Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

ABDOMINAL
Year
: 2010  |  Volume : 20  |  Issue : 4  |  Page : 284--288

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


Nilendu C Purandare, Sumeet G Dua, Abhishek Arora, Sneha Shah, Venkatesh Rangarajan 
 Bio-Imaging Unit, Tata Memorial Hospital, Dr. Ernest Borges Marg, Parel, Mumbai- 400 012, India

Correspondence Address:
Venkatesh Rangarajan
Bio-Imaging Unit, Tata Memorial Hospital, Dr. Ernest Borges Marg, Parel, Mumbai- 400 012
India

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.



How to cite this article:
Purandare NC, Dua SG, Arora A, Shah S, Rangarajan V. Colorectal cancer - patterns of locoregional recurrence and distant metastases as demonstrated by FDG PET / CT.Indian J Radiol Imaging 2010;20:284-288


How to cite this URL:
Purandare NC, Dua SG, Arora A, Shah S, Rangarajan V. Colorectal cancer - patterns of locoregional recurrence and distant metastases as demonstrated by FDG PET / CT. Indian J Radiol Imaging [serial online] 2010 [cited 2019 Nov 22 ];20:284-288
Available from: http://www.ijri.org/text.asp?2010/20/4/284/73545


Full Text

 Introduction



Recurrence of colorectal cancer (CRC) is seen in about 30 - 40% of patients who undergo primary curative surgical resection. The majority of these recurrences occur in the first two years after surgery. [1] Radical treatment of isolated local recurrences and hepatic and pulmonary metastases has been shown to improve survival; [2],[3] however, such interventions, in the presence of metastases at other sites, have failed to result in significant survival advantage. [4] Hence, imaging can play a very important role in detecting early recurrent disease, while the recurrence is still localized and resectable. Delbeke and colleagues [5] have shown that fluorodeoxyglucose PET (FDG-PET) can detect occult metastases in 32% of the patients, and thereby change the course of treatment in more than one-fourth of the cases. In addition, the role of FDG PET / CT as a problem-solving tool in patients on follow-up for a treated CRC, has been increasing in the setting of unexplained elevation of carcinoembryonic antigen and equivocal findings on conventional imaging modalities. [6] In this pictorial essay, we illustrate the spectrum of recurrence of CRC and the role of FDG PET / CT in its detection, characterization, and treatment response evaluation.

Local or locoregional recurrence

Pelvic recurrence in operated CRC occurs in as much as 30% of the cases. Recurrence may be seen in the pelvic nodes, at the anastomotic site or rectal stump, or in the presacral area, as a soft tissue mass. The importance of early detection of local recurrence at an operable stage cannot be overemphasized, in view of literature reports showing improved survival following resection of localized recurrences. [7]

Presacral and pelvic soft tissue recurrence

Surgery for CRC and radiation therapy-associated inflammatory changes can lead to both anatomic distortion in the pelvis, and often predispose to the development of a fibrotic presacral mass. This can occur in as many as 39% of the patients following anterior resection and in 19% of the patients after abdominoperineal resection. [8] CT scanning, due to its reliance on size and morphology, has limitations differentiating between fibrotic masses and soft tissue recurrences. On FDG-PET imaging, a recurrent mass in the presacral region shows increased tracer uptake, thus differentiating it from the fibrotic tissue [Figure 1] and [Figure 2]. PET / CT has shown higher accuracy when compared to PET and CT scan individually in differentiating a fibrotic presacral mass from recurrent disease. [9] Although FDG uptake shows disease in CT scan negative areas, a CT scan often solves the problem of physiological FDG uptake in normal structures such as the urinary bladder and bowel, which prolapse into the empty rectal fossa and may give rise to false positive PET results. In the perianal and rectal stump regions, however, the CT scan has limited contrast resolution and FDG-PET can be very useful in picking up subtle recurrence [Figure 3].{Figure 1}{Figure 2}{Figure 3}

