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Imaging of laryngeal cancer
Imaging of Laryngeal Cancer Jonas A. Castelijns, Robert Hermans, Michiel W. M. van den Brekel, and Suresh K. Mukherji CT and MRI are the main modalities for examination of laryngeal pathology. Generally, MRI seems to be the optimal method of examination in cooperative patients, especially for evaluation of their larynx before an attempted partial laryngectomy. The choice between the two modalities will also be determined by one's experience with these modalities. The possibilities of CT and MRI vary clearly from each other regarding detection of cartilage invasion. MRI seems to be more sensitive than CT in detection of neoplastic cartilage invasion, but seems to have a somewhat lower specificity, especially for thyroid cartilage involvement. There are increasing indications for imaging regarding tumor volume, and signs of cartilage involvement may have prognostic significance for the risk of tumor recurrence, Copyright © 1998 by W.B. Saunders Company
LMOST ALL laryngeal malignancies are squamous cell cancers. The main therapeutic approaches in laryngeal cancer are radiotherapy alone, and surgery alone or followed by radiotherapy. The choice of treatment is influenced by site and extent of the lesion. Speech-preserving partial laryngectomy in early cancer and total laryngectomy in advanced cancer are the main surgical treatment options. The position of the tumor relative to potential lines of resection determines the feasibility of voice-sparing partial laryngectomies. Correct treatment decisions require an accurate assessment of tumor extent. Large tumor volumes and sometimes also carriage invasion are considered to be a relative contraindiction for radiation therapy. The two most frequently used staging systems are those proposed by the American Joint Commission on Cancer (AJCC 1992), 1 and by the International Union Against Cancer (UICC 1997). 2 Both systems are almost identical with respect to laryngeal tumors, although they differ in several details. In both staging systems, the tumor is classified as T4 (supraglottic, glottic, subglottic) if it invades through one of the laryngeal cartilages (thyroid or cricoid cartilage) and/or extends to other tissues beyond the larynx (eg, to oropharynx, soft tissues of the neck).
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From the Departments of Radiology and Otolaryngology/ Head and Neck Surgery, Academic Hospital "Vrije universiteit, " Amsterdam, The Netherlands; the Department of Radiology, Catholic University Leuven, University Hospitals, UZ Gasthuisberg, Leuven, Belgium; and the Department of Radiology, The School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC. Address reprint requests to Jonas A. Castelijns, MD, Department of Radiology, Academic Hospital "Vrije universiteit," Postbus 7057, 1007 MB Amsterdam, The Netherlands. Copyright © 1998 by W.B. Saunders Company 0887-2171/98/1906-000658. 00/0 492
The validity of any classification is dependent on the diagnostic methods used. Therefore, the issue of staging procedures is generally recognized to be important) However, regarding their recommendations for recently developed imaging methods, these staging systems are not precise for staging of a given laryngeal tumor. AJCC, for instance, states that "a variety of imaging procedures are valuable in evaluating the extent of disease, particularly for advanced tumors and these include laryngeal tomograms, CT scans and MRI scans", but does not indicate when to use either or all of these imaging methods. Without further indication as to the type of imaging, UICC states that imaging should be included in the diagnostic work-up. There are increasing indications that both imaging parameters such as tumor volume and signs of cartilage involvement can provide important prognostic information in patients undergoing treatment with radiotherapy. Laryngeal cancer was evaluated by means of direct visualization, palpation, or (plain) radiography or tomography before the era of CT and MR imaging. Clarification of submucosal extent of disease became possible with the advent of CT and later MR imaging. Neither CT nor MR imaging shows mucosal detail. As in other areas of the head and neck, the primary role of CT and MR imaging in imaging the larynx is to define the extent of disease. Therefore, each modality is complementary to clinical examination. Soon after the introduction of MR imaging, it was recognized that one of its key advantages over other roentgenological imaging methods was the ability to discriminate between different soft tissue types, and between pathology and normal tissue. Gradually, the quality of both CT images (particularly with the introduction of high-resolution CT and spiral CT) and MR imaging (particularly with the introduction of faster scanning techniques) has improved strongly.
Seminars in Ultrasound, CT, and MRI, Vol 19, No 6 (December), 1998: pp 492-504
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Technical Aspects of Computer Tomography During CT imaging of the larynx, the patient's neck should be slightly hyperextended and the shoulders positioned as low as possible. The patient should be immobilized and instructed not to swallow or cough during image acquisition. The plane of section is chosen parallel to the true vocal cords; if these landmarks are not recognized on the lateral scout view, the sections should be made approximately parallel to the midcervical intervertebral disk spaces. 4 Sections made at other angles relative to the true vocal cords can cause interpretative errors, because parts of the false cords may appear at the same level as the true vocal cords. During conventional (incremental) CT, different images are generated separately. Section thickness should not exceed 3 to 4 mm in laryngeal studies. With the field of view focused on the larynx to maximize spatial resolution, adjacent slices should be obtained. Scan time should be 1 to 2 seconds to minimize motion artifacts. Most primary tumors will enhance, which will help to delineate tumor from surrounding structures, especially muscles. Therefore, intravenous contrast medium is always used in studies for laryngeal cancer. 5 The patients are asked to breathe quietly during scanning. With the short scanning times possible on modern CT devices, motion artifacts due to breathing occur rarely. The use of spiral CT offers a number of advantages, the most obvious being the fast data acquisi-
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tion. This allows, for example, to reduce motion artifacts in adults and to limit the dose of injected contrast material in enhanced studies. Another interesting feature of spiral CT is that during transport of the patient, a volumetric data set is obtained. The images can also be calculated retrospectively for each possible table position also in an overlapping fashion. These retrospectively calculated overlapping images allow for better multiplanar reconstructions and three-dimensional reconstructions than non-overlapping incremental scans. These overlapping images are acquired retrospectively, without any additional irradiation for the patient; the only expense is additional computing time. Multiplanar and three-dimensional reconstructions give another view on the pathology, possibly with a better demonstration of tumor extent. Such reconstructions may improve the communication with the clinician. 6 In the larynx, a somewhat better visualization of laryngeal abnormalities and subtle anatomic structures (like the paraglottic fat planes) was reported with dynamic incremental CT, but less motion and respiratory misregistration artifacts are observed with spiral CT. 7 Other investigators did not report a significant difference in the visualization of different laryngeal structures between incremental and spiral CT (Fig 1). 8 Spiral CT examination of the larynx always starts with a long spiral scan of approximately 30 to 40 seconds during quiet respiration. With a table
Fig1. Contrast-enhanced spiral CT of the larynx (2 mm slice thickness, 3 mm/s table feed), in a patient with a glottic carcinoma. (A) Axial section at the glottic level. The left true vocal cord appears thickened and slightly enhancing. The tumor reaches the anterior commissure. The left paraglottic space is infiltrated (compare to normal opposite side [arrowheads]). Marked sclerosis of the left arytenoid (arrows). (B) Axial section at the level of the left false vocal cord. The fatty submucosal tissue of the false vocal cord appears infiltrated (arrowheads): cranial tumor extension. Note also the slight sclerosis of the angle and left lamina of the thyroid cartilage (arrows). The patient was surgically treated. Pathological examination confirmed a well-differentiated squamous cell carcinoma. The arytenoid showed focal neoplastic invasion; in the thyroid cartilage, only inflammatory changes were noted,
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incrementation speed of 3 ram/s, a slice thickness of 2 or 3 mm is generally used. Because diffusion of the contrast medium into the tumor and the metastatic adenopathies takes some time, it is important to start image acquisition not too early after initiation of the contrast injection. Good tumor enhancement is very important because it improves the evaluation of its extension. To obtain both good tumoral and vascular enhancement, a dual injection technique can be used: 50 mL of contrast medium is injected between 120 and 60 seconds before the start of the acquisition, leaving enough time for the diffusion to take place into the soft tissues, and then another 30 mL is injected during the 30 seconds before the start of the acquisition to obtain a good vascular opacification. 9 Modem injection pumps allow such relatively complex injection schemes to be preprogrammed. Good results are also obtainable with a one-phase injection of contrast medium, eg, 80 mL of a contrast medium with 300 mg I/mL at 1 mL/s, starting the image acquisition at the end of the contrast medium injection. Dynamic laryngeal maneuvers during scanning of the larynx and hypopharynx can improve visualization of particular anatomic structures. During phonation, arytenoidal mobility can be judged and a better visualization of the laryngeal ventricle can be obtained; the slight distention of the pyriform sinuses also allows better delineation of the aryepiglottic folds. Modified Valsalvamaneuver (consist-
