TNM Staging Atlas with Oncoanatomy, 2e

CHAPTER 8. Hypopharynx

PERSPECTIVE, PATTERNS OF SPREAD, AND PATHOLOGY

The malignant gradient is an oblique plane following the hypopharyngeal circle. The circle begins with the valleculae at the base of the tongue and worsens as it extends to the piri-form recesses laterally. The poorest prognosis is posteriorly at the postcricoid region above the esophageal inlet with the completion of the circle.

PERSPECTIVE AND PATTERNS OF SPREAD

Although the hypopharynx (laryngopharynx) and larynx are anatomically distinct, they require presentation together. In hunting animals such as the wolf and fox, the larynx projects into the nasopharynx, providing continuity for airways. There is no oropharynx when the epiglottis overrides the uvula and soft palate, providing a continuous air column. With evolution the two-part pharynx arose; as in bipedal man, the food bypasses the larynx laterally in the piriform recess. In this anatomic arrangement, food and fluids can be aspirated and is a common complaint when tumors arise in the hypopharynx. There is a malignant gradient of cancers arising in this site, with the anterior location at the valleculae being more favorable than the lateral piriform fossae, with the least desirable location being the posterior pharyngeal and postcricoid. The common epithelial cancer is squamous cell, with other varieties occurring less often.

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The major sites of malignancy in the hypopharynx occur in the zones of food traffic. The hypopharynx can be viewed as a circular gutter designed to allow the food bolus to circumvent the larynx, which is closed during deglutition. The circle, starting anteriorly, begins with the valleculae at the base of the tongue, extends to the piriform recesses laterally, and is completed posteriorly at the postcricoid region above the esophageal inlet. The epithelial cancers of the piriform recess are by far the most common. Superiorly, they extend into the lateral pharyngeal wall and the base of the tongue, and inferiorly into the cricopharyngeal area. Medially, they can spill into the larynx by infiltrating over the aryepiglottic fold. Very often they invade laterally directly into the soft tissues of the neck. An obscure piriform sinus cancer can present as aspiration pneumonitis. A majority of patients complain of difficulty in swallowing with referral of pain to the external ear, which is attributed to Arnold's nerve, a branch of the vagus nerve (cranial nerve X). This neurologic sign indicates invasion of the larynx. Other signs of cancer progression are fetor oris, difficulty swallowing saliva, and dyspnea. Hoarseness also indicates laryngeal invasion. 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. 8.2Table 8.2).

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Figure 8.1| Squamous cell carcinoma. An infiltrative neoplasm is composed of cohesive nests of tumor.

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Figure 8.2 | Patterns of spread. A. Coronal, posterior view B. Sagittal. The primary cancer (hypopharynx) 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 8.2.

PATHOLOGY

Cancers of the piriform recess are usually squamous cell carcinomas, most often undifferentiated and advanced, spreading in all directions. The pharyngeal mucosa tends to be nonkeratinized stratified squamous epithelium, giving rise to squamous cell cancers predominantly with varying degrees of differentiation (Table 8.1 and Fig. 8.1).

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TNM STAGING CRITERIA

TNM STAGING CRITERIA

True postcricoid tumors are often difficult to distinguish from cancer of the cervical esophagus (Fig. 8.3). There are three definite groups of tumors: (i) cricopharyngeal, (ii) pharyngoesophageal, and (iii) cervical esophageal. There are certain peculiarities in these tumors. For example, they seem to be more common in women and are associated with difficulty in swallowing. The cricopharyngeus muscle, a muscular band formed by the lower part of the inferior constrictor, usually directs the tumor in an encircling fashion, where it tends to remain with extension superiorly. Involvement of the true larynx with invasion into the arytenoids and into the glottis is possible, but much less likely than inferior spread into the esophagus or superior spread into the posterior pharyngeal wall in the direction of peristalsis.

The most difficult cancers to recognize are those in the valleculae, which tend to burrow into the base of the tongue and destroy the epiglottis. Necrosis is common, and deep sinuses may develop in the tongue. Cartilage erosion and disfiguration of the epiglottis are frequently noted. Invasion of the preepiglottic, fat-filled space is common; it offers no resistance to cancer spread.

As stated, the malignant gradient of the hypopharynx is less anteriorly in the valleculae where the prognosis is better than posteriorly and laterally in the piriform recess and post-cricoid regions. However, direct invasion into the soft tissues of the neck and even the jugular vein often lead to distant metastases.

SUMMARY OF CHANGES SEVENTH EDITION AMERICAN JOINT COMMITTEE ON CANCER (AJCC)

The TNM stages according to the 7th Edition of AJCC are illustrated in color code of advancement (Fig. 8.3). 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 8.3).

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Figure 8.3 | TNM stage grouping. Hypopharyngeal cancers are aggressive malignancies that invade into the larynx and/or directly into cervical neck nodes. Vertical presentations of stage groupings, which follow same color code for cancer stage advancement, are organized in horizontal lanes: Stage 0, yellow; I, green; II, blue; III, purple; IVA, red; IVB, black. Definitions of TN on left and stage grouping on right.

T-ONCOANATOMY

ORIENTATION OF THREE-PLANAR ONCOANATOMY

The anatomic isocenter of the hypopharynx is at the C4–5 level. It is vertically in line with the anterior border of the ramus of the mandible and its inferior border anteriorly begins at level of the hyoid bone. The anterior bullet is the level of the hyoid bone to the left and right of midline (Fig. 8.4A) and the lateral bullet is just below the greater horns of the hyoid bone (Fig. 8.4B).

