PERSPECTIVE, PATTERNS OF SPREAD, AND PATHOLOGY
The TNM patterns of spread and the malignant gradient are predetermined by the underlying musculature anatomy of the tonsillar pillars.
PERSPECTIVE AND PATTERNS OF SPREAD
The oropharynx is the isocenter of the upper aerodigestive tract and is composed of a series of large sphincters, which receives the bolus of food and initiates the act of swallowing. The need for sphincteric mechanisms arises because the physiology of deglutition ensures that the contents of tubular structures move in one direction to ensure their proper digestion. Once the bolus is swallowed, a series of involuntary muscular movements of the tube propel the food onward. The chief sphincter of the upper aerodigestive tract is the muscular pharynx (Fig. 7.2).
Cancers of the anterior pillar follow the palatoglossal muscle, which either encircle the soft palate and uvula or, alternately, follow the fascial plane inferiorly and infiltrate the tongue. Cancers of the pharyngonasal sphincter (Passavant's fold) consist of palatal neoplasms that act as a nasopharyngeal neoplasm. This sphincter prevents nasal regurgitation and, in effect, ensures closure and separation of the nasal passage from the oral cavity and pharynx while swallowing. Cancers of the posterior pillar (palatopharyngeal muscle) of the tonsil invade the posterior wall of the pharynx (Fig. 7.2). The contraction of the superior constrictor muscle of the pharynx during swallowing forms a prominence known as Passavant's fold on the posterior wall of the nasopharynx, which acts as a protective barrier. Cancers in this area tend to appear as irregular surface lesions, spreading circumferentially on the oral and pharyngeal surface. Odynophagia (pain on swallowing) may be ignored and attributed to the common cold. To the astute clinician, dysphagia-producing pain referred to the middle ear is attributed to the referral of pain to the nerve of Jacobson, a branch of the glossopharyngeal nerve (cranial nerve IX). Patterns of Spread are presented as a cancer crab that can invade in six basic directions Superior-Inferior, Medial-Lateral, Anterior-Posterior (SIMLAP) of adjacent anatomic sites (Fig. 7.2; Table 7.2).
PATHOLOGY
Tumors of the oropharynx arise from the mucosal lining and are similar to those of the nasopharynx; the tonsil and base of the tongue are a continuation of Waldeyer's ring. The most common neoplasms are squamous cell cancers exhibiting varying degrees of differentiation and anaplasia; most of the discussion surrounding these neoplasms refers to their pattern of spread (Table 7.1; Fig. 7.1). Lymphomas tend to be bulky exophytic lesions. They enlarge the palatine tonsils and/or lingual tonsils without deep infiltration. Although cancers can be exophytic, they invariably have a significant endophytic component. Lymphoepitheliomas have both epithelial and lymphatic cells and behave in a fashion consistent with both of these two components. Large primaries with bilateral adenopathy are frequently present at their onset.
Figure 7.1| Squamous cell carcinoma. An infiltrative neoplasm is composed of cohesive nests of tumor.
Figure 7.2 | Patterns of spread. A. Sagittal view: highlights cancer spread from oropharynx into nasopharynx and hypopharynx. B. Coronial view: indicates the sphincter muscular of the pharynx: middle constrictor between superior constrictor of nasopharynx and inferior constrictor of the hypopharynx as to invasive pathways of pharyngeal tube. The primary cancer (oropharynx) invades in various directions, which are color-coded vectors (arrows) representing stage of progression: Tis, yellow; T1, green; T2, blue; T3, purple; T4a; red; and T4b, black. The concept of visualizing patterns of spread to appreciate the surrounding anatomy is well demonstrated by the six directional pattern i.e. SIMLAP Table 7.2.
TNM STAGING CRITERIA
TNM STAGING CRITERIA
The TNM patterns of spread are predetermined by the underlying musculature anatomy. The two pillars of the tonsillar fossa, which need to be distinguished from true tonsil remnants, are readily appreciated on surface anatomy. The two sphincters of the oropharynx are the pharyngonasal and buccopharyngeal sphincters.
