gms | German Medical Science

Objective: Recent studies have proven the value of intraoperative MRI (iop MRI) for achieving a more radical tumor removal while decreasing the associated neurological morbidity. Although high resolution 2D ultrasound (US) appears to be a more accessible alternative, its significance for tumor resection control has not been definitely proven. The direct comparison of the 2 imaging modalities has been the objective of the current study.

Methods: 27 patients with intrinsic brain tumors have been operated in a OR, equipped with 1,5 Tesla MRI (Siemens, Erlangen). A high resolution US device (SonoWand, Mison, Norway) was utilized. 5 patients had low grade gliomas, 21 with high grade gliomas and 1 with metastasis. Image acquisition with both modalities was performed prior to surgery (iop MRI) or prior to dural opening (US), as well as during and after tumor removal. The parameters that have been registered and compared were: quality of the images at different stages and availability of tumor remnants detectable with only one of the modalities but invisible on the other. The findings were correlated to the tumor histological type, location and size.

Results: US provided real-time information and the image acquisition time was significantly shorter. Further, it depicted useful tumors’ internal structure and vascularization. Prior to tumor resection the quality of the preoperative images was similar on both modalities. Both the low- and the high- grade tumors could be depicted well. After initial tumor resection US demonstrated all larger remnants; however, in 2 cases smaller remnants have been missed. Other shortcomings of US were the impossibility to depict reliably extensive gliomas occupying 2 or more lobes and the poor visualization of superficial tumor parts. Furthermore, iop MRI provided update of both the structural and functional (fiber tracking) data.

Conclusions: High resolution US is a cheaper and reliable alternative to iop MRI for resection control, especially in case of more confined deeply located low- or high-grade tumors. However, in superficial or extensive tumors its role is limited. The question if small remnants of low grade tumors can be reliably visualized with US remains open.