Evaluation of real-time qualitative sonoelastography of focal lesions in the parotid and submandibular glands: applications and limitations

Sonoelastography techniques in the evaluation and diagnosis of parotid neoplasms

Ultrasound is the first-line imaging investigation in the evaluation of parotid gland lesions; however, ultrasound alone cannot differentiate between benign and malignant lesions. An imaging technique with this capability would be of great value, as fine needle aspiration cytology (FNAC) is not always accurate and partial/total parotidectomy is associated with facial nerve palsy and Frey's syndrome. Sonoelastography is a novel imaging technique that has been employed in the research setting in the evaluation of tissues including breast, thyroid, prostate and the salivary glands. More recently it has been used as a diagnostic adjunct in the sonographic evaluation of major salivary gland lesions. This review article outlines the current role of sonoelastography in the diagnostic imaging of parotid lesions, with particular reference to the findings of two research papers published in European Radiology. These papers employ slightly different techniques: the first utilises shear wave elastography whilst the second uses real-time sonoelastography. Sonoelastography may have potential as a diagnostic imaging adjunct to conventional ultrasound. However, it seems likely that FNAC/core biopsy will continue to be necessary. Further studies to evaluate the reproducibility of sonoelastographic results across a range of operators and systems are also needed. Key Points • Ultrasound is the initial and often definitive investigation for parotid lesions • Ultrasound-based strain elastography has been attempted but offered little additional information • New shear wave elastographic techniques did not confer much advantage either • However, analysis of elastographic patterns seems to provide advantages over ultrasound alone.

Real-time sonoelastography of major salivary gland tumors

OBJECTIVE

The purpose of this study was to determine the performance of real-time sonoelastography in the differential diagnosis of salivary gland tumors.

SUBJECTS AND METHODS

Between 2007 and 2010, 74 salivary gland tumors were examined by ultrasound and sonoelastography in 66 patients. Lesions were graded according to a 4-point elastography score. Surgical excision and histopathologic examination were performed in all cases. The difference in elastographic score between benign and malignant masses and that between pleomorphic adenomas and Warthin tumors were evaluated.

RESULTS

Of the 74 salivary tumors, 63 were located in the parotid, and 11 were in the submandibular gland. There were 18 malignant and 56 benign tumors. The mean (± SD) elastographic score was 2.58 ± 0.87 for pleomorphic adenomas, 2.15 ± 0.80 for Warthin tumors, 2.00 ± 0.57 for other benign tumors, and 2.94 ± 0.87 for malignant tumors. For benign tumors overall, the mean elastographic score was 2.41 ± 0.87. The difference in elastographic score between benign and malignant tumors overall was statistically significant (p < 0.05), but the difference between malignant tumors and pleomorphic adenomas and that between Warthin tumors and pleomorphic adenomas were not statistically significant. Using cutoff values between scores 2 and 3 and scores 3 and 4, there was no statistically significant difference between benign and malignant tumors.

CONCLUSION

Although this study revealed a difference in elastographic score between benign and malignant tumors, detailed analysis did not provide consistent results. Consequently, real-time sonoelastography appears to be a limited technique in the differential diagnosis between benign and malignant salivary masses.

Elastography: the next step

In the past few decades, various tools have emerged that claim to enhance detection of oral cancer. The most important prognostic factor in patients with oral cancer is lymph node status: the presence of nodal spread decreases the 5-year survival rate by approximately 50%. Differentiation between reactive and metastatic lymphadenopathy is thus vital, and one differentiating criterion is hardness (elasticity) of the lymph node. The purpose of this review is to highlight a promising new ultrasound technique, known as elastography, which measures the characteristics of tissue compliance. The principles underlying elastography are that tissue compression produces strain (displacement) within the tissue - which is lower in harder tissues than in softer tissues - and that malignant tissues are generally harder than normal surrounding tissue. Therefore, elastography might yield clinical information useful in diagnosing cervical metastasis and improving prognosis in oral cancer. It has long been used for cancers of the breast, pancreas, and thyroid, and its use in cervical lymphadenopathy is now being explored, which could lead to great advancements in the diagnosis and prognosis of oral cancer.

AN OVERVIEW OF ELASTOGRAPHY - AN EMERGING BRANCH OF MEDICAL IMAGING

From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field.In this paper we present a brief history and theoretical basis of EI, describe various techniques of EI and, analyze their advantages and limitations, and overview main clinical applications. We present a classification of elasticity measurement and imaging techniques based on the methods used for generating a stress in the tissue (external mechanical force, internal ultrasound radiation force, or an internal endogenous force), and measurement of the tissue response. The measurement method can be performed using differing physical principles including magnetic resonance imaging (MRI), ultrasound imaging, X-ray imaging, optical and acoustic signals.Until recently, EI was largely a research method used by a few select institutions having the special equipment needed to perform the studies. Since 2005 however, increasing numbers of mainstream manufacturers have added EI to their ultrasound systems so that today the majority of manufacturers offer some sort of Elastography or tissue stiffness imaging on their clinical systems. Now it is safe to say that some sort of elasticity imaging may be performed on virtually all types of focal and diffuse disease. Most of the new applications are still in the early stages of research, but a few are becoming common applications in clinical practice.

[Current aspects in ultrasonography of the salivary glands]

Ultrasonography is a basic diagnostic tool in all diseases of the salivary glands. Due to their relatively superficial anatomic location, distinct borders and homogenous echotexture, the salivary glands are ideally positioned for sonographic assessment. The advantages of this technique include its high diagnostic accuracy, non-invasiveness, lack of radiation exposure, as well as high reproducibility and low costs. Progress in ultrasound equipment and ultrasound transducers in recent years, i.e. colour-coded Doppler sonography with and without contrast enhancers, tissue harmonic imaging and elastography have widened the spectrum of indications and diagnostic accuracy. Although unspecific, many diseases of the salivary glands have particular sonographic characteristics. In addition, ultrasound-guided fine-needle biopsy is able to obtain material for cytological analysis in a targeted fashion under visual control. Compared to other imaging techniques such as CT and MRI, ultrasound achieves the highest sensitivity in the identification of neoplasms in the salivary glands.

Elastography of the uterine cervix: implications for success of induction of labor

OBJECTIVES

To perform a preliminary investigation into the use of elastography for cervical assessment, in order to determine the effectiveness of this method for the evaluation of cervical consistency.

METHODS

Elastography of the uterine cervix was performed in 29 patients before induction of labor, with tissue surrounding the internal os described using a numeric scale called the elastography index (EI). A color map from purple to red was produced with the hardest tissues displayed as purple and assigned a score of 0 points and progressively softer tissues displayed as blue (1 point), green (2 points), yellow (3 points) and red (4 points). The EI of tissue around the internal os, in the middle part of the cervical canal and around the external os were analyzed in relation to the success of induction of labor using the t-test.

RESULTS

The mean EI of the internal os in the group of patients with successful induction of labor was 1.23, while in the group with failed induction of labor it was 0.39 (Student's t-test, P=0.024). No difference was found for the EI of the middle part of the cervical canal or for the EI of the external os in relation to the success of induction of labor (P>0.05).

CONCLUSION

Elastography of the uterine cervix may be an objective method for assessment of softening of tissue in the region of the internal os before induction of labor. Standardization of the cervical properties observed on elastography during pregnancy may help to guide the use of prostaglandins or oxytocin for induction of labor.