✓ Electrical stimulation of dental pulp is widely acknowledged to produce a sensation that is predominantly or exclusively noxious in character. The authors report the pattern of local cerebral glucose utilization evoked by dental-pulp stimulation in the barbiturate-anesthetized rat, using the [14C]2-deoxyglucose method of Sokoloff. Autoradiographs were prepared from cryostat-cut brain sections of animals given an intravenous pulse of [14C]2-deoxyglucose and sacrificed after 45 minutes of continuous bipolar stimulation of the incisor tooth pulp. Areas of high optical density on the autoradiographs identified brain regions where glucose consumption, and hence functional activity, was maximal. Stimulus-related increases in glucose utilization were seen ipsilaterally in an uninterrupted column from the lower levels of trigeminal nucleus caudalis to the rostral extent of the main sensory nucleus. Mandibular incisor pulp stimulation yielded increased deoxyglucose uptake in relatively restricted dorsal portions of the nuclei, while maxillary pulp stimulation produced a more extensive area of uptake ventrally. Elevated deoxyglucose uptake was also seen in the contralateral ventrobasal thalamus and sensory cortex with maxillary, but not mandibular, pulp stimulation. No changes in metabolic activity were detected in extralemniscal or limbic structures. These initial results suggest that the [14C]2-deoxyglucose method may be a useful means of mapping central structures involved in nociception.
Andrew G. Shetter and William H. Sweet
Howard H. Ginsburg, Andrew G. Shetter and Peter A. Raudzens
✓ Intraoperative somatosensory evoked potentials (SSEP's) are being used with increasing frequency to monitor neurological function during spinal surgery. The authors report a case of postoperative paraplegia that occurred despite preserved intraoperative SSEP's in an achondroplastic dwarf who underwent correction of a congenital kyphoscoliosis. Surgeons and anesthesiologists involved with SSEP monitoring should be aware that false-negative results may occur with this technique.
Peter A. Raudzens and Andrew G. Shetter
✓ Intraoperative brain-stem auditory evoked potentials (BAEP's) were monitored in 46 patients undergoing intracranial surgery for a variety of pathological conditions to determine whether this technique was capable of providing useful information to the operating surgeon. Intraoperative BAEP's were unchanged throughout surgery in 34 patients (74%), and these individuals had no postoperative hearing deficits. Four patients (9%) developed an abrupt ipsilateral loss of all waveform components beyond Wave I and had postoperative evidence of a pronounced hearing loss in the affected ear. An additional patient demonstrated BAEP loss contralateral to the side of surgery, and this was associated with subsequent signs of severe brain-stem dysfunction. Seven patients (15%) developed intraoperative delays of BAEP waveform latency values, but maintained recognizable waveforms beyond Wave I. Postoperatively, their hearing was either normal or mildly impaired, and there were no indications of other brain-stem abnormalities. This group represents the individuals who may have been benefited by evoked potential monitoring, since corrective surgical measures were taken when latency delays were observed. Intraoperative BAEP's can be reliably and routinely recorded in an operating room environment. They provide a good predictor of postoperative auditory status, and may have prevented permanent neurological deficits in a small segment of patients by alerting the surgeon to potentially reversible abnormalities.
Andrew G. Shetter, Joseph M. Zabramski and Burton L. Speiser
Object. The authors sought to determine whether the results of trigeminal microvascular decompression (MVD) are influenced by prior gamma knife surgery (GKS).
Methods. Gamma knife surgery is an established procedure for treating medically intractable trigeminal neuralgia but failures do occur. The authors assessed six patients (two men and four women; mean age 52 years) who experienced pain recurrence after GKS and elected to undergo trigeminal MVD via retrosigmoid craniotomy. Three patients underwent a single GKS to a maximal dose of 80 Gy, whereas three others underwent a second GKS to total of 120 to 135 Gy.
At surgery, none of the six patients demonstrated excess arachnoid thickening, grossly apparent changes in the nerve itself, or any other tissue alterations that made successful mobilization of a blood vessel from the trigeminal root entry zone technically more difficult. A single individual had a small atherosclerotic plaque in the superior cerebellar artery near its contact point with the trigeminal nerve. Follow up at a mean of 25.4 months (range 7.5–42 months) indicated that five patients were pain free. One patient had improved but still relied on medications for pain control.
