A 62-year-old man with a 40-year history of smoking presented with shortness
of breath and weight loss. Initial chest X-rays were unremarkable and the
patient subsequently underwent full body CT scan in search of a primary
malignancy. CT scan demonstrated a large central mass in the left lower lobe
inseparable from the hilum. There was complete encasement of the left pulmonary
artery and left mainstem bronchus, with postobstructive consolidation in the
left lower lobe. Incidentally noted were multiple hypodense masses scattered
throughout the liver, which were interpreted as metastases from a primary lung
carcinoma. A biopsy of the lung revealed small cell lung cancer; a PET scan/CT
study was requested to stage the full extent of disease.
As expected, PET/CT scan demonstrated abnormal uptake in the lung and liver,
with maximum SUVs of 7.0 and 7.2, respectively. However, there was also an
incidental note of abnormal nodular area of increased metabolic activity in the
sigmoid colon, demonstrating a maximum SUV of 8.1. Corresponding anatomic CT
images demonstrated the possibility of a sigmoid mass. Colonoscopy and eventual
histopathology of this region revealed adenocarcinoma of the sigmoid colon. The
hepatic masses were revealed to be metastases from the sigmoid adenocarcinoma,
and the small cell lung cancer was another synchronous primary cancer.
1: Initial PET/CT examination demonstrates hypermetabolic activity (yellow
circle) associated with primary lung carcinoma. Upper left image is axial
CT scan, upper right image is corresponding PET image, lower left image is
fusion image containing PET images displayed on a color scale and CT images
displayed on a gray scale. Lower right image is maximum intensity project
(MIP) image of whole body PET study.
2: Initial PET/CT examination demonstrates hypermetabolic activity (yellow
circle) within several hepatic masses. Display convention is the same as
3: Initial PET/CT examination demonstrates abnormal focal hypermetabolic
activity within the sigmoid colon with a maximum SUV of 8.1. Corresponding
anatomic images demonstrate an eccentric soft tissue mass arising from the
colonic wall. Display convention is the same as Figures 1 and 2.
Source: M. Ghesani
PET scan has been documented to incidentally detect unsuspected precancerous
and cancerous lesions. Agress et al studied a group of 1,750 patients who
underwent PET scanning for a variety of known or suspected malignancies.
Forty-two patients had unexpected findings of increased metabolic activity that
could not be explained by physiologic uptake and were in an unusual location
for spread of metastases given the type of primary tumors. Of these 42
patients, 30 (71%) had malignancies that were different than the known
malignancy. These incidental cancers included colonic adenomas/adenocarcinomas,
breast carcinoma, laryngeal squamous cell cancer, endometrial adenocarcinoma,
ovarian carcinoma, papillary thyroid cancer and fallopian tube adenocarcinoma.
Naydich and Ghesani et al performed a similar study evaluating incidental
abnormal metabolic uptake on PET scans that could not be explained by
physiologic uptake and were unlikely to be related to the primary tumor. In 21
patients in whom histopathologic correlation was available, 14 (66%) patients
were found to have malignant/premalignant conditions, including 10 colonic
adenomas/adenocarcinomas, two papillary thyroid cancers, one renal cell
carcinoma, and one parotid.
PET scan has been a useful adjunct for staging cancer and monitoring therapy
in oncology patients. However, several studies are demonstrating the incidental
detection synchronous malignancies by PET. This is not surprising, given that
the molecular marker used for PET, F-18 FDG, is an analogue of glucose that
reflects increased GLUT-1 transporters on cell surface and increased glycolytic
activity intracellularly, a process shared by several malignancies. The studies
cited demonstrate that a significant majority of cases with abnormal
nonphysiologic uptake that is unrelated to the primary tumor lead to the
eventual discovery of occult cancerous and precancerous lesions. In the
remainder of the patients, this abnormal localization represents increased
glucose metabolism in the inflammatory/infectious process. In our case, it led
to the discovery of unsuspected colonic adenocarcinoma. This stresses the vital
importance of working up suspicious and nonphysiologic metabolic activity
because incidentally discovered malignant and/or premalignant conditions could
have a potential impact on a patients clinical outcome and long-term
Munir Ghesani, MD, is Associate Clinical Professor of Radiology at
Columbia University College of Physicians and Surgeons and Attending
Radiologist at St.Lukes-Roosevelt Medical Center.
Robert Chen, MD, is a Radiology Resident at Beth Israel Medical Center.
For more information:
- Agress H, Cooper B. Detection of clinically unexpected malignant and
premalignant tumors with whole-body FDG PET: histopathologic comparison.
Radiology. 2004. 230;417-422.
- Naydich M, Ghesani M, et al. Incidental findings on whole body F-18 FDG PET
scans are frequently due to malignant of premalignant conditions. ACNP