Gross-total Surgery of Supratentorial Low-grade Gliomas under Intraoperative MR Guidance

Patient 2 (astrocytoma, WHO grade II).

Top left and top right, The Flashpoint Position Encoder is used to localize the borders of the tumor in projection onto the skull before craniotomy. The dotted lines (arrows) mark the calculated actual position of the hand-held device. Additionally, an MR Track Pointer (arrowheads) mounted on the hand-held device is used. On T2-weighted single-shot fast spin-echo sequences, the instrument, filled with a sodium chloride solution, is displayed with high signal intensity. The sagittal view (top right) shows a slight deviation between the calculated and imaged positions caused by a short delay between image update (every 3 seconds) and optical tracking update (four per second).

Bottom left and bottom right, After craniotomy, this approach is used again to define the borders of the tumor in projection to the dura.

Patient 9 (astrocytoma, WHO grade II).

Top left and top right, T2-weighted axial fast spin-echo images were used to determine the tumor area before resection.

Middle left and middle right, Comparable slices obtained at the point at which the neurosurgeon considered the resection to be complete (first control) were used to calculate the residual tumor volume.

Bottom left and bottom right, T2-weighted images at the same position were used to measure very small areas of residual tumor tissue at the end of the operation before closing the craniotomy.

Patient 10 (astrocytoma, WHO grade II).

A, First control at the point at which the resection was considered complete by the neurosurgeon. T2-weighted fast spin-echo image shows two hyperintense areas suspicious for tumor (arrows) at the border of resection.

B, Using the interactive scan mode (T2-weighted single-shot fast spin-echo, 3 seconds per image) and the MR Track Pointer (arrowhead) filled with sodium chloride solution, one lesion is marked (asterisks). Fluid (F) is at the bottom of the resection cavity while the patient is lying on the right side.

C, The last control (T2-weighted fast spin-echo image) shows complete removal of all tumor-suspicious tissue. There is no surgically induced edema evident in the bed of resection.

Patient 4 (oligodendroglioma, WHO grade II).

Top left, The first control image (T2-weighted fast spin-echo) shows hyperintense tumor-suspicious tissue (arrows) in the bed of resection.

Top right and bottom left, Abnormalities are also seen on the interactively guided single-shot fast spin-echo images (arrows). The MR Track Pointer is used to localize the suspicious area (arrowhead).

Bottom right, Before closure of the craniotomy, T2-weighted fast spin-echo image shows the final result of the resection. The tumor-suspicious tissue was reduced; nevertheless, some nodular areas are still suggestive of residual tumor. Because of the proximity of this region to the language cortex, the resection was stopped at this point. The patient had no postoperative neurologic deficit.

Patient 1 (astrocytoma, WHO grade II).

Top left, T2-weighted fast spin-echo image before craniotomy shows high signal intensity of the temporal astrocytoma (arrow).

Top right, T2-weighted fast spin-echo image after corticotomy for surgical access to the tumor.

Bottom left, T2-weighted fast spin-echo image at the point at which resection was considered complete by the neurosurgeon and by the radiologist reveals no residual tumor at this slice.

Bottom right, After closure of the craniotomy, the bed of resection is displayed with high signal intensity, probably caused by a mixture of blood, CSF, saline, and hemostatic material.