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Intraoperative Application of Real-time Tissue Elastography for the Diagnosis and Staging of Pancreatic Tumours Jorge Elias Jr1, Fernando M. Mauad1, Valdair Francisco Muglia1, Eduardo Caetano2, José Sebastião dos Santos3, Rafael Kemp3, Theo Z. Pavan4, Antonio Adilton O. Carneiro4 1Radiology Division, School of Medicine of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, SP, Brazil 2Department of Pathology, University of Sao Paulo, Ribeirao Preto, SP, Brazil 3Department of Surgery, School of Medicine of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, SP, Brazil 4Department of Physics and Matematics, School of Philosophy, Science and Letters of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, SP, Brazil

The principle of ultrasound elastography is to map the strain within the tissue induced by an external compression force, e.g., using the ultrasound transducer. Stiffer tissues will experience lower strains. By measuring the tissue strain induced by a external compression, elastography can be used to characterize pancreatic normal tissues and mass lesions [10], but because of restrictions related to anatomic location such evaluation has been done mainly associated with endoscopic ultrasonography [7-9, 11, 12]. It is our belief that this is the first study to evaluate pancreatic tumors with intraoperative ultrasound elastography. Many questions remain on this matter, mainly related to characterization and safety issues.

Abstract –– The present study provides preliminary data of the usefulness of elastography applied in intraoperative pancreatic ultrasound for diagnosis and staging of pancreas tumors. We have studied six cases of pancreatic tumors, four adenocarcinomas and one insulinoma, which have been submitted to surgery. Tumor resection was considered based on preoperative evaluation and also in intraoperative findings. Only one patient had no surgical excision of the tumor. All tumors were presented as a “hard” mass in elastography. At least in one case, elastography imaging contributed significantly to demonstrate that there was no vascular invasion when compared to intraoperative gray scale ultrasound alone. There were no identified postoperative complications related to compression during the elastographic evaluation. We conclude that ultrasound elastography is a safe technique to evaluate pancreas intraoperatively and may be useful to diagnose and stage pancreatic tumors.

II. METHODOLOGY From 11th November 2010 to 27th January 2011 six patients with pancreatic tumor evaluated preoperatively with MR imaging were submitted to intraoperative ultrasound with elastographic real-time capability. All patients were scanned using an Ultrasonix 500RP (Ultrasonix Medical Corporation, Bothell, WA) real-time scanner equipped with a 5-10 MHz linear-array transducer. After initial evaluation with gray-scale and color Doppler ultrasound imaging, elastographic images were obtained with repeated transducer compression at mass location and at pancreatic tissue free of tumor at IOUS and preoperative imaging exams.

Keywords –– Ultrasound, elastography, pancreas, tumor

I. INTRODUCTION Intraoperative ultrasound (IOUS) provides superior spatial and contrast resolution of the pancreas compared to any other preoperative imaging method, and is used mainly to identify nonpalpable lesions, guide surgical procedures, and stage local tumor disease [1, 2]. Ultrasound elastography is a semi-quantitative imaging method that evaluates tissue stiffness in real-time, and has been used for the analysis of superficial organ lesions, such as those of the breast and prostate [3, 4]. Deeper abdominal organs and lesions can be evaluated by ultrasound elastography only if associated with endocavitary transducer technology or with exposition at surgery procedures. Thus, ultrasound elastographic evaluation of liver lesions, intraoperatively [5, 6], and of pancreatic lesions, endoscopically [7-9], have been reported. Since palpation during surgical exploration provides important information about the existence, location and qualitative presumption of tumors in a given organ or anatomic location, ultrasound elastography can help to objectively evaluate these tumors. IOUS is also a powerful tool to evaluate the existence and location of pancreatic tumors and their correlation with adjacent vessels and important anatomic structures [1, 2]. MARCH 28 - APRIL 1, 2011, RIO DE JANEIRO, BRAZIL 978-1-61284-918-8/11/$26.00 ©2011 IEEE

III. RESULTS Demographic, ultrasound and surgery data of all patients are presented in table I and II. TABLE I Sex, Age, and Preoperative Diagnosis and Location of the Pancreas Tumor

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Case

Sex

Age

1 2 3 4 5 6

F F M F F F

57 56 69 72 63 43

Preoperative diagnosis, location Insulinoma, pancreas body Mass, pancreas head Mass, pancreas head Mass, pancreas head Mass, pancreas head Masses, pancreas head and tail ISBN: 978-1-61284-918-8 IEEE Catalog Number: CFP1118G-ART


