Histopathology of Pleomorphic Adenoma in the Parotid Gland: A Prospective Unselected Series of 100 Cases

Histopathological characteristics of pleomorphic adenomas, especially of capsular alterations such as thin capsule areas, capsule-free regions, capsule penetration, satellite nodules, and pseudopodia in the different subtypes, are described.Prospective unselected series of 100 consecutive cases from 1997 to 2000.Light microscopic examination and semiquantitative analysis of the pleomorphic adenomas.Fifty-one (51%) pleomorphic adenomas were classified as myxoid (stroma-rich) type, 35 (35%) specimens as cellular type, and 14 (14%) as classic subtype. Ninety-seven percent of all tumors showed areas with thin (<20 microm) capsule independent of the tumor subtype. Tumors of myxoid subtype showed the absolute greatest regions of a thin capsule. Especially, tumors of myxoid type (71%) often had a distinct focal absence of encapsulation with tumor merging into normal parotid gland tissue; 11% of the cellular subtype and 43% of the classic subtype presented capsule-free areas. Thirty-three percent of the myxoid pleomorphic adenomas, 23% of the cellular subtype, and 21% of the classic subtype had satellite nodules or pseudopodia.Almost all pleomorphic adenomas have focally thin capsules. One-fourth of all pleomorphic adenomas contain abnormalities such as satellite nodules or pseudopodia. More than two-thirds of pleomorphic adenomas of the myxoid (stroma-rich) subtype and at least half of all tumors show a focal absence of the capsule. Therefore, enucleation or local dissection of the pleomorphic adenoma is not a sufficient surgical treatment of this special tumor entity. We recommend, depending on the location of the tumor, a lateral or total parotidectomy as the treatment of choice.