Bernard B Omalley Md

Imaging the neck is unlike imaging any region of the torso or brain since maximal contrast resolution is necessary to differentiate lesions in cross-sectional exams of those solid organs. Because of the various organ systems, the neck has very good native contrast resolution between lesions and adjacent normal structures and at the interface with the skull base and thoracic inlet. Intravenous contrast is necessary, however, to differentiate veins (and arteries) from adenopathy and masses (Figure 3-1). Once a baseline scan has been obtained, contrast is less important for this particular consideration. Intravenous contrast also helps characterize internal lymph node architecture for necrosis. Bolus timing parameters are dependent on the equipment used1 and the medical condition of the patient. Oral contrast in the form of barium paste is helpful for lesions of the hypopharyngo-esophageal complex. The throat, being a semi-collapsed tube, is difficult to evaluate on cross-sectional images. The importance of cross-sectional imaging is in evaluating the submucosal component of lesions ( Figure 3-2 ), complementing the clinical and endoscopic exam. Imaging is therefore not valuable for detection of mucosal disease and cannot be a substitute for clinical inspection. Evaluating a palpable neck mass2 and staging a known mucosal or sinonasal lesion is the primary role for imaging of the neck and head. Lesions of the nasopharynx, parapharyngeal space, sinonasal tract and subglottic space are better staged by the cross-sectional exam, however. Familiarity with the imaging of lymphomas and benign3 or inflammatory lesions of the neck can prevent unnecessary surgical explorations in this functionally and cosmetically sensitive region.4 Imaging exams have been docu mented to improve upon the accuracy of clinical lymph node staging. This is true of either computed tomography (CT), magnetic resonance imaging (MRI) or sonography and nuclear imaging including fluorodeoxyglucose-positron emission tomography (FDG-PET). Intravenous contrast is necessary to characterize internal lymph node architecture on CT, but less important on MRI. Careful attention to lymph node sub-sites is needed at the lateral retropharyngeal (Figure 3-3) and tracheo-esophageal groove (Figure 3-4) when appropriate. The added value of sonography is the capacity to perform fine-needle aspiration (FNA) of suspicious lymph nodes,5 which might otherwise look unremarkable on other imaging modalities or feel unimportant to the examiner. With proper attention to technique,

Figure 3-1. Enhanced axial CT image through the oropharynx. (1) Partially necrotic pathologic lymph node (level II). (2) Normal sub-mandibular node (level I-b) with fatty hilum.
Figure 3-2. Enhanced axial CT images through the oropharynx. (1) Base of tongue squamous cancer extending to lateral pharyngeal wall. (2) Early extra-pharyngeal extension into parapharyngeal space.

both the neck and the primary lesion can be adequately scanned at one imaging visit. Whether or not there is a known primary tumor, the contrast bolus should be peak for the axial survey of the neck. The primary site, if it is known, can be scanned in whatever plane necessary in the post-bolus phase of the scan. These issues are less important in MRI. As many as one-third of all N0 neck dissections show histologically positive metastatic adenopathy.6 Imaging may demonstrate some of these occult metastases and thus improves upon the clinical exam.7 In the N0 neck, FDG-PET (Figure 3-5) has been reported to be more sensitive than CT or MRI8 and to have a sensitivity and specificity of approximately 90 percent.9 However, true micro-metastases will remain below the resolution of cross-sectional exams and current FDG-PET technology, but enlarged lymph nodes should not be overlooked. One half of all missed lymph nodes are less than or equal to one centimeter in size. Careful analysis of high quality scans is necessary to maintain a respectable accuracy rate for staging the neck. Both

CT and MRI improve upon the clinical accuracy of 71 percent.7 Conventional MR is not adequate10 and has no benefit over CT.11 The neck can be adequately staged if MR is chosen for staging of the primary site. FDG-PET is very accurate in the post-treatment setting compared to either CT or MRI.1213

As in other body regions, a diagnosis has often been established and the imaging is performed to round out the TNM staging. While radiology is complementary to the clinical staging, it is responsible for so-called stage creep,1415 increasing the T, N, or M component of the diagnosis. The radiologist and clinical oncologist need to establish a rapport and select the modality most appropriate for their collective expertise and imaging armamentarium. Scan protocols must be established for consistency within a practice and at the very least among sequential follow-up surveillance-type scans on a given patient. Consistent imaging parameters from contrast injection rates through scan technique16 to photography facilitate detection of subtle changes lending confidence to the diagnosis of often clinically occult

Figure 3-3. Axial T2-weighted MR image through the maxilla. (1) Metastatic left lateral retropharyngeal lymph node. (2) Palate tumor (hard and soft palate).

changes. Consistency also allows the other members of the clinical oncology team to work with reliable images for treatment planning.

Staging the index lesion involves evaluating for the possibility of clinical underestimation of the submucosal extent of disease17 (Figure 3-6), invasion of adjacent vital structures18 (Figure 3-7), and non-palpable adenopathy. Imaging for determination of the M stage of disease begins (and usually ends) with the chest radiograph. Cross-sectional imaging of the chest should be productive given the prevalence of smoking exposure in the head and neck cancer population. This would also serve as a baseline against which any developing apical pulmonary radiation changes or aspiration infiltrates could be compared. A well-designed scan of the neck that covers the superior mediastinum should provide adequate evaluation of the apical pulmonary region.

Detection and staging of neck lesions are very important for accurate assignment of initial treatment pathways for individual patients. High quality CT is usually adequate for most upper aerodigestive subsites. MRI is useful for skull base, larynx19 and equivocal CT findings.20 Follow-up imaging is very challenging, especially for the uninitiated. Distortion of tissue planes by biopsy, resection, neck dissection, flap reconstruction (Figure 3-8) and/or radiation therapy can be very distracting and misleading.21 Inflammatory changes related to chemotherapy-induced mucositis and superimposed radiation changes22 limit our ability to diagnose mucosal recurrences. Lymph node metastases take unconventional pathways after neck dissection.23 Different phases of contrast are beneficial for different modalities. Early phases are better for MRI1 and later phases are better for CT.24 Metabolic imaging in the form of FDG-PET will find a more important role for this stage of patient evaluation.13'25,26 This tool, while not perfect,27 will help triage previously operated patients into categories such as intervention or continued surveillance. In the "unresectable" or organ preservation groups, determining the relative degree of metabolic activity of a tumor prior to being treated will help determine the effects of radiation treatment28 or combined thera-pies.29 These images are best interpreted with some form of co-registration with a cross-sectional scan.30 Less expensive methods of imaging FDG-PET without a dedicated PET scanner (Figure 3-9) can be competitive.31 If the PET radionuclides are not available, SPECT imaging with Tl-201 can be used as an adjunct to the clinical exam.32,33

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