Colon Cancer (Staging)

Colon cancer may be diagnosed following a positive finding on a screening study (e.g. fecal occult blood testing), investigation of symptoms (e.g. PR blood loss, change in bowel habit, anaemia, abdominal pain and weight loss) and/or risk factors (family history, past personal history of colon adenoma, carcinoma).

The entire colon and rectum should be examined prior to surgery to assess for synchronous polyps and cancers. 1

Synchronous cancers have been reported in about 4% of patients presenting with sporadic colon cancer. 1

Synchronous adenomas are present in 30-50% of patients.1

Colonoscopy is the preferred method as it allows for colonoscopic polypectomy and/or biopsy of suspicious lesions 1.

In patients who have an incomplete colonoscopy due to technical reasons or an impassable lesion at colonoscopy, completion CT colonography is advised 1-3.

CT colonography may be more appropriate in patients who are elderly or frail, or where there is limited access to optical colonography.

CT Colonography (CTC)

• If colonoscopy fails to exclude synchronous lesions in patients with colorectal cancer, CT colonography can usually achieve this. If CTC is indicated, it is reasonably (if the patient has not already had a staging CT) to protocol the CTC as a “one-stop shop” – that is to:

• exclude synchronous large bowel lesions.  However, if surgery is planned which will, in any case,  remove the colon proximal to a cancer it may not be required to exclude synchronous proximal colorectal cancers

• provide locoregional staging and 

• assess for distant metastases. 

• To achieve this the CTC needs to be performed with IV contrast and the scan needs to cover the whole abdomen and pelvis and to extend to the chest to detect lung metastases.

• Faecal tagging should be used and administered a minimum of 3 hours before the study

•  If a CTC is being performed for staging purposes or as a “one-stop shop” procedure, the supine study should be performed as portal venous with standard mAs

The distension of colon lumen and bowel cleansing that are part of the protocol for CTC have the potential for improvement of T stage assessment over standard MDCT.

• A recent study 4 found a high sensitivity for detection of T3c or worse disease with 83% sensitivity and 88% specificity, for an experienced reader.

• Several other studies have reported CTC findings for staging of colorectal cancer, but most have failed to separate results for rectal and colon cancers 5.

• Retrospective studies published between 2012 and 2021 that have reported colon cancer staging with CTC have shown that for distinguishing T1-T2 from T3-4 lesions, sensitivities ranged from 86-100%, specificities from 55-95%. Most of the studies  reported sensitivity and specificity  for differentiating low and high risk colon cancers between 80 and 90% 5.

• Two studies 4, 6 reported sensitivities and specificities for distinguishing T1-T3ab (low-risk according to the criteria for the FOxTROT study 7 )of NAT from T3cd-T4 (high-risk) ranging from 74-86% and 80-84%, respectively

The most commonly used system of staging of colon cancer is the pathology-based TNM system developed by the American Joint Committee on Cancer (AJCC) currently in its 8^th Edition 8, 9.

T category (depth of wall invasion)

TX Primary tumor cannot be assessed

T0 No evidence of primary tumor

Tis Carcinoma in situ, intramucosal adenocarcinoma (involvement of lamina propria no extension through the muscularis mucosae)

T1Tumour invades submucosa

T2 Tumor invades muscularis propria

T3 Tumor invades through the muscularis propria into the pericolonic tissue *

T4a Tumor penetrates to the surface of the visceral peritoneum (serosa)

T4b Tumor invades and/or is adherent to other organs or structures

*T3 may be divided into T3a -d. T3a and b (combined as T3ab) transgress muscularis propria and 5mm or less extramurally. T3c and d (combined as T3cd) extend >5mm into extracolonic tissue.

