Imaging Studies

There are physicians who believe that radiologic studies of these patients have a minor role to play in the evaluation.20'21 However, most believe that radiologic evaluation should be undertaken and may yield valuable information.22,23 The purpose of pursuing radiologic evaluation is twofold: (1) to assess the extent of nodal disease in the ipsilateral neck and the possible presence of disease in the contralateral neck. Lymph nodes in the retropha-ryngeal area and the paratrachial region may also be assessed as these are often difficult to detect on clinical examination, (2) possible detection of the primary tumor. Radiologic studies should precede endoscopy and mucosal biopsies. Such studies undertaken after biopsy may be more difficult to interpret because of edema and inflammation at the biopsy sites. Before endoscopy, these studies may alert the physician to mucosal abnormalities that may harbor the primary tumor.

Computed tomography (CT) scanning is the recommended study for evaluation of nodal disease in the neck.24,25 This modality will assist in delineating the presence of single versus multiple lymph nodes, the presence of contralateral lymph nodes, and the possible extranodal extension of disease. Tumor involvement of the carotid artery, the skull base, and the prevertebral musculature may also be detected. Mancuso and others24-26 have defined the criteria for the diagnosis of tumor-bearing lymph nodes and also for the possible extranodal extension of disease. The CT criteria for suspecting metastatic disease in lymph nodes includes the following: (1) diameter of the lymph node >15 mm, (2) grouping of three or more 8- to 15-mm lymph nodes, (3) central decreased density of a lymph node, and (4) poorly defined mass in a lymph node-bearing area.

The CT criteria for possible extranodal extension of disease include (1) ill-defined margins around abnormal lymph nodes, (2) edema or thickening of adjacent fat and muscle, (3) loss of facial planes between a mass and adjacent structures such as the carotid sheath.

Magnetic resonance imaging (MRI) scans may also play a valuable role in assessing neck disease and possible location of the primary tumor.24,25 However, MRI scans have been shown to be less accurate than CT scans in demonstrating the presence of central necrosis in metastatic lymph nodes and in detecting the presence of extracapsular spread of disease. MRI appears to be superior to CT in detecting more subtle mucosal changes possibly due to neoplastic change. The consensus of opinion favors CT over MRI in evaluating these patients and, certainly, CT has been proved more cost effective. In a study by Mendenhall et al.22 CT and/or MRI correctly identified the primary site in 50% of patients evaluated who had no suggestive findings on physical examination.

The involvement of the carotid artery system by tumor can be quite difficult to ascertain. Van den Brekel et al.24 noted that tumor encircling a blood vessel more than 270 degrees on CT or MRI scans or tumor that is immobile from the vessel using sonopalpation [palpation with ultrasound] indicates involvement of the vessel wall. Angiography does not appear to enhance findings obtained from CT or MRI studies of vessel involvement.

The role of positron emission tomography (PET) in the evaluation of these patients has recently been reported.22,27 PET uses 18-F-labeled-floro-2-D-glucose (FDg) to assess the rate of glucose turnover in malignant cells. In limited studies to date, PET has shown promising results in detecting occult primaries and assessing lymph nodes for the presence of metastatic disease. However, this technique remains in the investigational stage for these purposes and its availability is limited due to cost factors.

Thallium-201 Spect scans have also been evaluated in the management of these patients. In a report by Valdes Olmos et al.,28 the primary site was successfully detected in five of six patients using this technique. This technology may complement the role of CT and/or MRI in the detection of primary tumors. Ultrasound has been reported to be a valuable adjunct to palpation in the detection of lymph node metastases in the neck.24

A chest radiograph should be obtained prior to endoscopy. Other radiologic studies are usually not undertaken at this point but may be indicated in certain circumstances. If there is increased concern regarding distant metastases, for example in patients with very extensive neck disease, a CT scan of the chest and the abdomen and a bone scan should be undertaken. If adenocarcinoma has been demonstrated on the fine needle aspirate, these studies should also be undertaken, and an upper and lower GI series may also be indicated. Radiologic evaluation of the sinuses may also be appropriate if no other site for a primary adenocarcinoma has been discovered. If thyroid carcinoma is detected on needle aspiration, then appropriate evaluation of the thyroid, including a thyroid scan is indicated.

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