MRI of Rectal Cancer: Tumor Staging, Imaging Techniques, and Management

Abstract

Rectal cancer is prone to local recurrence and systemic metastasis. However, owing to improvements in TNM staging and treatment, including a more widespread use of rectal MRI and increased radiologist awareness of the key rectal cancer TNM staging features, the mortality rate of rectal cancer has been declining over the past few decades in adults over 50 years of age. Currently, rectal MRI plays a key role in the pre- and posttreatment evaluation of rectal cancer, assisting the multidisciplinary team in tailoring the most appropriate treatment option. The benefits achieved with rectal MRI are strictly dependent on obtaining good-quality images, which is important for the characterization of the main anatomic structures and their relationship with the tumor. In primary staging, rectal MRI helps the radiologist (a) describe the tumor location and morphology, (b) provide its T and N categories, (c) detect the presence of extramural vascular invasion, and (d) identify its relationship with surrounding structures, including the sphincter complex and involvement of the mesorectal fascia. These features help diagnose locally advanced rectal tumors (categories T3c-d, T4, N1, and N2), for which neoadjuvant chemoradiotherapy (CRT) is indicated. In restaging after neoadjuvant CRT, in addition to reassessing the features noted during primary staging, rectal MRI can help in the assessment of treatment response, especially with the emergence of nonsurgical approaches such as "watch and wait." ^©RSNA, 2019.

Figure 1.

Schematic flowchart summarizes the current management concepts of rectal cancer in the United States and Europe.

Figure 2a.

Illustrations of the anatomy of the rectum depict various surgical techniques used to treat rectal cancer. Dotted blue lines = anatomic structures removed during the procedure. Red area = rectal tumor. (a) Illustration shows a transanal endoscopic microsurgery with focal endoscopic resection of a tumor. (b) Illustration depicts a low anterior resection and TME and resection of the whole sigmoid or part of it, which preserves the sphincter complex. (c) Illustration depicts an abdominoperineal resection and TME, with resection of the sphincter complex. (d) Illustration depicts an intersphincteric abdominoperineal resection and TME, with dissection within the intersphincteric plane and a portion of the internal sphincter. The entire external sphincter is preserved. (e) Illustration depicts an extralevator abdominoperineal resection and TME, with a broader dissection of the sphincter complex. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 2b.

Illustrations of the anatomy of the rectum depict various surgical techniques used to treat rectal cancer. Dotted blue lines = anatomic structures removed during the procedure. Red area = rectal tumor. (a) Illustration shows a transanal endoscopic microsurgery with focal endoscopic resection of a tumor. (b) Illustration depicts a low anterior resection and TME and resection of the whole sigmoid or part of it, which preserves the sphincter complex. (c) Illustration depicts an abdominoperineal resection and TME, with resection of the sphincter complex. (d) Illustration depicts an intersphincteric abdominoperineal resection and TME, with dissection within the intersphincteric plane and a portion of the internal sphincter. The entire external sphincter is preserved. (e) Illustration depicts an extralevator abdominoperineal resection and TME, with a broader dissection of the sphincter complex. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 2c.

Illustrations of the anatomy of the rectum depict various surgical techniques used to treat rectal cancer. Dotted blue lines = anatomic structures removed during the procedure. Red area = rectal tumor. (a) Illustration shows a transanal endoscopic microsurgery with focal endoscopic resection of a tumor. (b) Illustration depicts a low anterior resection and TME and resection of the whole sigmoid or part of it, which preserves the sphincter complex. (c) Illustration depicts an abdominoperineal resection and TME, with resection of the sphincter complex. (d) Illustration depicts an intersphincteric abdominoperineal resection and TME, with dissection within the intersphincteric plane and a portion of the internal sphincter. The entire external sphincter is preserved. (e) Illustration depicts an extralevator abdominoperineal resection and TME, with a broader dissection of the sphincter complex. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 2d.

