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Advanced adenoma diagnosis with FDG PET in a visibly normal mucosa: a case report
© Rehani et al; licensee BioMed Central Ltd. 2007
Received: 08 June 2007
Accepted: 20 September 2007
Published: 20 September 2007
An accurate, early diagnosis and treatment of adenomatous polyp can curtail progression to colorectal cancer. F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) reveals the biochemical changes associated with the development of many cancers which precede the appearance of gross anatomical changes that may be visualized during surgical resection or via imaging with MR or CT.
We detail the history of a 64 year old female who had a whole-body FDG PET scan as a part of an employee wellness program. A dose of 12.2 mCi of F-18 labeled FDG was administered.
A focal cecal uptake with a standardized uptake value (SUV) of 8.9 was found on the PET scan. Conversely, only normal mucosa was observed during a colonoscopy done 2 months after the PET scan. Motivated by the PET scan finding, the colonoscopist performed a biopsy which revealed a villous adenoma without high grade dysplasia. Pathology from tissue extracted during an exploratory laparatomy completed one month later found the lesion to be a villous adenoma with high grade dysplasia.
Whole-body FDG PET scan revealed the biochemical metabolic changes in malignancy that preceded the appearance of any gross anatomical abnormality. A positive FDG PET scan indicative of colorectal cancer should be followed up with a colonoscopy and biopsy even in a visibly normal mucosa.
We hereby report a case of advanced adenoma which was detected on a whole-body FDG PET scan despite the fact that the mucosa had a normal appearance on follow up colonoscopy. F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) reveals the biochemical changes associated with the development of many cancers which precede the appearance of gross anatomical changes that may be visualized during surgical resection or via imaging with MR or CT.
A dose of 12.2 mCi was given to the patient following a 4 hour fasting period. The tracer incorporated for 1 hour prior to image acquisition. A 6 bed position, whole-body PET scan was performed on a Siemens HR+ PET scanner. Each bed position included a 2 minute transmission followed by a 5 minute emission scan. Reconstruction parameters were 2 iterations/8 subsets (OSEM) with a 4 mm smoothing Guassian filter
Polyp is a small growth of tissue shaped like the head or stalk of a mushroom. They are classified histologically as neoplastic (adenomatous) or non neoplastic . Adenomas are traditionally divided into three types: tubular, tubulovillous, and villous. Advanced adenoma is defined by a national polyp study as being >= 1 cm in diameter or containing appreciable villous tissue or high grade dysplasia . Our patient had a villous adenoma with high grade dysplasia. Once diagnosed, advanced adenomas should be resected to prevent progression to cancer and thus early diagnosis is critical.
In this educational case report, the patient had a high grade villous adenoma which was discovered due to its increased FDG uptake on a whole-body PET scan but the mucosa looked normal on the colonoscopy. FDG PET scanning detects biochemical changes which precede gross morphological changes in cancerous tissue. Increased cell surface glucose transporter protein 1 to 5 and increased level of hexokinase pathway explain the high FDG uptake in malignancy.
Narrow Band imaging and Chromoendoscopy with indigo carmine can increase the yield of conventional colonoscopy. [3, 4] The reasons cancers may be missed on colonoscopy are attributed to incomplete colonoscopy, poor bowel preparation, misinterpretation of what was seen (mostly flat polyps), failure to carry out adequate biopsy of lesions, and system failures related to follow up investigations in patients who had incomplete colonoscopy [5–8]. However, these conditions are not applicable for this case in which the mucosa was visibly normal on colonoscopy. The gastroenterologist has 25 years of experience in Endoscopy. Two other endoscopists were shown the pictures; they both said they would have assumed a false positive scan and wouldn't have done a biopsy of the area.
According to the current guidelines , since a colonoscopy had been performed on this patient two years prior to the PET scan, another colonoscopy would not have been repeated for another eight years. A whole-body FDG PET scan enabled the early diagnosis and removal of the advanced adenoma preventing its progression to invasive cancer in this patient.
FDG PET has a high sensitivity in diagnosing premalignant and advanced colonic neoplasia [10–14]. Van Kouwen et al showed in a large prospective study that the sensitivity increases with size and grade of dysplasia . An interesting experimental study showed induced colonic adenomas and carcinomas may be detected in apparently normal mucosa .
Whole-body FDG PET scan revealed the biochemical metabolic changes in malignancy that preceded the appearance of any gross anatomical abnormality. A positive FDG PET scan with a focal uptake in colon should be considered a significant finding indicative of colorectal cancer and follow up colonoscopy and biopsy should be recommended even in a visibly normal mucosa.
We would like to acknowledge the faculty and staff of Nuclear Medicine department who were involved in the care of the patient. A written consent was obtained from the patient.
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