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ing of blowing air against closed lips, puffing out the cheeks) produces a substantial dilation of the hypopharynx, which may allow better evaluation of the pyriform sinuses, including the postcricoid region (Fig 2). 10 The success rate of these dynamic maneuvers in incremental CT is variable, strongly depending on the cooperation of the patient: consistent repetition of the maneuver for each incremental scan is difficult, spatial misregistration being an important drawback. Furthermore, the incremental acquisition of these additional scans during phonation or Valsalva maneuver is time-consuming. These problems can be largely overcome by spiral CT, because the patient has to do the maneuver only once during one rapid acquisition. The patient needs to be well-informed about what is expected from him/her during the spiral C T study. The dynamic maneuvers need to be exercised with the patient before the examination starts. Often the patients need to be accompanied and encouraged during the actual examination. This small time investment yields good results in the majority of cases. 9 Technical Aspects of MR Imaging MR imaging of patients with laryngeal cancer may be difficult because of these patients' dyspnea, coughing, and mucous secretion. A number of requirements need to be fulfilled to obtain diagnostic images. The use of a dedicated neck coil is indispensable to obtain optimal results. Ideally, the
Fig 2. Contrast-enhanced spiral CT of the larynx, in a patient with a pyriform sinus carcinoma. (A) Axial image during quiet breathing shows subtle soft tissue thickening in the apex of the right piriform sinus (large arrows; compare to opposite side); there is some evidence of subtle infiltration or displacement of the paraglot-tic space fat (arrowhead). (B) Axial image obtained during modified Valsalva maneuver. The right pyriform sinus expands somewhat less than the opposite side; the mucosal irregularity produced by the cancer is now better visible (small arrows),
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volume of the neck coil should match as closely as possible the size of the neck. As a general rule of thumb, effective penetration by the coil is approximately one half the coil diameter at its narrowest point. The neck coils enable one to obtain highresolution and thin-section images in spite of relatively short acquisition times. One needs constantly to take full account of three issues in MR imaging to obtain optimal images: signal-to-noise ratio, spatial resolution, and acquisition time. Signal averaging is the best technique to improve MR image quality. However, benefits of signal averaging must be weighed against the increased scanning time required. Thinner slices improve the visualization of anatomic detail but require longer scanning time to maintain an equivalent signal-to-noise ratio and to image an equal volume-of-interest Finer matrices, such as 512 × 512, improve visualization of anatomic detail, but scanning time increases and signal-to-noise ratio may decrease. Selection of an intermediate matrix size, such as 256 × 256 or 192 × 256, may be an appropriate compromise. The field of view should be reduced as much as possible to improve spatial resolution. For imaging of laryngeal cancer, spin-echo (SE) MR imaging is used because of its accurate and reproducible anatomic depiction of laryngeal tissue. 11The intensities of different tissue types in MR images are affected by a number of acquisition parameters, and the contrast can be manipulated by changes of the pulse sequences. The common timing parameters are repetition time (TR) and echo time (TE). The flip angle of excitation pulses can also be varied. By altering these parameters, it is possible to change the sensitivity of the images to three principal factors: proton density, longitudinal relaxation time (T1), and transverse relaxation time (T2). The Tl-weighted images appear ideal for the study of the laryngeal anatomy. They allow delineation and characterization of tissue more accurately than CT does. Tl-weighted SE images are most appropriate to demonstrate laryngeal anatomy and to assess extent of laryngeal pathology (Fig 3). 12 On T2-weighted SE images, tumor is found to have an increased signal intensity compared with that found on Tl-weighted SE images. The higher signal intensity of squamous cell carcinoma on T2-weighted images may be helpful in delineation of tumor tissue, but it may also be an disadvantage in the larynx because of the high signal areolar tissue within the larynx, which could obscure the
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tumor itself. With spin-echo imaging, the appropriate selection of TR and TE will determine the degree of T1- and T2-weighting. For Tl-weighted spin-echo MR imaging, the minimal length of the TR is based on the number of slices that are required, but must be kept under 800 ms to maintain Tl-weighting. A TR within the range of 400 to 800 ms will allow an adequate number of slices to cover the region of interest. The shortest TE possible (10 to 20 ms) is selected to attain the best signal-to-noise ratio and to minimize T2 effect. To obtain T2-weighted images, we typically use a TR of 2,500 ms and TEs of 20 to 30 ms and 100 ms for the first and later echos, respectively. The axial imaging technique is most appropriate to study location and extent of tumor in intralaryngeal compartments, the laryngeal cartilages, as well as in extralaryngeal structures, such as the infrahyoid muscles, pyriform sinus, and subcutaneous fat. Fast SE T2-weighted imaging should be applied instead of conventional SE techniques by reducing acquisition time and motion artifacts. It is of utmost importance that both sequences T1 and fast T2 SE images are obtained at exact corresponding levels. Interpretation of images that are not obtained at exact corresponding levels could easily lead to misinterpretations regarding the presence or absence of cartilage invasion. Motion artifacts are the most common, easily identifiable phenomena that degrade MR images of the laryngeal area. Motion artifacts due to respiratory movement and those due to random patient movement (swallowing, coughing) may be hard to distinguish from each other. Gross motions produce multiple ghosted images, which usually appear as curvilinear crescents of signal. An increase in either TR value or frequency of the motion increases spacing between parent signal and daughter ghosts. More subtle patient motion results in degraded image quality without obvious ghosting. Irrespective of the direction of the motion, motion ghosts are observed along the phase-encoding axis (normally in the vertical direction of the axial image). Motion artifacts are more prominent on images acquired over a longer examination time (ie, a long repetition time). Most patients can remain sufficiently immobile during approximately 5 to 8 minutes. However, a shorter scanning time will reduce motion artifacts due to coughing and swallowing. The use of turbo spin-echo MR images to obtain T2-weighted MR images may be necessary.
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Fig 3. (A) Coronal, Tl-weighted MR image shows vocal and thyro-arytenoid muscles (arrowheads) with intermediate signal intensity. False vocal cord is found with high signal intensity (arrows), being separated from vocoal muscle by laryngeal ventricle. (B) Axial, Tl-weighted MR image shows the false vocal cord with high signal intensity (arrows). Thyroid cartilage is almost entirely ossified, being found with high signal marrow surrounded by a low signal cortical rim. (C) Axial, Tl-weighted MR image at the true vocal cord level shows muscular tissue of the vocal and thyro-arytenoid muscles (arrows) with intermediate signal intensity,
Comfortable patient positioning and sedation may all be used to reduce these artifacts. Rigidly mounting the surface coil off the patient eliminates coil motion and improves image quality. One must encourage the patient to remain as immobile as possible. After all, the use of short examination times may necessitate some compromise on image resolution. The presence of motion artifacts may interfere in approximately 10% to 15% of the examinations with adequate diagnosis. 13,14The patient should be examined in supine position, the neck slightly hyperextended, the head immobilized. The patient is positioned so that the laryngeal airway is as parallel to the table-top as far as possible. Quiet breathing should occur during the examination with the use of abdominal rather than chest muscles. We begin with a mid sagittal and
parasagittal, Tl-weighted SE MR sequence. This identifies the orientation of the larynx. Axial T1weighted, proton density and relatively T2-weighted MR images are then obtained at exact corresponding levels. Section thickness is 4 mm, with no interslice gap. Four measurements are obtained with Tl-weighted and two measurements are obtained with T2-weighted MR images. For detection of lymph node metastasis, the neck should be examined as well. Appearance of Laryngeal Squamous Cell Carcinoma on CT
Criteria used for tumor involvement are abnormal contrast enhancement, soft tissue thickening, presence of a bulky mass, infiltration of fatty tissue (even without distortion of surrounding soft tis-
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Fig 4. Unenhanced spiral CT of the larynx in a patient with a large iaryngo-hypopharyngeal carcinoma. No contrast medium was injected because of renal failure. (A) Axial image at the level of the cricoid cartilage. Soft tissue thickening is seen in the retrocricoidal hypopharynx (arrow) and also beyond the thyroid cartilage, underneath the thyroid gland (arrowheads). Extensive sclerosis of the cricoid arch and inferior part of the thyroid lamina is seen at the left side. (B) Axial image at the glottic level. Thickening of the left vocal cord, with infiltration of the left paraglottic space (compare to opposite side). The mass is also seen in the apex of the piriform sinus (arrow), extending underneath the pharyngeal constrictor muscle posterolaterally from the thyroid lamina (arrowheads). Note again sclerosis of the left thyroid lamina and left arytenoid. (C) Axial image through the lower supraglottis. Large tumor mass in the left piriform sinus (arrows), extending into the left paraglottic space (arrowheads), (D) Axial image just above the thyroid cartilage. The hypopharyngeal tumor mass bulges into the soft tissues of the neck (arrows); carotid artery (star) is not reached yet. Infiltration of the upper paraglottic space (arrowhead). The patient was surgically treated. Pathologic examination showed a poorly differentiated squamous cell carcinoma; no neoplastic cartilage invasion was found.
