Recurrent pleomorphic adenoma of the parotid gland: a prospective histopathological and immunohistochemical study.

Objectives/hypothesis: Histopathological characteristics and proliferation indices of recurrent pleomorphic adenoma were described in a series of 31 patients who were referred to the authors' clinic for revision surgery.

Study Design: Prospective series of 31 patients.

Methods: Serial sections of surgical specimen using the whole-organ sectioning technique were carried out for light microscopic examination after total parotidectomy and periparotid fat resection. The nodules were examined with special reference to localization, amount, size, histological subtypes, capsular alterations, and the amount of nodule spilling. Expression of proliferation markers (Ki67/MIB-1) according to the size and histological subtypes of the nodules was also investigated.

Results: Most recurrences were multinodular, and the number of nodules was much higher than expected, ranging from 1 to 157. The myxoid subtype was predominant. Eighty percent of the patients exhibited widely distributed nodules also lying outside the scar. These nodules contained only a thin pseudocapsule and often lacked complete encapsulation. The majority of multinodular recurrences of parotid pleomorphic adenoma consisted of small nodules (less than 1 mm in diameter). Smaller nodules showed similar or higher levels of proliferative activity than larger nodules.

Conclusion: The extended multifocal distribution of tumor recurrences after insufficient resection of pleomorphic adenoma (most often after enucleation) can explain a high incidence of further recurrences. Therefore, a total parotidectomy including removal of surrounding fat tissue seems to be appropriate for the initial treatment of recurrent pleomorphic adenoma.