Is brain SPECT a suitable modality for evaluation of postradiotherapy posterior fossa brain tumours? A comparative evaluation with contrast enhanced computed tomography.

Single photon emission computed tomography (SPECT) of the brain is exquisitely sensitive in detecting viable tumour tissue in the supratentorial region, but its efficacy has not been properly evaluated till date in case of infratentorial posterior fossa tumours. Twenty-four patients with primary posterior fossa brain tumour were included in this study. In each case brain SPECT with 99mTc-glucoheptonate (GHA) was performed for the evaluation of disease status. Contrast enhanced computerised tomography of brain was also performed in all the patients. Brain SPECT was positive in four patients with recurrence of tumour as compared to fifteen cases with computed tomography with a mean GHA retention index 5.26 +/- 1.64. Patients with postradiation gliosis (n=9) showed lower GHA retention index of 1.24 +/- 0.27. This study demonstrates that brain SPECT is not sensitive in detecting recurrence of tumour tissue in infratentorial region, as it is in the supratentorial region, with a sensitivity of 20%, accuracy of 45.83% and negative predictive value of 40% and the chance of any single study coming as false negative is about 80%.