Can Imaging of the Neck Preclude an Elective Neck Dissection

One of the first controversies faced by the clinician during the process of determining whether to perform an elective neck dissection is the value of imaging studies of the neck. Admittedly, determination of the status of the lymph nodes of the neck by clinical examination is not always accurate in patients with cancer of the head and neck. Various imaging modalities have been shown to be more accurate in detecting minimal enlargement of lymph nodes in the neck.1-3 A clinician may be more inclined to recommend elective treatment of the neck when one or more enlarged nodes are demonstrated by an imaging study, as the probability of an enlarged lymph node containing metastasis is higher. However, not all enlarged lymph nodes contain metastatic deposits. More importantly, a negative ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI) scan cannot be relied on to withhold elective treatment of the neck, because none of these techniques can depict small tumor deposits within a lymph node. The presence of radiolucency within a lymph node, considered a very reliable criterion for the presence of metastasis, is not very useful in evaluating the NO neck, because necrosis seldom occurs in micrometastases. Furthermore, the size criteria currently used to consider a node positive on CT or MRI (largest diameter > 10 or 15 mm) are not optimal, especially for nodes in the submandibular triangle, a frequent site of metastases from cancers of the oral cavity. Recently, DiNardo4 studied the lymph nodes of the submandibular triangle in patients with floor-of-mouth cancer. DiNardo found that 88% of the nodes harboring metasta tic carcinoma were < 10 mm in diameter. The UCLA group has reported a similar study of neck dissection specimens, which showed that 67% of lymph nodes containing metastasis were < 10 mm in diameter.5 Yuen et al.6 recently studied neck dissection specimens by whole-organ sectioning at 3-mm intervals. Among 2826 lymph nodes examined, these investigators found that the median size of the metastatic foci was 3 mm and occupied a median of 6% of the cross-sectional area of the involved nodes. Clearly, ultrasound, CT, and MRI scans are unable to detect metastases of this size in a lymph node of any size, nor can they differentiate between reactive enlargement of a lymph node and enlargement caused by metastasis.

Multidirectional ultrasonography scanning has shown promise for improved preoperative evaluation of the NO neck.7 In experienced hands, this technique permits fine-needle aspiration of lymph nodes as small as 3 mm in diameter. Using this technique, Snow8 and several other investigative groups in the Netherlands1'9 have reportedly been able to identify 75 to 77% of patients with occult lymph node metastases. Despite the success reported by these groups and the results of a prospective multi-institutional study in the Netherlands, which showed that the results with ultrasound-guided fine-needle aspiration biopsy (FNAB) are not as investigator dependent as is often sug-gested,9 this technique has not gained wide acceptance outside Europe. Perhaps it is because the technique is demanding in terms of equipment and personnel time. More importantly, long-term assessment of the outcome in patients deemed node-negative by ultrasonography and FNA cytology, in whom an elective neck dissection was not performed, has only recently been published. These results are not as encouraging as was hoped. In a study of 92 patients whose necks were staged NO, and which were cytologically negative, followed for 1 to 3 years, 19 (21%) subsequently developed a neck node metastasis. Six of these 19 patients (32%) died of distant metastases or of loco-regional recurrence.10

It is hoped that positron emission tomography (PET) will be a more useful imaging technique for detecting metastases in the lymph nodes, without their removal and histopathologic examination. It relies on abnormal tissue metabolism to detect neoplasms. Myers and Wax11 recently reported that PET permitted accurate determination of the presence or absence of metastasis in a small group of 11 patients with squamous cell carcinoma of the oral cavity. These patients were staged clinically N0 and underwent 19 neck dissections. PET scans were positive in all 7 instances in which the neck dissection had histologically confirmed metas tasis and were negative in all 12 cases in which there was no histologic evidence of metastasis. Unfortunately, these investigators do not report examining the lymph nodes by more than one section. Although the results of this first study are encouraging, evaluation of this technique awaits studies of larger numbers of patients. These may not be forthcoming because of the limited accessibility to this technology and its prohibitive cost.11

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