The rectal tonsil in children: a reactive lymphoid proliferation that may mimic a lymphoma.

Prominent and localized lymphoid hyperplasia in the rectum is also known as rectal tonsil (RT) [1, 2]. When the reactive lymphoid infiltrate is very exuberant with atypical lymphoid cells it can be difficult to distinguish from lymphoma on histology [3]. To avoid overdiagnosis and overtreatment, immunophenotypic and genotypic studies are necessary [3–5]. A 4-year-old girl, without relevant medical antecedents, was referred to our department with rectal bleeding. The hemogram was normal. Rectal examination revealed a polypoid mass arising from posterior rectal wall. A pelvic MRI showed a 3 cm × 3 cm polypoid mass in the distal rectum without infiltration beyond the submucosa (Fig. 1a). Endoscopy revealed raised and nodular mucosa without ulceration arising from the posterior rectal wall (Fig. 1b). Two fragments were removed surgically to establish the correct diagnosis. At histology, a dense lymphoid infiltrate was present in the lamina propria and submucosa; there were abundant macrophages inside the germinal follicles, atypicalappearing enlarged and mature lymphocytes with numerous mitotic figures and well-formed germinal centers of different size. Immunohistochemistry suggested follicular type of proliferation with B cells markers (CD20+, CD10 and bcl-6+). The germinals centers were bcl-2 negative. Immunohistochemical staining for CD21 demonstrated a follicular pattern by delineating follicular dendritic cells. PCR studies helped to exclude a lymphoid malignancy because there was no evidence of monoclonal expansion of B cells. These studies confirmed a reactive lymphoid proliferation, and excluded lymphoma, and other forms of non-neoplastic lymphoid proliferation with intact follicles such as lymphoid follicular proctitis and lymphoid polyps of the rectum. A normal-appearing rectal mucosa was seen during endoscopy 14 months later. Histology and their inmunohistochemical and molecular studies help to differentiate benign condition from a malignant one [3–5]. The etiology of RT hyperplasia is unknown. Histologically RT hyperplasia may be distinguished from malignant lymphoma by the polymorphic nature of the infiltrate, absence of significant cytologic atypia and the presence of reactive follicles within the lesion. Mitotic figures are frequent in the germinal centers but absent in the surrounding lymphoid tissue. The lymphoid infiltrate usually is confined to the mucosa and the submucosa; the involvement of the muscularis mucosa is unlikely [2]. In contrast, lymphomas have an infiltrative growth pattern, an P. F. Eire (*) :M. P. Arias :A. L. Carril Department of Pediatric Surgery, Complejo Hospitalario Universitario de Vigo, Pizarro 22, 36204 Vigo, Spain e-mail: [email protected]