The Radiographic Effects of LITT
Besides history taking and physical examination, neuroradiological imaging such as MRI is the primary method to assess responses to brain tumor therapies. Hence, during the past several decades, radiographic responses to LITT have been reported by numerous groups. Although radiographic responses to LITT for HGGs are described in detail below, it is important to understand the basic general observations after LITT for brain tumors. The first effect that is seen after LITT (within days of treatment) is central coagulation, which is observed as T1-weighted hyperintensity consistent with coagulated blood products in the center of the lesion (Fig. 3A and B). This often has a semiuniform "ground glass" appearance. This may be observed on postoperative CT scans as central hyperdense blood products. Additionally, LITT often produces a rim of diffusion restriction at the edge of the treatment zone (Fig. 3C) and a peripheral rim of enhancement (Fig. 3D), which is thought to represent a degradation of the surrounding BBB.[47,59,60,62] Subsequent effects vary depending on the tumor, the patient, and responses to LITT, which are described below.
Exemplar MRI studies showing immediate postoperative effects of LITT on brain tumors. A: Preoperative (pre) T1-weighted MRI study obtained with Gd (T1+) demonstrates an enhancing insular tumor. B: Postoperative (post) T1-weighted MRI study obtained without Gd (T1−) on the day after surgery shows isointensity within the tumor center representing coagulation products. C: Postoperative (post) diffusion-weighted imaging (DWI) MRI study shows diffusion restriction at the peripheral edge of the tumor. D: Postoperative (post) T1-weighted MRI study obtained with Gd (T1+) shows a new contrast-enhancing rim just outside the periphery of the tumor corresponding with the edge of the ablation zone. Reproduced with permission from Neurosurgery. Hawasli AH et al: Magnetic resonance imaging-guided focused laser interstitial thermal therapy for subinsular metastatic adenocarcinoma: technical case report. Neurosurgery 70 (2 Suppl Operative):332–338, 2012.
Neurosurg Focus. 2014;37(6):e1 © 2014 American Association of Neurological Surgeons