Illustrations of the anatomy of the rectum depict various surgical techniques used to treat rectal cancer. Dotted blue lines = anatomic structures removed during the procedure. Red area = rectal tumor. (a) Illustration shows a transanal endoscopic microsurgery with focal endoscopic resection of a tumor. (b) Illustration depicts a low anterior resection and TME and resection of the whole sigmoid or part of it, which preserves the sphincter complex. (c) Illustration depicts an abdominoperineal resection and TME, with resection of the sphincter complex. (d) Illustration depicts an intersphincteric abdominoperineal resection and TME, with dissection within the intersphincteric plane and a portion of the internal sphincter. The entire external sphincter is preserved. (e) Illustration depicts an extralevator abdominoperineal resection and TME, with a broader dissection of the sphincter complex. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 2e.

Illustrations of the anatomy of the rectum depict various surgical techniques used to treat rectal cancer. Dotted blue lines = anatomic structures removed during the procedure. Red area = rectal tumor. (a) Illustration shows a transanal endoscopic microsurgery with focal endoscopic resection of a tumor. (b) Illustration depicts a low anterior resection and TME and resection of the whole sigmoid or part of it, which preserves the sphincter complex. (c) Illustration depicts an abdominoperineal resection and TME, with resection of the sphincter complex. (d) Illustration depicts an intersphincteric abdominoperineal resection and TME, with dissection within the intersphincteric plane and a portion of the internal sphincter. The entire external sphincter is preserved. (e) Illustration depicts an extralevator abdominoperineal resection and TME, with a broader dissection of the sphincter complex. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 3.

Chart categorizes rectal MRI protocol according to techniques that are frequently recommended (“Dos”), those that are not recommended (“Don’ts”), and some that are controversial practices (“Maybes.”) T2-weighted imaging with fat saturation is rarely necessary but may be useful for imaging mucinous tumors. AX = axial, COR = coronal, DWI = diffusion-weighted imaging, FOV = field of view, FSE = fast spin-echo, OBL-AX = oblique axial, SAG = sagittal, 3D = three dimensional.

Figure 4.

Chart shows the anatomic landmarks of the rectum, describes their clinical relevance, and summarizes their imaging appearance. A, Illustration and MR images in the oblique axial view best depict the MRF, mesorectum, rectal wall layers, and anterior peritoneal reflection. B, Illustration and MR image in the sagittal view best depict the retrorectal space, anorectal ring, and anal verge. Curved arrows = anterior peritoneal reflection, white * = mesorectum. C, Illustration and MR image in the coronal view best depict the internal sphincter, external sphincter complex, and intersphincteric space. (Illustrations adapted and reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 5.

Radiologic report template lists the key imaging findings and features that should be evaluated at primary staging and included in the rectal MRI report.

Figure 6a.

Tumor location in the craniocaudal direction. (a) Illustration depicts the sagittal view of the rectum and provides the measurements of the tumor from the anal verge, which help categorize tumor location. Blue lines separate the low, mid-, and high rectum. (Figure 6a reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.) (b–d) Sagittal T2-weighted MR images show tumors (arrow) in the high (b), mid- (c), and low (d) rectum. Dotted line = measurement from the rectum entrance to the tumor location.

Figure 6b.

Tumor location in the craniocaudal direction. (a) Illustration depicts the sagittal view of the rectum and provides the measurements of the tumor from the anal verge, which help categorize tumor location. Blue lines separate the low, mid-, and high rectum. (Figure 6a reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.) (b–d) Sagittal T2-weighted MR images show tumors (arrow) in the high (b), mid- (c), and low (d) rectum. Dotted line = measurement from the rectum entrance to the tumor location.

Figure 6c.

Tumor location in the craniocaudal direction. (a) Illustration depicts the sagittal view of the rectum and provides the measurements of the tumor from the anal verge, which help categorize tumor location. Blue lines separate the low, mid-, and high rectum. (Figure 6a reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.) (b–d) Sagittal T2-weighted MR images show tumors (arrow) in the high (b), mid- (c), and low (d) rectum. Dotted line = measurement from the rectum entrance to the tumor location.

Figure 6d.

