Performance of dedicated 18 F FDG PETCT and derived metabolic parameters in brain space occupying lesions (SOLs) suspicious for primary CNS lymphoma

Introduction: To asses the role of 18 F FDG PETCT in detection of brain lesions suspicious for primary CNS lymphoma (PCNSL)

Methods: 45 patients with brain SOLs who underwent pre treatment 18F FDG PETCT were retrospectively analysed. Out of these 3 were excluded; one was detected with systemic lymphoma and two with lung primary.

Of 42 patients, FDG PETCT findings were diagnostic of PCNSL in 37 patients, while remaining were diagnosed as glioma, metastases and inflammation. SUVmax, Tumor/contralateral white matter ratio (T/w), MTV, TLG were calculated.

FDG PETCT findings were correlated with histopathological diagnosis.

Results: Out of 37 Patients, diagnosis of PCNSL was confirmed on histopathological correlation in 34 patients and 3 were diagnosed as brain tumors. Overall diagnostic sensitivity was 94% and specificity of 50%, PPV 92%, NPV 60%

Roc analysis yielded:

SUVmax cutoff of 14 with sensitivity of 89%, specificity of 100%.

Tw cutoff of 2.18 with sensitivity 94%, specificity 100%

MTV cutoff of 25 with sensitivity 74%, specificity 83%

TLG cutoff of 103 with sensitivity 91% specificity 83%

Conclusions: In the setting of clinico radiological suspicion of PCNSL, 18 F FDG PETCT can be used as sensitive imaging modality to non invasively diagnose PCNSL but lacks specificity to correctly exclude it. Addition of metabolic PET parameters significantly increases the specificity and NPV of PET/CT. T/w ratio has shown the highest diagnostic accuracy amongst all.