Conclusions. In the authors' experience, trigeminal MVD can be performed without added difficulty in patients who have previously undergone GKS. The success rates seem similar to those normally associated with MVD. Patients who elect the less invasive option of GKS can be assured that trigeminal MVD remains a viable alternative at a later date if further surgery is required.
James J. Zhou, Tsinsue Chen, S. Harrison Farber, Andrew G. Shetter and Francisco A. Ponce
The field of deep brain stimulation (DBS) for epilepsy has grown tremendously since its inception in the 1970s and 1980s. The goal of this review is to identify and evaluate all studies published on the topic of open-loop DBS for epilepsy over the past decade (2008 to present).
A PubMed search was conducted to identify all articles reporting clinical outcomes of open-loop DBS for the treatment of epilepsy published since January 1, 2008. The following composite search terms were used: (“epilepsy” [MeSH] OR “seizures” [MeSH] OR “kindling, neurologic” [MeSH] OR epilep* OR seizure* OR convuls*) AND (“deep brain stimulation” [MeSH] OR “deep brain stimulation” OR “DBS”) OR (“electric stimulation therapy” [MeSH] OR “electric stimulation therapy” OR “implantable neurostimulators” [MeSH]).
The authors identified 41 studies that met the criteria for inclusion. The anterior nucleus of the thalamus, centromedian nucleus of the thalamus, and hippocampus were the most frequently evaluated targets. Among the 41 articles, 19 reported on stimulation of the anterior nucleus of the thalamus, 6 evaluated stimulation of the centromedian nucleus of the thalamus, and 9 evaluated stimulation of the hippocampus. The remaining 7 articles reported on the evaluation of alternative DBS targets, including the posterior hypothalamus, subthalamic nucleus, ventral intermediate nucleus of the thalamus, nucleus accumbens, caudal zone incerta, mammillothalamic tract, and fornix. The authors evaluated each study for overall epilepsy response rates as well as adverse events and other significant, nonepilepsy outcomes.
Level I evidence supports the safety and efficacy of stimulating the anterior nucleus of the thalamus and the hippocampus for the treatment of medically refractory epilepsy. Level III and IV evidence supports stimulation of other targets for epilepsy. Ongoing research into the efficacy, adverse effects, and mechanisms of open-loop DBS continues to expand the knowledge supporting the use of these treatment modalities in patients with refractory epilepsy.
Conrad T. E. Pappas, Joseph M. Zabramski and Andrew G. Shetter
✓ An unusual case of an iatrogenic dural arteriovenous fistula is reported. The patient presented with a history of progressive generalized headache over a period of 3 to 4 weeks. Computerized tomography demonstrated a chronic subdural hematoma that was successfully evacuated by burr-hole drainage. The patient's postoperative course was complicated by recurrent acute subdural hematomas at the drainage site. Coagulation studies were unremarkable. Selective external carotid angiography demonstrated a small dural arteriovenous fistula adjacent to the burr hole used for the initial operative procedure. Extension of the bone flap and coagulation of the fistula resulted in a good outcome. In the patient with recurrent acute subdural hematoma, the possibility of a vascular malformation must be considered. Selective internal and external carotid angiography is key to the correct diagnosis.
Colin J. Przybylowski, Tyler S. Cole, Jacob F. Baranoski, Andrew S. Little, Kris A. Smith and Andrew G. Shetter
The objective of this study was to assess long-term outcomes of facial pain and numbness after radiosurgery for multiple sclerosis (MS)–related trigeminal neuralgia (MS-TN).
The authors conducted a retrospective review of their Gamma Knife radiosurgeries (GKRSs) to identify all patients treated for MS-TN (1998–2014) with at least 3 years of follow-up. Treatment and clinical data were obtained via chart review and mailed or telephone surveys. Pain control was defined as a facial pain score of I–IIIb on the Barrow Neurological Institute (BNI) Facial Pain Intensity Scale. Kaplan-Meier analysis was performed to determine the rates of pain control after index and first salvage GKRS procedures. Patients could have had more than 1 salvage procedure. Pain control rates were based on the number of patients at risk during follow-up.
