CT

At many institutions, including the University of North Carolina (UNC), CT is the preferred imaging modality for initial evaluation of the larynx and the neck due to its widespread availability, familiarity to clinicians, and rapidity of image acquisition. The last feature is particularly advantageous for general imaging, because it allows CT to be less susceptible to artifacts caused by swallowing and breathing, which frequently result in suboptimal or nondiagnostic MR studies. A routine neck CT performed on a modern 64-slice multidetector CT scanner takes approximately 10 seconds to acquire with coverage from the skull base to the carina. Unlike early-generation scanners, current multidetector CT scanners also offer excellent spatial resolution and allow for high-quality multiplanar images to be reconstructed in any orientation. Although the soft tissue contrast of CT does not match that of MRI, it is usually adequate for diagnosis and for guiding treatment decisions. Furthermore, CT surpasses MRI in its ability to identify calcification within lesions and to assess fine bone detail.

Unless there is a clear contraindication, the authors recommend that all routine scans be performed with intravenous iodinated contrast. Patients with a documented allergy to iodinated contrast or a history of renal insufficiency can be scanned without contrast, but the absence of intravenous contrast on CT reduces the ability to detect, delineate, and characterize primary lesions; makes it difficult to differentiate blood vessels from lymph nodes; limits the ability to identify abnormal lymph node morphology; and makes it impossible to assess vascular patency. Routine use of multiphase CT scans performed “with and without” contrast or with early-phase (arterial) and late-phase (venous) postcontrast imaging should be avoided altogether, because the additional scanning multiplies patient radiation exposure, while typically providing little or no additional useful information.

MRI

MRI has at least 2 distinct advantages over CT for head and neck imaging:

• 1.
  

  It does not require exposure to ionizing radiation.

  
  
• 2.
  

  It provides superior soft tissue contrast compared with CT.

The second factor can be particularly advantageous for precisely delineating tumor boundaries and for evaluation of cartilaginous invasion by tumor. Nonetheless, MRI is primarily used as a second-line tool for laryngeal imaging at most centers because current imaging protocols take substantially longer to acquire, and the images are more likely to be degraded by motion caused by breathing and swallowing. Furthermore, MR cannot be performed in patients with certain implanted devices and retained metallic foreign bodies.

Fluorodeoxyglucose F 18–Positron Emission Tomography

In the head and neck, fluorodeoxyglucose F 18 (FDG)–positron emission tomography (PET) is primarily used for the staging and post-treatment follow-up of cancers, in particular squamous cell carcinomas. FDG is a glucose analog that is transported across cell membranes and subsequently becomes trapped within cells after phosphorylation. Increased uptake of the radiopharmaceutical is seen in processes in which there is increased cellular metabolism, including malignant tumors and their metastases and inflammatory processes. At UNC, whole-body PET imaging is performed 1 hour after intravenous injection of approximately 12 mCi of FDG. The acquired PET images are coregistered to CT images obtained concurrently on the same dedicated PET/CT scanner, which improves tumor localization.

Epiglottis

The epiglottis is an extremely flexible, leaf-shaped sheet of elastic cartilage, which tapers to a point inferiorly (the petiole) and attaches to the thyroid cartilage just above the anterior commissure. The suprahyoid portion of the epiglottis projects obliquely upward behind the tongue base and functions to protect the larynx during swallowing (see Fig. 2 ).

Laryngeal Cartilages

The thyroid cartilage spans the length of the true and false vocal folds. On axial CT and MRI, this cartilage has the appearance of a chevron or inverted V (see Fig. 1 ). The cricoid cartilage forms a complete ring, which is taller posteriorly and spans the length of the subglottis. The posterior lamina of the cricoid extends cranially to the level of the arytenoid cartilages with which it articulates to form the cricoarytenoid joints. The paired arytenoid cartilages are pyramidal shaped structures that are perched along the superior edge of the posterior cricoid lamina and span the laryngeal ventricle. At the base of each arytenoid is an anterior projection referred to as the vocal process, which serves as the posterior attachment of the vocal ligament and demarcates the level of the true vocal cord.

In most adults, the laryngeal cartilages are easy to identify on CT because they are, with the exception of the epiglottis, usually ossified. Ossified cartilage demonstrates high-attenuation (calcified) cortex peripherally and a central lower attenuation medullary space (see Fig. 1 ). There is, however, considerable variability in the normal degree of cartilage ossification, both between individuals and across ages. In addition, ossified cortex frequently appears discontinuous or can be asymmetric in normal individuals, which can make it difficult to differentiate tumor invasion from normal cortical discontinuity on CT. Ossification of the laryngeal cartilages typically begins in the second decade of life and increases with age, with men tending to show a greater degree of ossification than women later in life.

