Pleomorphic adenoma of parotid gland: delayed enhancement on computed tomography.

OBJECTIVES: To assess the efficacy of multiphasic CT with 8 min delayed acquisition in the differential diagnosis between pleomorphic adenomas and other parotid neoplasias.

METHODS: Between January 2004 and April 2007, 62 patients with parotid enlargement were enrolled in this prospective study. The CT protocol applied included the following four acquisitions: without contrast medium and 30 s, 120 s and 8 min after intravenous injection of contrast medium. We considered the degree of the enhancement of the lesions (rated as "low", "moderate" and "strong") and the degree of enhancement homogeneity (rated as "not homogeneous", "mildly homogeneous" and "uniform"). These parameters were compared with Hounsfield values of the lesions computed in each phase. The diagnosis was confirmed in all patients after surgery.

RESULTS: On histological examination, 36 tumours were classified as pleomorphic adenomas and 26 as non-pleomorphic adenomas. On the basis of a statistical comparison, the third phase proved to be the most effective in the differential diagnosis between pleomorphic adenoma and non-pleomorphic adenomas, both for the assessment of the degree of the enhancement (in this phase, strong enhancement showed a sensitivity of 61.11%, specificity of 100%, positive predictive value (PPV) of 100% and negative predictive value (NPV) of 53.33%) and, above all, for the homogeneity of the enhancement (in this phase, indeed, uniform enhancement showed sensitivity, specificity, PPV and NPV of 100%).

CONCLUSIONS: Our results seem to indicate that multiphasic CT with 8 min delayed acquisition allows the differential diagnosis between pleomorphic adenomas and other parotid neoplasias.