0.0740
Ill-defined margins
1 (2.6%)
18 (66.7%)
<0.0001*
Deep lobe involvement
6 (16.2%)
17 (63.0%)
0.0001*
Perineural invasion
7 (25.9%)
0.0013*
ADC (10^−3 mm^2/s)
1.71 ± 0.38
1.17 ± 0.34
≤ 1.18
1 (3.3%)
12 (66.7%)

9. Patient and MRI Characteristics, Part II
Benign
Malignant
p value
T1: isointense to CSF
15 (39.5%)
2 (7.4%)
0.0031*
T1: hyperintense to CSF
23 (60.5%)
23 (85.2%)
T1: hypointense to CSF
T2: isointense to CSF
24 (63.2%)
4 (14.8%)
0.0001*
T2: hypointense to CSF
14 (36.8%)
Enhancement: absent
2 (5.4%)
1 (3.7%)
0.4464
E.: mild homogeneous
5 (13.5%)
7 (25.9%)
E.: mild heterogeneous
30 (81.1%)
19 (70.4%)

10. Logistic Regression Model
Odds ratio estimate
p value
Intercept —
0.0243*
Age ≥ 70
30.6
0.0435*
Female sex
0.3
0.4108
Ill-defined margins
25.7
0.1327
Deep lobe involvement
17.5
0.0854
Perineural invasion
>999
0.9776
ADC ≤ 1.18
129.1
0.0145*
T2: hypointense to CSF
3.8
0.4208

11. Adenoid cystic with ill-defined margins
Enhanced Fat Saturated T1 T2

12. Pleomorphic with deep lobe involvement
Enhanced T1 T2

13. Adenocarcinoma with perineural invasion
Enhanced Fat Saturated T1 T2

14. Discussion
Christe et al. reported 84 parotid tumors with preoperative MRI
T2 hypointensity, ill-defined margins, diffuse growth, infiltration of subcutaneous tissue, and lymphadenopathy were associated with malignancy
DWI was helpful for distinguishing parotid adenoma from other pathologies but not helpful for distinguishing benign and malignant tumors
Freling et al. reported 116 parotid tumors with preoperative MRI
Infiltration into deep structures was associated with malignancy
T1 and T2 signal intensities, tumor margins, and tumor heterogeneity were not
Other series have been smaller or not focused specifically on MRI

15. Discussion, Part II
To the best of our knowledge, this is the first study which uses logistic regression to identify independent predictors of malignancy for MRI of parotid gland tumors
Findings suggest DWI is effective for distinguishing benign and malignant tumors
T1 and T2 signal, ill-defined margins, deep lobe involvement, and perineural invasion are associated with malignancy and may be helpful if DWI is unavailable
Contrast enhancement is not helpful for distinguishing benign and malignant
Radiologist performance similar to what was reported by Christe et al. (59.4%)

16. Conclusion
Older age and diffusion restriction were independently associated with increased odds of malignancy (OR = and OR = 30.6 respectively)

17. Limitations
Retrospective study
DWI unavailable for some patients

18. References
Christe A, Waldherr C, Hallett R, Zbaeren P, Thoeny H. MR imaging of parotid tumors: typical lesion characteristics in MR imaging improve discrimination between benign and malignant disease. AJNR Am J Neuroradiol Aug;32(7):
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El Shahat HM, Fahmy HS, Gouhar GK. Diagnostic value of gadolinium-enhanced dynamic MR imaging for parotid gland tumors. The Egyptian Journal of Radiology and Nuclear Medicine. 2013;44:203-7.
Freling NJ, Molenaar WM, Vermey A, Mooyaart EL, Panders AK, Annyas AA, Thijn CJ. Malignant parotid tumors: clinical use of MR imaging and histologic correlation. Radiology 1992; 185:691-6.
Grazioli L, Olivetti L, Stanga C, Matricardi L, Fugazzola C, Bergamo Andreis IA, Chiesa A. Comparison of ultrasound, CT and MRI in the assessment of parotid masses. Eur Radiol Dec;4(6):

19. References, Part II
Ikeda K, Katoh T, Ha-Kawa SK, Iwai H, Yamashita T, Tanaka Y. The usefulness of MR in establishing the diagnosis of parotid pleomorphic adenoma. AJNR Am J Neuroradiol Mar;17(3):555-9.
Joe VQ, Westesson PL. Tumors of the parotid gland: MR imaging characteristics of various histologic types. AJR Am J Roentgenol Aug;163(2):433-8.
Thoeny HC. Imaging of salivary gland tumours. Cancer Imaging Apr 30;7:52-62.
Yabuuchi H, Matsuo Y, Kamitani T, Setoguchi T, Okafuji T, Soeda H, Sakai S, Hatakenaka M, Nakashima T, Oda Y, Honda H. Parotid gland tumors: can addition of diffusion-weighted MR imaging to dynamic contrast-enhanced MR imaging improve diagnostic accuracy in characterization? Radiology Dec;249(3):
Yousem DM, Kraut MA, Chalian AA. Major salivary gland imaging. Radiology Jul;216(1):19-29.

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