On MRI, nonossified cartilage demonstrates intermediate to low signal on both T1-weighted and T2-weighted images. With ossification, the cortex eventually becomes calcified and demonstrates very low signal intensity on all MR sequences, whereas the medullary portion transitions to the signal intensity of fat (high on T1-weighted images).

The larynx is traditionally divided into 3 separate yet contiguous parts:

• 1.
  

  Supraglottis

  
  
• 2.
  

  Glottis

  
  
• 3.
  

  Subglottis

Supraglottis

The supraglottis extends from the base of the tongue (glossoepiglottic and pharyngoepiglottic folds, specifically) to the apex of the laryngeal ventricle and contains the epiglottis, the anterior aspect of the aryepiglottic folds, the false vocal cords, the laryngeal ventricle, and the arytenoid cartilages. An important midline imaging landmark in the supraglottis is the preepiglottic space, which is a fat-containing space situated between the ventral surface of the epiglottis posteriorly and the hyoid bone, thyrohyoid membrane, and thyroid cartilage anteriorly. Its upper margin is formed by the thyrohyoid ligament and its caudal margin is the thyroepiglottic ligament.

Posteriorly, the supraglottis communicates with the hypopharynx, with which it shares a significant continuous mucosal interface and is separated by the aryepiglottic folds. At the base of the supraglottis, demarcating it from the glottis, are the laryngeal ventricles and the upper arytenoid cartilages. Axial images through the supraglottis are useful for visualizing the epiglottis, aryepiglottic folds, false vocal cords, and arytenoids, whereas coronal images nicely demonstrate the false vocal folds and laryngeal ventricles (see Figs. 2 and 3 ).

Glottis

The glottis consists of the soft tissues of the thyroarytenoid musculature and vocal ligament, which are essentially indistinguishable on imaging studies and together make up the true vocal cords. The glottis is defined as extending from the apex of the laryngeal ventricle to 1 cm below that level. The vocal ligaments meet anteriorly at the anterior commissure. Axial and coronal images are most useful for assessing the true vocal folds, with the midcoronal plane best depicting the relationship between the true cords, laryngeal ventricles, and false cords (see Figs. 2 and 3 ). Axial images are most useful for evaluating the anterior commissures, which should normally measure no more than 2 mm in greatest thickness (see Fig. 2 ).

Spanning the lateral supraglottic and glottic regions is a paired compartment known as the paraglottic (or paralaryngeal) space, which resides between the laryngeal mucosa and the inner surface of the thyroid cartilage and is composed of fat, lymphatics, and the intrinsic laryngeal musculature. This space is continuous with the preepiglottic space superiorly and is bounded inferiorly by the conus elasticus. As in the preepiglottic space, fat in the paraglottic space is often replaced or obscured by pathologic processes, making it an important imaging landmark for detecting submucosal disease spread in the supraglottic larynx. At the glottis, there is generally no fat visible in the paraglottic space, because the thyroarytenoid muscle fills the space at this level. Neither the preepiglottic nor paraglottic spaces are visible endoscopically. Therefore, complete evaluation of these spaces requires cross-sectional imaging, on which they normally demonstrate low density on CT and high signal intensity on T1-weighted MR. The preepiglottic space is generally best viewed on axial and sagittal images, whereas the axial and coronal planes are usually best for depicting the paraglottic spaces (see Figs. 2 and 3 ).

Subglottis

The subglottis contains the inferior part of the cricoid cartilage and extends from the inferior surface of the glottis (as discussed previously, defined by a plane located 1 cm below the apex of the laryngeal ventricle) to the inferior margin of the cricoid cartilage. In the subglottis, the mucosa is closely apposed to the inner surface of the cricoid, so soft tissue is not normally seen between the airway and the cricoid cartilage (see Fig. 2 ).

Staging and Surveillance of Squamous Cell Carcinoma

At UNC, the most common indications for laryngeal imaging are initial staging of a suspected or biopsy-proved squamous cell carcinoma and post-treatment surveillance. In the former case, the primary goals of imaging are to evaluate the subsites of the larynx that are involved, to assess the extent of submucosal or extralaryngeal tumor spread, to detect tumor invasion of cartilage, and to identify regional spread to lymph nodes, all of which influence decisions regarding the most appropriate therapy (discussed later).

Evaluation of Submucosal Masses

Occasionally, patients present with an entirely submucosal mass with normal overlying mucosa by direct visualization. These lesions are more likely due to processes other than squamous cell carcinoma, and, in these cases, imaging is indicated to confirm the presence of a mass, to determine the deep structures involved, to characterize the potential etiology of the lesion, and, when necessary, to direct the endoscopist to the optimal site(s) from which to obtain deep biopsies. Although the imaging characteristics of submucosal tumors are often nonspecific, certain lesions may demonstrate typical imaging features that allow a specific diagnosis to be made or guide the differential diagnosis.

