MR Venography in Gamma Knife Radiosurgery for Parasagittal Meningiomas: A Technical Note with the Rationale of Venous Protection and a Review of Literature.

Postradiosurgery symptomatic brain edema may be seen with parasagittal meningioma owing to its proximity to major venous sinuses and cortical veins. Venous preservation radiosurgery planning is less described. Here, we discuss a new method of tumor volume contouring on postcontrast magnetic resonance venogram (CEMRV) images safely excluding the adjacent cortical veins and sinuses. Six cases of parasagittal meningiomas where Gamma Knife radiosurgery was planned on CEMRV sequence were studied in detail. A double-contrast injection method was used to obtain CEMRV images. The differential contrast enhancement showed the displaced and compressed sinuses and cortical veins in the vicinity of meningioma. Tumor was contoured on both contrast magnetic resonance imaging (CEMRI) and MRV image for comparative analysis. 15 Gy at 50% marginal isodose was prescribed and quantitative assessment showed reduced exposure to the adjacent veins and sinuses on the MRV plan as compared to the CEMRI plan. All patients remain asymptomatic at a mean follow-up of 34.2 months. Postcontrast MRV is a simple sequence and can delineate the adjacent venous structures in parasagittal meningiomas. Tumor contouring directly on this sequence guides the surgeon to prescribe adequate radiation dose while sparing cortical veins and sinuses in radiosurgery planning.