PET/CT picks up another 20% of lesions not found on chest CT alone

Fusion PET/CT detects an additional one-fifth of active lesions from the supraclavicular notch to the adrenals that are not found on chest CT alone, according to a retrospective study.

Though PET/CT has been proven to be more sensitive than chest CT alone in detecting some types of cancer, chest CT is still among the first exams prescribed to patients with a known or suspected malignancy, said author Dr. Jean-Charles Vinet, a radiology resident at the Hospital of the University of Montreal.

"In our everyday practice, we found that some lesions were not reported on the chest CT but were retrospectively visible when we did the PET/CT and knew where they were localized," he said.

Previous studies that compared PET/CT with CT alone did not consider patients with various malignancies in a specific region but rather the performance for a specific type of cancer, according to Vinet.

"We wanted to target our weakness when we interpret chest CT in order to improve our everyday practice and bring better care to the patient," he said.

Vinet and colleagues included 499 patients from a pool of 3000 individuals who underwent PET/CT for an oncologic purpose at their institution between March and December 2007. The study was presented at the RSNA meeting in December 2008.

PET/CT and CT reports were reviewed to identify all PET/CT active lesions from the supraclavicular notch to the adrenals that were not mentioned in the thoracic CT report. For each discordant report, a radiology resident, senior chest radiologist, and PET/CT specialized nuclear physician reviewed the images to characterize, localize, and determine if the lesion was visible but not reported or had radiologic benignity criteria.

If the lesion was not reported, or was reported as benign on the chest CT, it was considered to be a discordant lesion, Vinet said.

The discrepancy rate in the 499 patients included in the study was 21.4%, with a total of 138 lesions in 107 patients. Discordant lesions were mostly seen in the lymph nodes and bone structures, according to Vinet.

Suspicious lesions in the lymph nodes were larger than 10 mm, with a mean diameter of 10.9 mm. Other lesions missed with CT were located within bones, adrenals, liver, lung parenchyma, and soft tissues.

PET/CT demonstrated additional lesions not reported on chest CT in one-fifth of patients, according to the researchers.

"These additional findings can be explained by the increased intrinsic sensitivity of the PET/CT compared with CT alone," Vinet said.

In addition, some lesions were overlooked on the initial chest CT readings, most of which were proven to be malignant. PET/CT had a positive clinical impact in about one-third of patients, he said.

"A more careful scrutiny may be required to assess thoracic CT in an oncologic population, especially regarding supraclavicular nodes, since most of the discrepancies were found in this region," Vinet said.

If lesions remain undetected, the patient could be misstaged and possibly undertreated, according to Dr. Donald Podoloff, head of the diagnostic imaging division at M.D. Anderson Cancer Center in Houston.

"It has been known for a long time that nodes that are not enlarged by radiographic criteria can contain tumors and be PET-positive," he said.

Major weaknesses of the study include its retrospective design. Since the work was not performed at a cancer center, the level of expertise might be lower as well, according to Podoloff.

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