Version May 2024
INTRODUCTION — Accurate staging of rectal cancer is essential for selecting patients who can undergo sphincter-preserving surgery and identifying those who may benefit from neoadjuvant therapy. Clinical staging is usually accomplished by performing a physical examination, colonoscopy (if possible), and an imaging evaluation (computed tomography [CT] scan of the chest and abdomen [with or without pelvis] and either pelvic magnetic resonance imaging [MRI] or rectal endoscopic ultrasound [EUS]). The accuracy and comparative performance of these imaging modalities for staging are discussed separately. (See "Pretreatment local staging evaluation for rectal cancer".)
This topic will review the clinical application and procedure-related aspects of rectal EUS for patients with rectal cancer. The diagnosis, staging evaluation, and management of rectal cancer are presented separately.
●(See "Clinical presentation, diagnosis, and staging of colorectal cancer".)
●(See "Pretreatment local staging evaluation for rectal cancer".)
●(See "Overview of the management of rectal adenocarcinoma".)
●(See "Neoadjuvant therapy for rectal adenocarcinoma".)
●(See "Surgical treatment of rectal cancer".)
CLINICAL APPLICATIONS
Initial staging — For most patients with a new diagnosis of rectal cancer, and especially for those with locoregionally advanced tumors, magnetic resonance imaging (MRI) is generally preferred over rectal endoscopic ultrasound (EUS) for staging evaluation, unless there is a contraindication to MRI (eg, cardiovascular implantable electronic device). However, some patients are evaluated with both MRI and rectal EUS (eg, patients with suspected but unconfirmed internal iliac lymph nodes) because the imaging modalities provide complementary staging information [1,2]. The selection of imaging studies and their performance characteristics for determining tumor (T) and nodal (N) stage are presented in more detail separately (table 1 and table 2). (See "Pretreatment local staging evaluation for rectal cancer".)
Surveillance after surgical resection — For post-treatment surveillance after surgical resection for rectal cancer, rectal EUS may be more accurate than other imaging modalities for early detection of local recurrence. However, the optimal selection criteria for patients who would benefit from including rectal EUS in the surveillance strategy are uncertain. Consensus guidelines from professional societies vary in their approach to surveillance. Guidelines from the United States Multi-Society Task Force include EUS as an alternative to sigmoidoscopy in the testing strategy for patients at higher risk of recurrence [3], while the National Comprehensive Cancer Network includes EUS as an alternative to flexible sigmoidoscopy for patients with rectal cancer who undergo transanal excision only (table 3). Surveillance strategies after surgical resection and risk factors for cancer recurrence are discussed separately. (See "Post-treatment surveillance after colorectal cancer treatment", section on 'Transrectal endoscopic ultrasound'.)
Staging local recurrence — The pretreatment evaluation for patients with a locally recurrent rectal cancer typically includes pelvic MRI. In general, rectal EUS is a less helpful modality than MRI for staging a local recurrence after prior surgical resection [4]. The accuracy of rectal EUS is somewhat diminished in the post-treatment setting because of postoperative or post-radiation inflammatory soft tissue changes. These changes obscure the mucosal layers of the rectum, making ultrasonographic images more challenging to interpret [5-9]. (See "Treatment of locally recurrent rectal adenocarcinoma", section on 'Pretreatment evaluation'.)
However, rectal EUS with sampling of lesions that are suspicious for recurrence may be useful for patients in whom histologic confirmation of recurrence is required. (See 'Fine-needle aspiration' below.)
Other uses — A promising application is EUS-guided fiducial placement to enhance the precision of radiotherapy. In a study of 20 patients with rectal cancer undergoing neoadjuvant treatment, rectal EUS was used to guide placement of 64 fiducials in the mesorectal fat or into the tumor itself [10]. While fiducial placement was successful initially, mesorectal location was associated with higher fiducial retention rates after a median of 17 days compared with intratumoral placement (90 versus 55 percent). (See "Neoadjuvant therapy for rectal adenocarcinoma" and "Radiation therapy techniques in cancer treatment".)
CONTRAINDICATIONS — There are few relative contraindications to rectal endoscopic ultrasound (EUS):
●Patients who are hemodynamically unstable and/or cannot tolerate moderate sedation (see "Gastrointestinal endoscopy in adults: Procedural sedation administered by endoscopists")
●Patients with known or suspected perforated viscus
Patients with gastrointestinal obstruction may undergo rectal EUS, but the imaging may be limited to an area distal to the level of obstruction.
