Colorectal cancer - patterns of locoregional recurrence and distant metastases as demonstrated by FDG PET / CT

Abstract

Colorectal cancer (CRC) can recur locoregionally or at distant sites. Timely diagnosis of recurrence is of paramount importance, as radical treatment of the localized disease can prolong survival. Fluorodeoxyglucose positron emission tomography / computed tomography (PET / CT) is routinely used in restaging and surveillance of colorectal cancer, as it can demonstrate recurrent disease with good accuracy. This article illustrates the spectrum of standard as well as unusual patterns of local recurrence and distant metastases of colorectal cancer.

Keywords: Fluorodeoxyglucose (FDG) PET / CT; colorectal cancer; recurrence disease.

Figure 1 (A,B)

A 57-year-old man with a history of abdominoperineal resection (APR) for rectal cancer presented with symptoms of pelvic pain and underwent a restaging FDG PET / CT. Axial unenhanced CT scan (A) shows a heterogeneous soft tissue mass in the presacral region (arrow). Fusion PET / CT image (B) reveals increased FDG uptake within the soft tissue (arrow), suggestive of local recurrence

Figure 2 (A,B)

A 48-year-old woman with rectal cancer treated with APR and radiation therapy underwent a restaging FDG PET / CT for suspected recurrence. Axial unenhanced CT scan (A) shows a soft tissue mass in the presacral region (arrow). Fusion PET / CT image (B) shows no FDG concentration within the soft tissue (arrow), suggesting post-treatment fibrosis

Figure 3 (A,B)

A 60-year-old man treated with surgery for low rectal cancer presented with bleeding per rectum and underwent an FDG PET / CT study. Axial unenhanced CT scan (A) shows ill-defined soft tissue thickening in the perianal region (arrow) without definite evidence of a nodule / mass. Fusion PET / CT image (B) shows an intense focus of hypermetabolism corresponding to the soft tissue thickening, suggesting perianal recurrence

Figure 4 (A,B)

A 67-year-old man operated for rectosigmoid malignancy presented with rising tumor marker levels and underwent an FDG PET / CT study. The fusion FDG PET / CT image (A) reveals a tiny, but intense focus of FDG uptake (arrow) at the rectosigmoid anastomotic site. A contrast-enhanced CT scan of the abdomen and pelvis and colonoscopy, however, did not reveal recurrence; hence, the patient was kept under observation. A follow-up PET / CT study done after eight weeks (B) shows disease progression, by demonstrating increase in the extent and intensity of the FDG uptake, with the appearance of a soft tissue mass at the anastomotic site. A colonoscopic biopsy confirmed recurrence. Hyperdense surgical staples (arrowheads in A and B) mark the anastomotic site.

Figure 5 (A,B)

A 62-year-old man treated for CRC was imaged with FDG PET / CT during routine surveillance. An axial unenhanced CT scan (A) reveals a sub-centimeter-sized, round, right common iliac node (arrow) that shows increased FDG uptake (arrow) on the fusion PET / CT image (B). USG-guided fine needle biopsy confirmed nodal recurrence

Figure 6 (A,B)

FDG PET / CT evaluation of a solitary hepatic metastasis in an operated case of colon cancer, treated with radiofrequency ablation (RFA). Pre-RFA fused PET / CT (A) image shows an FDG-avid metastasis in the left lobe of the liver (arrow). Immediate post-RFA fused PET / CT (B) image shows complete photopenia at the ablated site (arrow), suggesting complete ablation

Figure 7 (A,B)

A 39-year-old woman with a history of CRC. Axial fusion PET / CT (A) image shows hypermetabolic FDG-avid nodular foci abutting the bowel surface. Axial contrast-enhanced CT scan at the same anatomical level (B) shows enhancing nodular serosal deposits along the bowel surface (arrows) corresponding to the hypermetabolic foci in (A). Note the striking conspicuity of the deposits in (A) as compared to the subtle findings in (B)

Figure 8 (A-C)

A 52-year-old man treated for CRC presented with abdominal distention and vomiting. Coronal unenhanced CT scan (A) shows multiple dilated small bowel loops (arrowhead). The coronal PET image (B) reveals discrete foci of abnormal FDG uptake in the abdominal cavity (arrows). These foci were mapped to the peritoneal surface of the small bowel (arrow) on the fusion PET / CT image (C), suggesting metastatic peritoneal implants as the cause of intestinal obstruction

Figure 9 (A,B)

A 59-year-old man who underwent an abdominoperineal resection for low rectal cancer came for follow-up. An FDG PET / CT image (A) reveals a focus of abnormal FDG uptake at the colostomy site (arrow). Close inspection of the CT scan (B) reveals an inconspicuous soft tissue nodule (arrow) corresponding to the increased FDG uptake, suggesting recurrence at the colostomy site. Postoperative changes in the anterior abdominal wall can often mask such recurrent nodules, which are detected on PET, by virtue of their hypermetabolism.

Figure 10 (A-F)

Restaging FDG PET / CT studies performed on two different patients of treated CRC. Axial PET (A), axial CT scan (B), and fused axial PET / CT (C) images show multiple FDG-avid lung metastases. Axial fused PET / CT images of another patient of CRC show FDGavid skeletal metastases in the left sacral ala (arrow in D), D8 vertebral body (arrow in E), and in the left transverse process of the D1 vertebra (arrow in F)

Figure 11 (A-C)

Restaging FDG PET / CT studies performed on three different patients of treated CRC for suspicion of disease recurrence show unusual metastatic sites; in the right lobe of the thyroid gland (arrow in A), in the subcutaneous region of the left upper arm (arrow in B), metastatic portal adenopathy (arrowhead in c), and a right adrenal metastasis (arrow in C)

Figure 12 (A,B)

A 52-year-old man with metastatic CRC imaged with FDG PET / CT before and after targeted therapy. Fusion PET / CT study (A) prior to targeted therapy shows an FDG-avid metastatic retroprostatic nodule (arrow). There is significant reduction in the metabolism and size of the recurrent nodule (arrow) on the post-therapy follow-up PET / CT image (B), suggesting therapeutic response