sues), or a combination of these (Figs 1, 2, and 4). A soft tissue thickness of more than 1 mm at the anterior commissure is considered pathological, and any tissue thickening between the airway and the cricoid ring is considered to represent subglottic tumor. Several studies have compared the CT findings with the results of whole-organ sectioning after total or partial laryngectomy, showing that computed tomography is an accurate method to visualize laryngeal pathology. 15-21 These correlation studies between whole organ sectioning and CT have also shown some pitfalls. Small foci of mucosal tumor may be difficult to detect or may be invisible on CT images, and associated inflamma~
tory and edematous changes can cause overestimation of the tumor extent on CT. Distortion of adjacent normal structures may mimic tumoral involvement. Gross cartilage invasion can be detected with CT. Because of the large variability in the ossification pattern of the laryngeal cartilages, CT often fails to detect early cartilage invasion. Nonossified hyaline cartilage shows the same density values as tumor on CT images. Demonstration of tumor on the extralaryngeal side of the cartilage is a reliable, but late sign of cartilage invasion. Asymmetrical sclerosis, defined as thickening of the cortical margin and/or increased medullary density, compar-
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ing one arytenoid to the other, or one side of the cricoid or thyroid cartilage to the other side, is a sensitive but nonspecific finding at CT. In only 45% of thyroid and cricoid cartilages displaying sclerosis are tumor cells found within the bone marrow; the other 55% have only perichondrial invasion or no invasion at all. Only 16% of sclerotic arytenoids display tumor cells within the bone marrow and 32% have only peripheral invasion of the fibroelastic process of the vocal process or the perichondrium; the remaining 52% not showing any neoplastic invasion at all (Fig 1).22 Erosion or lysis has been found to be a specific criteria for neoplastic invasion in all cartilages (Fig 5). Other signs, like cartilaginous blow-out or bowing, a serpiginous contour, or obliteration of the medullary space are not very reliable for cartilage invasion. The combination of several diagnostic CT criteria for neoplastic invasion of the laryngeal cartilages seems to constitute a reasonable compromise: when extralaryngeal tumor and erosion or lysis in the thyroid, cricoid, and arytenoid cartilages were combined with sclerosis in the cricoid and arytenoid (but not the thyroid) cartilages, an overall sensitivity of 82%, an overall specificity of 79%, and an overall negative predictive value of 91% were obtained. = Tumor volume is difficult to determine clinically, especially in the head and neck with its complex
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regional anatomy and the infiltrating behavior of the tumors occurring in this region. Volumetric assessment of soft tissue masses is possible with cross-sectional imaging techniques like CT. To determine the volume of a particular structure, its borders are traced on consecutive images. The segmented surface on each image is then calculated. This procedure can be done on the scanner's screen, using a mouse-controlled cursor, or indirectly using a digitizer. The obtained surfaces are then multiplied by the slice interval. The summation of all these obtained volumes represents the total volume of the structure of interest. This technique is called the summation-of-areas technique. 23 The reproducibility of laryngeal tumor volume measurements, based on CT images, has been shown to be acceptable if done by the same experienced observer54 Appearance of Laryngeal Squamous Cell Carcinoma on MRI
In several previous comparative studies, including comparison between MR images and wholeorgan histopathological sections, it has been suggested that Tl-weighted MR images assess accurately the extent of tumor tissue and delineate it with high contrast to surrounding fat, but much less contrast to surrounding muscular tissue. 12
Fig 5. Contrast-enhanced spiral CT of the larynx in a patient with a subglottic carcinoma. (A) Axial image through the subglottis. Semicircular soft tissue thickening in the right subglottic region (large arrowheads), growing anteriorly over the midline. There is sclerosis and lysis at the right side of the cricoid arch (small arrowheads). Some extralaryngeal soft tissue thickening and enhancement can be seen anterior to the larynx (arrows), suggesting tumoral extension through the cricothyroidal membrane. (B) Axial image at the glottic level; some enhancement of the thickened right true vocal cord. Some soft tissue thickening over the medial facet of the right (sclerotic) arytenoid (arrow). The patient was surgically treated. Pathological examination showed a subglottic well differentiated squamous cell carcinoma, extending over the midline and growing into the true vocal cord. The cricoid cartilage was invaded by the tumor, the arytenoid cartilage not. Extralaryngeal extension was not substantiated; an important peritumoral inflammatory reaction was present.
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However, it has been reported recently that inflammation may be frequently observed along the margin of squamous cell carcinoma and may not be differentiated from tumor tissue on Tl-weighted images. 21 Head and neck cancers often display the same signal patterns before and after contrast administration as benign or inflammatory lesions and cannot even be differentiated by means of dynamic contrast-enhanced MR imaging. 25 However, on the basis of Tl-weighted images, it can be maintained that MR images accurately depict the amount of pathological tissue, which may include cancerous and/or inflammatory tissue. Laryngeal cartilages are very difficult to investigate because of their irregular pattern of ossification. 26-28 The hyaline cartilages may be variably composed of calcified and noncalcified cartilage, or of bone with a marrow cavity (Fig 6). 17'26 MR imaging shows ossification patterns more accurately than CT does and allows detection of abnormal signal in cartilages. 12,22Cartilage invasion may be best assessed by the combination of unenhanced T1- and more T2-weighted MR images. The use of GdTPA does not increase the diagnostic accuracy because contrast enhancement does not enable us to differentiate between tumor tissue and inflammation. Several articles explored this issue of detection of cartilage invasion in MRI histopathological correlative studies. Castelijns et al have indicated that MR imaging can help to differentiate tumor tissue from nonossified tissue. 14,28However, num-
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bers of sliced surgical specimens in this study are small. Both tumor and non-ossified cartilage have low signal intensity with short repetition time sequences, tumor had substantially higher signal intensity than nonossified cartilage on more T2weighted sequences (Figs 7, 8). They reported an overall sensitivity of 89% for 0.6-T MR imaging in the detection of neoplastic invasion of cartilage and a specificity of 88%. 14The overall results of Becker et al obtained at 1.5T in a much larger MRI histopathological correlative study were almost identical (sensitivity, 89%; specificity, 84%). 21 However, they found that the ability of MR imaging to help to detect or exclude neoplastic cartilage invasion varied considerably with the histological degree of invasion and from one anatomic site to another. They reported that MR imaging is less reliable in the thyroid cartilage than in the cricoid cartilage and arytenoid cartilages because of relatively high number of false-positive findings. They claim that histopathological correlation indicated that these diagnostic errors were caused by nonneoplastic peritumoral reactions and changes in the cartilage, namely extensive fibrosis, inflammation, and bone resorption adjacent to the tumor without concomittant neoplastic invasion of the perichondrium. At MR imaging, these changes may result in a high signal intensity on T2-weighted images. As stressed before, it is very important that the T1- and T2-weighted images are at e x a c t corresponding level. Otherwise, interpretation may easily lead to false-positive or false-negative results regarding
Fig 6. (A) Patient w i t h a T3 glottic lesion. Axial, proton-density weighted MR image at the glottic level shows thyroid cartilage with l o w signal intensity, being entirely nonossified, Tumor tissue is found with increased signal intensity, being imaged with high contrast with non-ossified tissue. (B) Patient with a T2 glottic lesion. Axial, Tl-weighted MR image at the glottic level shows bone marrow of thyroid, cricoid and arytenoid cartilages with high signal intensity, being surrounded by a l o w signal cortical rim. Cartilages appear to be entirely ossified. Tumor tissue is found with low signal intensity at the anterior part of the left vocal cord, being imaged with high contrast with fatty bone marrow.
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Fig 7. Patient with glottic lesion, staged as "1"3.(A) Axial T1weighted image at the glottic level shows tumor tissue (arrows) with intermediate signal intensity. Both ventral parts of the thyroid laminae are seen with intermediate signal intensity, the dorsal parts being ossified. (B) Axial proton density image shows tumor tissue with increased signal intensity, including the ventral parts of both thyroid laminae (arrowheads), being suspicious for cartilage involvement by pathological tissue.
the presence of cartilage invasion. Interpretation of MR examinations in patients with smaller tumors that did not undergo surgical treatment, suggested that abnormal MR signal patterns in cartilage may be found in a large percentage of patients with laryngeal carcinoma. 29 In this study, a high frequency of abnormal signal in the area of the anterior commissure, suspicious for cartilage invasion, was observed. The study by Becker allows us to state that MR imaging is very accurate in determining that a cartilage is normal. 2~ If the signal intensity in cartilage is abnormal, the cartilage is almost certainly abnormal. However, there may be false-positive findings due to inflammatory disease adjacent to tumor tissue.
Manual outlining of lesions on MR images is moderately accurate when performed by an experienced observer. It is relatively straightforward to implement and, in experienced hands, has been shown to give fairly good intraobserver and interobserver variability.3° However, considerable operatorcomputer interaction time is needed to assess each patient. Comparison Between CT and MRI
Generally, MR imaging seems to be the optimal method of examination in cooperative patients. CT is recommended in patients who may have rapid breathing or coughing from chronic lung disease or if MR imaging is not a option, as in patients with a
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Fig8. Patient with a stage Tlb lesion. {A) Axial Tl-weighted image SE MR image at the true cord level shows tumor (arrowheads) in the anterior two thirds of the left vocal cord, the anterior commissure, and the anterior part of the right vocal cord. The ventral part (arrows) of the left thyroid lamina is either invaded by pathological tissue or consists of nonossified cartilage. (B) Axial proton-density SE MR image demonstrates tumor tissue with slightly increased signal intensity compared with the Tl-weighted image. The anterior part of the left thyroid lamina is also found with increased signal intensity, being suspicious for involvement by pathological tissue.