PROCEDURE
Patient preparation — The preprocedure preparation for patients undergoing rectal EUS is similar to that described for patients undergoing lower gastrointestinal endoscopy (see "Overview of colonoscopy in adults", section on 'Patient preparation'):
●Bowel preparation – Patients are given a bowel preparation regimen that is similar to preparing for colonoscopy or flexible sigmoidoscopy, and this is discussed separately. (See "Bowel preparation before colonoscopy in adults".)
●Adjusting medications – Most patients do not need to discontinue aspirin or nonsteroidal anti-inflammatories when undergoing diagnostic rectal EUS. The management of antiplatelet and anticoagulant therapy in patients undergoing endoscopy is typically individualized, managed in conjunction with the prescribing specialist, and is discussed separately. (See "Management of antiplatelet agents in patients undergoing endoscopic procedures" and "Management of anticoagulants in patients undergoing endoscopic procedures".)
●Antibiotic prophylaxis – Antibiotic prophylaxis is not typically used for patients undergoing diagnostic and/or staging rectal EUS.
The American Society for Gastrointestinal Endoscopy guidelines regarding prophylaxis for gastrointestinal procedures do not recommend antibiotic prophylaxis for endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) of solid lesions in the lower gastrointestinal tract because the risk of bacteremia is low [11,12]. However, endoscopists may choose to give antibiotics following transrectal fine-needle aspiration (FNA) for patients who are at higher risk for infection (eg, patients who are immunocompromised), and antibiotic prophylaxis is discussed in more detail separately. (See "Antibiotic prophylaxis for gastrointestinal endoscopic procedures".)
●Anesthesia – The procedure is typically performed on an outpatient basis with moderate sedation or without sedation, depending on patient preference. Anesthesia and sedation for endoscopic procedures is discussed separately. (See "Gastrointestinal endoscopy in adults: Procedural sedation administered by endoscopists" and "Anesthesia for gastrointestinal endoscopy in adults".)
Equipment — EUS is performed with an echoendoscope (an endoscope with an ultrasound transducer engineered into its tip). We use a flexible echoendoscope because it facilitates traversing a narrow, strictured lumen and assessing iliac lymph nodes. A rigid echoendoscope may also be used; however, imaging lesions in the proximal rectum or passing through a stricture may be more challenging because the endoscope is not flexible. Whether the use of a rigid echoendoscope limits staging accuracy is unclear [13-15]. Rigid endoscopes are usually less expensive than flexible echoendoscopes; however, rigid endoscopes cannot be used to perform FNA or to examine the upper gastrointestinal tract.
Technique
General steps — A digital rectal examination and flexible sigmoidoscopy are performed immediately prior to EUS to visualize the lesion (eg, size, location, morphology) and identify mucosal abnormalities that may limit the examination (eg, rectal stricture). (See "Overview of colonoscopy in adults".)
The technique for rectal EUS is summarized as follows [1,16]:
●Position the patient in the left lateral decubitus position.
●Insert the radial scanning echoendoscope into the rectum and advance it beyond the target lesion (ie, approximately 30 cm proximal to the anal verge) to identify the internal iliac lymph nodes (figure 1).
●Inspect the rectal wall and periluminal structures while slowly withdrawing the echoendoscope. On EUS, the rectal wall consists of five layers. The first and second layers correspond to the rectal mucosa, the third layer corresponds to the submucosa, the fourth layer is the muscularis propria, and the outermost (fifth) layer is the adventitia (figure 2).
●Identify the target lesion which usually appears as a hypoechoic mass on ultrasound.
●Assess the depth of tumor invasion into the rectal wall.
●Identify and characterize lymph nodes surrounding the lesion (eg, lymph node size, shape).
Staging evaluation — Rectal EUS evaluates the following (table 4):
●T stage – The tumor (T) stage of a rectal cancer is determined by the depth of invasion of the primary tumor, including involvement of adjacent anatomic structures.
●N stage – The nodal (N) stage of rectal cancer is determined by the number of regional lymph nodes that are involved by cancer and by the presence of isolated, non-nodal, perirectal tumor deposits.
Interobserver agreement for staging accuracy with rectal EUS has been moderate to good. As an example, in a study of 95 patients with rectal cancer who had tandem EUS evaluations, staging agreement among endosonographers was good for tumor (T) stage (kappa = 0.61) and was moderate for nodal (N) stage (kappa = 0.45) [17]. (See "Glossary of common biostatistical and epidemiological terms", section on 'Terms used to describe reliability of measurements'.)
Use of rectal EUS for staging is typically reserved for selected patients (eg, those with suspected but unconfirmed internal iliac lymph nodes or tumors of uncertain stage on radiographic imaging). Whether EUS staging results in improved outcomes for most patients with rectal cancer remains uncertain. In a study including 3408 patients with non-metastatic rectal cancer, preoperative staging with EUS and computed tomography (CT) of the abdomen and pelvis was associated with higher rates of neoadjuvant chemoradiotherapy compared with CT alone (50 versus 16 percent), while overall survival was not significantly different between groups (60 versus 57 months) [18].