N category (regional lymph nodes)

NX Regional lymph nodes cannot be assessed

N0 No regional lymph node metastasis

N1 One to three regional lymph nodes are positive (tumor in lymph nodes measuring ≥0.2mm), or any number of tumor deposits are

present and all identifiable lymph nodes are negative

N1a One regional lymph node is positive

N1b Two to three regional lymph nodes are positive

N1c No regional lymph nodes are positive, but there are tumour deposits in subserosa, mesentery, or nonperitonealized pericolic or perirectal

tissues without regional nodal metastases

N2a Four or more regional lymph nodes are positive

N2b Seven or more regional lymph nodes are positive

M category (distant metastasis)

M0 No distant metastasis by imaging

M1a Metastasis confined to one organ or site is identified without peritoneal metastasis

M1b Metastasis confined to two or more organs or sites is identified without peritoneal metastasis

M1c Metastasis to the peritoneal surface is identified alone or with other site or organ metastases

The TNM staging categories can be combined into prognostic groups:

Prognostic groups

Until recently, local T staging preoperatively for colon cancer was not considered of major importance, since surgery was the preferred option in most patients and detailed staging was achieved by operative staging and staging based on the pathological examination of the resected specimen.

However, with the expansion of the use of neoadjuvant therapy (NAT) in colon cancer, there has been increased interest in the importance of preoperative local staging, in addition to the continuing need for assessment for the presence of metastatic (M) disease.

Administration of NAT may help reduce microscopic disease and improve R0 resection rates. Studies have shown significant downstaging of tumour with NAT 5, 7, 10. However, studies to date on any survival benefit of NAT on patients with locally advanced colon cancer are limited 10.

• CT reports should include:

• Evaluation of wall infiltration (T stage) to identify high risk patients

• Assessment of loco-regional lymph nodes

• Tumoural involvement of extramural vasculature

• For ascending and descending colon tumours, the assessment of the retroperitoneal margins of the tumour and any evidence of peritoneal invasion.

CT in T staging

• In general, CT has a high sensitivity and a lower specificity for detection of tumour invasion beyond the bowel wall (T1–T2 vs. T3–T4) 

• Selection of patients with T3 or T4 disease for NAT can be made by CT scan with high sensitivity but specificity of 50%  5, 7.

• A 2016 systematic review and meta-analysis reported for detection of tumour beyond the bowel wall (T3-4) pooled sensitivity of 90%, specificity 69% and diagnostic OR 20.6% 11.

• A 2024 review 12 quoted a range of  79-92% sensitivity, specificity 42-75% and accuracy 71-84%, for extramural invasion  (T3-4)

• In selecting patients for NAT, the focus has shifted from T categorisation alone to distinguishing T1-3ab from T3cd -T4 7, the latter qualifying for NAT. 

• In studies using modern CT scanners, in distinguishing T3 or worse disease, sensitivities have ranged from 61-87% and specificities 49-89% 5.

• These studies demonstrate an inverse relationship between sensitivity and specificity.

• A 2016 systematic review and meta-analysis 11 of four studies reported pooled sensitivity of 77% and specificity of 70% for detection of T3cd-T4.

• It is possible to maintain high specificity in detecting locally advanced T stage disease (ie. low false positive rate) albeit at the expense of high sensitivity. This should reduce the number of patients receiving NAT unnecessarily. A large Danish study reported sensitivity and specificity of detecting T3 and T4 disease as 61% and 85%, respectively 13.

• A recent small study 14 demonstrated MRI to be slightly but significantly better than CT for identifying high-risk Stage II or Stage III (T3cd/T4) patients, but larger studies are required.(T3cd signifies extramural invasion greater than 5 mm) 

• Depending on where the tumour is located and what is involved (eg abdominal wall or inguinal canal or duodenum), and taking into account the patient’s fitness for surgery, MRI may be indicated for clarification

CT in nodal staging

• Both CT and MRI have limitations in nodal staging in colon cancer, due mainly to the difficulty in distinguishing inflammatory from metastatic nodes. Under-staging on imaging may occur due to the presence of microscopic deposits in normal appearing (on imaging) nodes. Over-staging may occur due to the presence of enlarged inflammatory nodes

• Attention to size (especially short axis), internal heterogeneity irregular borders and clustering of nodes near the primary tumour margin can increase accuracy 15-17.

• Using the above parameters, Swedish studies have shown 85% sensitivity and 75% specificity in detecting metastatic nodes 15, 16

• An unreliable accuracy of 61% was reported in a 2022 prospective study 18.

