Combined magnetic resonance imaging- and positron emission tomography-guided stereotactic biopsy in brainstem mass lesions: diagnostic yield in a series of 30 patients

Object. In the management of brainstem lesions, the place of stereotactic b iopsy sampling remains debatable. The authors compared the results of magne tic resonance (MR) imaging, positron emission tomography (PET) scanning, an d histological studies obtained in 30 patients who underwent MR imaging- an d PET-guided stereotactic biopsy procedures for a brainstem mass lesion. Methods. Between July 1991 and December 1998, 30 patients harboring brainst em mass lesions underwent a stereotactic procedure in which combined MR ima ging and PET scanning guidance were used. Positron emission tomography scan ning was performed using [F-18]fluorodeoxyglucose in 16 patients, methionin e in two patients, and both tracers in 12 patients. Definite diagnosis was established on histological examination of the biopsy samples. Interpretati on of MR imaging findings only or PET findings only was in agreement with t he histological diagnosis in 63% and 73% of cases, respectively. Magnetic r esonance imaging and PET findings were concordant in 19 of the 30 cases; in those cases, imaging data correlated with histological findings in 79%. Tr eatment based on information derived from MR imaging was concordant with th erapy based on histological findings in only 17 patients (57%). Combining M R imaging and PET scanning data, the concordance between the neuroimaging-b ased treatment and treatments based on histological findings increased to 1 9 patients (63%). In seven patients who underwent biopsy procedures with on e PET-defined and one MR imaging-defined trajectory, at histological examin ation the PET-guided samples were more representative of the tumor's nature and grade than the MR imaging-guided samples in four cases (57%). In 18 pa tients PET scanning was used to define a biopsy target and provided a diagn ostic yield in 100% of the cases. Conclusions. Although the use of combined PET and MR imaging improves radio logical interpretation of a mass lesion in the brainstem, it does not accur ately replace histological diagnosis that is provided by a stereotactically obtained biopsy sample. Combining information provided by MR imaging and P ET scanning in stereotactic conditions improves the accuracy of targeting a nd the diagnostic yield of the biopsy sample; an MR imaging- and PET-guided stereotactic biopsy procedure is a safe and efficient modality for the man agement of mass lesions of the brainstem.