Evaluation of Hoarseness and Vocal Cord Paralysis

Laryngoscopy remains the primary diagnostic tool for evaluating patients with dysphonia, and in most cases imaging studies are not indicated because a cause can be identified via direct assessment. Indications in which imaging is warranted include (1) vocal cord paralysis or paresis, (2) presence of a mass or lesion of the vocal fold or larynx that suggests malignancy or airway obstruction, and (3) the need to exclude a potentially reducible arytenoid subluxation or dislocation. If a true vocal fold palsy is identified and recent surgery can explain the paralysis, then imaging studies are not usually useful. If the cause of vocal fold paralysis is not evident by history or on laryngoscopy, however, then imaging should be performed rule out a lesion along the course of the vagus or recurrent laryngeal nerve (discussed later). In general, the authors prefer CT for this purpose and reserve MRI for evaluation of pathology suspected at or above the skull base.

Evaluation of Laryngeal Trauma

CT is the imaging study of choice for the initial evaluation of blunt or penetrating laryngeal trauma. It is typically performed in conjunction with direct fiberoptic laryngoscopy and is useful for demonstrating fractures of the laryngeal cartilages and hyoid bone, joint dislocations, submucosal hematomas, and the degree of airway obstruction. Whether imaging is indicated in all cases of laryngotracheal injury or only on a selective basis remains an area of debate. Some investigators suggest that CT is not indicated in patients with mild, isolated injuries or in those with severe injuries requiring immediate surgical intervention, whereas other investigators routinely order CT for cases of known or suspected laryngeal trauma once a patient has been stabilized and can be safely transported from an emergency department or operating room.

Evaluation of Laryngotracheal Stenosis

At many centers, CT imaging is routinely performed in the preoperative assessment of patients with laryngotracheal stenosis. The combination of unlimited multiplanar reformatting capabilities and 3-D viewing techniques available with modern multislice scanners and viewing software allows CT to accurately demonstrate the site, length, and severity of stenoses in a noninvasive fashion ( Fig. 4 ). Although endoscopy remains the gold standard for endoluminal evaluation of the upper airways, particularly with regards to assessment of the airway mucosa, CT often provides valuable complementary information, because it can demonstrate the presence and distribution of airway thickening, the overall length of the stenotic segment, the presence of associated cartilage fractures, multifocal stenoses, and whether a stenosis is due to external compression from an extraluminal process. Furthermore, CT imaging may be better at characterizing high-grade and total stenoses (Cotton grades III and IV), which often cannot be negotiated with a rigid endoscope.

Subglottic and tracheal stenosis in a 26-year-old man who previously underwent emergent cricothyroidotomy with prolonged intubation for trauma, now with persistent dyspnea since being decannulated. ( A ) Anteroposterior (AP), left anterior oblique (LAO), and lateral (LAT) projections from a 3-D CT surface shaded reconstruction of the airway demonstrate a long segment stenosis of the subglottis and trachea, with a focal area of severe proximal tracheal narrowing ( large arrows ). ( Arrowhead ) Anterior commissure; ( small arrows ) true vocal fold level. Axial CT image through the subglottis ( B ) Demonstrates circumferential soft tissue thickening along the airway wall and fragmentation of the cricoid cartilage.

Squamous Cell Carcinoma

Approximately 12,760 new cases of laryngeal cancer are diagnosed in the United States annually, with an estimated 3560 deaths caused by the disease every year. Of these, more than 90% are squamous cell carcinomas. Proper interpretation of imaging studies performed for known or suspected carcinomas of the larynx depends on knowledge of typical patterns of spread of disease based on the site of origin of the tumor, with particular attention to the findings that change the staging of the cancer and can, therefore, affect treatment planning and outcomes. Malignancies of the larynx are staged by the TNM system defined by the International Union Against Cancer and the American Joint Commission on Cancer, which is used to help determine patient treatment and prognosis and to facilitate clinical research. The clinical or pretherapeutic classification of the primary tumor (summarized in Table 1 ) is based on site of origin of the original lesion and the extent of invasion into the adjacent structures.

Staging and treatment for laryngeal cancers

Over the past decade, the paradigm for initial treatment of early to moderately advanced squamous cell cancers of the larynx has shifted away from open partial or total laryngectomy in favor of organ-preserving modalities, such as radiation therapy (RT) alone, combined concurrent chemoradiotherapy (CRT), and transoral endoscopic laser microsurgery with or without adjuvant postoperative RT or CRT. Still, open laryngectomies continue to be performed both primarily for advanced-stage disease and for salvage of initial treatment failures. The radiologic survey should, therefore, focus on findings that affect the overall staging and prognosis of a given cancer, determine the resectability of a tumor, and, finally, affect the feasibility of subtotal surgical options. In addition to the location and absolute volume of tumor, important features to assess on staging scans should include

• 1.
  