Tumor location in the craniocaudal direction. (a) Illustration depicts the sagittal view of the rectum and provides the measurements of the tumor from the anal verge, which help categorize tumor location. Blue lines separate the low, mid-, and high rectum. (Figure 6a reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.) (b–d) Sagittal T2-weighted MR images show tumors (arrow) in the high (b), mid- (c), and low (d) rectum. Dotted line = measurement from the rectum entrance to the tumor location.

Figure 7a.

Mucinous and nonmucinous tumors. Axial oblique T2-weighted MR images in two different patients show a mucinous tumor (arrow in a) and a nonmucinous tumor (arrow in b). Mucinous tumors typically show high signal intensity, and nonmucinous tumors show intermediate signal intensity.

Figure 7b.

Mucinous and nonmucinous tumors. Axial oblique T2-weighted MR images in two different patients show a mucinous tumor (arrow in a) and a nonmucinous tumor (arrow in b). Mucinous tumors typically show high signal intensity, and nonmucinous tumors show intermediate signal intensity.

Figure 8a.

Tumor within the middle rectum clinically staged as T3b, with positive mesorectal lymph nodes, accumulation of mucoid material within the rectal lumen (* in a and b), and elevated borders in the superior and inferior edge of the tumor. (a) Sagittal T2-weighted MR image shows a tumor with elevated borders (arrows) in the superior and inferior edge of the tumor. Dashed line = plane of the axial oblique MR image shown in b. (b, c) Axial oblique T2-weighted MR image (b) and magnified area of interest (square outline in b) (c) obtained perpendicular to the tumor, halfway in the craniocaudal direction, show a C-shape tumor (dashed arrows). An added gray overlay in c depicts the shape of the tumor. The most invasive portion of the tumor is frequently located around the center of the C shape. The tumor infiltrates beyond the muscularis propria, 2 mm into the mesorectum (T3b) (arrowhead in b), and two 7-mm round heterogeneous mesorectal lymph nodes (solid arrows in c) are depicted, making this tumor positive for lymph node involvement.

Figure 8b.

Tumor within the middle rectum clinically staged as T3b, with positive mesorectal lymph nodes, accumulation of mucoid material within the rectal lumen (* in a and b), and elevated borders in the superior and inferior edge of the tumor. (a) Sagittal T2-weighted MR image shows a tumor with elevated borders (arrows) in the superior and inferior edge of the tumor. Dashed line = plane of the axial oblique MR image shown in b. (b, c) Axial oblique T2-weighted MR image (b) and magnified area of interest (square outline in b) (c) obtained perpendicular to the tumor, halfway in the craniocaudal direction, show a C-shape tumor (dashed arrows). An added gray overlay in c depicts the shape of the tumor. The most invasive portion of the tumor is frequently located around the center of the C shape. The tumor infiltrates beyond the muscularis propria, 2 mm into the mesorectum (T3b) (arrowhead in b), and two 7-mm round heterogeneous mesorectal lymph nodes (solid arrows in c) are depicted, making this tumor positive for lymph node involvement.

Figure 8c.

Tumor within the middle rectum clinically staged as T3b, with positive mesorectal lymph nodes, accumulation of mucoid material within the rectal lumen (* in a and b), and elevated borders in the superior and inferior edge of the tumor. (a) Sagittal T2-weighted MR image shows a tumor with elevated borders (arrows) in the superior and inferior edge of the tumor. Dashed line = plane of the axial oblique MR image shown in b. (b, c) Axial oblique T2-weighted MR image (b) and magnified area of interest (square outline in b) (c) obtained perpendicular to the tumor, halfway in the craniocaudal direction, show a C-shape tumor (dashed arrows). An added gray overlay in c depicts the shape of the tumor. The most invasive portion of the tumor is frequently located around the center of the C shape. The tumor infiltrates beyond the muscularis propria, 2 mm into the mesorectum (T3b) (arrowhead in b), and two 7-mm round heterogeneous mesorectal lymph nodes (solid arrows in c) are depicted, making this tumor positive for lymph node involvement.

Figure 9.

Illustration depicts the anatomy of the rectum and the possible locations of rectal cancer, along with corresponding T categories and potential tumor sizes for each location.

Figure 10a.

