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Necrotizing Teflon Granuloma After Microvascular Decompression and Gamma Knife

Microvascular decompression surgery is a commonly performed operation for the treatment of trigeminal neuralgia in which the culprit vessel is mobilized away from the trigeminal nerve root and held in place by a Teflon implant. Although generally considered to be an inert substance, the Teflon implant used inmicrovascular decompression surgery has been implicated in rare instances of granuloma formation following implantation. We report a case of a 77-year-old female with remote history of breast cancer and mastectomy who was referred to our center for evaluation and treatment of an unusual mass lesion located in the posterior fossa (Figure 1). She had an onset of trigeminal neuralgia beginning in 2000 for which she underwent a microvascular decompression in 2006; a shredded Teflon felt implant was placed between the culprit superior cerebellar artery and the underlying trigeminal nerve root. Of note, we occasionally use fibrin glue in conjunction with the shredded Teflon implant; however, this was not used in this case and not used routinely. She received limited pain relief and in 2007 underwent a Gamma Knife procedure in which an 80-Gy dose was prescribed to the proximal trigeminal nerve root. Neither computed tomography nor magnetic resonance imaging demonstrated any abnormality aside from the Teflon implant. She experienced minimal, delayed pain relief, and continued with medical management until undergoing radiofrequency rhizotomy in 2009, which provided minimal pain relief. This also resulted in corneal anesthesias and 80% preservation of sensation in V1 and V2 distributions and full preservation of V3. Over the ensuing years, she developed a progressive full sensory loss of all three trigeminal nerve distributions, temporalis and masseter muscle atrophy, accompanied by alleviation of her neuralgia. In 2015, she developed a progressive gait ataxia with magnetic resonance imaging revealing a lobulated, enhancing 2.2 × 1.8× 1.6 cm mass in the region of the previously inserted Teflon implant along with significant edema involving adjacent brain. Based on the clinical presentation and imaging findings, the differential diagnosis included metastasis, meningioma, chronic infectious process involving Teflon implant, inflammatory or granulomatous lesion, and radiation-induced pathology. Given her progressive gait ataxia along with unknown diagnosis, we elected to proceed with posterior fossa exploration through a retrosigmoid craniectomy with the goal of alleviation of mass effect and tissue sampling for diagnosis. The lesion was noted to have a firm capsule surrounding the inner contents of the tumor, consisting of soft white material intermixedwith the Teflon implants. The lesionwas adherent to the cerebellum, pons, trigeminal root entry zone, and superior cerebellar artery. After internal debulking and meticulous dissection of the tumor from the neurovascular structures, a thin rim of residual tumor was left adherent to the nerve and superior cerebellar artery. The patient tolerated the procedure well and left hospital after several days with no new deficits. At 6-month follow-up, she reported a mild improvement of her gait instability however still required the use of a four-wheel walker for mobility. Neuropathology investigation revealed mixed inflammatory infiltrates in a dense collagenous tissue (Figure 2). The infiltrate was composed of lymphocytes, histiocytes, neutrophils, and plasma cells. Multiple necrotic foci were noted, which were likely associated with previous Gamma Knife treatment. No microorganisms were demonstrated on both hematoxylin and eosin stain, as well as special stains for bacterial (Gram stain), fungal (Grocott’s methenamine silver stain), or mycobacterial (Ziehl-Neelsen stain). Based on the absence of microorganisms, it is reasonable to conclude that granulomatous inflammation was associated with the Teflon implant. This case represents an interesting presentation, management, and histopathology of a rarely reported lesion associated with a Teflon implant several years after microvascular decompression and