pacemaker, surgical clips, or severe claustrophobia. Both modalities are able to delineate deep tissue anatomy. MR imaging has a better soft tissue contrast than CT. In contrast, high-resolution CT produces images with thinner slice thickness and higher spatial resolution than MR imaging. CT studies of the larynx can be acquired in less time, and adequate images are obtained in nearly all patients. Both modalities do not enable differentiation between tumor tissue and surrounding inflammatory tissue, which may be present to a more or less extent. Both Tl-weighted MR images and high-resolution CT are appropriate to assess tumor extent in various laryngeal compartments such as pre-epiglottic space, paraglottic space and both commissures. The possibilities of CT and MRI vary clearly from each other regarding detection of cartilage invasion. CT criteria for the presence of cartilage invasion are mainly based on bony abnormalities. In contrast, MR imaging shows alterations in (ossified) cartilage directly. MRI seems to be more sensitive than CT in detection of neoplastic cartilage invasion, but seems to have a somewhat lower specificity, especially for thyroid cartilage involvement. 31,32 Most probably CT findings cause an underestimation, whereas MRI findings produce an
overestimation of the actual presence of cartilage invasion. The choice between CT and MRI may partly be settled by the clinical question. If it is important to exclude cartilage invasion, as in considerations regarding partial laryngectomy, MR imaging may be indicated. If cartilage invasion should be shown with more confidence, CT may be more appropriate. Self-evidently, the prognostic value of each of the modalities and its defined criteria are of high value to determine the choice of treatment. Consequently, the number of studies evaluating the prognostic value of imaging findings are increasing. At present, this theme has been elaborated more extensively and in more detail for CT than for MRI. In CT studies, tumors have been classified for tumor location (glottic, supraglottic) and tumor stage. Freeman et al, whose study (31 patients) was updated by Mancuso (63 patients), were able to identify those patients with T1-T4 supraglottic carcinomas who had a higher likelihood of local control after definitive radiotherapy based on pretreatment CT volumetric analysis (tumors of < 6 mL had a probability of 83%, respectively 89% of local control, whereas tumors of > 6 mL had only a control rate of 46%, respectively 40%). 31,32 Lee et al, whose study (18 patients) was updated by
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Pameijer et al (42 patients), could stratify in a similar way patients with T3 glottic carcinoma into groups with different likelihood of local control (tumors of <3.5 mL had a probability of 92%, respectively 85% of local control after definitive radiotherapy, whereas tumors of >3.5 mL had only a local control rate of 33%, respectively 22%). 33,34 The results of the study by Hermans corroborate well these previous findings. 24 It seems to be no question that tumor volume as determined by CT or MRI is a predictor for risk of tumor recurrence in patients treated by irradiation. The results regarding the prognostic value of cartilage abnormalities seem to be somewhat contradictory. Generally, in studies evaluating CT, cartilage abnormalities as shown by this modality seem to have somewhat less prognostic value for local failure after irradiation, whereas MRI findings for cartilage involvement are reported to be more indicative for an increased risk of tumor recurrence. 29,3° We agree with Million that the "myth about the radiocurability and bone and/or cartilage" should be replaced by an understanding of relative rates of control by radiotherapy. 35 If voice conservation surgery is being considered, MR imaging is useful for assessing those structures (such as laryngeal cartilages) whose involvement would contraindicate partial laryngectomy. MR imaging is helpful, and probably more so than CT, in ensuring that these requirements are met when conservation therapy is being considered. MRI is especially helpful in assessing the cranio-caudal extent of disease. Because MR imaging seems to be very accurate in determining the normal part of the cartilage, a type of partial laryngectomy may be designed in the future for tumors in which cartilage involvement is present. Post-Treatment Evaluation
After radiation therapy, endoscopic examination is more limited than in untreated patients. Residual or recurrent carcinoma is often difficult to detect. Radiological investigations seem to be less effective in patients suspected of having a recurrent or residual tumor after previous irradiation treatment, due to diffuse tissue changes including varying amounts of fibrosis and edema. Accurate diagnosis on the basis of CT or MRI in patients who underwent radiation therapy requires knowledge of expected radiological changes. These changes in-
clude symmetric thickening of the false cords, aryepiglottic folds and the epiglottis, and a changed appearance of paralaryngeal fat. Glottic changes include a changed appearance of the paraglottic fat planes and thickening of the anterior and posterior commissures. Subglottic changes include thickening of the mucosa and submucosa. 3v However, neither on CT nor on MRI, definite distinction can be made among cancer, edema, and irradiation fibrosis.e8,37 Follow-up CT is probably not cost-effective in patients who were irradiated for a small-sized carcinoma of the larynx, because the local control rates for such tumors after radiation therapy are very high. However, there are indications that patients with a higher likelihood of local failure, such as supraglottic, T3- or T4-glottic, and hypopharyngeal carcinomas may benefit from a baseline follow-up CT study about 4 months after completion of RT.34,38 If the baseline CT study shows complete resolution of the tumor at the primary site and symmetrically appearing laryngeal and hypopharyngeal tissues (ie, expected RT related changes), the patient is very likely to be controlled locally and fm'ther follow-up CT studies are not necessary. If less than 50% estimated volume reduction or a focal mass with a diameter larger than 1 cm is found, immediate further investigation is warranted, because the likelihood of local failure is high. 7 If the laryngeal tissues seem asymmetric, or a focal mass with a diameter smaller than 1 cm is found, unless clinical examination is already suspect for local failure, further follow-up CT studies are needed; a time interval of 3 to 4 months is recommended, to be continued up to 2 years after completion of radiotherapy. In a substantial number of cases, it seems possible to detect local failure earlier by CT than by clinical examination alone. These patients can then be salvaged at an earlier stage of local recurrence. 34 Control by FDG-PET may well be more useful than CT or MRI in monitoring tumor response to irradiation treatment of head and neck carcinomas generally.38-4°Normal structures retain their appearance on FDG-PET images after radiation therapy. In addition, FDG-PET imaging can be performed to follow tumor response to radiation therapy on the basis of quantitative changes in tumor glucose metabolism and, therefore, FDG uptake. 4° Seifert
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r e p o r t e d t h a t F D G - P E T also e n a b l e s t u m o r m o n i t o r ing d u r i n g a n d after t r e a t m e n t w i t h c h e m o t h e r apy. 41 F D G - S P E C T a v o i d s the h i g h cost o f P E T i m a g i n g . H o w e v e r , the u l t i m a t e v a l u e o f this m o d a l ity f o r m o n i t o r i n g t h e r a p e u t i c e f f e c t i v e n e s s or e v a l u a t i n g t u m o r r e c u r r e n c e a n d its v a l u e c o m p a r e d w i t h t h a t o f C T or M R I r e m a i n s to b e d e t e r m i n e d in p a t i e n t s w i t h s q u a m o u s cell carcin o m a o f t h e larynx.
L a r y n g e a l d e f o r m i t y a n d loss o f s y m m e t r y d u e to c o n s e r v a t i o n s u r g e r y c o m p l i c a t e t h e i n t e r p r e t a t i o n o f r a d i o l o g i c a l findings. A c c u r a t e d i a g n o s i s i n p a t i e n t s w h o u n d e r w e n t c o n s e r v a t i o n s u r g e r y requires k n o w l e d g e o f e x p e c t e d a n a t o m i c c h a n g e s . B a s e l i n e studies, w h i c h s h o u l d b e d o n e 2 or 3 m o n t h s p o s t o p e r a t i v e l y , m a y b e essential. 42 F D G P E T m a y b e u s e f u l as w e l l i n e v a l u a t i n g p o s t s u r g e r y p a t i e n t s for r e c u r r e n t t u m o r s . 38
REFERENCES
1. American Joint Committee on Cancer (AJCC): Manual for Staging of Cancer, 4th ed. Philadelphia, PA, Lippincott, 1992 2. Hermanek P, Sobin LH (eds): International Union Against Cancer (UICC): TNM Classification of Malignant Tumors, 5th ed. New York, NY, John Wiley & Sons, 1997 3. Snow GB, Gerritsen GJ: TNM classification according to the UICC and AJC, in Ferlito A (ed): Neoplasms of the Larynx. Edinburgh, Churchill Livingstone, 1993, pp 425-434 4. Mancuso AA, Hanafee WN: Larynx and hypopharynx, in Computed Tomography and Magnetic Resonance Imaging of the Head and Neck, 2nd ed. Baltimore, MD, Williams & Wilkins, 1985, p 247 5. Million RR, Cassisi NJ, Mancuso AA: Larynx, in Million RR, Cassisi NJ (eds): Management of Head and Neck Cancer: A Multidisciplinary Approach. Philadelphia, PA, Lippincott Company, 1994, p 447 6. Silverman PM, Zeiberg AS, Sessions RB, et al: Threedimensional imaging of the hypopharynx and larynx by means of helical (spiral) computed tomography. Comparison of radiological and otolaryngological evaluation. Ann Otol Rhinol Laryugol 104:425-431, 1995 7. Mukherji SK, Mancuso AA, Kotzur IM, et al: Radiologic appearance of the irradiated larynx. Part I. Expected changes. Radiology 193:i41-148, 1994 8. Robert Y, Rocourt N, Chevalier D, et al: Helical CT of the larynx: A comparative study with conventional CT scan. Clin Radio151:882-885, 1996 9. Dubrulle F, Robert Y, Delerne C, et al: Int~r~t du scanner spiral6 dans la pathologie du larynx et de l'hypo-pharynx. Feuillets Radiol 37:118-131, 1997 10. Robert YH, Chevalier D, Rocourt NL, Lemaitre LG: Dynamic manoeuver acquired with spiral CT in laryngeal disease. Radiology 189:298-299, 1993 11. Castelijns JA, Doornbos J, Berbeeten B Jr, et al: Magnetic resonance imaging of the normal larynx. J Comput Assist Tomogr 9:919-925, 1985 12. Castelijns JA, Kaiser MC, Valk J, et al: MRI of laryngeal cancer. J Comput Assist Tomogr 11:134-140, 1987 13. Castelijns JA, Gerritsen GJ, Kaiser MC, et al: Invasion of laryngeal cartilage by cancer: Comparison of CT and MR imaging. Radiology 167:199-206, 1988 14. Phelps PD: Review: Carcinoma of the larynx- the role of imaging in staging and pre-treatment assessments. Clin Radiol 46:77-83, 1992 15. Mafee MF, Schild JA, Valvassori GE, Capek V: Computed tomography of the larynx: Correlation with anatomic and