• A 2019 comparison of CT and MRI in nodal staging, using two radiologists, reported similar sensitivities and specificities for both modalities – sensitivity 64-85%, specificity 71-95% for CT and sensitivity 64-93%, specificity 83-87% for MRI. 14

• The radiology report should include comments on location of enlarged nodes in the locoregional and distant locations.

CT in M staging

• The commonest distant metastases from colon cancer are to the liver.

• Multi-detector CT with IV contrast (CECT) has a high negative predictive value (90%) for the exclusion of liver metastases and, when performed as a multiphase examination with appropriate contrast administration and timing , and optimal scanning parameters  3, this is the initial imaging modality recommended 1-3, 19, 20.

• CECT is accurate for the presence/absence of liver metastases, with but is less accurate than MRI on a lesion-by-lesion assessment of liver metastases 21, 22 particularly for small lesions

• Therefore, a CECT positive for liver metastatic disease which appears amenable to surgery or ablative therapy should be followed by MRI MR for liver metastases to further characterise the liver lesions and detect any additional lesions not visible on CT 2, 22.

• Such patients should also undergo FDG-PET/CT as an aid in determining the presence and extent of any extrahepatic distant metastases Roles of FDG-PET/CT 19.

• Indeterminate liver lesions should also be further investigated with MRI if there are no other sites of  metastatic disease (other than lung) MR for liver metastases

• CT of the chest has a yield of 6-8% for lung metastases 1.

• The National Comprehensive Cancer Network recommends that patients with newly diagnosed colorectal cancer undergo staging chest CT, because staging chest CT has been shown to detect more lung metastases than chest radiography 20, 23 .

• CT has limitations in detecting peritoneal deposits and bone lesions 2, 19, but a 2017 systematic review and meta-analysis 24 analysing studies of peritoneal metastases from a variety of abdominal tumours found the cumulative sensitivity and specificity (on a per patient basis) of CT to be 83% and 86% , respectively. Figures for MRI were similar, but given considerably lesser data available for MRI, CT was the modality recommended by the authors. Peritoneal carcinomatosis is an important finding. The peritoneal cancer index is an important surgical prognostic score. CT and MRI are comparably effective in assessing this 2.

• MRI is more accurate than CT in fatty livers 25.

CT Colonography (CTC)

• If colonoscopy fails to exclude synchronous lesions in patients with colorectal cancer, CT colonography can usually achieve this. If CTC is indicated, it is reasonably (if the patient has not already had a staging CT) to protocol the CTC as a “one-stop shop” – that is to:

• exclude synchronous large bowel lesions. However, if surgery is planned which will, in any case,  remove the colon proximal to a cancer it may not be required to exclude synchronous proximal colorectal cancers.

• provide locoregional staging and 

• assess for distant metastases. 

• To achieve this the CTC needs to be performed with IV contrast ant the scan needs to cover the whole abdomen and pelvis and to extend to the chest to detect lung metastases.

• Faecal tagging should be used and administered a minimum of 3 hours before the study

•  If a CTC is being performed for staging purposes or as a “one-stop shop” procedure, the supine study should be performed as portal venous with standard mAs

The distension of colon lumen and bowel cleansing that are part of the protocol for CTC have the potential for improvement of T stage assessment over standard MDCT.

• A recent study 4 found a high sensitivity for detection of T3c or worse disease with 83% sensitivity and 88% specificity, for an experienced reader.

• Several other studies have reported CTC findings for staging of colorectal cancer, but most have failed to separate results for rectal and colon cancers 5.

• Retrospective studies published between 2012 and 2021 that have reported colon cancer staging with CTC have shown that for distinguishing T1-T2 from T3-4 lesions, sensitivities ranged from 86-100%, specificities from 55-95%. Most of the studies  reported sensitivity and specificity  for differentiating low and high risk colon cancers between 80 and 90% 5.

• Two studies 4, 6 reported sensitivities and specificities for distinguishing T1-T3ab (low-risk according to the criteria for the FOxTROT study 7 of NAT from T3cd-T4 (high-risk) ranging from 74-86% and 80-84%, respectively.

