Introduction: Several publications highlight reactions around DBS electrodes which manifest as symptomatic or asymptomatic cerebral edema. We encountered a severe form of this phenomenon which started as edema around the leads progressing to cystic cavities. We present a detailed review of the literature involving immune response of the brain, pre-clinical and post-mortem studies and present a concise review of possible mechanisms.

Methods: We conducted a review of all the publications from 1980 to the present. Search terms included DBS, silicone, brain implant, CNS immunological reaction, pre-clinical and post mortem DBS studies. About 36 manuscripts were reviewed.

Results: There were five manuscripts with DBS mediated cerebral edema. Possible etiologies include immune reaction to the biomaterials of the DBS causing cerebritis, luxury perfusion due to breakdown of the blood-brain-barrier(BBB), micro-hemorrhage, mechanical trauma, and transependymal edema. Pre-clinical animal studies and post mortem human studies reveal similar changes with 5-25 microns of scar around the electrodes with the presence of activated astrocytes and a rim of GFAP positive gliosis up to 1 mm in thickness. Acute and chronic phases of foreign body response (FBR) of the brain to drug delivery implants, have shown the formation of a barrier created by astrocytes and macrophages trying to contain the foreign body leading to cyst formation around the implants.

Conclusions: Although, several theories are proposed for this phenomenon, we think it is most likely a combination of brief breakdown of the BBB with insertion of the DBS lead followed by a foreign body response. In its severest form, this reaction manifests as a cystic encephalopathy.

Patient Care: Edema around the leads is not always infection and DBS leads do not need to be removed. DBS lead edema is self limited

Learning Objectives: 1. Edema around the DBS leads have not been well explained 2. Highlights brain immune reactions to DBS 3. Severe cases of DBS leads forms cysts around the leads

References: Abnormal T2-weighted MRI signal surrounding leads in a subset of deep brain stimulation patients. Englot DJ, Glastonbury CM, Larson PS. Stereotact Funct Neurosurg. 2011;89(5):311-7. doi: 10.1159/000329365. Epub 2011 Aug 31. PMID: 21894061 Transient, symptomatic, post-operative, non-infectious hypodensity around the deep brain stimulation (DBS) electrode. Deogaonkar M, Nazzaro JM, Machado A, Rezai A. J Clin Neurosci. 2011 Jul;18(7):910-5. doi: 10.1016/j.jocn.2010.11.020. Epub 2011 May 14. PMID: 21571534