Squamous cell carcinoma
Squamous epithelium lines the mucosal spaces of the oropharynx, the hypopharynx, and the orocavity. Therefore, squamous cell cancer of the tongue, tonsillar fossa, hypopharynx, and orocavity, including the lip, are very prevalent. In the oropharynx, the most common site of origin of squamous cell carcinoma is the anterior tonsil. Squamous cell cancer from this site can spread deeply beneath intact mucosa very subtly and silently. It can spread to deep spaces through the superior constrictor muscles into the parapharyngeal and carotid spaces. The internal jugular chain of nodes are often affected, particularly in the jugulodigastric region. Because mucosal lesions are very hard to evaluate on imaging, correlation and knowledge of the physical exam is essential in staging these lesions. Deep lesions, of course, are more accurately evaluated on imaging as opposed to physical examination.
The staging of oropharyngeal squamous cell cancer is based upon size of the tumor and invasion of adjacent structures. Therefore, one needs to pay particular attention to tumor extension to deep spaces, especially to the parapharyngeal, carotid, and prevertebral spaces. Evaluation of adenopathy should be made accordingly, particularly in the carotid space.
Tongue base squamous cell cancer can also invade the adjacent deep spaces. Perineural spread is also a possibility. In addition, one should assess for midline crossing, as this can determine whether there can be a hemi rather than total glossectomy. Squamous cell cancer of the tongue base has the propensity to invade inferiorly into submandibular space and extend down to the vallecula and pre-epiglottic space directly. In addition, one should evaluate any oropharyngeal or orocavity cancer for mandibular invasion. Squamous cell cancer of the lip, particularly the lower lip, is the second most common site of squamous cell cancer of the head and neck, the skin being the most common. Squamous cell cancer of the lip can invade the buccal mucosa and the mandible as well as extending into deep spaces.
Squamous cell cancer of the hypopharynx most commonly involves the pyriform sinuses. Cancers that arise in this location tend to be silent and very aggressive. They invade deep spaces early with numerous abnormal nodes. They can invade cartilage and even the larynx. Staging of squamous cell cancer of the hypopharynx is based on location (number of subsites), fixation of the larynx, and invasion of local structures.
Concerning the deep structures, special attention should be made to invasion
of the prevertebral space, as this could be an indication of inoperability.
Violation of the deep cervical fascia, the longus colli muscles, or the
spine itself with bone marrow replacement should be reported. Also, invasion
of the carotid artery with encasement would be a prime concern in regard
to resectability. Some feel that if tumor involvement of the carotid artery
is less than 50%, the tumor likely can be dissected off the carotid. The
likelihood of nonresectability increases markedly when the tumor encases
more than 75% of the carotid. Involvement of the masticator space can also
occur with oropharyngeal and/or orocavity cancers. Involvement of the masticator
space should alert one to the possibility of skull base invasion, particularly
through foramen ovale and/or along the pterygopalatine fossa. Other routes
of skull base entry are along the carotid canal, jugular foramen, and eustachian