Cancers can arise in the posterior pharyngeal wall in the area of the mucous membrane between the posterior pillars on the posterior pharyngeal wall over the bodies of C2 and C3. More frequently, the base of the tongue, which seals off regurgitation by pressing against the oropharyngeal bar, is a favored site for malignancy. The malignant gradient increases as the cancer arises in an anteromedial location versus a posterolateral site. Again, the intimate relationship of the tongue and tonsillar region is reflected in their anatomic structure and muscular arrangements. Deeply penetrating cancers from either site usually extend into and invade the other region. Unlike the oral tongue, the base of tongue contains some fat and lymphoid tissue in between the fibers, as well as a less distinct midline septum, making invasion across to the opposite side a more likely clinical occurrence.
SUMMARY OF CHANGES SEVENTH EDITION AMERICAN COMMITTEE ON CANCER (AJCC)
The TNM stages according to the 7th Edition of AJCC are illustrated in color code of advancement (Fig. 7.3). T4 lesions have been divided into T4a (moderately advanced local disease) and T4b (very advanced local disease), leading to the stratification of Stage IV into Stage IVA (moderately advanced local/regional disease), Stage IVB (very advanced local/regional disease), and Stage IVC (distant metastatic disease). The TNM Staging Matrix is color coded for identification of Stage Group once T and N stages are determined (Table 7.3).
OROPHARYNX
Figure 7.3 | TNM stage grouping. Oropharyngeal cancers spread via the muscle planes into tongue and pharynx from palate in a circumferential fashion. Vertical presentations of stage groupings, which follow the same color code for cancer stage advancement, are organized in horizontal lanes: Stage 0, yellow; I, green; II, blue; III, purple; IVA, red; and IVB, black. Definitions of TN on left and stage grouping on right.
T-ONCOANATOMY
ORIENTATION OF THREE-PLANAR ONCOANATOMY
The anatomic isocenter is located at the C2-3 level and located along the anterior border of the ramus of the mandible and medial to it. A vertical line from the center of the ramus runs through the center of the pharyngeal tube. The anterior surface bullet is at the level of the lips in the midline (Fig. 7.4A) and the lateral bullet penetrates at the angle of the mandible (Fig. 7.4B).
T-oncoanatomy
The pharynx is a fibromuscular tube extending from the base of the skull to the esophagus, regulating the flow of food and air in the upper aerodigestive passage. The pharynx is composed of three sections: (i) the nasal, (ii) the oral, and (iii) the laryngeal pharynx.
• Coronal plane (Fig. 7.5A): There are four major sphincters in the pharynx that regulate the passage of air and food to their ultimate destinations. The sphincters, at the point of the entry, are the buccopharyngeal sphincters guarding the communication between the mouth and the pharynx (fauces). They are formed by the base of the tongue and the oropharyngeal bar, which is produced by a synchronized peristaltic contraction of the posterior oropharyngeal muscular wall. The upper or pharyngonasal opening between the nasopharynx and the oropharynx is protected by a sphincter formed by the soft palate and Passavant's fold. The lower or esophageal opening is protected by the cricopharyngeal sphincter formed by the cricopharyngeal bar and the back of the cricoid cartilage. Cancers invade posteriorly to the pterygoid plate and superiorly into the nasopharynx to the skull.
The fibrous coat (pharyngobasilar fascia) is strong and anchors the pharynx to the base of the skull and the medial pterygoid plate. In a dissection of mucous membranes and tonsils from the lateral oropharyngeal wall, the following muscles may be identified: palatopharyngeus, superior constrictor, styloglossus, stylopharyngeus, and middle constrictor. As in all peristaltic activity in the digestive tract, there are constrictor muscles and longitudinal muscles. This pattern is seen in the pharyngeal wall. There are three inner constrictor muscles: (i) superior, (ii) middle, and (iii) inferior—and an outer, more longitudinal coat—the stylopharyngeus, stylohyoid, and palatopharyngeus muscles. The constrictor muscles are strategically attached to the mandible, the hyoid bone, and the thyroid and cricoid cartilages. They provide the form and structure of the pharyngeal tube.
