Radiography
Findings
Soft tissue radiographs of the neck are good survey studies. Air is used as a natural contrast agent to visualize the lumen of the larynx and trachea. Retropharyngeal tissue thickness can be appreciated. Epiglottis and the aryepiglottic folds are visualized. However, radiography has no role in the current management of laryngeal cancer.
The barium swallow is used to evaluate the pharyngeal wall. The motility and pliability of the pharyngeal wall and the mucosal surfaces are assessed. Tumor infiltration causes lack of pliability or distensibility, as well as mucosal irregularity.
Computed Tomography
Findings
Currently, the imaging of laryngeal cancer includes contrast-enhanced helical CT scanning from the C1 vertebral body to the thoracic inlet, with the section plane parallel to the true vocal cords or the hyoid bone. The section thickness should not exceed 3 mm. Patients should be instructed to breathe quietly. With new multidetector-row CT scanners, collimation can be 1 mm, and the larynx can be imaged in a few seconds, providing near-isometric Z -axis resolution with minimal motion artifacts.
All laryngeal studies should be reconstructed using soft tissue algorithms. The area extending from the thyroid bone to the base of the cricoid cartilage is additionally reconstructed with a high-resolution bone algorithm to evaluate for cartilage invasion by tumor. Intravenous contrast enhancement helps to distinguish vascular structures from lymph nodes.
Magnetic Resonance Imaging
Findings
Anatomy
On coronal MRIs, the junction of the supraglottic and glottic larynx is defined by the upper edge of the thyroarytenoid muscle.
MRI technique
MRI is performed by using an anterior neck surface coil. T1- and T2-weighted images are obtained in the axial and coronal planes by using 3- or 5-mm-thick sections with a 1-mm gap. Peripheral gating and/or flow compensation may be used to decrease artifact from vascular flow.
Unlike CT, portions of the MRI examination should be performed before and after contrast enhancement. On nonenhanced studies, tumors are of intermediate signal intensity and easily distinguished from adjacent fat. After gadolinium enhancement, fat suppression helps in differentiating enhancing tumor from the normal pre-epiglottic and paraglottic fat.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble
movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Supraglottic carcinomas
Epiglottic carcinomas
The epiglottis is the most frequent location for cancers that arise in the supraglottic larynx. Tumors may arise from either the suprahyoid or infrahyoid epiglottis. Radiographically, these lesions are often exophytic and circumferential masses that, when detected early, are confined to the midline of the supraglottis. On MRI, these lesions are of intermediate signal intensity and homogeneously enhancing with the administration of contrast material.
Advanced lesions may extend superiorly to invade the vallecula and base of the tongue and also laterally to involve the aryepiglottic folds, false vocal cord, and paralaryngeal space. Direct inferior extension to involve the anterior commissure and subglottis is seen only in advanced lesions.
Tumors arising from the epiglottis may extend anteriorly to involve the pre-epiglottic space. This form of spread is facilitated by the presence of numerous foramina that provide access for tumoral invasion. Invasion of the pre-epiglottic space is often difficult to detect by means of clinical examination and, when present, alters the tumor stage (stage T3). Invasion of the pre-epiglottic space is readily seen on MRIs and best evaluated with nonenhanced T1 weighted images, which show replacement of normal high-signal-intensity fat by intermediate-signal-intensity tumor.
Aryepiglottic fold carcinomas
Tumors of the aryepiglottic fold are typically exophytic lesions that, when detected early, are confined laterally along the aryepiglottic fold. Advanced lesions may extend laterally to involve the adjacent wall of the pyriform sinus or medially to invade the epiglottis. These malignancies may also grow superiorly to involve the pharyngoepiglottic folds, and they may eventually involve the suprahyoid portion of the epiglottis. Inferiorly, these lesions may involve the false vocal cords and ventricle.
Advanced lesions may extend to involve the cricoarytenoid joint, resulting in fixation of the true vocal cord. They may invade the laryngeal cartilages, and they may also extend into the base of the tongue and pharyngeal walls.
Radiographically, early lesions are identified as lobulated masses arising from the aryepiglottic fold. Early mucosal lesions may not be depicted on MRIs.
False vocal cord carcinomas
Squamous cell cancers that arise from the false vocal cords and laryngeal ventricle tend to be ulcerative and infiltrative with a limited exophytic component. Deep invasion by such tumors results in their access to the paraglottic space, and this may lead to fixation of the supraglottic larynx. Because of their close proximity, these tumors may extend inferiorly to involve the true vocal cords. Such submucosal spread is often occult on clinical examination, and understaging of the lesions is possible if this extension is undetected before surgery.
