Biomimetic tissue phantoms for neurosurgical near-infrared fluorescence imaging.

Significance: Neurosurgical fluorescence imaging is a well-established clinical approach with a growing range of indications for use. However, this technology lacks effective phantom-based tools for development, performance testing, and clinician training. Aim: Our primary aim was to develop and evaluate 3D-printed phantoms capable of optically and morphologically simulating neurovasculature under fluorescence angiography. Approach: Volumetric digital maps of the circle of Willis with basilar and posterior communicator artery aneurysms, along with surrounding cerebral tissue, were generated. Phantoms were fabricated with a stereolithography printer using custom photopolymer composites, then visualized under white light and near-infrared fluorescence imaging. Results: Feature sizes of printed components were found to be within 13% of digital models. Phantoms exhibited realistic optical properties and convincingly recapitulated fluorescence angiography scenes. Conclusions: Methods identified in this study can facilitate the development of realistic phantoms as powerful new tools for fluorescence imaging.

FDA Regulation of Neurological and Physical Medicine Devices: Access to Safe and Effective Neurotechnologies for All Americans.

The United States Food and Drug Administration (FDA) ensures that patients in the U.S. have access to safe and effective medical devices. The Division of Neurological and Physical Medicine Devices reviews medical technologies that interface with the nervous system. This article addresses how to navigate the FDA's regulatory landscape to successfully bring medical devices to patients.

Experience with 25 years of dorsal root entry zone lesioning at a single institution.

BACKGROUND: The authors sought to assess long-term efficacy, surgical morbidity, and postoperative quality of life in patients who have undergone dorsal root entry zone (DREZ) lesioning. METHODS: We utilized the electronic chart system at our institution to identify patients who underwent DREZ lesioning since 1986. Of the patients that were able to be identified, 19 (12 males and 7 females) patients were able to be contacted at time of data collection. The mean age was 47 years (ranging from 23 to 70 years) with average preoperative pain duration of 12.5 years and average follow-up of 4.9 years. RESULTS: Of the 19 patients we were able to contact, 7 (37%) patients experienced "excellent" postoperative (complete) pain relief with another 6 (32%) reporting "good" improvement. Three (16%) patients reported "mild" pain relief, while three (16%) patients reported poor results. Sixteen patients (84%) stated they would undergo DREZ lesioning again, if given a choice. Two patients (11%) had objective evidence of a new, mild motor deficit postoperatively. More than half of the patients, who answered, reported "good" quality of life. Two-sample unequal variance t-test showed no statistically significant difference in pain improvement between brachial plexus avulsion and end-zone spinal cord injury pain. CONCLUSION: With appropriate patient selection, DREZ lesioning is an efficacious and durable procedure that can be performed with low morbidity and good patient outcomes.

Seizure freedom off antiepileptic drugs after temporal lobe epilepsy surgery.

Data are limited on seizure recurrence after antiepileptic drug (AED) discontinuation in operated seizure-free patients. We reviewed seizure outcome in patients who came off AEDs after being seizure-free for 2 years following temporal lobe surgery in our center. Thirty-nine (68%) of 57 patients who discontinued AED therapy remained seizure-free. They had a younger age at surgery than the group with seizure recurrence (p=0.01). Earlier surgery may be a favorable predictor for seizure freedom after AED discontinuation.

Studies in autotomy: its pathophysiology and usefulness as a model of chronic pain.

