|LETTER TO EDITOR
|Year : 2011 | Volume
| Issue : 3 | Page : 374-375
Value of delayed PET imaging in mucinous adenocarcinoma rectum: Should this be employed while evaluating mucinous tumors with FDG-PET?
S Basu, NS Baghel
Radiation Medicine Centre, Bhabha Atomic Research Centre, Tata Memorial Hospital Annexe, Mumbai, India
|Date of Web Publication||14-Sep-2011|
Radiation Medicine Centre, Bhabha Atomic Research Centre, Tata Memorial Hospital Annexe, Mumbai
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Basu S, Baghel N S. Value of delayed PET imaging in mucinous adenocarcinoma rectum: Should this be employed while evaluating mucinous tumors with FDG-PET?. Indian J Cancer 2011;48:374-5
|How to cite this URL:|
Basu S, Baghel N S. Value of delayed PET imaging in mucinous adenocarcinoma rectum: Should this be employed while evaluating mucinous tumors with FDG-PET?. Indian J Cancer [serial online] 2011 [cited 2019 Aug 24];48:374-5. Available from: http://www.indianjcancer.com/text.asp?2011/48/3/374/84923
The role of Fluorodeoxyglucose positron emission tomography FDG-PET has been reported to be limited in the evaluation of mucinous tumors, particularly in hypocellular lesions with abundant mucin.  The observation has been postulated to be related to lower glucose metabolic rate of these malignancies. It has been reported that the sensitivity of FDG-PET imaging for detection of mucinous carcinoma is significantly lower than that for detection of non-mucinous carcinoma. , Such observation calls for newer approaches to be tested to better the sensitivity of this promising imaging technique in this clinical setting.
We herein present the value of delayed FDG imaging in mucinous carcinoma of the rectum by illustrating a case vignette. A 15-year-old male who presented with bleeding per rectum and was detected to have concentric wall thickening of the rectum extending up to anorectal junction in contrast-enhanced CT, was diagnosed to have mucinous carcinoma of the rectum on sigmoidoscopic biopsy. The carcinoembryonic antigen CEA level was 5.3 ng/mL. He was referred for FDG-PET study for disease staging. The baseline FDG-PET study at 1 hour [[Figure 1] upper panel] showed moderately intense FDG uptake in the primary region (maximum standardized uptake value SUV max , 3.929), which demonstrated a significant increase in the delayed images at 4 hours [[Figure 1] lower panel] following FDG injection (SUV max , 10.743), i.e., around 2½ hours after the first image. The sensitivity of FDG-PET has been described to be relatively less in mucinous malignancies; the present case underscores the importance of delayed imaging in such malignancies.
|Figure 1: Baseline FDG-PET (upper panel) demonstrates uptake in the rectosigmoid region corresponding to the site of primary and CT-described concentric wall thickening. The SUVmax was found to be 3.929 g/mL. A delayed image (lower panel) that was acquired at 4 hours following FDG injection (i.e., 2½ hours after first image) demonstrated a clear increase in the FDG uptake both qualitative visual assessment and quantitatively with an SUVmax of 10.743 g/mL|
Click here to view
Two intracellular enzymes (hexokinase and glucose-6-phosphatase), responsible for the phosphorylation and dephosphorylation of FDG, respectively, are the key to the principle of dual-time point FDG-PET imaging. It has been reported in the literature that inflammatory and malignant lesions exhibit a differential FDG uptake pattern over time and hence this technique has been primarily investigated for distinguishing malignant from benign inflammatory processes. ,, An increased ratio of hexokinase to glucose-6-phosphatase in malignant cells forms the basis of gradual accumulation of FDG-6-phosphate in these cells. The normal tissues, on the other hand, express greater levels of glucose-6-phosphatase than malignant cells; and therefore, FDG-6-phosphate can be rapidly dephosphorylated in these cells and cleared gradually over time.  This phenomenon at the cellular level contributes to a higher contrast of FDG uptake observed between malignant lesions and surrounding normal tissues over time. 
The SUV max in the 4-hour delayed view in the presented case demonstrated more than 2 times the value calculated at the 1-hour post-injection image. On visual assessment too, the delayed image depicted the malignancy better compared to the baseline image. The aforementioned finding warrants further investigation of this simple yet very useful technique in the setting of FDG-PET/CT imaging that if proven can be routinely employed in evaluating this group of tumors.
| » References|| |
|1.||Berger KL, Nicholson SA, Dehdashti F, Siegel BA. FDG PET evaluation of mucinous neoplasms: Correlation of FDG uptake with histopathologic features. AJR Am J Roentgenol 2000;174:1005-8. |
|2.||Sarikaya I, Bloomston M, Povoski SP, Zhang J, Hall NC, Knopp MV, et al. FDG-PET scan in patients with clinically and/or radiologically suspicious colorectal cancer recurrence but normal CEA. World J Surg Oncol 2007;5:64. |
|3.||Sanz-Viedma S, Torigian DA, Parsons M, Basu S, Alavi A. Potential clinical utility of dual time point FDG-PET for distinguishing benign from malignantlesions: Implications for oncological imaging. Rev Esp Med Nucl 2009;28:159-66. |
|4.||Mavi A, Basu S, Cermik TF, Urhan M, Bathaii M, Thiruvenkatasamy D, et al. Potential of dual time point FDG-PET imaging in differentiating malignant from benign pleural disease. Mol Imaging Biol 2009;11:369-78. |
|5.||Basu S, Alavi A. Partial volume correction of standardized uptake values and the dual time point in FDG-PET imaging: Should these be routinely employed in assessing patients with cancer? Eur J Nucl Med Mol Imaging 2007;34:1527-9. |