Consensus Recommendations on MRI, CT and PET/CT for Ovarian and Colorectal Cancer Peritoneal Metastases
In newly published guidelines, researchers discuss the utility of CT, MRI and PET/CT in the diagnosis, staging, treatment monitoring and follow-up imaging for peritoneal metastases in patients with ovarian or colorectal cancer.
Which imaging modality offers the highest accuracy for evaluating the extent of peritoneal metastases? What are the advantages of diffusion-weighted imaging magnetic resonance imaging (DWI-MRI) in patients with colorectal cancer? Could positron emission tomography/computed tomography (PET/CT) be utilized in preoperative staging for peritoneal metastases?
Researchers addressed these questions and more in new guidelines for imaging of peritoneal metastases in patients with colorectal or ovarian cancer. Recently published in European Radiology, the guidelines are joint recommendations from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR), the European Society of Urogenital Radiology (ESUR), the European Association of Nuclear Medicine (EANM) and the Peritoneal Surface Oncology Group International (PSOGI).
Here are seven key takeaways from the joint recommendations.
1. While CT may be adequate for initial evaluation of ovarian and colorectal cancer at a primary diagnosis, the researchers noted questionable accuracy for peritoneal metastases in abdominopelvic and small bowel lesions. They also noted low sensitivity of CT for < 1 cm lesions in subdiaphragmatic, omental, serosal, and mesenteric locations, and on scans with accompanying ascites. In light of these limitations, the recommendation authors emphasized that CT lacks accuracy in the staging of peritoneal metastases.
Here one can see faint diffuse uptake over the small bowel mesentery on PET/CT imaging along with a CT scan showing minimal mesenteric infiltration and ascites. For MRI imaging, whole-body diffusion-weighted imaging (DWI) also shows the ascites as well as diffuse linear and micronodular infiltration of the serosa and small bowel mesentery. Subsequent laparoscopy confirmed diffuse miliary metastases in a patient diagnosed with fallopian tube cancer. (Images courtesy of European Radiology.)
2. Short T1 inversion recovery (STIR) DWI-MRI offers higher accuracy than fluorine-18-deoxyglucose (FDG) PET/CT and CT for peritoneal metastases, particularly for site-based analysis and cases involving sub-centimeter lesions, according to the authors of the joint recommendations.
3. In treatment planning for patients with colorectal cancer slated to have hyperthermic intraperitoneal chemotherapy (HIPEC), the researchers maintained that abdominal DWI MRI is more advantageous than CT for diagnosing abdominopelvic extraperitoneal metastases.
4. Noting challenges with CT in evaluating varied presentations of peritoneal metastases and calculating the peritoneal cancer index (PCI), the authors of the consensus guidelines cited a meta-analysis that revealed between 12 to 33 percent underestimation of surgical PCI with CT. Alternatively, research has demonstrated a strong correlation between DWI-MRI-based PCI and surgical PCI for peritoneal metastases detection in cases of colorectal and ovarian cancer as well as recurrent peritoneal metastases in patients with ovarian cancer.
5. While pointing out 87 percent sensitivity and 92 percent specificity for FDG-PET/CT’s detection of peritoneal metastases, the researchers noted that limitations with small lesions and hypometabolic metastases limit the modality’s accuracy for pre-operative staging.
6. Noting DWI’s ability for background signal suppression of organs and ascites, the consensus guideline authors said use of a STIR pre-pulse as opposed to spectral attenuated inversion recovery (SPAIR) pre-pulse optimizes DWI sequencing for large volume body imaging and helps bolster detection for serosal metastases.
7. Emphasizing the capabilities of STIR-DWI-MRI for post-neoadjuvant chemotherapy assessment, tumor recurrence evaluation and determining whether patients with ovarian or colorectal cancer are candidates for cytoreductive surgery, the researchers maintained the modality offers the best imaging accuracy for ascertaining the extent of peritoneal metastases.
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