Salivary Gland Type Adenocarcinoma of the Nasopharynx

grade carcinoma of salivary gland origin because they do not metastasise.

ICD-O:9370/3

Chordomas are tumours arising from remnants of the notochord in the axial skeleton near its cranial and caudal ends. The cranially located chordomas comprise about one-third of all chordomas, arise earlier than the sacral chordomas, around the 3rd to the 5th decade and in children. Most chordomas in nasopharyngeal location are extensions of cranial chordomas, but they rarely arise de novo in the nasopharynx and paranasal sinuses [19, 34, 54]. For a more detailed description of chordoma, see Chap. 4.

The most common sarcoma in the head and neck area is the rhabdomyosarcoma, specifically the embryonal rhabdomyosarcoma (ICD-O:8910/3) in children less than 5 years of age [49]. Primary nasopharyngeal rhabdomyosarcomas are rare [20, 39, 50] as are primary nasopharyngeal chondrosarcomas (ICD-O:9220/3) [54, 56]. Case reports of primary nasopharyngeal sarcomas include an osteosarcoma in an 11-year-old girl after multi-agent chemotherapy and radiation treatment of a retinoblastoma, a liposarcoma and a granulocytic sarcoma in a 37-year-old Chinese man [5, 42, 139]. The fol-licular dendritic cell sarcoma, a tumour of antigen-presenting cells of B-follicles of lymphoid tissues, is commonly found extranodally in the head and neck area, but rarely in the nasopharynx [10, 22, 23]. It is characterised by positivity for CD21, CD35 and CD23, as well as indolent clinical behaviour and a low risk of recurrence and metastasis [87].

The term Waldeyer's ring refers to the ring of lymphoid tissues occurring in the nasopharynx and oropharynx. The oropharynx is separated from the nasopharynx by the oropharyngeal isthmus, which is formed by the merging muscular pillars of the palatoglossal and the palatopharyngeal muscles. In the lateral walls, at the widest points of the pharynx, lies the triangular tonsillar fossa, which contains the palatine tonsil. The tonsils of Waldeyer's ring belong to the gut-associated lymphoepithelial organs, which show a close morphological and functional correlation between lymphatic tissue of mes-enchymal origin and the endodermal epithelium of the second pharyngeal pouch. The Waldeyer's ring tonsils are composed of the paired palatine tonsils in the tonsillar fossa, the unpaired (naso)pharyngeal tonsil in the roof of the nasopharynx, the bilateral tubal tonsils in the lateral walls of the nasopharynx at the entrance to the auditory tube and the lingual tonsil in the retrolingual region. Lymphoid aggregations close to the epiglottis are also counted as part of Waldeyer's ring.

The palatine tonsils are the largest of the tonsils and lie in the tonsillar fossa along the anterolateral border of the oropharynx between the palatoglossal and palatopharyngeal muscle arches. The lateral surface of the palatine tonsil has a fibrous capsule, but skeletal muscle fibres and islands of mostly elastic cartilage are normal findings there. The medial surface has 10-30 epithelium-lined, extensively branching and anastomosing ton-sillar crypts that extend deeply into the lymphoid tissue. The surface of the palatine tonsils is lined by stratified squamous epithelium, the crypts are covered by non-keratinising stratified ("transitional-type") epithelium with a discontinuous basement membrane and numerous intraepithelial lymphoid cells. This so-called lym-phoepithelium represents the specialised epithelium of the tonsils and contains M-cells (resembling the intestinal membranous [M] cells of the Peyer's patches), T- and B-cells, and patchily distributed macrophages and dendritic cells [140, 152]. The surface epithelium is evenly infiltrated by T-cells and B-cells; up to 30% of the intraepithelial T-cells are y8T-cells, which are involved in antigen recognition independent of MHC restriction and prior antigen processing [66, 149]. A clustering of CD4+ T-cells with B-cells is typical within the lympho-epithelium of the crypts and in the submucosa [66]. The submucosal lymphoid tissue contains numerous primary and secondary lymph follicles with germinal centres, a mantle zone and a network of follicular dendritic cells. T-cells, interdigitating dendritic cells, plasma cells, macrophages and high-endothelial venules are found in the extrafollicular regions [140]. The palatine tonsils have no afferent lymph vessels. The rich efferent lymphatic drainage is via the retropharyngeal lymph nodes to the upper deep cervical lymph nodes.

The small unencapsulated (naso)pharyngeal tonsil with about 12-15 shallow crypts is lined with a columnar ciliated respiratory surface epithelium with numerous goblet cells, which may also be seen in the lympho-epithelial lining of the short and plump crypts [200]. The lymphoid tissue contains numerous lymph follicles with germinal centres. Minor salivary glands in the periph-

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