Extranodal follicular dendritic cell tumor of the tonsil: report of a diagnostic pitfall and literature review.

Follicular dendritic cell tumor (FDCT) usually arises in the dendritic reticulum cells of the lymph nodes. Extranodal cases are rare; only 24 cases have been reported in the head and neck region, and most are in the oropharynx. Nine cases of primary FDCT of the tonsil have been reported in English-language literature, to which we add the 10th case. This 77-year-old white woman presented with a tonsillar mass that was misdiagnosed as squamous cell carcinoma. She underwent neoadjuvant radiotherapy plus combined oropharyngeal and mandibular resection with radical neck dissection. Eight years later, she presented with dyspnea and was found to have a lung mass with hilar lymphadenopathy. A biopsy specimen was taken from the hilar lymph nodes, and histologic analysis yielded results similar to those found in the original tumor. Immunohistochemical analysis confirmed that FDCT was present at both sites. We wish to highlight this potential diagnostic pitfall because the treatment and prognosis for FDCT are vastly different from the treatment and prognosis for squamous cell carcinoma of the tonsil.