Case Report Ectopic Oral Tonsillar Tissue: A Case Series with Bilateral and Solitary Presentations and a Review of the Literature Masashi Kimura, 1 Toru Nagao, 2 Terumi Saito, 2 Saman Warnakulasuriya, 3 Hiroyuki Ohto, 1 Akihito Takahashi, 2 Kanji Komaki, 4 and Yoshiyuki Naganawa 1 1 Department of Dentistry Oral and Maxillofacial Surgery, Ogaki Municipal Hospital, 4-86 Minaminokawa, Ogaki, Gifu 503-8502, Japan 2 Department of Oral and Maxillofacial Surgery and Stomatology, Okazaki City Hospital, 3-1 Goshoai, Koryuji-cho, Okazaki, Aichi 444-8553, Japan 3 Department of Oral Medicine, King’s College London Dental Institute, WHO Collaborating Centre for Oral cancer/Precancer, Bessemer Road, London SE5 9RS, UK 4 Department of Oral and Maxillofacial Surgery, Yokkaichi Municipal Hospital, Yokkaichi, Mie 510-8567, Japan Correspondence should be addressed to Toru Nagao; tnagao@topaz.ocn.ne.jp Received 4 December 2014; Accepted 22 December 2014 Academic Editor: Pablo I. Varela-Centelles Copyright © 2015 Masashi Kimura et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An ectopic tonsil is defined as tonsillar tissue that develops in areas outside of the four major tonsil groups: the palatine, lingual, pharyngeal, and tubal tonsils. e occurrence of tonsillar tissue in the oral cavity in ectopic locations, its prevalence, and its developmental mechanisms that belong to its formation remain unclear. In this report, we describe a rare case of bilateral symmetric ectopic oral tonsillar tissue located at the ventral surface of the tongue along with two solitary cases arising from the floor of the mouth. e role of immune system and its aberrant response leading to ectopic deposits desires further studies. As an ectopic tonsil may simulate a benign soſt tissue tumor, this case series highlights the importance of this entity in our clinical differential diagnosis of oral soſt tissue masses. 1. Introduction e tonsils form part of a circular band of adenoid tissue known as Waldeyer’s ring, which guard the opening of the digestive and respiratory tracts. is circular band is comprised of four major tonsil groups: the palatine, lingual, pharyngeal, and tubal tonsils. An ectopic tonsil is tonsillar tissue that develops in areas outside of these regions. e existence of ectopic oral tonsils was described by Knapp in 1970 [1]. It was shown that such structures, resembling pharyngeal and other tonsils, can be found within the oral cavity. Ectopic tonsils have been reported in different anatomic locations of the oral cavity, for example, on the floor of the mouth [1–6], ventral surface of the tongue [1, 2, 4], and soſt palate [1, 2], and in other parts of the aerodigestive tracts, for example, larynx [7], hypopharynx [8], nasal septum [9], or in the orbit [10](Table 1). Collection of tonsillar tissue in ectopic sites can cause diagnostic confusion; however, none of the reported cases have been described with a bilateral presentation and/or symmetrically such as that found in the oropharynx. Here we report a rare case of bilateral symmetric ectopic oral tonsillar tissue observed on the ventral surface of the tongue and two other solitary cases arising from floor of the mouth along with a review of the literature. 2. Case Presentations 2.1. Case 1. A 53-year-old Japanese male, referred by his general dental practitioner, presented with small, bilaterally symmetric masses on the ventral surface of the tongue, noticed during a routine dental examination 2 months ago. e areas affected were painless and remained unchanged in size over the previous 2 months. Intraoral examination revealed hard masses of 8 mm diameter (right) and 6 mm Hindawi Publishing Corporation Case Reports in Dentistry Volume 2015, Article ID 518917, 6 pages http://dx.doi.org/10.1155/2015/518917