Colorectal Cancer (CRC), is the 4th most common cancer in England, with 34″,952 cases diagnosed and registered in 2016 (Office for National Statistics, 2018). According to Cancer Research UK (2018a), in 2016, CRC mortality was 13″,417, approximately a third of the figure of those diagnosed. This is due to slow diagnosis affecting survival.
CRC incidence rates (2013-2015), outline greater prevalence in men, and those aged over fifty (Cancer Research UK, 2018b). Symptomatic patients, especially those eligible for screening, should be promptly and accurately imaged, allowing subsequent treatment, to maintain good quality of life.
Most CRC arises from adenocarcinomas: malignancies which can develop from polyps, forming from intestinal glands of the colon or rectum. CRC location influences signs and symptoms, and subsequent treatment (Chu, 2011). Although sometimes asymptomatic, indications include weight loss, palpable masses, blood within faeces, anaemia, and bowel habit change. These are commonly disregarded by patients, delaying diagnosis (John et al., 2010).
This essay discusses Ms X’s (a hypothetical patient) pathway, evaluating the imaging procedures for diagnosis, and treatment. Some modalities use radiation, so dose is kept as low as reasonably practicable (ALARP), reducing stochastic and deterministic effects, ensuring imaging benefits outweigh the risks (The Department of Health and Social Care, 2018).
The 80-year-old came to her General Practitioner, reporting weight loss and bowel habit change. A faecal occult blood test showed blood within the stool, while blood tests detected anaemia (haemoglobin: 9.5g/dL). CRC was suspected, due to these symptoms. Unraised inflammatory markers, contraindicated infection. Subsequently, Ms ‘X’ was referred under the ‘2-week pathway’ to a gastroenterologist.
She was sent for flexible sigmoidoscopy, where a camera displayed the distal 60cm of the bowel. The procedure was inconclusive as nothing was seen distally, the remaining colon required imaging. Next, Ms X was sent for a non-invasive, virtual endoscopy: computed tomography (CT) colonography (CTC), lesions were demonstrated and later biopsied with colonoscopy. With CRC diagnosed, and liver lesions identified through CTC, CRC was staged with an magnetic resonance imaging (MRI) liver and CT chest, determining her consequent treatment [NICE(National Institute for Health and Care Excellence), 2011].
The CTC was a day case at a hospital. Prior to her appointment, the clinic gave her a leaflet explaining the preparation and procedure, and 50ml Gastrografin; a contrast medium which enhances the bowel lining. Ms X was requested to stop taking iron supplements four days prior to the scan to prevent constipation. For two days before her appointment, she followed a low fibre diet. On the second day, she drank 25ml of Gastrografin at 08:00, another at 16:00, and drank water to avoid dehydration. The leaflet warned of loose stool. She could not eat the day of the procedure.
At the CT waiting area, Ms X had an identification check. She wore a gown after removing clothing and jewellery which could mimic pathology. The procedure was explained and consent was taken. A questionnaire eliminated any contraindications surrounding renal impairment and allergies to intravenous contrast. A finger-prick device presented 1.0mg/dL creatinine suggesting kidney function could tolerate contrast. A cannula was inserted into her arm. Ms X came into the examination room and laid feet first on the couch on her left side. A flexible tube was placed through her rectum and 20mg Buscopan was injected through the canula to decrease peristalsis. Carbon dioxide was introduced through the tube inflating the bowel. For adequate insufflation she retained the gas. Ms X turned supine (East Cheshire NHS Trust, 2016). The contrast pump was connected, and arms positioned above her head. A scout was taken (sternal angle to symphysis pubis), on arrested expiration, allowing colon expansion. Contrast was administered with a 65sec scan delay. The radiographer felt for extravasation, and warned her to expect a metallic taste, a warm flush, but to report other symptoms. The full scan began. Ms X turned prone, the bowel was re-inflated, and another scout was taken, (diaphragm to symphysis pubis). The full scan commenced (Radiology Info.org, 2018).
120mL iodinated intravenous contrast was injected at 3 mL/sec to highlight extracolonic findings. This scan used 210Auto-mA to improve image quality (Ridereau-Zins et al., 2012). Both scans were at 120kVp with 1.25mm slice thickness, and the prone scan at 80Auto-mA (American Association of Physicists in Medicine, 2017). Scans complete, Ms X was monitored for 15 minutes. Feeling well, she was decannulated, shown the bathroom, got dressed and advised to eat as normal, increasing water uptake to help excrete contrast. She was collected by family and advised to not drive that day as Buscopan causes blurred vision (East Cheshire NHS Trust, 2016).