TABLE I Sex, Age, and Preoperative Diagnosis and Location of the Pancreas Tumor

Case

IOUS finding

1

Two hypoechoic nodules at pancreatic body

2 3 4 5 6

Irregular hypoechoic mass Irregular hypoechoic mass Irregular hypoechoic mass Irregular hypoechoic mass Irregular hypoechoic masses

Elastographic finding Nodules with same elastographic characteristics ("Hard") Hard mass Hard mass Hard mass Hard mass Hard massess in the head and in the tail of pancreas

Surgery Body and tail pancreatectomy Cephalic duodenopancreatectomy Cephalic duodenopancreatectomy Cephalic duodenopancreatectomy Cephalic duodenopancreatectomy

Fig. 2. Ultrasound elastography scan through the short ax of the pancreas body of the same patient presented at Fig. 1. At this site the pancreatic tissue (arrowheads) is free of tumor but shows elastographic changes which is related to proximal pancreatitis due to mass in the head of pancreas. The dilated main pancreatic duct is also showed).

Biliary derivation surgery (palliative)

All tumors were hypoechoic at gray scale ultrasound and “hard” at elastography (Fig. 1). Pancreatic tissue free of tumor was less “hard” but yet presented with higher stiffness when compared to adjacent tissue (Fig. 2). At least in one patient, the elastographic image showed that there was no invasion of the superior mesenteric vein as the gray scale ultrasound depicted (Fig. 3). There were no identified postoperative complications related to compression during the elastography evaluation.

Fig.3. Ultrasound elastography scan through the long ax of the pancreas head of another patient. There is a large pancreatic hypoechoic mass (M) which seems to involve the superior mesenteric vein (SMV) showed by the gray scale image (right image). The elastographic image (left) shows the presence of soft tissue between the mass and the SMV, not considered as tumoral tissue. This finding was interpreted as no vascular invasion and the tumor was resected. This finding was confirmed by anatomopathology correlation. Fig. 1. Ultrasound elastography scan through the long ax of pancreas showing a mass (M) in the pancreatic head causing invasion and dilatation of the main pancreatic duct. The elastographic image (color, left) shows a hard tissue beyond the hypoecoic irregular lesion showed by gray scale image only (right).

IV. DISCUSSION Adenocarcinoma is the most frequent pancreatic malignancy accounting for 95% of malignant tumors of the pancreas and the fourth most common cause of cancer death in the United States. The age range for tumor occurrence is the fourth through the eighth decade, with tumor incidence peaking in the eighth decade. The tumor has a poor prognosis, with a 5-year survival of 5%. Early diagnosis is difficult and the main treatment is surgical resection. Thus,

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preoperative staging is paramount and is mainly obtained by imaging exams such ultrasound, CT and MRI. Nonetheless, there is no preoperative imaging exam with accuracy of 100% [13]. Intraoperative ultrasound has gained an important role in the diagnosis of nonpalpable lesions, guidance of surgical procedures, and staging local tumor disease [1, 2]. The advent of elastography as an adjunct of ultrasound technique has permitted to evaluate the relative stiffness distribution of different tissues and thus permitted to evaluate a new characteristic of pancreatic tumors. In this preliminary study, we have presented the feasibility of such technique in the evaluation of pancreatic tumors. The elastographic characteristics of pancreatic tumors seem to be correlated to many others tumors in different organs already reported as with EUS elastography, i.e., they are “hard” compared to the background glandular tissue [6-9]. Moreover, we had no cases of postoperative complications due to glandular compression in order to obtain the elastographic evaluation. We had only one case of benign pancreatic tumor, an insulinoma, which had the same elastographic aspect compared to adenocarcinoma cases. The fact that insulinomas can be very difficult to be identified in selected cases indicates that elastography could have a role by increasing the sensitivity of the intraoperative ultrasound. However, more data would be necessary to confirm that. An interesting finding was that elastography could differentiate hypoechoic fibrous tissue surrounding a vascular structure from tumoral tissue in one case. This finding was sufficient to increase the confidence of no vascular invasion corroborating the surgical decision for tumor resection. That is why we believe that elastography can collaborate in the staging of pancreatic malignant tumors. It is not infrequent that pancreatic glandular tissue proximal to a tumor location presents pancreatitis changes due to increased pancreatic ductal pressure. When this occurs it is showed as hypoechogenic alterations by gray scale ultrasound images, which worsen the ability of ultrasound to depict the margins of the tumor. With this preliminary data we are confident that elastography evaluation can also help in this differentiation.

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V. CONCLUSION Ultrasound elastography is a safe technique to evaluate pancreas intraoperatively and may be useful to diagnose and stage pancreatic tumors. .

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