HISTORY: The patient is a 57 year old female with a history of breast cancer nine years ago who is referred for evaluation of a newly diagnosed left lung nodule. A PET/CT with intravenous contrast evaluation of the neck, chest, abdomen and pelvis was ordered.

FINDINGS: The exam demonstrates moderate intensity hypermetabolism in a lobulated left lung nodule (click image to see an enlargement).

A mass is also identified in the brain within the right periventricular white matter and is seen to have moderate intensity hypermetabolism.

INTERPRETATION: The degree of uptake in the lung nodule is very suspicious for malignancy. The differential would include a primary lung cancer, metastatic disease from the patient’s breast cancer, as well as an active granulomatous nodule. A biopsy is recommended for pathologic correlation. The newly identified brain mass is also suspicious for malignancy given the hypermetabolism and is most likely a metastatic lesion.

DISCUSSION: This case demonstrates the utility of PET/CT imaging in evaluation of the lung nodules. It is estimated that up to 40% of patients with newly diagnosed lung cancer have metastatic disease and that up to 10% have disease outside of the mediastinum. PET/CT’s ability to screen the whole body with high sensitivity and specificity allows more accurate initial staging of patients resulting in more appropriate treatment options being selected. Multiple studies have demonstrated that PET imaging results in a change in management of the patients in up to 20-40% of cases.

In this case, the likely metastatic lesion is identified in the brain. This is unusual in that PET has a lower sensitivity at detecting metastatic lesions within the brain as compared to its high sensitivity in other sites in the body. Studies have shown PET imaging of the brain detects only 61-68% of metastatic lesions that are identified by MRI and this is likely a result of the normal high FDG uptake within the brain obscuring uptake in metastatic lesions. For this reason, if there is any clinical suspicion for metastases to the brain an MRI should be considered the study of choice and should be performed even in the setting of a negative PET scan.