• There is an increasing role for neoadjuvant therapy (NAT) 26, 27 in colon cancer, although further studies are awaited. 

• The standard of care to date has been surgical resection with post-surgical adjuvant therapy for patients with Stage 3 disease or those with Stage 2 disease and adverse features 1, 26, 28.

• However, there is a move to expand neoadjuvant chemotherapy (NAC)  to patients with other high-risk cancers 26 since there are recent studies showing significant rates of R1 resection with surgery alone 29, 30. Currently studies of NAC have been reported with locally advanced cancer (T3/4, N0-2, M0)

• A 2020 systematic review 27 reported that NAC was of benefit inpatients with T4b tumours. A survival benefit for patients with T4b tumours treated with NAC was reported in a 2018 retrospective analysis by the National Cancer Database 10.

• The 2022 guidelines of the American Society of Colon and Rectal Surgeons 1 have a weak recommendation, based on moderate quality evidence, for neoadjuvant  chemotherapy or radiotherapy for locally advanced tumours.

• The NCCN guidelines 20 recommend consideration of NAC in T4b or bulky nodal disease (NCCN)

• NICE guidelines recommend consideration of preoperative systemic anti-cancer therapy for people with T4 colon cancer 31.

Therefore, imaging is important in identifying high risk patients who may benefit from NAT. This means 

• reporting of degrees of colon wall infiltration (higher degrees of T3 or involvement of visceral peritoneum [T4a]), 

• tumour involvement of extramural veins 

• and, for ascending and descending colon cancers, assessment of the retroperitoneal margin for possible tumour involvement 2.

• If locally advanced and cannot safely undergo R0 resection as per imaging or would be morbid, then neoadjuvant chemotherapy (NAC) should be considered

• Re-staging should be performed following NAC.

• MRI is not widely used for T and N staging in colon cancer (unlike rectal cancer) 5. Difficulty in usage may be due to the mobility of the colon and rectum in comparison to the relatively fixed rectum, and the longer acquisition times for MR compared to CT.

• However, some studies have reported satisfactory results. 

• One study examined sigmoid cancers only and reported a sensitivity of 89% and specificity of 88-96% in distinguishing T3ab from T3cd-T4 cancers, with acceptable levels of accuracy for extramural venous invasion (EMVI) and lymph node involvement 32.

• A 2017 retrospective study 33 reported high accuracy for detecting T3/4 tumours, but for distinguishing T3ab from T3cd-T4, there was low sensitivity (43–67%), although specificity remained high (75–88%).

• A study of left-sided colon cancers 34 comparing CT and MRI found MRI to be superior for detecting T3-4 disease (AUC 0.88 for MRI versus 0.71 for CT) and for detection of EMVI, but equal to CT for diagnosis of lymph node involvement.

• In a study comparing CT and 3T MRI (35), MRI identified more tumours and was superior to CT for distinguishing T3cd from T3ab (sensitivity of CT was 51.1% and of MRI 80.0%). CT and MRI showed a sensitivity of 21.4% and 46.4% in detecting pT4 tumours and a specificity of 79.0% and 85.0%, respectively. CT and MRI had comparable sensitivity and specificity in diagnosing lymph node involvement.

• Depending on where the tumour is located and what is involved (eg abdominal wall or inguinal canal or duodenum), and taking into account the patient’s fitness for surgery, MRI may be indicated for clarification

• In summary, most published studies are retrospective, and although MRI is promising in determining depth of tumour involvement and EMVI, further prospective studies are needed. In particular, the standardisation of MRI technique is needed. MRI may be useful for problem-solving in locoregional staging of colon cancer after indeterminate CT imaging.

The majority of quoted studies included metastases from both colonic and rectal cancer primary tumours (ie colorectal liver metastases : CRLM)

• MRI using extracellular contrast medium (ECCM) is more accurate on a per lesion basis than contrast-enhanced CT for detection of CRLM 36. In a 2018 study involving 2 readers, the per lesion sensitivity of MRI was 85.9% and 83.8%; the sensitivity of CT was 69.1% and 62.3% and the sensitivity of  PET-CT 72.0% and 72.1%. The modalities had equal specificity 22.

