Early Postoperative FDG-PET-CT Imaging Results in a Relevant Upstaging in the pN2 Subgroup of Stage III Colorectal Cancer Patients

Variants and Pitfalls in PET/CT Imaging of Gastrointestinal Cancers

In the past two decades, PET/CT has become an essential modality in oncology increasingly used in the management of gastrointestinal (GI) cancers. Most PET/CT tracers used in clinical practice show some degree of GI uptake. This uptake is quite variable and knowledge of common patterns of biodistribution of various radiotracers is helpful in clinical practice. 18F-Fluoro-Deoxy-Glucose (FDG) is the most commonly used radiotracer and has quite a variable uptake within the bowel. 68Ga-Prostate specific membrane antigen (PSMA) shows intense uptake within the proximal small bowel loops. 11C-methyl-L-methionine (MET) shows high accumulation within the bowels, which makes it difficult to assess bowel or pelvic diseases. One must also be aware of technical artifacts causing difficulties in interpretations, such as high attenuation oral contrast material within the bowel lumen or misregistration artifact due to patient movements. It is imperative to know the common variants and benign diseases that can mimic malignant pathologies. Intense FDG uptake within the esophagus and stomach may be a normal variant or may be associated with benign conditions such as esophagitis, reflux disease, or gastritis. Metformin can cause diffuse intense uptake throughout the bowel loops. Intense physiologic uptake can also be seen within the anal canal. Segmental bowel uptake can be seen in inflammatory bowel disease, radiation, or medication induced enteritis/colitis or infection. Diagnosis of appendicitis or diverticular disease requires CT correlation, as normal appendix or diverticulum can show intense uptake. Certain malignant pathologies are known to have only low FDG uptake, such as early-stage esophageal adenocarcinoma, mucinous tumors, indolent lymphomas, and multicystic mesotheliomas. Response assessment, particularly in the neoadjuvant setting, can be limited by post-treatment inflammatory changes. Post-operative complications such as abscess or fistula formation can also show intense uptake and may obscure underlying malignant pathology. In the absence of clinical suspicion or rising tumor marker, the role of FDG PET/CT in routine surveillance of patients with GI malignancy is not clear.

Reliability of Contrast CT and Positron Emission Tomography in Post-Surgical Colorectal Cancer and Its Association with Obesity

BACKGROUND

Post-surgical recurrence of cancer colon occurs in one-third of patients within the first two years, so early detection is important. The assessment of the therapeutic response is important to change protocol strategy. Positron emission tomography/computed tomography PET/CT, a valuable tool gives both metabolic and anatomic information for whole-body regions. Obesity is an important risk factor for colorectal cancer.

AIM

To evaluate post-surgical and therapeutic colorectal cancer by PET/CT and study obesity association to its prognosis.

METHODS

This was a prospective study involved 93 patients with, post-surgical colorectal cancer examined by PET/CT, then follow up after 4-6 months.

RESULTS

There was a statistically significant difference between PET/CT and contrast CT. The sensitivity& the specificity were (96.4%-100% & 92.3%-98.2%) for PET/CT and (84.2%-90.2% & 76.5%-85.4%) for contrast CT respectively. Post-therapeutic follow up showed; progressive course (24.5%), stationary course (26.4%), partial regression (28.3%) and complete regression course (20.8%). Obesity is a risk factor for progression with highly statistically significant to treatment response. Obese patients had a progressive or stationary course of the disease. Also, there was a highly statistically significant association between total abdominal fat & visceral abdominal fat areas with good response of treatment.

CONCLUSION

PET/CT is the most appropriate imaging technique to detect any recurrence or metastases in post-surgical colorectal cancer with high sensitivity and specificity comparing to CT. Obesity is a predictor risk factor for prognosis of the disease, as generally and abdominally (total & visceral fat) had an association with therapeutic response.