Fine-needle aspiration — If a lesion requires sampling (eg, lymph nodes that are suspicious for malignancy), the linear scanning echoendoscope is used because it allows for needle passage under direct visualization (image 1). The technical aspects of performing EUS with FNA or fine needle biopsy (FNB) are discussed separately. (See "Endoscopic ultrasound-guided fine needle aspiration in the gastrointestinal tract", section on 'Procedure' and "Endoscopic ultrasound-guided fine needle biopsy in the gastrointestinal tract", section on 'Procedure'.)
●Perirectal lymph nodes – We typically perform FNA of perirectal lymph nodes for patients with T1 or T2 disease by MRI staging in whom a positive node will inform the treatment strategy (ie, neoadjuvant chemoradiotherapy).
EUS-guided FNA may be used in addition to visual inspection to identify lymph node involvement, although studies on the benefit of FNA have been mixed [16,19-22]. In a study including 141 patients with rectal cancer, staging with EUS-FNA was associated with lower risk of tumor recurrence compared with radiographic staging alone (hazard ratio [HR], 0.72, 95% CI 0.52 to 0.97) [20]. EUS-FNA staging likely facilitated selecting patients with locally advanced disease who benefited maximally from preoperative neoadjuvant therapy. However, in an earlier study including 80 patients with nonmetastatic rectal cancer, EUS with FNA did not result in significant changes in management compared with radiographic or EUS imaging alone [19]. For some patients, EUS-FNA may not add significantly to EUS alone because perirectal lymph nodes are typically too small to be visualized by EUS unless they contain metastatic disease. Thus, FNA would not be expected to improve accuracy when compared with visual criteria alone (eg, node size, homogeneity, contour). The use of EUS-FNA to evaluate regional lymph nodes in other parts of the intestinal tract is discussed separately. (see "Endoscopic ultrasound-guided fine needle aspiration in the gastrointestinal tract", section on 'Peri-intestinal lymph nodes').
For patients with regionally advanced disease (ie, T3 or more advanced lesions) in whom neoadjuvant chemoradiation is planned, confirming malignancy within perirectal nodes with FNA will not impact the treatment plan, and thus, rectal EUS with FNA is less useful for such patients. Other limitations to FNA include that it cannot be performed when node sampling requires passing the needle through the primary tumor because of the risk of false positive results and potential for seeding nodes with malignant cells [16].
●Suspected recurrent cancer – We perform FNA for patients with suspected but unconfirmed recurrent cancer despite mucosal biopsies and EUS visualization (eg, rectal wall thickening).
EUS-FNA may be useful to detect the extent of recurrent disease or very small lesions with recurrent cancer (ie, <5 mm), and thus, FNA results may guide the treatment strategy (eg, potentially curative resection) [23-26]. In a study including 116 patients with biopsy-proven tumor recurrence, accuracy for detecting recurrence was 79 percent with EUS alone, but rose to 100 percent when EUS-guided FNA was used to sample perirectal lesions [24]. The primary advantage of rectal EUS-FNA in this population was the ability to detect very small perirectal recurrences (the smallest detected tumor was 3 mm). 31 of 116 patients (27 percent) with local recurrence detected by FNA were suitable candidates for surgical excision.
Circumferential resection margin — In patients with anterior rectal cancer, rectal EUS can assess the extent of tumor involvement of the mesorectal fascia (MRF, the lateral margin) by predicting the distance of the tumor to the circumferential resection plane after rectal cancer surgery, and this is referred to as the circumferential resection margin (CRM). For posterior or posterolateral tumors, the distance to the CRM cannot be estimated using rectal EUS because neighboring structures that allow assessment of the CRM are lacking. In such cases, the distance to the CRM can be estimated using MRI.