Of the 50 living patients who underwent GKRS, 42 responded to surveys (31 women [74%], median age 59 years, range 32–76 years). During the initial GKRS, the trigeminal nerve root entry zone was targeted with a single isocenter, using a 4-mm collimator with the 90% isodose line completely covering the trigeminal nerve and the 50% isodose line abutting the surface of the brainstem. The median maximum radiation dose was 85 Gy (range 50–85 Gy). The median follow-up period was 78 months (range 36–226 months). The rate of pain control after the index GKRS (n = 42) was 62%, 29%, 22%, and 13% at 1, 3, 5, and 7 years, respectively. Twenty-eight patients (67%) underwent salvage treatment, including 25 (60%) whose first salvage treatment was GKRS. The rate of pain control after the first salvage GKRS (n = 25) was 84%, 50%, 44%, and 17% at 1, 3, 5, and 7 years, respectively. The rate of pain control after the index GKRS with or without 1 salvage GKRS (n = 33) was 92%, 72%, 52%, 46%, and 17% at 1, 3, 5, 7, and 10 years, respectively. At last follow-up, 9 (21%) of the 42 patients had BNI grade I facial pain, 35 (83%) had achieved pain control, and 4 (10%) had BNI grade IV facial numbness (very bothersome in daily life).
Index GKRS offers good short-term pain control for MS-TN, but long-term pain control is uncommon. If the index GKRS fails, salvage GKRS appears to offer beneficial pain control with low rates of bothersome facial numbness.
C. Leland Rogers, Andrew G. Shetter, Francisco A. Ponce, Jeffrey A. Fiedler, Kris A. Smith and Burton L. Speiser
Object. The authors assessed the efficacy and complications from gamma knife radiosurgery (GKS) for multiple sclerosis (MS)-associated trigeminal neuralgia (TN).
Methods. There were 15 patients with MS-associated TN (MS—TN). Treatment involved three sequential protocols, 70 to 90-Gy maximum dose, using a single 4-mm isocenter targeting the ipsilateral trigeminal nerve at its junction with the pons with the 50% isodose. Pain was appraised by each patient by using Barrow Neurological Institute (BNI) Scores I through IV: I, no pain; II, occasional pain not requiring medication; IIIa, no pain but continued medication; IIIb, some pain, controlled with medication; IV, some pain, not controlled with medication; and V, severe pain/no pain relief.
With a mean follow up of 17 months (range 6–38 months), 12 (80%) of 15 patients experienced pain relief. Three patients (20%) reported no relief (BNI Score V). For responders, the mean latency from treatment to the onset of pain relief was 13 days (range 1–61 days). Maximal relief was achieved after a mean latency of 56 days (range 1–157 days). Five patients underwent a second GKS after a mean interval of 534 days (range 231–946 days). The mean maximum dose at this second treatment was 48 Gy. The target was unchanged from the first treatment. All five patients who underwent repeated GKS improved. Complications were limited to delayed facial hypesthesias. Two (13%) of 15 patients experienced onset of numbness after the first GKS, as well as two of five patients following a second GKS. The patients found this mild and not bothersome. Each patient who developed hypesthesias also experienced complete pain relief.
Conclusions. Gamma knife radiosurgery is an effective treatment for MS—TN. Radiosurgery carries an acceptable small risk of mild facial hypesthesias, and hypesthesia appears predictive of a favorable outcome.
Andrew G. Shetter, C. Leland Rogers, Francisco Ponce, Jeffrey A. Fiedler, Kris Smith and Burton L. Speiser
Object. Pain may fail to respond or may recur after initial gamma knife radiosurgery (GKS) for trigeminal neuralgia (TN). The authors examined their experience with performing a second GKS procedure in these patients.
Methods. Twenty-nine patients underwent repeated GKS for TN at our institution between March 1997 and March 2002. Questionnaires were mailed to patients to assess the degree of their pain relief and the extent of facial numbness. Nineteen patients responded. All patients underwent repeated GKS involving a single 4-mm isocenter directed at the trigeminal nerve as it exited the brainstem (mean maximum dose 23.2 Gy). At a mean follow up of 13.5 months after the second procedure, 10 patients (53%) were pain free and medication free. Four patients (21%) were pain free but elected to continue medication in reduced dose, and two patients (11%) had incomplete but satisfactory pain control and were still taking medication. There was new-onset facial numbness in eight patients (42%), rated as tolerable in all instances.
Conclusions. Patients with facial numbness had a greater likelihood of being pain free than those with no sensory loss. The authors observed no cases of corneal anesthesia, keratitis, or deafferentation pain.