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Background
Endoscopic ultrasound (EUS) elastography represents an imaging procedure used for the visualization of tissue elasticity during usual EUS examinations. The principle of elastography is that tissue compression produces displacement within the tissue, while the strain is smaller in hard tissues as compared to soft tissues. Consequently, by measuring the tissue strain induced by compression, it is possible to estimate the tissue hardness, which may be useful in diagnosing and differentiating malignant tumors. Ultrasound elastography estimates the axial strain of the tissues along the direction of compression, which can be obtained in real-time with recent state-of-the-art ultrasound systems1,2.
Similarly with color Doppler applications, a region of interest (ROI) for visualization of tissue elastography is selected manually and should include the targeted lesion, as well as the soft surrounding tissues, with a ratio of about 50%. The ROI needs to be set to include sufficient surrounding tissue because elasticity values are displayed relative to the average strain inside the ROI. The system is set-up by default to use a hue (rainbow) color map, where hard tissue areas are marked with dark blue, medium hard tissue areas with cyan, intermediate tissue areas with green, medium soft tissue areas with yellow and soft tissue areas with red.
EUS elastography might be useful for the differentiation of benign and malignant focal hepatic lesions3. The diagnosis of liver metastases represents important staging information for deciding the best approach for therapy. Transabdominal US, dynamic contrast-enhanced CT and magnetic resonance imaging (MRI) are the most commonly used imaging methods for evaluating liver metastases. All these methods are however limited in their ability to diagnose small liver lesions and endoscopic ultrasound has been proposed as a useful preoperative staging tool, possibly avoiding the need of intraoperative ultrasonography4. EUS-guided fine needle aspiration can confirm these lesions and establish a definitive M stage that allows a change in clinical management5,6.
To the best of our knowledge, EUS elastography did not have a significant clinical role in the imaging of the liver, especially in the depiction of small lesions (less than 1 cm).
Case Presentation
We present the case of a 50 years old patient, admitted in the Gastroenterology Department due to weight loss, pain in upper abdomen and fatigue. Initial blood tests were normal. Transabdominal ultrasound revealed several, very small (under 10 mm) anechoic round zones in the liver, suspicious of metastases. Because there were no evident causes for primary localization of the tumor, EUS with elastography was performed for a better assessment of these lesions. The elastography aspect (Figure 1, 2) also suggested metastatic malignant disease considering the increased hardness of the liver lesions, as compared to the surrounding normal parenchyma. Furthermore, the pancreatic head appeared very inhomogeneous with enlarged surrounding lymph nodes delete word “around”. EUS-FNA of the pancreas and lymph nodes was performed. The cytology exam of the specimen diagnosed pancreatic cancer (Figure 3).
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Figure 1 |
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Discussions
Percutaneus liver biopsy is a feasible method for tissue sampling in patients with suspected liver lesions. However, it is an invasive method associated with patient discomfort and, in rare cases, with serious complications. EUS-guided FNA of liver lesions located far away from the tip of the echoendoscope is often more difficult than FNA of lesions closer to the probe. The needle may bend or curve as it traverses normal liver to reach the target liver lesion. The needle tip may then miss the target if the lesion is small5. Therefore, research is nowadays focused on the evaluation of noninvasive methods for the assessment of suspected liver lesions.
Ultrasound elastography is a new imaging technique used for visualization of tissue elasticity. The method reveals the physical properties of the tissue by characterizing the difference of hardness between pathological tissue and normal tissue. The method is increasingly used for the diagnosis and differentiation of breast lesions7 and prostate cancer8. Our previously published results revealed a very good sensitivity and specificity for the differential diagnosis between benign and malignant lymph nodes9, and also for the differentiatial diagnosis of pseudotumoral chronic pancreatitis and pancreatic cancer.10 Recently, liver elastography was also used and showed promising results in the evaluation of fibrosis in chronic liver diseases11, 12. To the best of our knowledge, there are not yet published any extended prospective studies considering the assessment of EUS elastography of focal liver lesions. Our recent experience with these lesions depicted a very good correlation between the EUS elastography aspect of focal liver lesions and pathological diagnosis. The utility of EUS and EUS elastography of the liver lies in the ability to make the initial cancer diagnosis, upstage cancer, avoid surgery or other invasive staging procedures, with an increased cost-efficiency.
In conclusion, future prospective studies, with blinded comparisons and multicentric design should aim to compare EUS elastography with other non-invasive or minimal invasive methods for the assessment of focal liver lesions.
References:
1. Frey H. Real-time elastography. A new ultrasound procedure for the reconstruction of tissue elasticity. Radiologe 2003;43:850-855.
2. Konofagou EE. Quo vadis elasticity imaging? Ultrasonics 2004; 42: 331-336.
3. Rustemovic N, Hrstic I, Opacic M, et al. EUS elastography in the diagnosis of focal liver lesions. Gastrointest Endosc 2007;66:823-824.
4. Awad SS, Fagan S, Abudayyeh S, Karim N, Berger DH, Ayub K. Preoperative evaluation of hepatic lesions for the staging of hepatocellular and metastatic liver carcinoma using endoscopic ultrasonography. Am J Surg 2002;184:601-604.
5. Chang KJ, Katz KD, Durbin TE, Erickson RA, Butler JA, Lin F, et al. Endoscopic ultrasound–guided fine-needle aspiration. Gastrointest Endosc 1994;40:694-9.
6. Nguyen P, Feng JC, Chang KJ. Endoscopic ultrasound (EUS) and EUS-guided fine-needle aspiration (FNA) of liver lesions. Gastrointest Endosc. 1999;50:357-361.
7. Bercoff J, Chaffai S, Tanter M, Sandrin L, Catheline S, Fink M, Gennisson JL, Meunier M. In vivo breast tumor detection using transient elastography. Ultrasound Med Biol. 2003;29:1387-1396.
8. Cochlin DL, Ganatra RH, Griffiths DF. Elastography in the detection of prostatic cancer. Clin Radiol. 2002;57:1014-1020.
9. Saftoiu A, Vilmann P, Ciurea T, et al. Dynamic analysis of EUS used for the differentiation of benign and malignant lymph nodes. Gastrointest Endosc. 2007;66:291-300.
10. Saftoiu A, Vilmann P, Gorunescu F, et a. Neural network analysis of dynamic sequences of EUS elastography used for the differential diagnosis of chronic pancreatitis and pancreatic cancer. Gastrointest Endosc, in press 2008.
11. Friedrich-Rust M, Ong MF, Herrmann E, Dries V, Samaras P, Zeuzem S, Sarrazin C. Real-time elastography for noninvasive assessment of liver fibrosis in chronic viral hepatitis. AJR Am J Roentgenol. 2007;188:758-64.
12. Saftoiu A, Gheonea DI, Ciurea T. Hue histogram analysis of real-time elastography images for noninvasive assessment of liver fibrosis. AJR Am J Roentgenol. 2007;189:W232-233.
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