pathologic studies in cases of laryngeal carcinoma. Radiology 147:123-128, 1983 16. Reid MH: Laryngeal carcinoma: High-resolution computed tomography and thick anatomic sections. Radiology 151:689-696, 1984 17. Hoover LA, Calcaterra TC, Walter GA, Larsson SG: Preoperative CT scan evaluation for laryngeal carcinoma: Correlation with pathological findings. Laryngoscope 94:310315, 1984 18. Silverman PM, Bossen EH, Fisher SR, et al: Carcinoma of the larynx and hypopharynx: Computed tomographichistopathologic correlations. Radiology 151:697-702, 1984 19. Katsantonis GP, Archer CR, Rosenblum BN, et al: The degree to which accuracy of preoperative staging of laryngeal carcinoma has been enhanced by computed tomography. Otolaryngol Head Neck Surg 95:52-62, 1986 20. Sufaro S, Barzan L, Quefin F, et al: T staging of the laryngohypopharyngeal carcinoma. Arch Otolaryngol Head Neck Snrg 115:613-620, 1989 21. Becker M, Zb~iren P, Laeng H, et al: Neoplastic invasion of the laryngeal cartilage: Comparison of MR imaging and CT with histopathologic correlation. Radiology 194:661-669, 1995 22. Becker M, Zb~en P, Delavelle J, et al: Neoplastic invasion of the laryngeal cartilage: Reassessment of criteria for diagnosis at CT. Radiology 203:521-532, 1997 23. Breiman RS, Beck JW, Korobkin M, et al: Volume determinations using computed tomography. AJR 138:329-333, 1982 24. Hermans R: Value of computed tomography as treatment outcome predictor of head and neck cancer treated with irradiation. Doctoral dissertation, Catholic University of Leuven, 1998 25. Yousem DM: Dynamic MR imaging in the head and neck: an idea whose time has come . . . and gone? Radiology 189:659-660, 1993 26. Isaacs JH, Mancuso AA, Mendenhall WM, Parsons JT: Deep spread patterns in CT staging of T2-4 squamous cell laryngeal carcinoma. Otolaryngnl Head Neck Surg 99:455-464, 1988 27. Yeager VL, Archer CR: Anatomical routes of cancer invasion of laryngeal cartilages. Laryngoscope 92:449, 1982 28. Castelijns JA, Gerritsen GJ, Kaiser MC, et al: MRI of normal and cancerous laryngeal cartilages: Histopathological correlation. Laryngoscope 97:1085-1093, 1987 29. Castelijns JA, Golding RP, van Schaik C, et al: MR findings of laryngeal cartilage invasion by laryngeal cancer:
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Value in predicting outcome of radiation therapy. Radiology 174:669-673, 1990 30. Castelijns JA, van den Brekel MWM, Smit EMT, et al: Predictive value of MR imaging-dependent and non-MR imaging dependent parameters for recurrence of laryngeal cancer after radiation therapy. Radiology 196:735-739, 1995 31. Freeman DE, Mancuso AA, Parsons JT, et al: Irradiation alone for supraglottic larynx carcinoma: Can CT findings predict treatment results? Int J Radiat Oncol Biol Phys 19:485490, 1990 32. Mancuso AA, Mukherji SK, Mendenhall WM, et al: Value of pretreatment CT as a predictor of outcome in supraglottic cancer treated with readiotherapy alone. Radiology 193(P): 262, 1994 33. Lee WR, Mancuso AA, Saleh EM, et al: Can pretreatment computed tomography findings predict local control in T3 squamous cell carcinoma of the glottic larynx treated with radiotherapy alone? Int J Radiat Oncol Biol Phys 25:683-687, 1993 34. Pameijer FA, Mancuso AA, Mendenhall WM, et al: Can pretreatment computed tomography predict local control in T3 squamous cell carcinoma of the glottic larynx treated with definitive radiotherapy? Int J Radiat Oncol Biol Phys 37:10111021, 1997 35. Million RR: The myth regarding bone or cartilage involvement by cancer and the likelihood of cure by radiotherapy. Head Neck 11:30-40, 1989
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36. Mancuso AA: Evaluation and staging of laryngeal and hypopharyngeal cancer by computed tomography and magnetic resonance imaging, in Silver CE (ed): Laryngeal Cancer. New York, NY, Thieme Medical Publishers, 1991, pp 46-95 37. Pameijer FA, Herrnans R, Mancuso A, et al: Post radiotherapy computed tomography surveillance in laryngeal and hypopharyngeal cancer. Int J Radiat Oncol Biol Phys (submitted) 1998 38. Bailet JW, Abemayor E, Jabour BA, et al: Positron emission tomography: A new, precise imaging modality for detection of primary head and neck tumors and assessment of cervical adenopathy. Laryngoscope 102:281-288, 1992 39. Muldlerji SK, Drane WE, Tart RP, et ah Comparison of Thallium-201 and F-18 FDG SPECT uptake in squamous cell carcinoma of the head and neck. AJNR 15:1837-1842, 1994 40. Zeitouni AG, Lucas Yamamoto Y, Black M, et al: functional imaging of head and neck tumors using positron emission tomography. J Otolaryngo123:77-80, 1994 41. Seifert E, Schadel A, Haberkom U, et al: Die beurteilung der effektivitaet einer chemotherapie bei patienten mit Kopf-halstumoren mittels postron emission tomographie. HNO 40:90-93, 1992 42. Maroldi R, Battaglia G, Nicolai P, et al: CT appearance of the larynx after conservative and radical surgery for carcinoma. Eur Radiol 7:418-431, 1997
LMOST ALL laryngeal malignancies are squamous cell cancers. The main therapeutic approaches in laryngeal cancer are radiotherapy alone, and surgery alone or followed by radiotherapy. The choice of treatment is influenced by site and extent of the lesion. Speech-preserving partial laryngectomy in early cancer and total laryngectomy in advanced cancer are the main surgical treatment options. The position of the tumor relative to potential lines of resection determines the feasibility of voice-sparing partial laryngectomies. Correct treatment decisions require an accurate assessment of tumor extent. Large tumor volumes and sometimes also carriage invasion are considered to be a relative contraindiction for radiation therapy. The two most frequently used staging systems are those proposed by the American Joint Commission on Cancer (AJCC 1992), 1 and by the International Union Against Cancer (UICC 1997). 2 Both systems are almost identical with respect to laryngeal tumors, although they differ in several details. In both staging systems, the tumor is classified as T4 (supraglottic, glottic, subglottic) if it invades through one of the laryngeal cartilages (thyroid or cricoid cartilage) and/or extends to other tissues beyond the larynx (eg, to oropharynx, soft tissues of the neck).
A
From the Departments of Radiology and Otolaryngology/ Head and Neck Surgery, Academic Hospital "Vrije universiteit, " Amsterdam, The Netherlands; the Department of Radiology, Catholic University Leuven, University Hospitals, UZ Gasthuisberg, Leuven, Belgium; and the Department of Radiology, The School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC. Address reprint requests to Jonas A. Castelijns, MD, Department of Radiology, Academic Hospital "Vrije universiteit," Postbus 7057, 1007 MB Amsterdam, The Netherlands. Copyright © 1998 by W.B. Saunders Company 0887-2171/98/1906-000658. 00/0 492
The validity of any classification is dependent on the diagnostic methods used. Therefore, the issue of staging procedures is generally recognized to be important) However, regarding their recommendations for recently developed imaging methods, these staging systems are not precise for staging of a given laryngeal tumor. AJCC, for instance, states that "a variety of imaging procedures are valuable in evaluating the extent of disease, particularly for advanced tumors and these include laryngeal tomograms, CT scans and MRI scans", but does not indicate when to use either or all of these imaging methods. Without further indication as to the type of imaging, UICC states that imaging should be included in the diagnostic work-up. There are increasing indications that both imaging parameters such as tumor volume and signs of cartilage involvement can provide important prognostic information in patients undergoing treatment with radiotherapy. Laryngeal cancer was evaluated by means of direct visualization, palpation, or (plain) radiography or tomography before the era of CT and MR imaging. Clarification of submucosal extent of disease became possible with the advent of CT and later MR imaging. Neither CT nor MR imaging shows mucosal detail. As in other areas of the head and neck, the primary role of CT and MR imaging in imaging the larynx is to define the extent of disease. Therefore, each modality is complementary to clinical examination. Soon after the introduction of MR imaging, it was recognized that one of its key advantages over other roentgenological imaging methods was the ability to discriminate between different soft tissue types, and between pathology and normal tissue. Gradually, the quality of both CT images (particularly with the introduction of high-resolution CT and spiral CT) and MR imaging (particularly with the introduction of faster scanning techniques) has improved strongly.