Rectal MR images that show distinct tumor stages obtained from three different patients. (a, b) Sagittal (a) and axial (b) T2-weighted MR images show a polypoid lesion (solid arrow) surrounded by mucoid material, with a thin stalk attached to the rectal wall and the intact muscularis propria (dashed arrow), findings characteristic of a T1 or T2 tumor. (c) Oblique axial T2-weighted MR image in another patient shows a tumor infiltrating 7 mm beyond the muscularis propria (T3c), with positive MRF infiltration (arrowhead). (d) Oblique axial T2-weighted MR image in a third patient shows a tumor invading the anterior peritoneal reflection (arrowhead), a characteristic finding of a T4a grade tumor.

Figure 10b.

Rectal MR images that show distinct tumor stages obtained from three different patients. (a, b) Sagittal (a) and axial (b) T2-weighted MR images show a polypoid lesion (solid arrow) surrounded by mucoid material, with a thin stalk attached to the rectal wall and the intact muscularis propria (dashed arrow), findings characteristic of a T1 or T2 tumor. (c) Oblique axial T2-weighted MR image in another patient shows a tumor infiltrating 7 mm beyond the muscularis propria (T3c), with positive MRF infiltration (arrowhead). (d) Oblique axial T2-weighted MR image in a third patient shows a tumor invading the anterior peritoneal reflection (arrowhead), a characteristic finding of a T4a grade tumor.

Figure 10c.

Rectal MR images that show distinct tumor stages obtained from three different patients. (a, b) Sagittal (a) and axial (b) T2-weighted MR images show a polypoid lesion (solid arrow) surrounded by mucoid material, with a thin stalk attached to the rectal wall and the intact muscularis propria (dashed arrow), findings characteristic of a T1 or T2 tumor. (c) Oblique axial T2-weighted MR image in another patient shows a tumor infiltrating 7 mm beyond the muscularis propria (T3c), with positive MRF infiltration (arrowhead). (d) Oblique axial T2-weighted MR image in a third patient shows a tumor invading the anterior peritoneal reflection (arrowhead), a characteristic finding of a T4a grade tumor.

Figure 10d.

Rectal MR images that show distinct tumor stages obtained from three different patients. (a, b) Sagittal (a) and axial (b) T2-weighted MR images show a polypoid lesion (solid arrow) surrounded by mucoid material, with a thin stalk attached to the rectal wall and the intact muscularis propria (dashed arrow), findings characteristic of a T1 or T2 tumor. (c) Oblique axial T2-weighted MR image in another patient shows a tumor infiltrating 7 mm beyond the muscularis propria (T3c), with positive MRF infiltration (arrowhead). (d) Oblique axial T2-weighted MR image in a third patient shows a tumor invading the anterior peritoneal reflection (arrowhead), a characteristic finding of a T4a grade tumor.

Figure 11a.

Tumor in the lower rectum. (a) Colonoscopic image shows a semicircumferential ulcerated tumor. Rectal MRI was performed for local staging. (b) Sagittal T2-weighted MR image shows a semicircumferential tumor (arrowhead) in the lower rectum. (c, d) Axial oblique (c) and coronal (d) T2-weighted MR images show the tumor (solid arrow in c) infiltrating beyond the muscularis propria and invading the left external sphincter and levator ani muscle (dashed arrow), which are thickened and have intermediate signal intensity.

Figure 11b.

Tumor in the lower rectum. (a) Colonoscopic image shows a semicircumferential ulcerated tumor. Rectal MRI was performed for local staging. (b) Sagittal T2-weighted MR image shows a semicircumferential tumor (arrowhead) in the lower rectum. (c, d) Axial oblique (c) and coronal (d) T2-weighted MR images show the tumor (solid arrow in c) infiltrating beyond the muscularis propria and invading the left external sphincter and levator ani muscle (dashed arrow), which are thickened and have intermediate signal intensity.

Figure 11c.

Tumor in the lower rectum. (a) Colonoscopic image shows a semicircumferential ulcerated tumor. Rectal MRI was performed for local staging. (b) Sagittal T2-weighted MR image shows a semicircumferential tumor (arrowhead) in the lower rectum. (c, d) Axial oblique (c) and coronal (d) T2-weighted MR images show the tumor (solid arrow in c) infiltrating beyond the muscularis propria and invading the left external sphincter and levator ani muscle (dashed arrow), which are thickened and have intermediate signal intensity.