  Preepiglottic and/or paraglottic space invasion

  
  
• 2.
  

  Anterior or posterior commissure involvement

  
  
• 3.
  

  Transglottic tumor extension

  
  
• 4.
  

  Subglottic extension

  
  
• 5.
  

  Neoplastic cartilage invasion

  
  
• 6.
  

  Involvement of the carotid artery and/or prevertebral soft tissues

  
  
• 7.
  

  Regional nodal disease

Supraglottic and glottic carcinomas demonstrating preepiglottic or paraglottic space invasion are staged as at least T3 tumors, regardless of whether vocal cord fixation is evident clinically (see Table 1 ). Because these spaces communicate, there is no barrier to prevent spread of tumor between them once one is invaded. Furthermore, tumor involvement of these spaces is associated with a greater likelihood of nodal metastases and has been reported to be associated with poorer cure rates after RT. Preepiglottic space invasion also affects reconstruction options for supracricoid laryngectomies, because minor preepiglottic invasion is a contraindication for supracricoid laryngectomies with cricohyoidoepiglottopexy, whereas massive preepiglottic space even precludes supracricoid laryngectomies with cricohyoidopexy. Submucosal tumor spread into the preepiglottic and paraglottic spaces can be impossible to appreciate on clinical examination, and, therefore, imaging is necessary to exclude its presence. On both CT and MR, tumor invasion can be identified as soft tissue replacement of the normal fat within these spaces ( Figs. 5 and 6 ).

Preepiglottic space invasion by squamous cell carcinoma. Axial postcontrast CT image at the level of the hyoid bone in a patient with an epiglottic cancer demonstrates enhancing tumor extending from the epiglottis into the normally fat-containing preepiglottic space ( arrow ).

Paraglottic space invasion by squamous cell carcinoma. Axial contrast-enhanced CT image demonstrates an enhancing tumor of the right false vocal fold with deep extension in the right paraglottic space ( arrows ). Compare this with the normal-appearing fat in the paraglottic space on the left.

Anterior or posterior commissure involvement by a glottic tumor does not actually affect T staging but can drastically affect options for treatment and overall prognosis. Endoscopic exposure of the anterior commissure can be problematic, making complete transoral resection more difficult, and outcomes for laser excision of tumors involving the anterior commissure tend to be poorer compared with those confined to the membranous cord. The lack of submucosal tissue overlying the commissures places the mucosa in nearly direct contact with the subjacent thyroid cartilage anteriorly and between the medial aspects of the arytenoid cartilages posteriorly. Therefore, on endoscopy or imaging, the presence of soft tissue thickening (>2 mm) in either the anterior or posterior commissure should be viewed with suspicion, whereas, conversely, the absence of soft tissue in these locations generally excludes tumor involvement ( Fig. 7 ).

Glottic carcinoma with anterior commissure involvement. Axial contrast-enhanced CT image through the glottis demonstrates an enhancing lesion originating on the left true vocal fold ( arrow ) extending across the anterior commissure ( arrowhead ) to involve the anterior third of the right true vocal fold ( curved arrow ). The anterior commissure should normally measure no more than 2 mm in thickness.

Transglottic tumors cross the laryngeal ventricle or anterior commissure to involve both the supraglottis and glottis. Extension of a supraglottic tumor below the laryngeal ventricle to the glottis is a contraindication to performing a standard horizontal supraglottic partial laryngectomy. Coronal imaging can be particularly useful for demonstrating transglottic tumor spread ( Fig. 8 ).

Glottic carcinoma with transglottic and subglottic tumor spread. Coronal contrast-enhanced CT image demonstrates a left glottic carcinoma ( arrows ), which extends across the laryngeal ventricle ( arrowhead ) to involve the supraglottis, as well as inferiorly into the subglottis. The fat of the paraglottic space on the left is infiltrated ( curved arrow ), raising the possibility of paraglottic space invasion (compare with the contralateral paraglottic fat). Note also the presence of asymmetric sclerosis of the right thyroid and cricoid cartilage, which is a suggestive but nonspecific finding of possible cartilage invasion. ( Asterisk ) Right true vocal fold.

Subglottic extension of tumor can be difficult to evaluate endoscopically, and cross-sectional imaging plays a useful role in its identification. The normal subglottis features only a thin layer of mucosa along the endoluminal surface of the cricoid and tracheal cartilages. Thus, any soft tissue thickening seen in this region is suspicious for possible extension of tumor (see Fig. 8 ; Fig. 9 ). Subglottic extension generally precludes any type of partial laryngectomy, leaving only total laryngectomy as a surgical option.

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