• MRI is more accurate than CT in fatty livers 25, 37

• MRI with a hepatospecific contrast agent (such as Gd-EOB-DTPA) is superior to MDCT 38-42. In a 2008 study, a change in surgical therapy was documented in 19 of 131 patients (14.5%) post Gd-EOB-DTPA-enhanced MRI 42.

• There is significant weight of evidence that MRI with a hepatospecific agent is superior to MRI performed with ECCM(40) The evidence is summarised in the 2021 update of the ACR appropriateness criteria 3.

• Diffusion-weighted imaging (DWI) at MRI is more accurate than MDCT 43 but is less sensitive than MRI with a hepatospecific contrast agent 44.

• Combining DWI MRI with Gd-EOB-DTPA-enhanced MRI significantly improves the detection of colorectal liver metastases 45.

• A 2016 meta-analysis 44 reported the combination of DWI and MRI with a hepatospecific agent gave the best per lesion sensitivity (87%, 91% and 96% for DWI, gadoxetic acid-enhanced MRI and the combination of these techniques, respectively). There were similar results when only metastases  <1cm were considered. 

• A hepatobiliary IV contrast agent–enhanced MRI may improve outcomes in the era of highly active neoadjuvant chemotherapy 46.

• 2024 recommendation by the European Society of Gastrointestinal and Abdominal Radiology (ESGAR)(2024) is that MRI using a combination of DWI and  a hepatospecific contrast agent is the imaging modality of choice in patients referred to liver surgery 2.

• In patients in whom there is uncertainty on CT regarding the presence of liver metastases, and in CT-positive patients where surgery or ablative management of liver metastases are contemplated, MRI with a combination of DWI and a hepatospecific contrast agent is recommended being, per lesion, the most accurate examination 2, 3.

• FDG-PET/CT is not routinely indicated but useful selectively. Published practice guidelines do not recommend FDG-PET/CT in initial staging 1, 2, 20.

• FDG-PET/CT does not supplant a contrast-enhanced diagnostic CT or MRI. It can be used to evaluate an equivocal finding on a contrast-enhanced CT (such as a lung lesion) or MRI scan or in patients with strong contraindications to IV contrast administration 20.

• To exclude further metastases in patients with potentially surgically curable M1 and in patients considered for image-guided liver-directed therapies to exclude further metastases in patients with known metastatic disease which would change management 1, 19.

• May be useful in patients with increased tumour markers without evidence of metastases on other imaging 19.

• FDG-PET/CT is only indicated in patients with M disease diagnosed by other modalities if it will potentially change management

Data supporting FDG-PET/CT roles

• FDG-PET/CT has a sensitivity of 89% and specificity of 64% for detecting the presence of metastatic disease, but lower accuracy on a lesion by lesion basis compared to CECT and MRI 3, 47-49.

• In the detection of locoregional nodal metastases, FDG-PET/CT sensitivity is 43%, specificity 80% 3.

• Superiority of FDG-PET/CT over contrast-enhanced CT in the detection of peritoneal metastasis has not been demonstrated 1, 50, although combining the modalities in contrast-enhanced FDG-PET/CT may perform better 51.

• It is not clear whether FDG-PET/CT offers an advantage in detecting pulmonary metastases from colorectal cancer over CT alone 52.

• A meta-analysis of 100 pts with colorectal metastases showed PET or FDG-PET/CT findings changed management in 24% 49. However, other studies have suggested that change in management is occasioned in 8-15.4% of patients 3, 47, 53, 54. A 2011 publication found that FDG-PET/CT provided additional useful information in 8% of patients but also incorrect and potentially harmful data in 9% 47.

• FDG-PET/CT using newer radiopharmaceutical agents such as [68Ga]Ga-DOTA-FAPI-04 may improve the role of FDG-PET/CT 55, but further studies are required.

N.B. Treatment options will not be dealt with in detail here.

