3. Anatomical classification of oropharynx and hypopharynx – Oropharyngeal and Hypopharyngeal Carcinoma

In the clinical-epidemiological literature, it is more difficult to differentiate the hypopharynx and in particular the oropharynx from other parts of the head and neck region than many other cancers.

The oropharynx extends from the palatine tonsils, lingual tonsils, base of the tongue to the vallecula and the lingual epiglottis, soft palate (bordering the hard palate, which is considered part of the oral cavity), uvula and posterior pharyngeal wall. The plica pharyngoepiglottica is seen as the anatomical boundary between the oropharyngeal and hypopharyngeal side walls. The hypopharynx includes the lower part of the pharynx adjacent to the oropharynx, which extends from the hyoid bone to the cricoid cartilage. The hypopharynx is bounded inferiorly by the upper esophageal orifice. The anatomical classification is according to ICD-10-GM version 2022: The International Statistical Classification of Diseases and Related Health Problems, 10th Revision, German Modification (ICD-10-GM) is the official classification for coding diagnoses in outpatient and inpatient care in Germany. The 2022 version of ICD-10-GM has been in use since January 1, 2022.

Oropharynx

In fact, oropharyngeal carcinomas mainly occur at the base of the tongue and in the palatine tonsils, i.e. the epithelia of Waldeyer's pharyngeal ring. The oropharynx is bounded upwards by the transition line between the hard and soft palate. The soft palate together with the uvula is included. However, the posterior surface of the soft palate including the uvula is included in the anterior wall of the nasopharynx (C11.3). Laterally, the nasopharynx is separated from the oropharynx by an imaginary line at the upper edge of the palatine tonsil including the palatine arches. The posterior wall follows the same medial dividing line. The tongue is divided by the linea terminalis into the posterior third of the tongue base (oropharynx) and the anterior two thirds (oral cavity). The larynx begins on the upper edge of the epiglottis and includes the laryngeal part of the epiglottis (supraglottis). The oropharynx contains the lingual tonsil (tonsilla lingualis), the vallecula and the lingual epiglottis. The demarcation to the hypopharyngeal sides and posterior wall is made on an imaginary line at the level of the laryngeal entrance or the upper borders of the two piriform recesses (Fig. 1).

When considering the classification of overlapping malignancies according to ICD-10, there is still some blurring in the demarcation to neighbouring regions. A very typical case of insufficient differentiation is "Tongue, unspecified" (C02.9), as the lower third of the tongue (the base of the tongue) belongs to the oropharynx, while the front two thirds belong to the oral cavity. The tonsil at the base of the tongue, as distinct from the base of the tongue, was still included in ICD-9, but has been subsumed in ICD.10 under the heading "Malignant neoplasm of other and unspecified parts of the tongue" under C02.4 (due to a lack of specific classification of the neoplasm). Kreimer et al. [3] undertook a systematic attempt to exclude unclear definitions on the basis of ICD codes and included a "mixed sites" category for this purpose: "oral cavity (C020-C023, C030-C050, C060-69), oropharynx (C019, C024, C051, C052, C090-C109), and larynx (C320-C329); The "mixed sites" category is proposed for overlapping lesions for better classification and comparability in scientific considerations (C028, C029, C058, C059, C140, C142, C148, C149)". This concept has been incorporated into the BROADEN study, a multicentre study to investigate "HPV attributable fractions in multiple head and neck sites" [4].

Hypopharynx

Three subsites are defined for the hypopharynx itself: [5]. The piriform sinus, which extends caudally on both sides of the aryepiglottic fold (plica aryepiglottica) to the esophageal orifice. The transition to the oesophagus is fluid and, due to the phylogenetic co-evolution of the hypopharynx and oesophagus, should be seen in a closer oncological context than the transition between the oropharynx and hypopharynx. Initial proteomic analyses have shown that molecular field carcinogenization often shows parallel development in the hypopharynx and oesophagus in the same individual [6]. The upper edge of the aryepiglottic fold forms the dividing line between the hypopharynx and the supraglottic part of the larynx. Approximately 60% of all hypopharyngeal carcinomas arise in the piriform sinus. The postcricoid region extends from the outer posterior wall of the larynx to the lower edge of the cricoid cartilage. Approximately 30% of hypopharyngeal carcinomas arise in this region. The posterior wall of the hypopharynx is the origin of around 10% of all hypopharyngeal carcinomas. [5]