Anastomotic site recurrences

Recurrence at the anastomotic site is often encountered. Resection of such localized recurrences offers a survival advantage. The typical PET / CT appearance is of a hypermetabolic soft tissue mass or subtle wall thickening at the anastomotic site, [10] which is often identified by a surgical ring of radio-opaque staples [Figure 4]. Although colonoscopy would be the ideal technique for diagnosing and confirming anastomotic site recurrences, FDG PET / CT imaging can prove to be an excellent noninvasive modality when such recurrences are suspected. {Figure 4}

Pelvic nodal recurrence

Categorization of nodes as metastatic on conventional imaging modalities, including CT scan and magnetic resonance imaging (MRI), is based on their size. This approach results in a decrease in the reporting of metastatic recurrence in centimeter-sized nodes, which are often seen in CRC. By virtue of its ability to superimpose metabolic information on the anatomic detail, the PET / CT helps characterize even centimeter-sized metastatic nodes [Figure 5], with a resultant reduction in false negative restaging studies. [11] {Figure 5}

Distant metastases

Liver and lung metastases

Resection of operable hepatic and pulmonary metastases offers the only chance of cure and serves to prolong survival in CRC; however, the presence of extrahepatic or extrapulmonary metastases is associated with poor survival despite metastatectomy. According to a recent prospective multicenter study, which evaluated the role of FDG-PET in recurrent colorectal cancer, 23.5% of the patients with potentially resectable hepatic and pulmonary metastases, on conventional imaging, were deemed inoperable as a result of their PET scan findings. [12] As mentioned earlier, the PET / CT can detect occult metastases in about one-third of the patients with CRC, and thereby alter the management. [13]

In a meta-analysis, when comparing FDG-PET, CT scan, and 1.5 T MRI in colorectal liver metastases, FDG was found to be the most accurate modality on a per-patient basis, whereas, the modalities were more or less comparable on a per-lesion basis. [14] However, the MRI using liver-specific contrast agents was found to be superior to FDG-PET in the detection of small liver metastases. [15] In addition, PET / CT also showed significantly higher specificity (100%) than the contrast-enhanced CT scan (50%) in the detection of recurrences following hepatic resection, [16] as well as following radiofrequency ablation (RFA). [17] Complete photopenia at the ablated site on the FDG-PET scan suggested a metabolic response and completeness of the ablation [18],[19] [Figure 6].{Figure 6}

Peritoneal deposits

The development of peritoneal disease [Figure 7],[Figure 8] in the setting of CRC carries a grave prognosis, with little - if any - response to surgical therapy or chemotherapeutic agents. [20] The prognosis is slightly better in the localized foci of peritoneal disease, as they are amenable to complete resection and thus call for accurate and timely detection. [20,21] Occasionally these deposits can result in bowel adhesion and consequent intestinal obstruction [Figure 8].{Figure 7}{Figure 8}

Abdominal wall and colostomy site recurrence

Scars from open or laparoscopic surgery, as well as drain, port, and stoma sites, are potential locations of metastatic CRC recurrence [Figure 9]. Resection of such metastases can be considered in the absence of disease in the abdomen or elsewhere as it can result in adequate local control with minimal procedural complications. [22],[23] PET / CT is a sensitive tool in the detection of abdominal wall, stoma / port-site metastases of CRC. [24] {Figure 9}

Infrequent sites

The incidence of metastases to infrequent sites is increasing due to the improved survival of patients. Skeletal [Figure 10]D-F and brain metastases are more likely to occur in the setting of lung metastases, [Figure 10]A-C and in a primary rectal cancer as compared to colon cancer. [25] Occasional cases of metastases from CRC to thyroid, [26] adrenals, [27] and subcutaneous tissues [28] [Figure 11] have also been documented in literature. {Figure 10}{Figure 11}

FDG-PET in monitoring response to systemic therapy

Morphological imaging techniques are limited in assessing therapeutic response, as they rely on changes in tumor size, which often lag behind biological response. FDG-PET has been used to monitor early response to primary as well as secondary chemotherapeutic agents after the first or the second cycle in advanced CRC [29] [Figure 12]. Furthermore, with the advent of newer molecular targeted therapies that often target biological effects like angiogenesis, more accurate surrogate endpoints are required, to assess therapeutic response. FDG PET / CT can be very useful in this regard to identify responders early in the course of therapy.{Figure 12}

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