• It is highly recommended that management options should be discussed at Multidisciplinary Meetings

• Stage IV disease will include:

• Patients with potentially resectable metastatic disease. These patients may benefit from neo-adjuvant therapy prior to surgical resection of metastases

• Patients who may benefit from chemotherapy by conversion of non-resectable to resectable disease

• Patients with non-resectable disease and/or disseminated disease 

• In patients with oligometastatic colorectal metastases, other treatments as alternatives or additions to surgical resection may be considered. These include:

• percutaneous ablative procedures (radiofrequency ablation, microwave ablation)

• intra-arterial perfusional techniques (chemo-embolization, radio-embolization) 

• stereotactic radiotherapy.

These techniques have been recently reviewed 56.

Until recently, local T staging preoperatively for colon cancer was not considered of major importance, since surgery was the preferred option in most patients and detailed staging was achieved by operative staging and staging based on the pathological examination of the resected specimen.

However, with the expansion of the use of neoadjuvant therapy (NAT) in colon cancer, there has been increased interest in the importance of preoperative local staging, in addition to the continuing need for assessment for the presence of metastatic (M) disease.

Administration of NAT may help reduce microscopic disease and improve R0 resection rates. Studies have shown significant downstaging of tumour with NAT 5, 7, 10. However, studies to date on any survival benefit of NAT on patients with locally advanced colon cancer are limited 10.

• CT reports should include:

• Evaluation of wall infiltration (T stage) to identify high risk patients

• Assessment of loco-regional lymph nodes

• Tumoural involvement of extramural vasculature

• For ascending and descending colon tumours, the assessment of the retroperitoneal margins of the tumour and any evidence of peritoneal invasion.

CT in T stagin

• In general, CT has a high sensitivity and a lower specificity for detection of tumour invasion beyond the bowel wall (T1–T2 vs. T3–T4) 

• Selection of patients with T3 or T4 disease for NAT can be made by CT scan with high sensitivity but specificity of 50%  5, 7.

• A 2016 systematic review and meta-analysis reported for detection of tumour beyond the bowel wall (T3-4) pooled sensitivity of 90%, specificity 69% and diagnostic OR 20.6% 11.

• A 2024 review 12 quoted a range of  79-92% sensitivity, specificity 42-75% and accuracy 71-84%, for extramural invasion  (T3-4)

• In selecting patients for NAT, the focus has shifted from T categorisation alone to distinguishing T1-3ab from T3cd -T4 7, the latter qualifying for NAT. 

• In studies using modern CT scanners, in distinguishing T3 or worse disease, sensitivities have ranged from 61-87% and specificities 49-89% 5.

• These studies demonstrate an inverse relationship between sensitivity and specificity.

• In a 2016 systematic review and meta-analysis 11 of four studies reported pooled sensitivity of 77% and specificity of 70% for detection of T3cd-T4.

• It is possible to maintain high specificity in detecting locally advanced T stage disease (ie. low false positive rate) albeit at the expense of high sensitivity. This should reduce the number of patients receiving NAT unnecessarily. A large Danish study reported sensitivity and specificity of detecting T3 and T4 disease as 61% and 85%, respectively 13.

• A recent small study 14 demonstrated MRI to be slightly but significantly better than CT for identifying high-risk Stage II or Stage III (T3cd/T4) patients, but larger studies are required.(T3cd signifies extramural invasion greater than 5 mm) 

• Depending on where the tumour is located and what is involved (eg abdominal wall or inguinal canal or duodenum), and taking into account the patient’s fitness for surgery, MRI may be indicated for clarification

CT in nodal staging

• Both CT and MRI have limitations in nodal staging in colon cancer, due mainly to the difficulty in distinguishing inflammatory from metastatic nodes. Under-staging on imaging may occur due to the presence of microscopic deposits in normal appearing (on imaging) nodes. Over-staging may occur due to the presence of enlarged inflammatory nodes

• Attention to size (especially short axis), internal heterogeneity irregular borders and clustering of nodes near the primary tumour margin can increase accuracy 15-17.

• Using the above parameters, Swedish studies have shown 85% sensitivity and 75% specificity in detecting metastatic nodes 15, 16

• An unreliable accuracy of 61% was reported in a 2022 prospective study 18.

