Case of the Month—November 2003

Solitary Pulmonary Nodule

History
A 41-year-old female was found to have an 8-mm nodule in the superior segment of the right lower lobe on CT scan. A three-month follow-up CT (Figure 1) in June 2002 showed no change from prior scan. A repeat chest CT one year later in June 2003 (Figure 2) was interpreted as “unchanged in position, size, or shape.” An FDG PET study was requested to further characterize the nature of this nodule.

clinical image

Figure 1

Figure 2

Findings
The PET FDG whole-body scan demonstrated a focus of increased uptake corresponding to the right lower lobe nodule (Figure 3). The estimated maximum SUV (standardized uptake value) was 2.65, which is highly suspicious for malignancy. No other abnormalities are seen.

clinical image

Figure 3

Follow-up
The patient underwent right lower lobectomy. Pathology confirms that the nodule was indeed malignant and consistent with adenocarcinoma.

How Did PET Help?
PET identified a malignancy that was not evident through the follow-up CT scans. The patient’s management was altered based on the PET result.

Discussion
The stable pulmonary nodule seen on the series CT scans suggested the nodule was benign. Misdiagnosis can happen, however, due to subtle morphologic change.

PET provides additional metabolic information and can assist in characterizing pulmonary nodules. Studies have shown that PET is a very useful tool for differentiating benign from malignant pulmonary lesions, with both sensitivity and specificity close to 90%. A false positive scan can be seen due to infection. False negative studies have been reported in small nodules and in slow-growing tumor such as BAC and typical carcinoid. A positive PET scan warrants further evaluation, while a negative scan may spare invasive biopsy. Clinically, follow-up with CT scan for two years appears adequate in a patient who has had a negative PET FDG scan.

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