الفهرس 
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Abstract
Laryngeal cancer represents 4.5% of all malignancies and 28% of cancers of the upper aerodigestive tract. 90% of the malignant tumors of the larynx are composed of squamous cell carcinoma, so the larynx is the most common site of squamous cell carcinoma of the head and neck.
In cases of laryngeal carcinoma, thyroid cartilage invasion is associated with a lower response rate to radiation therapy and a higher risk of tumor recurrence. Hence, accurate assessment of any thyroid cartilage invasion by the tumor is vital for staging and treatment.
According to the current American Joint Committee on Cancer (AJCC) staging guidelines, minor thyroid cartilage invasion is classified as T3, whereas invasion throughout the cartilage is considered as T4. These definitions are inherently problematic owing to the subjective nature of cartilage invasion.
Survival is related to the stage of disease at diagnosis. Five-year survival rates are highest for patients presenting at stage I (94% to 100%) and lowest for those diagnosed with stage IV disease (40% to 65%).
Accurate assessment of tumor extension is critical in determining the method of treatment in laryngeal cancer and achieving a favorable outcome. Maintaining the quality of life is as important as achieving oncologic cure. Thus, patient preference has a significant bearing on the type of treatment chosen.
Clinical and endoscopic examination alone failed to identify tumor invasion of the laryngeal cartilages and of the extralaryngeal soft tissues, resulting in a low staging accuracy (57.5%). Many T4 tumors (according to the International Union against Cancer TNM Staging System) were clinically unrecognized. The combination of clinical/endoscopic evaluation and an additional radiologic examination, either Computerized Tomography (CT) or Magnetic Resonance imaging (MRI), resulted in significantly improved staging accuracy (80% for CT vs. 87.5% for MRI).
There is a controversy about the role of CT in detection of thyroid cartilage invasion, limited evidence in the 1990s suggested that CT has the tendency towards “over-calling” thyroid cartilage invasion, largely due to reactive inflammation. Therefore, overstating with pre-treatment CT study could potentially result in loss of the possible benefit of organ preservation in many patients.
On the other hand, other studies suggested that CT tends to underestimate neoplastic cartilage invasion and may lead to inadequate therapy.
MRI is significantly more sensitive but less specific than CT in detecting neoplastic cartilage invasion. Recently, the introduction of DWMRI seems promising as a functional imaging technique. It is a noninvasive MRI technique that shows potential in the characterization of lesions. A number of reports suggest that this technique may have interesting applications in the evaluation of head and neck cancer, by distinguishing tumoral from non tumoral tissue.
The advantage of diffusion-weighted imaging (DWI), which is an emerging noninvasive functional MRI technique, is that it can be acquired without the administration of intravenous contrast agent and seems to be quite reliable in distinguishing between benign and malignant tissues. DWI provides image contrast dependent on the molecular motion of water, and any architectural changes in the proportion of extracellular to intracellular water protons will alter the diffusion coefficient of the tissue.
Compared to CT, diffusion weighted MRI has a similar ability to define the interface between fat and tumor, but it is superior for assessing muscle and cartilage invasion. It may be indicated if there are equivocal findings in CT including possible cartilage invasion.
DW MRI showed high validity and precision in detecting inner and outer thyroid lamina invasion. This can have an important impact on decision making for management of laryngeal carcinoma.