• A 2019 comparison of CT and MRI in nodal staging, using two radiologists, reported similar sensitivities and specificities for both modalities – sensitivity 64-85%, specificity 71-95% for CT and sensitivity 64-93%, specificity 83-87% for MRI. 14

• The report should include comments on location of enlarged nodes in the locoregional and distant locations.

CT in M staging

• The commonest distant metastases from colon cancer are to the liver.

• Multi-detector CT with IV contrast (CECT) has a high negative predictive value (90%) for the exclusion of liver metastases and, when performed as a multiphase examination with appropriate contrast administration and timing , and optimal scanning parameters  3, this is the initial imaging modality recommended 1-3, 19, 20.

• CECT is accurate for the presence/absence of liver metastases, with but is less accurate than MRI on a lesion-by-lesion assessment of liver metastases 21, 22 particularly for small lesions

• Therefore, a CECT positive for liver metastatic disease which appears amenable to surgery or ablative therapy should be followed by MRI MR for liver metastases to further characterise the liver lesions and detect any additional lesions not visible on CT 2, 22.

• Such patients should also undergo FDG-PET/CT as an aid in determining the presence and extent of any extrahepatic distant metastases Roles of FDG-PET/CT 19.

• Indeterminate liver lesions should also be further investigated with MRI if there are no other sites of  metastatic disease (other than lung) MR for liver metastases

• CT of the chest has a yield of 6-8% for lung metastases 1.

• The National Comprehensive Cancer Network recommends that patients with newly diagnosed colorectal cancer undergo staging chest CT, because staging chest CT has been shown to detect more lung metastases than chest radiography 20, 23 .

• CT has limitations in detecting peritoneal deposits and bone lesions 2, 19, but a 2017 systematic review and meta-analysis 24 analysing studies of peritoneal metastases from a variety of abdominal tumours found the cumulative sensitivity and specificity (on a per patient basis) of CT to be 83% and 86% , respectively. Figures for MRI were similar, but given considerably lesser data available for MRI, CT was the modality recommended by the authors. Peritoneal carcinomatosis is an important finding. The peritoneal cancer index is an important surgical prognostic score. CT and MRI are comparably effective in assessing this 2.

• MRI is more accurate than CT in fatty livers 25.

CT Colonography (CTC)

• If colonoscopy fails to exclude synchronous lesions in patients with colorectal cancer, CT colonography can usually achieve this. If CTC is indicated, it is reasonably (if the patient has not already had a staging CT) to protocol the CTC as a “one-stop shop” – that is to:

• exclude synchronous large bowel lesions. However, if surgery is planned which will, in any case,  remove the colon proximal to a cancer it may not be required to exclude synchronous proximal colorectal cancers.

• provide locoregional staging and 

• assess for distant metastases. 

• To achieve this the CTC needs to be performed with IV contrast ant the scan needs to cover the whole abdomen and pelvis and to extend to the chest to detect lung metastases.

• Faecal tagging should be used and administered a minimum of 3 hours before the study

•  If a CTC is being performed for staging purposes or as a “one-stop shop” procedure, the supine study should be performed as portal venous with standard mAs

The distension of colon lumen and bowel cleansing that are part of the protocol for CTC have the potential for improvement of T stage assessment over standard MDCT.

• A recent study 4 found a high sensitivity for detection of T3c or worse disease with 83% sensitivity and 88% specificity, for an experienced reader.

• Several other studies have reported CTC findings for staging of colorectal cancer, but most have failed to separate results for rectal and colon cancers 5.

• Retrospective studies published between 2012 and 2021 that have reported colon cancer staging with CTC have shown that for distinguishing T1-T2 from T3-4 lesions, sensitivities ranged from 86-100%, specificities from 55-95%. Most of the studies  reported sensitivity and specificity  for differentiating low and high risk colon cancers between 80 and 90% 5.

• Two studies 4, 6 reported sensitivities and specificities for distinguishing T1-T3ab (low-risk according to the criteria for the FOxTROT study 7 of NAT from T3cd-T4 (high-risk) ranging from 74-86% and 80-84%, respectively.