Figure 11d.

Tumor in the lower rectum. (a) Colonoscopic image shows a semicircumferential ulcerated tumor. Rectal MRI was performed for local staging. (b) Sagittal T2-weighted MR image shows a semicircumferential tumor (arrowhead) in the lower rectum. (c, d) Axial oblique (c) and coronal (d) T2-weighted MR images show the tumor (solid arrow in c) infiltrating beyond the muscularis propria and invading the left external sphincter and levator ani muscle (dashed arrow), which are thickened and have intermediate signal intensity.

Figure 12.

Illustration depicts sagittal and axial views of the peritoneal and MRF coverage of the rectum. Note that the potential CRM described in the radiologic report corresponds to the distance between the tumor and the MRF and does not include the portions of the rectum surrounded by peritoneum. (Reprinted, under a CC BY-ND 4.0 license, from Memorial Sloan Kettering Cancer Center.)

Figure 13a.

EMVI. Sagittal T2-weighted MR images in two different patients show signs of EMVI, characterized by focal enlargement of the vessel, signal intensity of the tumor replacing the flow void, and wall irregularity (arrow).

Figure 13b.

EMVI. Sagittal T2-weighted MR images in two different patients show signs of EMVI, characterized by focal enlargement of the vessel, signal intensity of the tumor replacing the flow void, and wall irregularity (arrow).

Figure 14a.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 14b.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 14c.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 14d.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 14e.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 14f.

Low rectal cancer in a 56-year-old man who underwent neoadjuvant CRT and had clinical complete response, with tumor regrowth 9 months later. (a, b) Oblique axial T2-weighted MR image (a) obtained during primary staging shows an infiltrative tumor (arrow) with the most invasive border between the 1-o’clock and 3-o’clock positions, infiltrating 1 mm beyond the muscularis propria (T3a), which corresponds to a polypoid lesion seen on the colonoscopic image (b). (c, d) Oblique axial T2-weighted MR image (c) obtained after neoadjuvant CRT shows an area with low signal intensity (arrow), and colonoscopic image (d) shows a scar in the tumor bed, without residual tumor. Note the wall thickening and mucosal edema within the normal rectal wall, which were caused by CRT (arrowhead in c). The patient was selected for a watch-and-wait protocol. (e) Oblique axial T2-weighted MR image obtained 9 months later shows thickening in the tumor bed, with areas of intermediate signal intensity (arrow), a finding suspicious for tumor regrowth. (f) Colonoscopic image shows tumor regrowth.

Figure 15a.

Partial response after neoadjuvant CRT. (a, b) Oblique axial T2-weighted MR image (a) and diffusion-weighted image (b) obtained during primary staging shows a tumor (arrow) in the lower rectum, with intermediate signal intensity in a and restricted diffusion in b. (c) Oblique axial T2-weighted MR image obtained after neoadjuvant CRT at restaging shows areas of low signal intensity (black arrow) in the tumor bed and residual tumor (white arrows) with intermediate signal intensity. (d, e) Axial diffusion-weighted image (d) shows restricted diffusion within the areas of the residual tumor (arrowhead), which was confirmed on the corresponding ADC map (e).

Figure 15b.

Partial response after neoadjuvant CRT. (a, b) Oblique axial T2-weighted MR image (a) and diffusion-weighted image (b) obtained during primary staging shows a tumor (arrow) in the lower rectum, with intermediate signal intensity in a and restricted diffusion in b. (c) Oblique axial T2-weighted MR image obtained after neoadjuvant CRT at restaging shows areas of low signal intensity (black arrow) in the tumor bed and residual tumor (white arrows) with intermediate signal intensity. (d, e) Axial diffusion-weighted image (d) shows restricted diffusion within the areas of the residual tumor (arrowhead), which was confirmed on the corresponding ADC map (e).

Figure 15c.