Tumors of the false vocal cords may extend laterally to involve the medial wall of the pyriform sinus and medially to the inferior portion of the epiglottis, thereby increasing the likelihood of invasion of the pre-epiglottic space. MRI is well suited for the imaging of false vocal cord carcinomas. Coronal imaging is beneficial for evaluating the superior and inferior extent of these lesions and for evaluating the presence of transglottic spread.
Glottic carcinomas
The true vocal cords are the most common site of laryngeal carcinomas; the ratio of glottic carcinomas to supraglottic carcinomas is approximately 3:1. The anterior portion of the true vocal cord is the most common location of squamous cell cancer, with most lesions occurring along the free margin of the vocal cord. Anteriorly, the tumor may extend to anterior commissure, where it may involve the contralateral true vocal cord.
Advanced lesions arising within the anterior aspect of the vocal cord or tumors arising along the posterior one third of the cord may extend posteriorly to involve the cricoarytenoid joint and interarytenoid region. Tumors may extend inferiorly, either mucosally or submucosally, to involve the subglottic region.
Early superficial mucosal lesions may not be detected with either CT or MRI. Larger lesions may result in thickening of the involved vocal cord.
The combination of coronal and axial images may be used to determine the amount of subglottic extension and the presence of cartilage invasion. Because the mucosa is near the perichondrium of the thyroid cartilage anteriorly and the cricoid cartilage posteriorly, the presence of soft tissue thicker than 1 mm in both of these areas is considered abnormal.
Invasion of the cartilage may be detected with both CT and MRI, and is more common in glottic tumors than in subglottic carcinomas. MRI is more sensitive, but less specific, than CT in demonstrating cartilage involvement. The fatty marrow in the ossified cartilage has high signal intensity on T1-weighted images. Tumor infiltration into the cartilage results in decreased signal intensity of the marrow. If the cartilage is nonossified, T2-weighted images are more helpful because the tumor is usually hyperintense relative to the non-ossified cartilage. Unfortunately, edema may be mistaken for tumor invasion on T2-weighted images.
The likelihood of nodal involvement associated with glottic carcinomas depends on the stage of the tumor. The incidence of early T1 lesions has been reported to be as low as 2%. This figure increases to approximately 20% for T3 and T4 lesions. The lymph nodes most at risk of metastases are those of the internal jugular chain. Paratracheal lymph nodes may be involved in glottic tumors that have significant subglottic spread.
Subglottic carcinomas
Subglottic carcinomas are rare and account for only 5% of all laryngeal carcinomas. The subglottic region is more commonly involved by the direct extension of a glottic or supraglottic carcinoma than by tumors elsewhere.
When present, these lesions are characteristically circumferential and often extend to involve the undersurface of the true vocal cords. They have a tendency for early invasion of the cricoid cartilage and extension through the cricothyroid membrane.
Primary subglottic carcinomas have a propensity to drain to the paratracheal lymph nodes. The reported incidence of clinically positive nodes in patients with subglottic carcinoma is 10%.
Hypopharyngeal carcinomas
Hypopharyngeal tumors can remain relatively asymptomatic for a long time. Extensive submucosal growth is common. At the time of diagnosis, as many as 75% of patients with hypopharyngeal tumors have metastases to cervical lymph nodes. Systemic metastases also develop in 20-40% of patients with hypopharyngeal tumors.
CT or MRI studies of hypopharyngeal cancer may demonstrate tumor that is more extensive than is apparent on clinical examination, usually because of submucosal spread of the cancer. Carcinoma of the hypopharynx is most common in the pyriform sinus (60%), followed by the postcricoid region (25%) and the post-pharyngeal wall (15%).
Tumors of the pyriform sinus
Superficial mucosal extension into the apex of the pyriform sinus is not well seen with cross-sectional imaging, and it is best evaluated by means of endoscopy. A pyriform sinus tumor may spread submucosally into the posterior wall of the hypopharynx, the postcricoid region, or the aryepiglottic fold. Large tumors also extend up into the paraglottic fat, the pre-epiglottic fat, and the base of the tongue. These tumors may erode the posterosuperior cricoid cartilage and invade the upper pole of the thyroid gland. Tumors arising from the lateral wall or apex of the pyriform sinus have often already invaded the thyroid cartilage at the time of diagnosis.
