First-pass CT-perfusion in differentiating primary extra-axial brain tumours: Added value of MTT and TTP in characterisation beyond CBV and CBF

Purpose: Prospective evaluation of the efficacy of perfusion-CT (PCT) in differentiating Meningioma (low-grade and high-grade), Schwannoma and Macroadenoma. Material and methods: PCT was performed in 48 patients [16 low-grade-meningiomas, 9 high-grade-meningiomas, 11 Schwannomas, and 12 Macroadenomas]. Perfusion parameters included cerebral-blood-volume [CBV], cerebral-blood-flow [CBF], mean-transit-time [MTT] and time-to-peak [TTP]. These were derived both from the lesion and normal parenchyma and were normalised [n] by obtaining the ratio. Lesions were statistically compared using student t-test and ROC analysis. Results: The mean nCBV and nCBF of low and high-grade meningiomas showed statistical difference (P < 0.05). For identifying high-grade meningioma, nCBV > 12.43, nCBF > 6.43 yielded good sensitivity and specificity. The mean nCBV, nCBF and nMTT of macroadenomas and benign meningiomas showed statistical difference (P < 0.05). For identifying macroadenoma, nCBV < 3.67, nCBF < 1.08, nMTT > 2.81 yielded good sensitivity and specificity. The mean nCBV, nCBF, nMTT and nTTP of schwannomas and benign meningiomas showed statistical difference (P < 0.05). For identifying schwannomas, nCBV < 1.68, nCBF < 0.89, nMTT > 3.34, nTTP < 1.06 yielded good sensitivity and specificity. Conclusion: Perfusion CT helps in the characterisation of common extra-axial lesions when their diagnosis based solely on morphological characteristics is uncertain. Apart from CBV and CBF, the added value of MTT in characterising macroadenoma, and both MTT and TTP in characterising schwannoma is noteworthy which is not emphasized in the available literature.