Learning Objectives:
- Understand the anatomy of the oropharynx and its relationship to surrounding structures
- Assess the Lymph nodal stations/levels and drainage patterns in oropharyngeal primaries
- Identify subsites of the oropharynx and common locations of primary SCC
- Common patterns of spread of primary tumors and how they influence the TNM staging
Introduction:
Oropharynx is the part of the pharynx which lies between the soft palate and the upper edge of the epiglottis at the level of the hyoid bone.
(Fig. 1) It contains extensive lymphatic drainage and also structures that are in close proximity to one another.
This can add difficulty to the diagnosis of primary oropharyngeal malignancies particularly squamous cell carcinomas (SCC) and assessment of the spread.
Fortunately,
SCC of different regions of the oropharynx displays their distinctive pattern of spread.
Knowledge of the anatomy and the common spread patterns have significant role in the assessment of primary SCC of the oropharynx and the staging process which in turn dictates the treatment plans.
This exhibit discusses the anatomy of the oropharynx,
imaging findings of mucosal primary and lymph nodal spread and how imaging can influence the TNM staging.
The common pathways of tumour spread of oropharyngeal subsites are also elaborated.
Anatomy:
The squamous epithelium within the oropharynx is derived from endoderm and demonstrates greater potential for the development of poorly differentiated,
aggressive carcinomas as compared to the oral cavity which is derived from ectoderm.
Therefore,
knowledge of the anatomical divisions will allow better prognostic prediction [1].
Anteriorly,
the oropharynx is separated from the oral cavity by the junction between the hard palate and the soft palate,
the oral tongue and the base of tongue,
and the floor of the mouth and the anterior tonsillar pillars.
The superior and inferior margins of the oropharynx are delineated by the plane of the soft palate and the upper border of the epiglottis respectively.
Posteriorly,
the oropharynx is bounded by prevertebral facia and the bodies of the C2 and upper part of the C3 vertebrae.
Within the boundaries of the oropharynx,
the structures of note are the base (posterior one third) of the tongue,
the palatine tonsils enclosed by the anterior and posterior tonsillar pillars,
the soft palate and the posterior wall.
(Fig. 2,
Fig. 3,
Fig. 4, Fig. 5, Fig. 6,
Fig. 7)
Epidemiology:
Oral and pharyngeal cancers,
when grouped together are the sixth most common cancer in the world with a 5 year survival rate of 50% in most countries[2].
In Australia,
the incidence of oropharyngeal malignancies reported by Ariyawardana A and Johnson N showed an annual increase of 1.2% from 1982 to 2008 despite a decline in the overall rates of lip/oral/oropharyngeal cancer [3].
Squamous cell carcinoma (SCC) accounts for more than 90% of the malignant lesions in the oral cavity and the oropharynx with the most commonly recognised risk factors being prolonged use of alcohol and tobacco smoking[1].
Furthermore,
Human Papilomavirus (HPV),
(particularly HPV16,
90-95% of all HPV+ve oropharyngeal SCC) has been shown to be associated with SCC of the upper aerodigestive tract with increasing incidence from 19% in 1987-90 to 47% in 2001-05 and 60% in 2005-06[4].
Trials have demonstrated a better prognosis associated with HPV+ve SCC with an improvement in 2 year survival rate of both stage 3 and 4 SCCs as compared with HPV-ve SCCs (87.5% and 95% compared with 67.2% and 62%)[5,6].
The better prognosis should warrant the diagnosis of HPV status in patients.