Seminars in Ultrasound, CT, and MRI, Vol 19, No 6 (December), 1998: pp 492-504
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Technical Aspects of Computer Tomography During CT imaging of the larynx, the patient's neck should be slightly hyperextended and the shoulders positioned as low as possible. The patient should be immobilized and instructed not to swallow or cough during image acquisition. The plane of section is chosen parallel to the true vocal cords; if these landmarks are not recognized on the lateral scout view, the sections should be made approximately parallel to the midcervical intervertebral disk spaces. 4 Sections made at other angles relative to the true vocal cords can cause interpretative errors, because parts of the false cords may appear at the same level as the true vocal cords. During conventional (incremental) CT, different images are generated separately. Section thickness should not exceed 3 to 4 mm in laryngeal studies. With the field of view focused on the larynx to maximize spatial resolution, adjacent slices should be obtained. Scan time should be 1 to 2 seconds to minimize motion artifacts. Most primary tumors will enhance, which will help to delineate tumor from surrounding structures, especially muscles. Therefore, intravenous contrast medium is always used in studies for laryngeal cancer. 5 The patients are asked to breathe quietly during scanning. With the short scanning times possible on modern CT devices, motion artifacts due to breathing occur rarely. The use of spiral CT offers a number of advantages, the most obvious being the fast data acquisi-
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tion. This allows, for example, to reduce motion artifacts in adults and to limit the dose of injected contrast material in enhanced studies. Another interesting feature of spiral CT is that during transport of the patient, a volumetric data set is obtained. The images can also be calculated retrospectively for each possible table position also in an overlapping fashion. These retrospectively calculated overlapping images allow for better multiplanar reconstructions and three-dimensional reconstructions than non-overlapping incremental scans. These overlapping images are acquired retrospectively, without any additional irradiation for the patient; the only expense is additional computing time. Multiplanar and three-dimensional reconstructions give another view on the pathology, possibly with a better demonstration of tumor extent. Such reconstructions may improve the communication with the clinician. 6 In the larynx, a somewhat better visualization of laryngeal abnormalities and subtle anatomic structures (like the paraglottic fat planes) was reported with dynamic incremental CT, but less motion and respiratory misregistration artifacts are observed with spiral CT. 7 Other investigators did not report a significant difference in the visualization of different laryngeal structures between incremental and spiral CT (Fig 1). 8 Spiral CT examination of the larynx always starts with a long spiral scan of approximately 30 to 40 seconds during quiet respiration. With a table
Fig1. Contrast-enhanced spiral CT of the larynx (2 mm slice thickness, 3 mm/s table feed), in a patient with a glottic carcinoma. (A) Axial section at the glottic level. The left true vocal cord appears thickened and slightly enhancing. The tumor reaches the anterior commissure. The left paraglottic space is infiltrated (compare to normal opposite side [arrowheads]). Marked sclerosis of the left arytenoid (arrows). (B) Axial section at the level of the left false vocal cord. The fatty submucosal tissue of the false vocal cord appears infiltrated (arrowheads): cranial tumor extension. Note also the slight sclerosis of the angle and left lamina of the thyroid cartilage (arrows). The patient was surgically treated. Pathological examination confirmed a well-differentiated squamous cell carcinoma. The arytenoid showed focal neoplastic invasion; in the thyroid cartilage, only inflammatory changes were noted,
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incrementation speed of 3 ram/s, a slice thickness of 2 or 3 mm is generally used. Because diffusion of the contrast medium into the tumor and the metastatic adenopathies takes some time, it is important to start image acquisition not too early after initiation of the contrast injection. Good tumor enhancement is very important because it improves the evaluation of its extension. To obtain both good tumoral and vascular enhancement, a dual injection technique can be used: 50 mL of contrast medium is injected between 120 and 60 seconds before the start of the acquisition, leaving enough time for the diffusion to take place into the soft tissues, and then another 30 mL is injected during the 30 seconds before the start of the acquisition to obtain a good vascular opacification. 9 Modem injection pumps allow such relatively complex injection schemes to be preprogrammed. Good results are also obtainable with a one-phase injection of contrast medium, eg, 80 mL of a contrast medium with 300 mg I/mL at 1 mL/s, starting the image acquisition at the end of the contrast medium injection. Dynamic laryngeal maneuvers during scanning of the larynx and hypopharynx can improve visualization of particular anatomic structures. During phonation, arytenoidal mobility can be judged and a better visualization of the laryngeal ventricle can be obtained; the slight distention of the pyriform sinuses also allows better delineation of the aryepiglottic folds. Modified Valsalvamaneuver (consist-
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ing of blowing air against closed lips, puffing out the cheeks) produces a substantial dilation of the hypopharynx, which may allow better evaluation of the pyriform sinuses, including the postcricoid region (Fig 2). 10 The success rate of these dynamic maneuvers in incremental CT is variable, strongly depending on the cooperation of the patient: consistent repetition of the maneuver for each incremental scan is difficult, spatial misregistration being an important drawback. Furthermore, the incremental acquisition of these additional scans during phonation or Valsalva maneuver is time-consuming. These problems can be largely overcome by spiral CT, because the patient has to do the maneuver only once during one rapid acquisition. The patient needs to be well-informed about what is expected from him/her during the spiral C T study. The dynamic maneuvers need to be exercised with the patient before the examination starts. Often the patients need to be accompanied and encouraged during the actual examination. This small time investment yields good results in the majority of cases. 9 Technical Aspects of MR Imaging MR imaging of patients with laryngeal cancer may be difficult because of these patients' dyspnea, coughing, and mucous secretion. A number of requirements need to be fulfilled to obtain diagnostic images. The use of a dedicated neck coil is indispensable to obtain optimal results. Ideally, the
Fig 2. Contrast-enhanced spiral CT of the larynx, in a patient with a pyriform sinus carcinoma. (A) Axial image during quiet breathing shows subtle soft tissue thickening in the apex of the right piriform sinus (large arrows; compare to opposite side); there is some evidence of subtle infiltration or displacement of the paraglot-tic space fat (arrowhead). (B) Axial image obtained during modified Valsalva maneuver. The right pyriform sinus expands somewhat less than the opposite side; the mucosal irregularity produced by the cancer is now better visible (small arrows),
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volume of the neck coil should match as closely as possible the size of the neck. As a general rule of thumb, effective penetration by the coil is approximately one half the coil diameter at its narrowest point. The neck coils enable one to obtain highresolution and thin-section images in spite of relatively short acquisition times. One needs constantly to take full account of three issues in MR imaging to obtain optimal images: signal-to-noise ratio, spatial resolution, and acquisition time. Signal averaging is the best technique to improve MR image quality. However, benefits of signal averaging must be weighed against the increased scanning time required. Thinner slices improve the visualization of anatomic detail but require longer scanning time to maintain an equivalent signal-to-noise ratio and to image an equal volume-of-interest Finer matrices, such as 512 × 512, improve visualization of anatomic detail, but scanning time increases and signal-to-noise ratio may decrease. Selection of an intermediate matrix size, such as 256 × 256 or 192 × 256, may be an appropriate compromise. The field of view should be reduced as much as possible to improve spatial resolution. For imaging of laryngeal cancer, spin-echo (SE) MR imaging is used because of its accurate and reproducible anatomic depiction of laryngeal tissue. 11The intensities of different tissue types in MR images are affected by a number of acquisition parameters, and the contrast can be manipulated by changes of the pulse sequences. The common timing parameters are repetition time (TR) and echo time (TE). The flip angle of excitation pulses can also be varied. By altering these parameters, it is possible to change the sensitivity of the images to three principal factors: proton density, longitudinal relaxation time (T1), and transverse relaxation time (T2). The Tl-weighted images appear ideal for the study of the laryngeal anatomy. They allow delineation and characterization of tissue more accurately than CT does. Tl-weighted SE images are most appropriate to demonstrate laryngeal anatomy and to assess extent of laryngeal pathology (Fig 3). 12 On T2-weighted SE images, tumor is found to have an increased signal intensity compared with that found on Tl-weighted SE images. The higher signal intensity of squamous cell carcinoma on T2-weighted images may be helpful in delineation of tumor tissue, but it may also be an disadvantage in the larynx because of the high signal areolar tissue within the larynx, which could obscure the
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tumor itself. With spin-echo imaging, the appropriate selection of TR and TE will determine the degree of T1- and T2-weighting. For Tl-weighted spin-echo MR imaging, the minimal length of the TR is based on the number of slices that are required, but must be kept under 800 ms to maintain Tl-weighting. A TR within the range of 400 to 800 ms will allow an adequate number of slices to cover the region of interest. The shortest TE possible (10 to 20 ms) is selected to attain the best signal-to-noise ratio and to minimize T2 effect. To obtain T2-weighted images, we typically use a TR of 2,500 ms and TEs of 20 to 30 ms and 100 ms for the first and later echos, respectively. The axial imaging technique is most appropriate to study location and extent of tumor in intralaryngeal compartments, the laryngeal cartilages, as well as in extralaryngeal structures, such as the infrahyoid muscles, pyriform sinus, and subcutaneous fat. Fast SE T2-weighted imaging should be applied instead of conventional SE techniques by reducing acquisition time and motion artifacts. It is of utmost importance that both sequences T1 and fast T2 SE images are obtained at exact corresponding levels. Interpretation of images that are not obtained at exact corresponding levels could easily lead to misinterpretations regarding the presence or absence of cartilage invasion. Motion artifacts are the most common, easily identifiable phenomena that degrade MR images of the laryngeal area. Motion artifacts due to respiratory movement and those due to random patient movement (swallowing, coughing) may be hard to distinguish from each other. Gross motions produce multiple ghosted images, which usually appear as curvilinear crescents of signal. An increase in either TR value or frequency of the motion increases spacing between parent signal and daughter ghosts. More subtle patient motion results in degraded image quality without obvious ghosting. Irrespective of the direction of the motion, motion ghosts are observed along the phase-encoding axis (normally in the vertical direction of the axial image). Motion artifacts are more prominent on images acquired over a longer examination time (ie, a long repetition time). Most patients can remain sufficiently immobile during approximately 5 to 8 minutes. However, a shorter scanning time will reduce motion artifacts due to coughing and swallowing. The use of turbo spin-echo MR images to obtain T2-weighted MR images may be necessary.