Partial response after neoadjuvant CRT. (a, b) Oblique axial T2-weighted MR image (a) and diffusion-weighted image (b) obtained during primary staging shows a tumor (arrow) in the lower rectum, with intermediate signal intensity in a and restricted diffusion in b. (c) Oblique axial T2-weighted MR image obtained after neoadjuvant CRT at restaging shows areas of low signal intensity (black arrow) in the tumor bed and residual tumor (white arrows) with intermediate signal intensity. (d, e) Axial diffusion-weighted image (d) shows restricted diffusion within the areas of the residual tumor (arrowhead), which was confirmed on the corresponding ADC map (e).

Figure 15d.

Partial response after neoadjuvant CRT. (a, b) Oblique axial T2-weighted MR image (a) and diffusion-weighted image (b) obtained during primary staging shows a tumor (arrow) in the lower rectum, with intermediate signal intensity in a and restricted diffusion in b. (c) Oblique axial T2-weighted MR image obtained after neoadjuvant CRT at restaging shows areas of low signal intensity (black arrow) in the tumor bed and residual tumor (white arrows) with intermediate signal intensity. (d, e) Axial diffusion-weighted image (d) shows restricted diffusion within the areas of the residual tumor (arrowhead), which was confirmed on the corresponding ADC map (e).

Figure 15e.

Partial response after neoadjuvant CRT. (a, b) Oblique axial T2-weighted MR image (a) and diffusion-weighted image (b) obtained during primary staging shows a tumor (arrow) in the lower rectum, with intermediate signal intensity in a and restricted diffusion in b. (c) Oblique axial T2-weighted MR image obtained after neoadjuvant CRT at restaging shows areas of low signal intensity (black arrow) in the tumor bed and residual tumor (white arrows) with intermediate signal intensity. (d, e) Axial diffusion-weighted image (d) shows restricted diffusion within the areas of the residual tumor (arrowhead), which was confirmed on the corresponding ADC map (e).

Figure 16a.

No significant change in lymph node size after CRT. (a) Axial T2-weighted MR image obtained during primary staging shows a suspicious left lateral node (arrow). (b) Axial T2-weighted MR image obtained after CRT shows the lymph node (arrow), which did not reduce in size. (c, d) Axial T2-weighted MR image (c) and axial PET/CT image (d) obtained 10 months after TME without lateral pelvic lymph node dissection shows the metastatic node with marked enlargement (arrow in c) and FDG uptake (arrow in d).

Figure 16b.

No significant change in lymph node size after CRT. (a) Axial T2-weighted MR image obtained during primary staging shows a suspicious left lateral node (arrow). (b) Axial T2-weighted MR image obtained after CRT shows the lymph node (arrow), which did not reduce in size. (c, d) Axial T2-weighted MR image (c) and axial PET/CT image (d) obtained 10 months after TME without lateral pelvic lymph node dissection shows the metastatic node with marked enlargement (arrow in c) and FDG uptake (arrow in d).

Figure 16c.

No significant change in lymph node size after CRT. (a) Axial T2-weighted MR image obtained during primary staging shows a suspicious left lateral node (arrow). (b) Axial T2-weighted MR image obtained after CRT shows the lymph node (arrow), which did not reduce in size. (c, d) Axial T2-weighted MR image (c) and axial PET/CT image (d) obtained 10 months after TME without lateral pelvic lymph node dissection shows the metastatic node with marked enlargement (arrow in c) and FDG uptake (arrow in d).

Figure 16d.

No significant change in lymph node size after CRT. (a) Axial T2-weighted MR image obtained during primary staging shows a suspicious left lateral node (arrow). (b) Axial T2-weighted MR image obtained after CRT shows the lymph node (arrow), which did not reduce in size. (c, d) Axial T2-weighted MR image (c) and axial PET/CT image (d) obtained 10 months after TME without lateral pelvic lymph node dissection shows the metastatic node with marked enlargement (arrow in c) and FDG uptake (arrow in d).

Figure 17.

Chart shows a step-by-step approach to imaging and staging rectal cancer. The mnemonic RECTAL CANCER facilitates the comprehension of the key features that should be addressed in a rectal MRI report. Red areas = features to identify and steps to complete at restaging.