Carcinoma ex pleomorphic adenoma of major salivary glands: CT and MR imaging findings

Objectives: To describe the CT and MR imaging characteristics of primary carcinoma ex pleomorphic adenoma (Ca-ex-PA) in major salivary glands and present more information for recognizing this malignancy. Methods: 212 patients with primary Ca-ex-PA in major salivary glands (169 in the parotid gland, 36 in the submandibular gland, 7 in the sublingual gland) underwent CT and MR imaging (plain and contrast-enhanced scans) prior to surgical management and histopathological examination. The CT and MR imaging findings of this condition were retrospectively reviewed and correlated with their pathological types: non-invasive carcinoma (Type I, 37 cases), minimally invasive carcinoma (Type II, 18 cases), and widely invasive carcinoma (TypeIII, 157 cases). The binary logistic regression analysis was used to analyze the independent influencing factors of morphology and boundary for differentiating between Type I/II and Type III of Ca-ex-PA, and the sensitivity, specificity and positive predictive value were calculated. Differences in apparent diffusion coefficient (ADC) values between Type I/II and Type III of Ca-ex-PA were calculated by independent sample t-tests. Results: On CT and MR imaging, there were 190/212 cases (89.6%) identified as lobular, 203/212 cases (95.8%) with enhancement, and 173/212 cases (81.6%) with inhomogeneous after contrast administration.Calcification within the mass was shown in 76 of 192 cases (39.6%) on plain CT examination. Of 55 neoplasms with Type I and II, 38 (69.1%) were presented as round or oval and 42 (76.4%) as well-defined margins. Of 157 neoplasms with Type III, 103 (65.6%) were presented as irregular form and 110 (70.1%) as uneven margins or with partial uneven margins.The sensitivity, specificity and positive predictive value for distinguishing Type I/II and Type III tumors according to the morphology and boundary were 78.34%, 63.64% and 86.01%, respectively. The mean ADC value of Ca-ex-PA (22 cases) in major salivary glands was about 0.93 × 10−3 mm2 s−1, and there was no significant difference in mean ADC value between Type I/II and Type III of this neoplasm. Cervical lymph node metastasis and distance metastasis were found in 67 patients (31.6%, Type III) and 32 patients (15.1%, Type I in 1; Type II in 1; and Type III in 30), respectively. Conclusions: Most Ca-ex-PA is characterized by an irregular, lobular, and inhomogeneous enhanced neoplasm with uneven margin or partial uneven margin on CT and MR imaging, which is frequently corresponding with Type III. And a round or oval mass with well-defined margin usually correlates with Type I and II. Morphology and boundary are important basis for distinguishing Type I/II and Type III tumors. Calcification within the neoplasm shown on CT may be regarded as a specific sign for indicating this malignancy. Low ADC value is an important manifestation of this neoplasm.Ca-ex-PA with Type III is more likely to have cervical lymph node metastasis and distant metastasis.