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Fig 3. (A) Coronal, Tl-weighted MR image shows vocal and thyro-arytenoid muscles (arrowheads) with intermediate signal intensity. False vocal cord is found with high signal intensity (arrows), being separated from vocoal muscle by laryngeal ventricle. (B) Axial, Tl-weighted MR image shows the false vocal cord with high signal intensity (arrows). Thyroid cartilage is almost entirely ossified, being found with high signal marrow surrounded by a low signal cortical rim. (C) Axial, Tl-weighted MR image at the true vocal cord level shows muscular tissue of the vocal and thyro-arytenoid muscles (arrows) with intermediate signal intensity,
Comfortable patient positioning and sedation may all be used to reduce these artifacts. Rigidly mounting the surface coil off the patient eliminates coil motion and improves image quality. One must encourage the patient to remain as immobile as possible. After all, the use of short examination times may necessitate some compromise on image resolution. The presence of motion artifacts may interfere in approximately 10% to 15% of the examinations with adequate diagnosis. 13,14The patient should be examined in supine position, the neck slightly hyperextended, the head immobilized. The patient is positioned so that the laryngeal airway is as parallel to the table-top as far as possible. Quiet breathing should occur during the examination with the use of abdominal rather than chest muscles. We begin with a mid sagittal and
parasagittal, Tl-weighted SE MR sequence. This identifies the orientation of the larynx. Axial T1weighted, proton density and relatively T2-weighted MR images are then obtained at exact corresponding levels. Section thickness is 4 mm, with no interslice gap. Four measurements are obtained with Tl-weighted and two measurements are obtained with T2-weighted MR images. For detection of lymph node metastasis, the neck should be examined as well. Appearance of Laryngeal Squamous Cell Carcinoma on CT
Criteria used for tumor involvement are abnormal contrast enhancement, soft tissue thickening, presence of a bulky mass, infiltration of fatty tissue (even without distortion of surrounding soft tis-
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Fig 4. Unenhanced spiral CT of the larynx in a patient with a large iaryngo-hypopharyngeal carcinoma. No contrast medium was injected because of renal failure. (A) Axial image at the level of the cricoid cartilage. Soft tissue thickening is seen in the retrocricoidal hypopharynx (arrow) and also beyond the thyroid cartilage, underneath the thyroid gland (arrowheads). Extensive sclerosis of the cricoid arch and inferior part of the thyroid lamina is seen at the left side. (B) Axial image at the glottic level. Thickening of the left vocal cord, with infiltration of the left paraglottic space (compare to opposite side). The mass is also seen in the apex of the piriform sinus (arrow), extending underneath the pharyngeal constrictor muscle posterolaterally from the thyroid lamina (arrowheads). Note again sclerosis of the left thyroid lamina and left arytenoid. (C) Axial image through the lower supraglottis. Large tumor mass in the left piriform sinus (arrows), extending into the left paraglottic space (arrowheads), (D) Axial image just above the thyroid cartilage. The hypopharyngeal tumor mass bulges into the soft tissues of the neck (arrows); carotid artery (star) is not reached yet. Infiltration of the upper paraglottic space (arrowhead). The patient was surgically treated. Pathologic examination showed a poorly differentiated squamous cell carcinoma; no neoplastic cartilage invasion was found.
sues), or a combination of these (Figs 1, 2, and 4). A soft tissue thickness of more than 1 mm at the anterior commissure is considered pathological, and any tissue thickening between the airway and the cricoid ring is considered to represent subglottic tumor. Several studies have compared the CT findings with the results of whole-organ sectioning after total or partial laryngectomy, showing that computed tomography is an accurate method to visualize laryngeal pathology. 15-21 These correlation studies between whole organ sectioning and CT have also shown some pitfalls. Small foci of mucosal tumor may be difficult to detect or may be invisible on CT images, and associated inflamma~
tory and edematous changes can cause overestimation of the tumor extent on CT. Distortion of adjacent normal structures may mimic tumoral involvement. Gross cartilage invasion can be detected with CT. Because of the large variability in the ossification pattern of the laryngeal cartilages, CT often fails to detect early cartilage invasion. Nonossified hyaline cartilage shows the same density values as tumor on CT images. Demonstration of tumor on the extralaryngeal side of the cartilage is a reliable, but late sign of cartilage invasion. Asymmetrical sclerosis, defined as thickening of the cortical margin and/or increased medullary density, compar-
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ing one arytenoid to the other, or one side of the cricoid or thyroid cartilage to the other side, is a sensitive but nonspecific finding at CT. In only 45% of thyroid and cricoid cartilages displaying sclerosis are tumor cells found within the bone marrow; the other 55% have only perichondrial invasion or no invasion at all. Only 16% of sclerotic arytenoids display tumor cells within the bone marrow and 32% have only peripheral invasion of the fibroelastic process of the vocal process or the perichondrium; the remaining 52% not showing any neoplastic invasion at all (Fig 1).22 Erosion or lysis has been found to be a specific criteria for neoplastic invasion in all cartilages (Fig 5). Other signs, like cartilaginous blow-out or bowing, a serpiginous contour, or obliteration of the medullary space are not very reliable for cartilage invasion. The combination of several diagnostic CT criteria for neoplastic invasion of the laryngeal cartilages seems to constitute a reasonable compromise: when extralaryngeal tumor and erosion or lysis in the thyroid, cricoid, and arytenoid cartilages were combined with sclerosis in the cricoid and arytenoid (but not the thyroid) cartilages, an overall sensitivity of 82%, an overall specificity of 79%, and an overall negative predictive value of 91% were obtained. = Tumor volume is difficult to determine clinically, especially in the head and neck with its complex
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regional anatomy and the infiltrating behavior of the tumors occurring in this region. Volumetric assessment of soft tissue masses is possible with cross-sectional imaging techniques like CT. To determine the volume of a particular structure, its borders are traced on consecutive images. The segmented surface on each image is then calculated. This procedure can be done on the scanner's screen, using a mouse-controlled cursor, or indirectly using a digitizer. The obtained surfaces are then multiplied by the slice interval. The summation of all these obtained volumes represents the total volume of the structure of interest. This technique is called the summation-of-areas technique. 23 The reproducibility of laryngeal tumor volume measurements, based on CT images, has been shown to be acceptable if done by the same experienced observer54 Appearance of Laryngeal Squamous Cell Carcinoma on MRI
In several previous comparative studies, including comparison between MR images and wholeorgan histopathological sections, it has been suggested that Tl-weighted MR images assess accurately the extent of tumor tissue and delineate it with high contrast to surrounding fat, but much less contrast to surrounding muscular tissue. 12
Fig 5. Contrast-enhanced spiral CT of the larynx in a patient with a subglottic carcinoma. (A) Axial image through the subglottis. Semicircular soft tissue thickening in the right subglottic region (large arrowheads), growing anteriorly over the midline. There is sclerosis and lysis at the right side of the cricoid arch (small arrowheads). Some extralaryngeal soft tissue thickening and enhancement can be seen anterior to the larynx (arrows), suggesting tumoral extension through the cricothyroidal membrane. (B) Axial image at the glottic level; some enhancement of the thickened right true vocal cord. Some soft tissue thickening over the medial facet of the right (sclerotic) arytenoid (arrow). The patient was surgically treated. Pathological examination showed a subglottic well differentiated squamous cell carcinoma, extending over the midline and growing into the true vocal cord. The cricoid cartilage was invaded by the tumor, the arytenoid cartilage not. Extralaryngeal extension was not substantiated; an important peritumoral inflammatory reaction was present.
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However, it has been reported recently that inflammation may be frequently observed along the margin of squamous cell carcinoma and may not be differentiated from tumor tissue on Tl-weighted images. 21 Head and neck cancers often display the same signal patterns before and after contrast administration as benign or inflammatory lesions and cannot even be differentiated by means of dynamic contrast-enhanced MR imaging. 25 However, on the basis of Tl-weighted images, it can be maintained that MR images accurately depict the amount of pathological tissue, which may include cancerous and/or inflammatory tissue. Laryngeal cartilages are very difficult to investigate because of their irregular pattern of ossification. 26-28 The hyaline cartilages may be variably composed of calcified and noncalcified cartilage, or of bone with a marrow cavity (Fig 6). 17'26 MR imaging shows ossification patterns more accurately than CT does and allows detection of abnormal signal in cartilages. 12,22Cartilage invasion may be best assessed by the combination of unenhanced T1- and more T2-weighted MR images. The use of GdTPA does not increase the diagnostic accuracy because contrast enhancement does not enable us to differentiate between tumor tissue and inflammation. Several articles explored this issue of detection of cartilage invasion in MRI histopathological correlative studies. Castelijns et al have indicated that MR imaging can help to differentiate tumor tissue from nonossified tissue. 14,28However, num-
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bers of sliced surgical specimens in this study are small. Both tumor and non-ossified cartilage have low signal intensity with short repetition time sequences, tumor had substantially higher signal intensity than nonossified cartilage on more T2weighted sequences (Figs 7, 8). They reported an overall sensitivity of 89% for 0.6-T MR imaging in the detection of neoplastic invasion of cartilage and a specificity of 88%. 14The overall results of Becker et al obtained at 1.5T in a much larger MRI histopathological correlative study were almost identical (sensitivity, 89%; specificity, 84%). 21 However, they found that the ability of MR imaging to help to detect or exclude neoplastic cartilage invasion varied considerably with the histological degree of invasion and from one anatomic site to another. They reported that MR imaging is less reliable in the thyroid cartilage than in the cricoid cartilage and arytenoid cartilages because of relatively high number of false-positive findings. They claim that histopathological correlation indicated that these diagnostic errors were caused by nonneoplastic peritumoral reactions and changes in the cartilage, namely extensive fibrosis, inflammation, and bone resorption adjacent to the tumor without concomittant neoplastic invasion of the perichondrium. At MR imaging, these changes may result in a high signal intensity on T2-weighted images. As stressed before, it is very important that the T1- and T2-weighted images are at e x a c t corresponding level. Otherwise, interpretation may easily lead to false-positive or false-negative results regarding
Fig 6. (A) Patient w i t h a T3 glottic lesion. Axial, proton-density weighted MR image at the glottic level shows thyroid cartilage with l o w signal intensity, being entirely nonossified, Tumor tissue is found with increased signal intensity, being imaged with high contrast with non-ossified tissue. (B) Patient with a T2 glottic lesion. Axial, Tl-weighted MR image at the glottic level shows bone marrow of thyroid, cricoid and arytenoid cartilages with high signal intensity, being surrounded by a l o w signal cortical rim. Cartilages appear to be entirely ossified. Tumor tissue is found with low signal intensity at the anterior part of the left vocal cord, being imaged with high contrast with fatty bone marrow.
