Comparison of peritoneal tumor imaging using conventional MR imaging and diffusion-weighted MR imaging with different b values
Introduction
The peritoneum is a serous sac made of a thin mesothelial membrane that lines the abdominal and pelvic cavities [1], [2], and it is divided into the visceral peritoneum and the parietal peritoneum [1].
Primary tumors of the peritoneum are rare, whereas metastatic disease is the most commonly encountered neoplastic process involving the peritoneum [1]. The most common locations of peritoneal metastases are the pouch of Douglas, ileocecal region, right paracolic gutter, sigmoid mesocolon, greater omentum, and right subdiaphragmatic parietal peritoneum [3].
Treatment protocols (medical treatment or surgery) are determined by the location and spread of peritoneal tumors, and a planned surgical approach reduces the extent of exploration and anesthesia time. Therefore, imaging modalities that identify and localize tumors are very important. Various imaging modalities, such as computed tomography (CT), ultrasonography (US) and magnetic resonance imaging (MRI) are used to detect peritoneal tumors [4]. Ultrasonography is recognized as a cumbersome, operator-dependent, time consuming technique when careful evaluation of structural identification of disease is required [4]. CT is undoubtedly the most used imaging modality in the evaluation of peritoneal tumors. It is non-invasive but carries the risk associated with radiation. Furthermore, CT examinations of the abdomen and pelvis are insensitive to small volumes (<5 mm) of diffuse peritoneal seeding. However, CT can be helpful when larger volume peritoneal tumors are present [5]. MRI of the abdomen is noninvasive, non-ionizing, and capable of providing multiplanar images. However, compared with CT scan time, MR image acquisition time is somewhat longer and more influenced by respiratory movement artifacts, its spatial resolution is lower, and clinicians find it harder to interpret [4].
Recently, diffusion-weighted imaging (DWI) of the abdomen and pelvis, which has a widespread usage for diagnostic aid, has been shown to provide a new contrast mechanism to evaluate patients with abdominal pathologies and solid abdominal and pelvic organs [6]. Recent studies have shown that adding DWI to routine MRI examination increases diagnostic accuracy [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Most solid tumors show restricted diffusion due to the high cellularity and a significant number of cell membranes per unit volume, which results in the restriction of water movement in a corresponding high signal intensity on DW images [17], [18], [19]. Thus, we considered the use of DWI for the evaluation of peritoneal tumors. We hypothesized that adding DW MRI to conventional MRI would improve the specificity and sensitivity for identifying peritoneal tumors in the abdomen.
In this study, the aim was to evaluate the utility of DW MRI with two different b values in identifying peritoneal tumors in oncology patients.
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Patients
Nineteen patients with known malignancy (12 men, 7 women, mean ± SD age: 64 ± 6 years, range: 46–82 years) were involved in this study. Written informed consent was acquired from all patients. This retrospective study was approved by the institutional review board. The study group consisted of patients with confirmed diagnoses of ovarian cancer (n = 3), colon cancer (n = 7), esophageal cancer (n = 3), gastric cancer (n = 4) and pancreatic cancer (n = 2). All patients had abdominal and pelvic MRI examinations
Results
For each of 19 patients, peritoneal metastasis was confirmed upon surgical and histopathological evaluation.
Metastatic lesion findings for all patients from three imaging sessions are shown in Table 1. One hundred and twenty-five peritoneal metastasis sites were confirmed by surgical and histopathological findings, and 65 sites showed no tumor involvement. Table 2 shows the consensus interpretation by two observers of imaging results for each peritoneal metastasis site.
Table 1, Table 2 show
Discussion
DW MR imaging detects abnormalities on the basis of tumor cellularity. With this new technique, information is extracted from diffusion of water molecules in tissues, and this technique produces different contrasts than conventional MR imaging sequences. Therefore, DW MR imaging enables the characterization of tissues at the microscopic level and utilizes a mechanism that is different from T1 and T2 relaxation [21]. Tumors are more cellular than the tissue from which they originate and, thus,
Conclusion
Using DWI with a high b value provides increased specificity that can improve imaging of peritoneal tumors when added to conventional MRI. We recommend combined MR and DW imaging with high b values for increased sensitivity and accuracy of preoperative imaging of peritoneal tumors.
Conflict of interest
None.
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