Lesions of the medial wall of the pyriform sinus may spread along the aryepiglottic fold into the false vocal cord and anterior cartilage. They also may grow posteriorly into the postcricoid region and then cross the midline to involve the contralateral pyriform sinus. Medial wall lesions also invade paraglottic and pre-epiglottic fat.
Tumors of the postcricoid region
Tumors confined to the postcricoid region are rare. The exception occurs in patients (mostly women) with Plummer-Vinson syndrome. Often, tumors of the posterior wall invade the posterior larynx (arytenoids and posterior cricoid cartilage), causing vocal cord paralysis and hoarseness. Large tumors concentrically infiltrate and narrow the lumen of the hypopharynx. These tumors may extend to the cervical esophagus. The junction of the postcricoid region with the esophageal verge should be evaluated for tumor involvement.
Degree of Confidence
MRI has several advantages over CT that may be helpful for presurgical planning. The multiplanar capabilities of MRI are superior to the reformations available with traditional CT, although multidetector-row CT shows early promise. Coronal imaging is helpful for determining involvement of the laryngeal ventricle and transglottic spread. Midsagittal images are helpful for demonstrating the relationship between the tumor and the anterior commissure. MRI is also superior to CT for specific tissue characterization. However, the longer imaging time may contribute to image degradation by motion.
Focal sclerosis or low signal intensity on T1-weighted images is suggestive of cartilage involvement. However, the only truly diagnostic finding is involvement of the strap muscles due to anterior extension of the tumor through the cartilage.
Interest in the use of dextran-coated ultrasmall supramagnetic iron oxide (USPIO) to detect metastatic nodal disease is growing. Patients are usually imaged 24-36 hours after the intravenous administration of USPIO. Compared with its noncontrast signal intensities, the signal intensity of a normally functioning lymph node after the administration of USPIO is markedly reduced on T1- and T2-weighted MRI as a result of both T2 relaxation and magnetic susceptibility effects due to the uptake of the iron particles by macrophages. A metastatic lymph node does not have a signal loss on contrast-enhanced images because the macrophages of the node have been replaced.
The reported sensitivity and specificity in detecting nodal metastases are in the range of 87% to 90%, respectively. These results suggest that the use of USPIO contrast agents may become an important adjunct in evaluating metastatic nodal disease.
Nuclear Imaging
Findings
PET with or without CT is emerging as a critical modality in the staging and monitoring of many head and neck cancers. Although PET provides little information about the extent of tumor within the larynx, the detection of metastases and the follow-up of treated patients increasingly relies on these modalities. PET with CT is also becoming a critical component of intensity-modulated radiation treatment (IMRT).
PET imaging relies on the increased glycolytic activity of neoplastic cells. Although highly sensitive, it does not provide the same anatomic detail that CT or MRI does, and therefore, it does not necessarily allow for precise localization of pathology or determination of involved structures within the larynx. Combined PET and CT scanners may help circumvent this limitation.
FDG PET has been used to look for unknown primary lesions and second primaries, to stage disease prior to therapy, to detect residual and or recurrent disease after therapy, to assess the response to therapy, and to detect distant metastases. A significant limitation of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) PET scanning is its insensitivity to small tumor deposits, in the order of 3-4 mm or less.
To interpret FDG PET images accurately, one must be aware of the normal physiologic distribution of tracer, the spectrum of normal variations in uptake and benign causes of FDG uptake that may be confused with malignancy.
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References
Castelijns JA, Gerritsen GJ, Kaiser MC, et al. Invasion of laryngeal cartilage by cancer: comparison of CT and MR imaging. Radiology. Apr 1988;167(1):199-206. [Medline].
Castelijns JA, van den Brekel MW, Niekoop VA, Snow GB. Imaging of the larynx. Neuroimaging Clin N Am. May 1996;6(2):401-15. [Medline].
Curtin HD. Imaging of the larynx: current concepts. Radiology. Oct 1989;173(1):1-11. [Medline].
Horowitz BL, Woodson GE, Bryan RN. CT of laryngeal tumors. Radiol Clin North Am. Mar 1984;22(1):265-79. [Medline].
Som PM, Curtin HD. Larynx. Head and Neck Imaging. 4th ed. St Louis: Mosby-Year Book;. 2003: 1595-699.
Further Reading
Keywords
cancer of the larynx, laryngeal cancer, laryngeal tumor, glottic tumor, glottic cancer, subglottic tumor, head and neck cancer, smoking, throat cancer