T-oncoanatomy

The hypopharynx is the lower continuation of the pharyngeal tube and is anatomically defined laterally and posteriorly by the middle and inferior constrictor muscles and anteriorly by the hyoid bone, thyroid, and cricoid cartilage (Fig. 8.5). If the larynx were postnasal, anatomy would be less complex and the oropharynx and hypopharynx functionally and structurally would be one. The descent of the larynx transforms the tube into a series of symmetrical gutters surrounding the larynx (Fig. 8.5).

• Coronal view (Fig. 8.5A): The hypopharynx is best understood anatomically from a posterior coronal view, obtained by separating the inferior constrictor muscles at the mid-line. The hypopharyngeal sphincters and the piriform recesses circumvent the larynx to lead food into the esophagus. The superior laryngeal nerve enters the larynx and can be trapped by piriform sinus cancers.

• Sagittal plane (Fig. 8.5B) allows identification of the post-cricoid region and establishes the relationship to the larynx of the beginning of the trachea and the beginning of the esophagus.

• Transverse plane and a cross-section at C4–5 (Fig. 8.5C) basically identifies the intimate relationship of the pharyngeal tube to the cartilages, bones, and muscles in the neck. The carotid artery and its branches, as well as the jugular vein in the retropharyngeal space, has only cranial nerve X and the cervical sympathetics. Most of the neck volume is posterior to the prevertebral fascia, which contains the spinal cord and nerve trunks to form the brachial plexus.

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Figure 8.4 | Orientation of three-planar T-oncoanatomy. The anatomic isocenter is at the axial level at C4/C5. A. Coronal. B. Sagittal

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Figure 8.5 | T-oncoanatomy. The Color Code for the anatomic sites correlates with the color code for the stage group (Fig. 8.3) and patterns of spread (Fig. 8.2) and SIMLAP table (Table 8.2). Connecting the dots in similar colors will provide an appreciation for the 3D Oncoanatomy.

N-ONCOANATOMY AND M-ONCOANATOMY

N-ONCOANATOMY

The major lymph node drainage is into the jugular chain of nodes (Fig. 8.6Table 8.4). The deep cervical node and posterior triangle nodes are also readily related to the hypopharynx. The vagus nerve (cranial nerve X) plays an important role in sensation and muscular innervation of the hypopharynx and larynx. Note that only the vagus nerve is left in the lower neck as the other cranial nerves terminate in the head with the exception of the spinal accessory XI nerve. The jugulo-omohyoid node is often the sentinel node for hypopharyngeal cancers. There is a high degree of lymph node involvement including the parapharyngeal and retropharyngeal nodes, as well as the jugulodigastric and jugulo-omohyoid nodes. The incidence and distribution of clinically negative neck node (N0) Table 8.5A and clinically positive (N+) Table 8.5B according to AJCC levels (Fig. 8.7A,B).

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 is an arterial chemoreceptor and baroreceptor area, respectively (see Fig. 8.6).

The target organ for hypopharyngeal spread is classically the lung.

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Figure 8.6 | N-oncoanatomy. The red node highlights the sentinel node, which is the jugulo-omohyoid node. A. Anterior view. B. Lateral view. M-oncoanatomy is determined by the right internal jugular vein, which joins with the right subclavian vein to form the right brachiocephalic vein, which drains into the superior vena cava on the right, and the left brachiocephalic vein, which drains into the superior vena cava and then the right side of the heart and then into the lung.

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Sentinel and Regional Nodes: Hypopharynx (Unilateral and Bilateral) TABLE 8.4

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Figure 8.7 | A. Incidence and distribution of N0 neck node regional matastases. B. Incidence and distribution of N+ neck according to AJCC neck regions. Fig. 8.7A correlates with Table 8.5AFig. 8.7B correlates with Table 8.5B.

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STAGING WORKUP

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Imaging Modalities and Strategies for Diagnosis and Staging for Head and

RULES OF CLASSIFICATION AND STAGING

Clinical Staging and Imaging

For hypopharyngeal cancers, careful history taking, inspection, and palpations of the face and neck are essential. Testing all cranial nerves is critical. Both direct and indirect endoscopy are useful. Despite patient cooperation, pharyngeal cancers are inaccessible and imaging is important. To determine the true extent of primary hypopharyngeal 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 8.6 and Fig. 8.8).

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, but 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

• With hypopharyngeal carcinomas, cartilage invasion is often clinically occult and is therefore best detected by imaging. Submucosal extension is also better detected with imaging.

• All CT studies should be performed after contrast enhancement is administered by using a bolus technique.

• A collapsed (paralyzed) piriform sinus may mimic a tumor on both CT and MRI studies.

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.

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Figure 8.8 | Neck and Larynx—Axial CT scan. The CT/MRI transverse section can be correlated with the anatomy in Figure 8.5C as an assist to staging.

CANCER STATISTICS AND SURVIVAL

Generally, cancers of the oral cavity, pharynx, and 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 8.2). Long-term survival is exceptional in thyroid cancers, 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%. A multidisciplinary approach is vital, and normal tissue conservation and reconstructive techniques have both 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, hypopharyngeal cancers are found in advanced stages, particularly pyriform sinus and postcricoid cancers, with the poorest survival in head and neck sites at 20% to 25% at 5 years. Localized early cancers have a 5-year survival rate of 50% (Fig 8.9A and Fig 8.9B), whereas advanced malignancies hover in the 25% range.

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Figure 8.9 | 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.)



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