It is in the coronal plane that the prestyloid compartment can be identified by the fatty or areolar content from the lateral pharyngeal space with the stylopharyngeus and styloglossus muscles. The posterior belly of the digastric muscle arises posteriorly and spreads inferiorly in this space, as does the stylohyoid. Using these same muscles and the styloid process as landmarks, the lateral pharyngeal space is better appreciated with its contents. Posterior to the styloid process is the neurovascular bundle, identified previously in the nasopharyngeal wall.
• Sagittal plane (Fig. 7.5B): The palatopharyngeus muscle is shown, innervation by cranial nerve IX into the base of the tongue. On deep dissection of the tonsillar fossa, the palatopharyngeal and the stylopharyngeus muscles form the longitudinal coat. The constrictor muscles, superior and mainly middle, are the circular inner coat that controls swallowing. The glossopharyngeal nerve supplies one muscle, the stylopharyngeus, and provides special taste to the posterior third of the tongue and sensation to an entire half of the pharyngeal wall; absent gag reflex result when the nerve is lost.
• Transverse plane (Fig. 7.5C): At C2, it demonstrates the medial and lateral pterygoid muscles, than posteriorly the retropharyngeal nodes alongside the carotid and jugular vessels in the retroparotidian space laterally. Deep invasion of the posterior glossopharyngeal muscle along the posterior pillar into retropharyngeal nodes leads to neurologic loss, namely, cranial nerves IX, X, XI, and XII.
Figure 7.4 | Orientation of three-planar T-oncoanatomy. The anatomic isocenter is at the axial level at C3. A. Coronal. B. Sagittal.
Figure 7.5 | T-oncoanatomy. The Color Code for the anatomic sites correlates with the color code for the stage group (Fig. 7.3) and patterns of spread (Fig. 7.2) and SIMLAP table (Table 7.2). Connecting the dots in similar colors will provide an appreciation for the 3D Oncoanatomy.
N-ONCOANATOMY AND M-ONCOANATOMY
N-ONCOANATOMY
There are three major collecting lymphatic trunks in the oropharynx: (i) the middle collecting, (ii) the palatine tonsil, and (iii) the posterior lingual. These drain into the parapharyngeal or retropharyngeal nodes (Fig. 7.6; Table 7.4). The jugulodigastric and jugulo-omohyoid are the most common draining nodes, although upper and lower deep cervical nodes also are first-station nodes. Because of the location of palatine tonsillar lymphoid tissue between the anterior and posterior pillars and the location of lingual tonsils in the base of the tongue, lymphomas commonly arise at these sites. Occasionally, all of Waldeyer's ring can be involved with lymphomatous infiltration, obstructing the oropharynx and nasopharynx. These tumors can become large, growing rapidly and remaining submucosal. Both lymphomas and carcinomas often spread into the jugulodigastric and omodigastric nodes. Rapid spread into other cervical nodes and bilateral involvement is common, reflecting the bilateral drainage of the base of the tongue (Tables 7.5A and 7.5B; Fig. 7.7A). The incidence of neck node metastasis in clinical negative (N0) neck as presented in Figure 7.7A and Table 7.7A compared to a clinical positive neck (Table 7.5B).
M-ONCOANATOMY
Distant metastases are also possible because of the plexus of pharyngeal veins that drain into the jugular vein, and then into the superior vena cava, the right heart, and finally the lungs. The vascular supply of the pharynx arises from the external carotid. The carotid body and sinus located at the bifurcation of the common carotid are arterial chemoreceptor and baroreceptor areas, respectively (see Fig. 7.7B).
Figure 7.6 | N-oncoanatomy: The red node highlights the sentinel node, which is the jugulodigastric node. A. Anterior view. B. Lateral view. M-oncoanatomy is determined by the jugular vein, which joins with the subclavian vein to form the superior vena cava on the right, and the innominate vein, which drains into the right side of the heart and then into lung.
Figure 7.7 | A. Incidence and distribution of N0 neck node regional metastases. B. The Incidence and Distribution of Distant Metastases of Oropharynx Cancers. The Oropharyngeal Cancers can serve as a prototype for head and neck cancers. Lung (58%) is the target organ with liver metastases next (29%) and bone metastases third (22%) followed by distant lymph nodes (17%), mediastinum (14%). The remainder of sites are 11% (kidney) or less than 10%.
