PET/CT a dependable differentiator of types, origins of space-occupying brain lesions

PET/CT with fluorine-18-fluorodeoxyglucose (18F-FDG), the most commonly used radiotracer for PET neuroimaging and cancer patient management, is effective for differentiating between tumors, metastases and lymphomas in the brain and central nervous system, according to a study conducted in India and published online Sept. 15 in Nuclear Medicine Communications.

The researchers further found that 18F-FDG PET/CT helped distinguish primary from secondary malignancies, with ramifications for planning care pathways.

Radiologist Nilendu Purandare, DNB, DMRD, and multidisciplinary colleagues at Tata Memorial Hospital and cancer-research center in Mumbai reviewed the cases of all patients with space-occupying lesions in the brain who were referred for an 18F-FDG PET/CT scan.

The researchers determined metabolic characteristics of the lesions, based primarily on maximum standardized uptake value (SUVmax), and they compared differences using nonparametric statistical equations.

Using histopathological confirmation as the gold standard for accurate lesion characterization, they found that metastases (n = 46), glioblastoma multiforme (GBM, n = 30) and lymphoma (n = 25) accounted for most malignancies.

Lymphomas showed a significantly high metabolic uptake (median SUVmax 20.3) compared with glioblastoma multiforme (median SUVmax 10.3) and metastases (median SUVmax 11.5).

A SUVmax more than 15.5 showed an 84 percent sensitivity and an 80 percent specificity to diagnose lymphomas, the authors report.

The tumor-to-background activity ratios for lymphomas were also significantly higher than those for the other lesion types.


  • There was an overlap in the metabolic uptake of GBM and metastases, with no significant difference between their SUVmax values.
  • Four patients with brain lymphoma had extracranial disease on 18F-FDG PET.
  • Lung cancer was the most common primary malignancy in patients with brain metastases.

“Central nervous system lymphomas can be differentiated from GBM and metastases by their higher metabolic activity,” the authors conclude. “In addition, 18F-FDG PET/CT can potentially impact therapeutic decisions by detecting primary malignancy in patients with metastatic brain lesions and extracranial disease sites in patients with brain lymphoma.”