As demonstrated in figure 1, the radiologist observed faecal tagging through differential attenuation between enhanced faeces and un-enhanced lesions. Prone and supine images were compared: enhanced faeces moved due to gravity, lesions remained in place. Without Gastrografin, differentiating normal and abnormal appearances becomes difficult due to similar tissue attenuation.
CTC was best for Ms X even though colonoscopy more accurately diagnoses smaller lesions than CTC (Martín-López et al., 2013). Issa and Noureddine’s study (2017) shows that CTC is less invasive, preventing bowel perforation and post-procedure hospitalisation, making it acceptable for frail patients. Colonoscopy preparation is commonly less successful in the elderly, causing inconclusive results (Ho et al., 2017). Colonoscopy’s use of sedation increases cardio-pulmonary complications in the elderly, CTC does not use sedation, making it safer (Lord et al., 2017). CTC can additionally identify extracolonic masses, colonoscopy visualises only the bowel wall. CTC uses radiation. Ms X is elderly, so developing cancer from this dose in her lifetime is unlikely. CTC was deemed more appropriate that colonoscopy, due to these age specific benefits.
A developing diagnostic modality is magnetic resonance colonography. It’s high sensitivity (97%) and specificity (92%) values mean 97% of lesion-positive patients will be test positive, whereas 92% of well patients will be test negative, making diagnosis accurate. Lack of radiation makes it suitable for younger patients. It is not actively recommended by NICE: scanning is timely, and waiting lists are long, delaying diagnosis (Shuangyan et al., 2018).
A possibly cancerous lesion was detected in the ascending colon. Figure 2 demonstrates suspected CRC. The scan also revealed some liver lesions.
Ms X was sent for a colonoscopy. The lesion was located and biopsied. Biopsy analysis confirmed grade 2 adenocarcinoma cells (moderately differentiated with reasonable growth speed), (National Cancer Institute, 2013).
Next, Ms X had staging scans to determine her treatment. Her CTC showed liver lesions. The amount was unclear. A 1.5T MRI liver followed which detects and localises lesions better than CT, followed by an enhanced CT chest to identify lung metastases (Fowler et al., 2017). Further imaging was avoided due to sufficient CTC coverage, following ALARP principles. Brain and bone metastases are uncommon, therefore not imaged for (Tirumani et al., 2014).
Ms X did not eat 6 hours prior to the MRI liver appointment. At the hospital, her identification was checked, and she was given a gown to change into. Ms X completed a safety form confirming absence of metal in her body which could be affected by the magnet. The radiographer explained the procedure, as with CTC, contrast was deemed suitable. A cannula was placed into Ms X’s arm. It was highlighted that patients are occasionally claustrophobic; Ms X was to press the attention button if needed. She was informed of the importance of not moving, and breathing only when instructed, to prevent movement unsharpness. Ms X laid supine, wore earphones to protect her hearing and a pad was placed under her knees to protect her painful back (Cancer Research UK, 2018c). With a body phased array coil she had a localizer, followed by T1 and T2 sequences. The cannula was flushed with saline for extravasation then 30mL of gadolinium were injected, T1 images were made during arterial, portal venous, equilibrium and delayed hepatobiliary phases, with sequences in the axial plane. Different sequences allow differentiation of metastases from other conditions. The left lobe of the liver is affected by respiratory and cardiac motion artefacts, so produces ghost images, as in figure 3. Gating techniques eliminated these artefacts, reducing mis-diagnosis (Donato et al., 2017b).
As the liver metastases were unclear on CTC, further imaging options were MRI or PET(position emission tomography)/CT. PET/CT and MRI have a sensitivity of 93% and 100% respectively per patient, showing MRI best detects liver metastases. The opposite is true for specificity per patient, with 81% and 70% respectively, for PET/CT and MRI, diagnosing those without liver metastases correctly. PET/CT sometimes detects smaller lesions before they are visible on MRI. It was shown that 24% of patients who had a PET/CT scan, had their treatment plan altered to be more specific. Although treatment could be more specific, MRI is still preferred. PET/CT only shows liver metastases in 60% of patients. This is higher in MRI, improving accuracy. MRI scanners are more common and cheaper than PET/CT making it quicker to get Ms X an MRI appointment (Kitajima’s et al., 2017).