STAGING WORKUP
RULES OF CLASSIFICATION AND STAGING
Clinical Staging and Imaging
For oropharyngeal cancers, careful history taking, inspection, and palpation of the face and neck are essential. Testing of all cranial nerves is critical. Both direct and indirect endoscopy are useful. Despite cooperation of the patient, pharyngeal cancers may be inaccessible and imaging is important. To determine the true extent of primary oropharyngeal cancers, imaging is essential. Magnetic resonance imaging (MRI) is superior to computed tomography (CT) in demonstrating soft tissue extension, skull base changes, and perineural invasion (see Table 7.6 and Fig. 7.8 Axial CT).
Pathologic Staging
The gross specimen should be evaluated for margins. Unresected gross residual tumor must be included and marked with clips. All resected lymph node specimens should describe size, number, and level of involved nodes and whether there is extracapsular spread. Specimens taken after radiation, chemotherapy, or both need to be so noted; specimen shrinkages may occur up to 30% after resection itself. Designations pT and pN should be used after histopathologic evaluation. Perineural invasion deserves special notation.
Oncoimaging Annotations
• Staging systems for oropharyngeal carcinomas are based mainly on tumor size criteria and deep extensions.
• All CT studies should be performed after contrast enhancement administered by using a bolus technique.
• Thirty percent of patients with squamous cell carcinoma of the base of the tongue have bilateral metastatic nodes at the time of initial clinical presentation. Many of these nodes are clinically silent and are detected on imaging studies.
• Evaluation of tonsillar and soft palate carcinomas is best done with MRI to determine soft tissue invasion.
PROGNOSIS AND CANCER SURVIVAL
PROGNOSTIC FACTORS
The seventh edition of the AJCC Cancer Staging Manual lists the following prognostic factors for nasal ethmoid sinus cancers:
• Size of lymph nodes
• Extracapsular extension from lymph nodes for head and neck
• Head and neck lymph nodes levels I-III
• Head and neck lymph nodes levels IV-V
• Head and neck lymph nodes levels VI-VII
• Other lymph node group
• Clinical location of cervical nodes
• Extracapsular spread (ECS) clinical
• Extracapsular spread (ECS) pathologic
• Human papillomavirus (HPV) status
• Tumor thickness*
*The foregoing passage is from Edge SB, Byrd DR, and Compton CC, et al, AJCC Cancer Staging Manual, 7th edition. New York, Springer, 2010, p. 99.
Figure 7.8 | Neck and Larynx—Axial CT view. The axial view at C3 provides relationships of oropharynx to oral cavity, and the parapharyngeal space with major blood vessels: carotid artery, jugular vein, and lymph nodes.
CANCER STATISTICS AND SURVIVAL
Generally, cancers of the oral cavity, pharynx, and the upper digestive passage account for 36,540 new cases per year. In addition, cancer of the larynx affects another 12,720 patients and thyroid cancers 44,670. Approximately 25% of head and neck cancer patients die annually, often due to other causes (Table 7.2). Long-term survival for patients with thyroid cancers is an exception, with only 1,500 deaths (5%). The improvement in oral cavity and pharyngeal tumors from 1950 to 2000 was modest at 14% and matches larynx at 15% (see Fig. 1.10). A multidisciplinary approach is vital and both normal tissue conservation and reconstructive techniques have added greatly to quality of life. Unfortunately, this patient population abuses ethanol and nicotine and it is difficult to change these habits. Persistence of smoking and drinking contributes to their demise often from second malignant tumors in adjacent sites.
Specifically, oropharyngeal cancer is often advanced stage II or III when detected and overall survival is only 30% to 40%. The best outcome is with early stage I tonsillar cancers and soft palate as compared to base of tongue and pharyngeal wall, that is, 85% to 90% versus 50% to 60%, respectively. The recent AJCC Survival data indicate T1 and T2 cancers without nodes yields a 5 year survival above 50%, where as nodal involvement stage decreases survival to less then 50%.
Figure 7.9 | Five-year survival rates by stage at diagnosis. (Data from Edge SB, Byrd DR, and Compton CC, et al, AJCC Cancer Staging Manual, 7th edition. New York, Springer, 2010.)