An interesting behavioral syndrome results in animals from the same or similar types of lesions that lead to deafferentation pain in humans; many neurectomized animals begin to scratch, bite, or self-mutilate their denervated limb, a phenomenon termed autotomy. The proposition that this behavior in animals is a response to the chronic pain of peripheral nerve injury has met with considerable controversy. If this issue were resolved, then a better understanding of the neurophysiology of autotomy might help elucidate the mechanisms of the human conditions. To determine the association between deafferentation and the autotomy behavior, we developed a pharmacologically induced functional deafferentation preparation using chronic perineural lidocaine infusion of the sciatic nerve. This 'chronic lidocaine' model's behavior was compared with that of the neurectomy model. While autotomy was noted in 80% of the latter group, no animal undergoing a chronic perineural infusion of lidocaine autotomized. We thus conclude that autotomy is not a response to non-painful sensory deafferentation, but rather that this behavior is a response to pain. We also studied the development of autotomy in a variety of other focal denervation preparations. On the basis of these data, we conclude that autotomy is not due to loss of sensory input on a functional basis nor to an action potential-mediated process. Rather, nerve damage which coincidentally involves sensory loss is necessary and sufficient for the development of this behavior. We suggest that interruption of a humoral feedback process homeostatically operating within the first order sensory neuron with its effect exerted post-synaptically leads to autotomy. The evidence supports the existence of a loss of a transportable, humoral autotomy inhibitory factor.

Comparison of subjective and objective analgesic effects of intravenous and intrathecal morphine in chronic pain patients by heat beam dolorimetry.

The pain tolerance latencies of 10 chronic pain patients were evaluated by heat beam dolorimetry (stimulus intensity 15.33 mW.cm-2.sec-1) prior to and following administration of morphine by intrathecal (n = 5) or intravenous (n = 5) routes. Patients not undergoing opiate withdrawal evinced increased baseline pain tolerance latencies prior to drug administration compared with normal volunteers. Two patients undergoing the opiate withdrawal syndrome at the time of test experienced reduced pain tolerance latencies compared with normal volunteers, most probably corresponding to the hyperesthesia symptom of the syndrome. Intravenous morphine infusion (30 mg) induced a time-dependent increase in cutaneous pain tolerance with peak effect occurring 1-2 h after administration. This persisted for up to 4 h and thereafter declined. The time course of subjective pain self-report by visual pain analog scale (VPAS) measurements corresponded to the time course of increasing cutaneous pain tolerance latency assessed by dolorimetry. Pain self-reports following intrathecal morphine infusion (2.25 or 1 mg) followed a similar though slower onset to that reported by patients receiving intravenous morphine and was of lesser degree. In contrast, heat beam dolorimetric evidence of increased cutaneous pain tolerance (which was of lesser degree than following i.v. morphine) did not reach its maximum during the 4 h measuring period. A dissociation was noted therefore between the self-reported relief of endogenous pain and dolorimetrically measured cutaneous analgesia following intrathecal morphine administration. Linear regression correlation analysis characterized this phenomenon as a positive correlation between cutaneous pain tolerance and pain relief self-report following intravenous morphine infusion and a negative correlation following intrathecal administration. We propose that the phenomenon may be due to intrathecal morphine acting via two separate compartments: one spinal and one supraspinal.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic pain assessment using heat beam dolorimetry.

The heat beam dolorimeter (HBD) was developed to evaluate cutaneous pain thresholds in humans. In the present study, the hypothesis that a patient's underlying pain status affects his pain tolerance to an incident HBD stimulus was tested. Twenty-seven chronic pain patients with a variety of clinical problems unresponsive to conventional algological therapy were scheduled for neurosurgical procedures. These patients were evaluated pre- and postoperatively by the HBD procedure. On initial testing, drug-free pain patients showed significantly higher pain tolerance thresholds than normal volunteers (P less than 0.02, Mann-Whitney U test). Postoperatively, incident pain tolerance thresholds in the HBD test were reduced from pre-surgical levels in these patients and were indistinguishable from the second evaluation latencies of volunteers (P greater than 0.05). Twenty-four of the 27 patients reported significant pain relief following surgery. Our results show that, in chronic pain patients, endogenous pain significantly affected incident pain perception in the HBD test when compared with the responses of normal pain-free volunteers. Consequently, HBD may be useful in objectively assessing chronic pain and its relief by neurosurgical procedures.