In the last 20 years, endorectal ultrasound (ERUS) has been one of the main diagnostic methods for locoregional staging of rectal cancer. ERUS is accurate modality for evaluating local invasion of rectal carcinoma into the rectal wall layers (T category). Adding the three-dimensional modality (3-D) increases the capabilities of this diagnostic tool in rectal cancer patients. We review the literature and report our experience in preoperative 3-D ERUS in rectal cancer staging. In the group of 71 patients, the staging of preoperative 3-D endorectal ultrasonography was compared with the postoperative morphologic examination. Three-dimensional ERUS preoperative staging was confirmed with morphologic evaluation in 66 out of 71 cases (92.9%). The detection sensitivities of rectal cancer with 3-D ERUS were as follows: T1, 92.8%; T2, 93.1%; T3, 91.6%; and T4, 100.0%; with specificity values of T1, 98.2%; T2, 95.4%; T3, 97.8%; and T4, 98.5%. Three-dimensional ERUS correctly categorized patients with T1, 97.1%; T2, 94.3%; T3, 95.7%; and T4, 98.5%. The percentage of total overstaged cases was 2.75% and that of understaged cases was 6.87%. The metastatic status of the lymph nodes was determined with a sensitivity of 79.1% (19 of 24), specificity of 91.4% (43 of 47), and diagnostic accuracy of 87.3% (62 of 71). In our experience, 3-D ERUS has the potential to become the diagnostic modality of choice for the preoperative staging of rectal cancer.Key words:
Three-dimensional endorectal ultrasound, Rectal cancerEndorectal ultrasound (ERUS) has been used as a diagnostic tool for evaluation and staging of rectal cancer since the 1980s.
1 According to the literature, in studies with more than 50 patients included, an overall accuracy of approximately 81.8% was reported.
2 Most of the studies present data between 85% and 95%, but in the studies with more than 200 patients, the accuracy rates are relatively lower—63.3% and 69%, respectively.
3,4 A common disadvantage of ERUS and magnetic resonance imaging (MRI) is the overstaging of T2 tumors owing to an irregular outer rectal wall resulting from transmural tumor extension or inflammation around the tumor. Another challenge for the ERUS, and especially the rigid probes, are the locally advanced, stenotic tumors, where the probe may not be able to pass above the lesion.
5 The nodal staging accuracy of ERUS ranges from 70% to 75%.
1,5,6 The metastatic lymph nodes are distinguished by hypoechoic appearance, round shape, peritumoral location, and size >5 mm.
7,8 Lymph nodes >5 mm have a 50% to 70% chance of being malignant, while those <4 mm have only a 20% chance.
9,10 A new modality of endorectal ultrasound represents a three-dimensional (3-D) ERUS that provides better visual images of the tumor volume and spatial relations to the adjacent organs and structures, even better than those of MRI, which leads to better diagnostic accuracy than MRI and standard ERUS.
11–15 The unique 3-D–ERUS longitudinal scan can precisely assess the tumor size and location.
16 The most important feature of this upgraded modality is the ability to reduce interpreter errors and offer potential predictive value. Three-dimensional ERUS provides the possibility to distinguish blood vessels from lymph nodes and allow precise fine needle aspiration (FNA) biopsies.
13,17 The infiltration of circumferential margin has been proven to correlate with T category, lymph node metastasis histologic tumor differentiation, and lymphovascular invasion.
13,17 Three-dimensional ERUS gives the possibility of multiplane evaluation of the tumor, allowing visualization of more subtle changes in the tumor characteristics and therefore better T and N categorizing.
18 A review of 86 patients who underwent standard 3-D ERUS, ERUS and 4-channel detector computed tomography (CT) demonstrated T-category accuracy of 78%, 69%, and 57%, respectively.
19 After analysis of the examiner''s error, the accuracy of 3-D ERUS for T category has reached 91% for 3-D ERUS and 88% for standard ERUS, and the N category accuracy improved to 90% and 76%, respectively. Also, ERUS can be used for diagnosis of premalignant lesions such as adenomas and polyps.
20 The main goal is to properly identify any chance of tumor invasion in the primary lesion and involvement of the surrounding lymph nodes in case the absence of those alarming characteristics allows for endoscopic resection of the lesion. Using higher-resolution probes, ERUS can distinguish T0 from T1 lesions. According to a meta-analysis of 258 biopsy-negative tumors, ERUS identified tumor mass in 81% of the 24 lesions, which were found to be invasive tumors on morphologic examination.
20 Another series of 60 patients with pT0/pT1 lesions demonstrated sensitivity and specificity of ERUS 89% and 88%, respectively.
21 As with MRI, 3-D ERUS could provide an evaluation of the mesorectal fascia.
14,22The reported data lead to the position that 3-D ERUS combines the high-resolution images of the rectal wall and cost-effectiveness of standard ERUS with the multiplanar and stereoscopic imaging capabilities of MRI. Three-dimensional ERUS may be the future premier imaging modality used in rectal cancer management.
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