What is MR-gLITT?

Stereotactic magnetic-resonance-guided laser interstitial thermal therapy (MR-g LITT) is a minimally invasive procedure that offers advantages to patients who are not optimal candidates for open resection. MR-G LITT may be used for elderly patients with comorbid medical and psychiatric concerns and for patients who require reoperation for retained mesial structures.

The best candidates for MR-g LITT are patients with a well-defined epileptogenic focus. When focal seizures are uncontrolled by antiseizure drugs, a solitary lesion < 2 cm on high-resolution magnetic resonance imaging (MRI) of the brain and a concordant presurgical evaluation is the optimal preoperative situation for MR-g LITT. 

How is MR-g LITT done?

Under general anesthesia, a small 1 cm stab wound overlying a burr hole is placed to accommodate a standard stereotactic system. Patients undergo insertion of a saline-coiled fiber-optic laser applicator into the region of interest. Subsequently, computer-guided laser ablation is performed during continuous real-time MRI of the brain. After two to three lesions are placed in the area of interest, a confirmatory contrast-enhanced MRI of the brain with volumetric reconstruction is performed.

The most common target has been the temporal lobe. The mesial structures (most internal) of the temporal lobe are particularly amenable to MR-g LITT, given the ease of approaching the long axis of the temporal lobe from an occipital trajectory. Thermal injury to surrounding tissues is guided by placement of the probe.

Mesial temporal ablation is contained because it is shielded by the lateral ventricle, which serves as a heat sink. This prevents aberrant heat from affecting the surrounding tissue by using monitored thermography to provide feedback. For safety, an automatic shutdown is triggered if the immediate surrounding area has temperatures that exceed computer-regulated limits. 

How well does MR-g LITT work?

Thus far, small series have reported the efficacy of MR-g LITT.

  • In 15 procedures performed in 13 adult patients with a median follow-up of 14 months, 77% achieved meaningful seizure reduction, with 54% becoming free of disabling seizures. 
  • In 19 MR-g LITT procedures performed in pediatric epilepsy patients with a mean age of 15.3 years, an Engel class 1 outcome was achieved in 7/17 (41%).4 
  • In adults, mesial temporal sclerosis has been the most common pathology, while in pediatrics, cortical dysplasia is the most common. 3, 4  
  • Visual field defects are a rare complication; however, the neuropsychological profile may be improved compared to open resection.5  
  • Most patients leave the hospital less than 24 hours after MR-g LITT. 

Recent interest in super-selective stereotactic laser ablation has emerged as a new minimally invasive surgical option that is best suited for patients with symptomatic localization-related epilepsy. While MR-g LITT may not yet be at its peak, interest in it is growing and reflects a significant advancement in the surgical treatment for patients with drug-resistant focal seizures.

References

  1. Wiebe S, Blume WT, Girvin JP, Eliasziw M. A randomized, controlled trial of surgery for temporal lobe epilepsy. N Engl J Med 2001;345:311-318.
  2. Josephson CB, Bykeman J, Fiest KM, Liu X, Sadler RM, Jette N, et al. Systematic review and meta-analysis of standard vs selective temporal lobe epilepsy surgery. Neurology 2013;80:1669-1676.
  3. Willie JT, Healen L, Drane DL et al. Real-time Magnetic Resonance-guided stereotactic laser amygdalohippocampotomy for mesial temporal lobe epilepsy.  Neurosurgery 2014;74(6):569-585.
  4. Lewis EC, Weil AG, Duchowny M, Bhatia S, Ragheb J, Miller I. MR-guided laser interstitial thermal therapy for pediatric drug-resistant lesional epilepsy. Epilepsia 2015;56(10):1590-1598.
  5. Drane DI, Loring DW, Voets NL et al. Better object recognition and naming outome with MRI-guided stereotactic laser amygdalohippocampotomy for temporal lobe epilepsy.  Epilepsia 2015;56:101-113.
Authored by: William O. Tatum DO | Epilepsy Foundation Professional Advisory Board on 12/2015