Surgical site after resection of a meningioma.

PURPOSE Our goal was to characterize MR changes over time at the site of meningioma resection in order to determine optimal timing for detecting residual and recurrent tumor.

METHODS Twenty-one patients were studied with enhanced MR imaging during the first 5 postoperative days and additional studies were obtained 3 to 8 weeks after surgery (16 studies), 3 months to 1 year after surgery (17 studies), and 1 year or more after surgery (32 studies). Images were analyzed for residual tumor, membrane enhancement, parenchymal enhancement, edema, and blood collections.

RESULTS Early postoperative images showed extensive, thin membrane enhancement that thickened by 3 to 8 weeks after surgery and that thinned or resolved and became less extensive by 6 months or more postoperatively. Twelve of 20 patients with long-term follow-up studies had membrane enhancement. Thin, serpiginous foci of enhancement in the surgical bed were identified only on early postoperative studies and probably represent gradual thrombosis of feeding vessels.

CONCLUSION Residual foci of meningioma are best detected on studies obtained within the first 5 days after surgery because membrane thickness increases by 3 to 8 weeks after surgery and may obscure a small residual meningioma. Our study confirms the presence of prolonged membrane enhancement after surgery, although it thins with time and becomes confined to the craniotomy site.