The MRI scan showed three lesions in the liver’s left lobe. A biopsy was unnecessary as the metastases were isolated to the liver, originating from the primary tumour. The location and size of the metastases deemed hepatic resection suitable (Venook and Curley, 2018)
Ms X then had a CT chest. She was nil by mouth four hours before the scan. At the hospital, her ID was checked and she changed into a gown. After explaining the procedure and checking that Ms X could have contrast, a cannula was inserted. She laid supine on the table and had a scout, (lung apices to the adrenal glands), during arrested inspiration. With area of interest selected the contrast pump injected 60ml Omnipaque-350. The radiographer felt for extravasation. The full scan was at portal venous phase, with 3mm image thickness, 120kVp and Auto-mA. The raw data was then reconned into coronal, sagittal and axial MIPS images (Geisel School of Medicine, 2017).
The CT chest was recommended by NICE. Chest x-rays have low spatial resolution meaning smaller metastases could be missed. MRI chest, on the other hand, has high overall sensitivity for metastases of 80.5%. Unfortunately, a significant amount of results were deemed falsely positive, leading to inappropriate treatment. Therefore, CT was preferred over MRI even though it produces dose. CT’s higher spatial resolution ensures smaller metastases are imaged, making diagnosis precise (Cieszanowski et al., 2016). PET-CT chest evidence suggests radiopharmaceutical uptake is poor in metastases <9mm, meaning smaller proportions of results are truly negative (reduced negative predictive value) making it inferior in detecting pulmonary metastases. PET-CT is less accurate, less common and more expensive than CT and therefore used less (Bamba et al., 2011).
The CT chest showed no pulmonary metastases. High N-staging accuracy, (80-85%) for enhanced CTC (CT Scan in Abdominal Emergency Surgery, 2018), means further imaging for nodule involvement is not required. 10 lymph nodes were sampled, all were CRC-negative.
The gastroenterologist explained the results after each scan. At the end of staging, she was diagnosed with T3, N0, M1a staged CRC. T3 was determined from the CTC showing the tumour had likely grown into the ascending colon’s outer lining without penetration. The N0 represents no lymph node involvement and the M1a represents metastatic spread to one area (Bowel Cancer UK, 2018).
Treatment and follow-up
The gastroenterologist discussed the treatment options with Ms X, providing the benefits and drawbacks. These were colectomy, targeted therapy, chemotherapy, liver lobectomy and palliative care. Ms X made an informed decision, in line with NICE guidelines, increasing her life expectancy; First, Ms X had laparoscopic surgery under general anaesthetic for a colectomy and left lobectomy (liver) to remove all metastases. Both were completed at once to decrease the time this elderly patient spent under general anaesthetic. Laparoscopic surgery decreased the recovery time. She was warned that a colostomy may be required, however, a successful procedure meant this was not applicable. All removed anatomy underwent laboratory analysis. Ms X was advised to avoid heavy lifting, for successful healing. Next, Ms X had an enhanced CT chest-abdomen-pelvis scan to identify any remaining metastases. Afterwards, a central venous catheter was inserted for long term chemotherapy drug administration (FOLFOX and XELOX), which she had for eight cycles every 2-3 weeks (The National Comprehensive Cancer Network, 2018).
To ensure recurrence was caught early, frequent follow-ups were arranged. Ms X was encouraged to report any complications to her gastroenterologist at their appointments every three months. For the first three years after treatment, Ms X had serum carcinoembryonic antigen tests every 6 months, and three CT chest abdomen and pelvis scans. A colonoscopy took place one year after treatment, in accordance to NICE (2011).
CRC is the 4th most common cancer in England, with high mortality. This essay discussed Ms X’s pathway and evaluated the imaging modalities used for diagnosis. Her CTC had fairly high sensitivity and gentler bowel preparation (compared to colonoscopy), making it suitable for her age. With a lesion detected, a biopsy showed CRC. After unclear liver metastases an MRI liver was chosen, due to its sensitivity and lack of radiation. A CT chest was imaged for metastases as recommended by NICE guidelines. Following subsequent diagnosis, Ms X had surgery, eight cycles of chemotherapy and regular follow-ups in the coming years.