Anatomic Divisions of the Pharynx
The pharynx is divided into three main anatomic regions: the nasopharynx (superior), oropharynx (middle), and hypopharynx (inferior), each with distinct boundaries and clinical significance for staging and treating head and neck cancers. 1
Nasopharynx
The nasopharynx represents the superior division of the pharynx, located behind the nasal cavity and above the soft palate 1. This region has unique staging criteria compared to other pharyngeal subsites, with T-stage based on subsite involvement rather than tumor size 1. The nasopharynx extends from the skull base down to the level of the soft palate 1.
Oropharynx
The oropharynx comprises the middle division and includes four clinically distinct subsites 2:
- Base of tongue (posterior one-third of tongue) 1
- Soft palate (anterior two-thirds) 1
- Tonsillar pillar and fossa (palatine tonsils and surrounding pillars) 1
- Pharyngeal wall (posterior and lateral oropharyngeal walls) 2
The oropharynx is bounded superiorly by the soft palate and inferiorly by the hyoid bone 1. T-staging for oropharyngeal tumors is based on tumor size, similar to oral cavity cancers 1. This region has gained particular clinical importance due to the strong association between HPV type 16 and oropharyngeal cancer development 1.
Hypopharynx
The hypopharynx represents the inferior division of the pharynx, extending from the hyoid bone superiorly to the lower border of the cricoid cartilage inferiorly 1. This region includes the pyriform sinuses (hypopharyngeal spaces formed by the lateral pharyngeal wall and larynx) 1. T-staging for hypopharyngeal tumors is based on subsite involvement rather than size alone 1.
Clinical Significance
Staging Implications
The distinction between these three pharyngeal divisions is critical because:
- T-classification differs by region: Nasopharynx and hypopharynx use subsite-based staging, while oropharynx uses size-based staging similar to oral cavity 1
- N-staging varies: Nasopharyngeal carcinoma has unique nodal staging criteria, with retropharyngeal lymph nodes considered N1 regardless of laterality 1
- Treatment approaches differ: Each region requires specific surgical approaches and radiation field planning 1
Anatomic Boundaries for Treatment Planning
Understanding precise boundaries is essential for radiation therapy planning and surgical resection 1:
- The nasopharynx-oropharynx junction occurs at the level of the soft palate 1
- The oropharynx-hypopharynx junction occurs at the level of the hyoid bone 1
- The hypopharynx-esophagus junction occurs at the lower border of the cricoid cartilage 1
Common Pitfall
A critical error is failing to recognize that approximately 60% of hypopharyngeal cancer patients present with locally advanced disease, requiring aggressive combined modality therapy rather than single-modality treatment 3. The anatomic complexity and late presentation in hypopharyngeal cancers contribute to poorer outcomes compared to other pharyngeal subsites 3.