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Fig 7. Patient with glottic lesion, staged as "1"3.(A) Axial T1weighted image at the glottic level shows tumor tissue (arrows) with intermediate signal intensity. Both ventral parts of the thyroid laminae are seen with intermediate signal intensity, the dorsal parts being ossified. (B) Axial proton density image shows tumor tissue with increased signal intensity, including the ventral parts of both thyroid laminae (arrowheads), being suspicious for cartilage involvement by pathological tissue.
the presence of cartilage invasion. Interpretation of MR examinations in patients with smaller tumors that did not undergo surgical treatment, suggested that abnormal MR signal patterns in cartilage may be found in a large percentage of patients with laryngeal carcinoma. 29 In this study, a high frequency of abnormal signal in the area of the anterior commissure, suspicious for cartilage invasion, was observed. The study by Becker allows us to state that MR imaging is very accurate in determining that a cartilage is normal. 2~ If the signal intensity in cartilage is abnormal, the cartilage is almost certainly abnormal. However, there may be false-positive findings due to inflammatory disease adjacent to tumor tissue.
Manual outlining of lesions on MR images is moderately accurate when performed by an experienced observer. It is relatively straightforward to implement and, in experienced hands, has been shown to give fairly good intraobserver and interobserver variability.3° However, considerable operatorcomputer interaction time is needed to assess each patient. Comparison Between CT and MRI
Generally, MR imaging seems to be the optimal method of examination in cooperative patients. CT is recommended in patients who may have rapid breathing or coughing from chronic lung disease or if MR imaging is not a option, as in patients with a
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Fig8. Patient with a stage Tlb lesion. {A) Axial Tl-weighted image SE MR image at the true cord level shows tumor (arrowheads) in the anterior two thirds of the left vocal cord, the anterior commissure, and the anterior part of the right vocal cord. The ventral part (arrows) of the left thyroid lamina is either invaded by pathological tissue or consists of nonossified cartilage. (B) Axial proton-density SE MR image demonstrates tumor tissue with slightly increased signal intensity compared with the Tl-weighted image. The anterior part of the left thyroid lamina is also found with increased signal intensity, being suspicious for involvement by pathological tissue.
pacemaker, surgical clips, or severe claustrophobia. Both modalities are able to delineate deep tissue anatomy. MR imaging has a better soft tissue contrast than CT. In contrast, high-resolution CT produces images with thinner slice thickness and higher spatial resolution than MR imaging. CT studies of the larynx can be acquired in less time, and adequate images are obtained in nearly all patients. Both modalities do not enable differentiation between tumor tissue and surrounding inflammatory tissue, which may be present to a more or less extent. Both Tl-weighted MR images and high-resolution CT are appropriate to assess tumor extent in various laryngeal compartments such as pre-epiglottic space, paraglottic space and both commissures. The possibilities of CT and MRI vary clearly from each other regarding detection of cartilage invasion. CT criteria for the presence of cartilage invasion are mainly based on bony abnormalities. In contrast, MR imaging shows alterations in (ossified) cartilage directly. MRI seems to be more sensitive than CT in detection of neoplastic cartilage invasion, but seems to have a somewhat lower specificity, especially for thyroid cartilage involvement. 31,32 Most probably CT findings cause an underestimation, whereas MRI findings produce an
overestimation of the actual presence of cartilage invasion. The choice between CT and MRI may partly be settled by the clinical question. If it is important to exclude cartilage invasion, as in considerations regarding partial laryngectomy, MR imaging may be indicated. If cartilage invasion should be shown with more confidence, CT may be more appropriate. Self-evidently, the prognostic value of each of the modalities and its defined criteria are of high value to determine the choice of treatment. Consequently, the number of studies evaluating the prognostic value of imaging findings are increasing. At present, this theme has been elaborated more extensively and in more detail for CT than for MRI. In CT studies, tumors have been classified for tumor location (glottic, supraglottic) and tumor stage. Freeman et al, whose study (31 patients) was updated by Mancuso (63 patients), were able to identify those patients with T1-T4 supraglottic carcinomas who had a higher likelihood of local control after definitive radiotherapy based on pretreatment CT volumetric analysis (tumors of < 6 mL had a probability of 83%, respectively 89% of local control, whereas tumors of > 6 mL had only a control rate of 46%, respectively 40%). 31,32 Lee et al, whose study (18 patients) was updated by
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Pameijer et al (42 patients), could stratify in a similar way patients with T3 glottic carcinoma into groups with different likelihood of local control (tumors of <3.5 mL had a probability of 92%, respectively 85% of local control after definitive radiotherapy, whereas tumors of >3.5 mL had only a local control rate of 33%, respectively 22%). 33,34 The results of the study by Hermans corroborate well these previous findings. 24 It seems to be no question that tumor volume as determined by CT or MRI is a predictor for risk of tumor recurrence in patients treated by irradiation. The results regarding the prognostic value of cartilage abnormalities seem to be somewhat contradictory. Generally, in studies evaluating CT, cartilage abnormalities as shown by this modality seem to have somewhat less prognostic value for local failure after irradiation, whereas MRI findings for cartilage involvement are reported to be more indicative for an increased risk of tumor recurrence. 29,3° We agree with Million that the "myth about the radiocurability and bone and/or cartilage" should be replaced by an understanding of relative rates of control by radiotherapy. 35 If voice conservation surgery is being considered, MR imaging is useful for assessing those structures (such as laryngeal cartilages) whose involvement would contraindicate partial laryngectomy. MR imaging is helpful, and probably more so than CT, in ensuring that these requirements are met when conservation therapy is being considered. MRI is especially helpful in assessing the cranio-caudal extent of disease. Because MR imaging seems to be very accurate in determining the normal part of the cartilage, a type of partial laryngectomy may be designed in the future for tumors in which cartilage involvement is present. Post-Treatment Evaluation
After radiation therapy, endoscopic examination is more limited than in untreated patients. Residual or recurrent carcinoma is often difficult to detect. Radiological investigations seem to be less effective in patients suspected of having a recurrent or residual tumor after previous irradiation treatment, due to diffuse tissue changes including varying amounts of fibrosis and edema. Accurate diagnosis on the basis of CT or MRI in patients who underwent radiation therapy requires knowledge of expected radiological changes. These changes in-
clude symmetric thickening of the false cords, aryepiglottic folds and the epiglottis, and a changed appearance of paralaryngeal fat. Glottic changes include a changed appearance of the paraglottic fat planes and thickening of the anterior and posterior commissures. Subglottic changes include thickening of the mucosa and submucosa. 3v However, neither on CT nor on MRI, definite distinction can be made among cancer, edema, and irradiation fibrosis.e8,37 Follow-up CT is probably not cost-effective in patients who were irradiated for a small-sized carcinoma of the larynx, because the local control rates for such tumors after radiation therapy are very high. However, there are indications that patients with a higher likelihood of local failure, such as supraglottic, T3- or T4-glottic, and hypopharyngeal carcinomas may benefit from a baseline follow-up CT study about 4 months after completion of RT.34,38 If the baseline CT study shows complete resolution of the tumor at the primary site and symmetrically appearing laryngeal and hypopharyngeal tissues (ie, expected RT related changes), the patient is very likely to be controlled locally and fm'ther follow-up CT studies are not necessary. If less than 50% estimated volume reduction or a focal mass with a diameter larger than 1 cm is found, immediate further investigation is warranted, because the likelihood of local failure is high. 7 If the laryngeal tissues seem asymmetric, or a focal mass with a diameter smaller than 1 cm is found, unless clinical examination is already suspect for local failure, further follow-up CT studies are needed; a time interval of 3 to 4 months is recommended, to be continued up to 2 years after completion of radiotherapy. In a substantial number of cases, it seems possible to detect local failure earlier by CT than by clinical examination alone. These patients can then be salvaged at an earlier stage of local recurrence. 34 Control by FDG-PET may well be more useful than CT or MRI in monitoring tumor response to irradiation treatment of head and neck carcinomas generally.38-4°Normal structures retain their appearance on FDG-PET images after radiation therapy. In addition, FDG-PET imaging can be performed to follow tumor response to radiation therapy on the basis of quantitative changes in tumor glucose metabolism and, therefore, FDG uptake. 4° Seifert
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r e p o r t e d t h a t F D G - P E T also e n a b l e s t u m o r m o n i t o r ing d u r i n g a n d after t r e a t m e n t w i t h c h e m o t h e r apy. 41 F D G - S P E C T a v o i d s the h i g h cost o f P E T i m a g i n g . H o w e v e r , the u l t i m a t e v a l u e o f this m o d a l ity f o r m o n i t o r i n g t h e r a p e u t i c e f f e c t i v e n e s s or e v a l u a t i n g t u m o r r e c u r r e n c e a n d its v a l u e c o m p a r e d w i t h t h a t o f C T or M R I r e m a i n s to b e d e t e r m i n e d in p a t i e n t s w i t h s q u a m o u s cell carcin o m a o f t h e larynx.
L a r y n g e a l d e f o r m i t y a n d loss o f s y m m e t r y d u e to c o n s e r v a t i o n s u r g e r y c o m p l i c a t e t h e i n t e r p r e t a t i o n o f r a d i o l o g i c a l findings. A c c u r a t e d i a g n o s i s i n p a t i e n t s w h o u n d e r w e n t c o n s e r v a t i o n s u r g e r y requires k n o w l e d g e o f e x p e c t e d a n a t o m i c c h a n g e s . B a s e l i n e studies, w h i c h s h o u l d b e d o n e 2 or 3 m o n t h s p o s t o p e r a t i v e l y , m a y b e essential. 42 F D G P E T m a y b e u s e f u l as w e l l i n e v a l u a t i n g p o s t s u r g e r y p a t i e n t s for r e c u r r e n t t u m o r s . 38
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