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Science to Practice |
Department of Radiology,
Thomas Jefferson University Hospital,
Room 763E Main Bldg, 132 S 10th St,
Philadelphia, PA 19107-5244,
levon.nazarian@jefferson.edu
SUMMARY
Imaging diagnosis of cervical lymph node metastases may be difficult because of overlap in size and morphologic features between benign and metastatic nodes. Sonoelastography is a noninvasive technique that may improve detection of lymph node metastases, thereby guiding biopsy and facilitating follow-up. For sonoelastography to be accepted into clinical practice, however, the techniques and diagnostic criteria need to be further refined.
THE SETTING
In patients with head and neck cancer, treatment and prognosis depend on whether tumor has spread to cervical lymph nodes. Because cervical lymph node metastases may be impalpable, imaging techniques, including computed tomography (CT) and magnetic resonance (MR) imaging, are often needed for accurate staging. Imaging diagnosis of malignancy relies on size and morphologic criteria, which include nodal enlargement, round shape, presence of necrosis, and obliteration of the fatty hilum (1). The problem with size criteria is that larger nodes may be benign and smaller nodes may harbor metastases (1). There is a similar overlap in the morphologic criteria for nodal metastases (1). In this issue of Radiology, Lyshchik et al (2) show that a relatively new technique, sonoelastography, can be used to distinguish benign and metastatic cervical lymph nodes in patients with thyroid or hypopharyngeal cancers.
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Elastography is based on a principle similar to manual palpation, in which the examiner detects tumors because they feel harder than surrounding tissues (3). In elastography, a mechanical force (compression or vibration) is applied to the soft tissues, and a conventional imaging technique such as US or MR imaging is used to create a map of soft-tissue deformation (3). The results are displayed on an image called an elastogram, on which hard areas appear dark and soft areas appear bright. Elastography has been shown to be useful in diagnosis of breast, thyroid, and prostate cancers (4–6).
Lyshchik et al (2) performed sonoelastography in 43 patients suspected of having thyroid or hypopharyngeal cancer. This technique showed 85% sensitivity, 98% specificity, and 92% accuracy in the distinction of benign and metastatic cervical lymph nodes. The cancers tended to be harder (strain index > 1.5), and the benign nodes tended to be softer (strain index < 1.5). The sonoelastography criteria for malignancy outperformed the gray-scale US criteria—the best of which was a short-to-long-axis diameter ratio greater than 0.5, which showed 75% sensitivity, 81% specificity, and 79% accuracy (2).
THE PRACTICE
Clinical use:
Lymph node detection techniques must be sensitive enough to allow detection and eradication of all cancer deposits and specific enough to avoid unnecessary treatment. However, because no imaging technique is perfect, tissue diagnosis is needed for definitive staging. US-guided fine-needle aspiration cytology is both sensitive and specific for diagnosing nodal metastases (1,7), but it can yield false-negative results. Sonoelastography has the potential to improve the accuracy of percutaneous biopsy and/or nodal dissection. It may also increase the accuracy of postoperative imaging follow-up, especially when metastatic deposits cause lymph nodes to harden before they become larger.
Future opportunities and challenges:
The elastographic technique described by Lyshchik et al (2), despite its potential, is labor intensive and time consuming, requiring 30–40 minutes for off-line computer processing. For sonoelastography to become adopted widely in practice, image acquisition and reconstruction algorithms need to be improved. Investigators in future studies also need to analyze inter- and intraobserver variability, which may be an important limitation of sonoelastography, especially when compression is performed free hand instead of with a mechanical device (3,6).
FOOTNOTES
See also the article by Lyshchik et al in this issue.
References
Related Article
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