Case of the Month—April 2004

Incidental Finding of Colon Cancer

History
A 76-year-old male was found to have infiltrate in the right lobe of the lung and three nodules in the left lower lobe of the lung through CT. A repeat CT study three months later showed slightly increased size of the nodules and was suspicious for metastatic disease. A CT of the abdomen and pelvis was performed and showed misty mesentery and diverticulosis of the sigmoid colon. A PET scan was requested for further evaluation of the pulmonary nodules.

Finding
The PET FDG scan demonstrated a focus of intense uptake in the ileocecal region, suspicious for malignancy. However, there was no significant uptake in the lung parenchyma.

Follow-Up
A barium enema performed after the PET study showed a 4 cm polypoid lesion in the cecal area. The patient underwent right colectomy. Pathology report showed mucin-secreting adenocarcinoma arising from two polypoid villous adenomas.

How Did PET Help?
PET helped to identify unexpected malignancy in the cecum. The original area of interest in the lung, however, did not demonstrate significant uptake of FDG.

Discussion
In this case, a PET study was ordered to evaluate pulmonary nodules, yet led to a finding of colon cancer.

In a recent study, Agress and Cooper (1) consider the role PET can play in detecting unsuspected abnormalities unrelated to the primary tumor for which the patient was scanned. The authors evaluated 1,750 PET scans of patients with known or suspected malignancies. These were examined to determine the clinical importance and malignant potential of additional, unanticipated abnormal findings encountered during routine PET evaluation. Fifty-eight such abnormalities were identified in 53 patients. Of the 42 incidental lesions confirmed with biopsy, 30 (71%) were either malignant or pre-malignant tumors that differed from the cancer that led to the original scan.

Unexpected abnormalities are found with PET because the scans include the entire body, and because PET can frequently identify metabolically active lesions that may not be easily identified as anatomic abnormalities on CT.

(1) Agress, Harry and Benjamin Z. Cooper, “Detection of Clinically Unexpected Malignant and Premalignant Tumors with Whole-Body FDG PET: Histopathologic Comparison,” Radiology, 2004, 230:417-422.

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