The distance from the tumor to the CRM has important prognostic implications and may influence which patients are offered neoadjuvant chemoradiotherapy. A "positive" CRM, defined variably as a tumor that invades or is in close proximity to the MRF, is a risk factor for local recurrence after surgery. If the MRF is involved or if the tumor extends to a point that is within 1 to 2 mm of the MRF, there is a risk that the CRM will be involved if total mesorectal excision alone (ie without preoperative chemoradiation) is performed. As a result, the treatment strategy for such patients is initial chemoradiotherapy or short-course radiotherapy, with or without additional neoadjuvant chemotherapy. In a study including 152 patients whose preoperative staging suggested either a lymph node-positive T2 tumor or a T3 tumor regardless of lymph node involvement, no patient received neoadjuvant chemoradiotherapy [27]. The estimated CRM was determined using rectal EUS alone (49 percent of patients), rectal EUS plus MRI (41 percent), or MRI alone (10 percent of patients). The CRM was considered "threatened" if the tumor was within 2 mm, and "non-threatened" if it was more than 2 mm from the CRM based upon EUS and/or MRI. If the preoperative staging categorized the CRM as potentially free, then the histologic margin was clear in 92 percent of cases. If the CRM was not assessed or was defined as threatened, it was involved in 33 percent and 44 percent of patients, respectively. Upon histologic review of the resected specimen, the distance from the tumor to the CRM was an important predictor of local recurrence, disease-free survival, and cancer-specific survival on multivariable analysis. (See "Neoadjuvant therapy for rectal adenocarcinoma", section on 'Indications for neoadjuvant treatment' and "Pretreatment local staging evaluation for rectal cancer", section on 'Circumferential resection margin'.)
Postprocedure care — After the procedure, patients are recovered from sedation or anesthesia and are monitored until they have completely recovered (ie, breathing spontaneously, hemodynamically stable, responding to commands). (See "Gastrointestinal endoscopy in adults: Procedural sedation administered by endoscopists", section on 'Postprocedure care'.)
The equipment is cleaned per procedural protocol. (See "Preventing infection transmitted by gastrointestinal endoscopy", section on 'Overview of endoscope reprocessing'.)
Complications — EUS for diagnosis or staging is generally a safe procedure. Some complications are due to the effect of procedural sedation (eg, hypotension), while others are due to the endoscopy itself. (See "Adverse events related to procedural sedation for gastrointestinal endoscopy in adults".)
Adverse events such as bleeding or bacteremia have been infrequently reported with EUS-FNA of solid rectal or perirectal lesions, although published data are limited [12,28,29]. As an example, in a study including 100 patients who underwent a total of 471 FNA sampling procedures for solid lesions in the lower gastrointestinal tract and had surveillance blood cultures, bacteremia was detected in two patients (2 percent) [12]. However, none of the patients in the study developed symptoms or signs of infection.
Complications related to EUS of the upper gastrointestinal tract are discussed separately. (See "Endoscopic ultrasound: Examination of the upper gastrointestinal tract", section on 'Adverse events'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Colorectal cancer".)
SUMMARY AND RECOMMENDATIONS
●General principles – Accurate staging of rectal cancer is essential for selecting patients who can undergo sphincter-preserving surgery and identifying those who may benefit from neoadjuvant therapy. Staging evaluation includes performing a physical examination, colonoscopy (if possible), and an imaging evaluation (computed tomography of the chest and abdomen [with or without pelvis] and either pelvic magnetic resonance imaging [MRI] or rectal endoscopic ultrasound [EUS]). The selection of imaging studies and their performance characteristics for determining tumor (T) and nodal (N) stage are presented separately (table 1 and table 2). (See "Pretreatment local staging evaluation for rectal cancer".)
●Clinical applications – For patients with rectal cancer, clinical applications for rectal EUS with or without sampling include (see 'Clinical applications' above):
•Initial staging for selected patients (eg, those with suspected but unconfirmed iliac lymph nodes on radiographic imaging, those who cannot have magnetic resonance imaging)
•Surveillance after surgical resection
•Staging local recurrence
●Patient preparation – The preprocedure preparation for patients undergoing rectal EUS is similar to that described for patients undergoing lower gastrointestinal endoscopy. (See 'Patient preparation' above and "Overview of colonoscopy in adults", section on 'Patient preparation'.)
●Staging – Rectal EUS evaluates the tumor (T) stage of a rectal cancer by determining the depth of invasion of the primary tumor and the nodal (N) stage by determining number of regional lymph nodes that are involved by cancer and by the presence of isolated, non-nodal, perirectal tumor deposits (table 4). (See 'Staging evaluation' above.)
●EUS-guided sampling – EUS with fine-needle aspiration (FNA) or fine needle biopsy (FNB) may be performed to sample perirectal lymph nodes for patients with T1 or T2 disease by MRI staging in whom a positive node will inform the treatment strategy. (See 'Fine-needle aspiration' above.)
●Complications – EUS for diagnosis or staging is generally a safe procedure. Some complications are due to the effect of procedural sedation, while others are due to the endoscopy itself. EUS-guided sampling of solid rectal or perirectal lesions is infrequently associated with bleeding or bacteremia, although published data on complications related to use of rectal EUS in this setting are limited. (See 'Complications' above.)
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