A novel method for subarachnoid drug delivery in the medullary region of rats

This study describes a novel method for direct subarachnoid drug delivery to the medullary dorsal horn region of rats, without introducing a catheter. The reliability of the method was demonstrated by a pharmacological validation; that is, morphine administration to the medullary region blocked the nociceptive response to formalin injected in the temporomandibular joint (TMJ) region, an effect that was prevented by co-administration of naloxone. The method proposed offers many advantages over the existing methods for medullary drug delivery with catheter implantation. It is easy to be employed, it does not induce any sign of motor impairment, and it does not require the neck surgery performed to implant a catheter in the medullary dorsal horn region. Therefore, it is a useful method for subarachnoid drug delivery in behavioral trigeminal pain studies, particularly when nociceptive behavioral measures that require normal neck muscle activity to occur, such as head withdraw or head flinch, are evaluated.

The surgical treatment of chronic pain: destructive therapies in the spinal cord

Stereotactic pain surgery is accepted as a group of procedures. These are usually highly sophisticated and technically risky procedures. In practice, the most important part of this discipline is not the technical abilities of the surgeon, but selection of the most appropriate patients for the available procedures. We must remember that we are performing all these procedures with the cooperation of patients. The energy that is used for lesioning can be stopped when desired. The target we want to approach can be definitely and anatomically visualized and demonstrated, and the function of the target is evaluated with neurophysiologic impedance techniques and stimulation. Thus, if we are able to understand the language of the central nervous system, these are available, effective, and safe procedures in neurosurgical practice. We must remember that if intractable pain can be controlled by minimally invasive destructive techniques, the patients will not be dependent on implantable systems, drugs,and medical units. This independent lifestyle is a critical goal central to quality of life for patients having intractable pain.

The caudalis DREZ for facial pain

During a 3-year period, 25 caudalis dorsal root entry zone (DREZ) operations were done for severe, facial pain. Intraoperative brainstem recordings were done before and after DREZ in all patients. Primary diagnosis included refractory trigeminal neuralgia, atypical headaches or facial pain, posttraumatic closed head injuries, postsurgical anesthesia dolorosa, multiple sclerosis, brainstem infarction, postherpetic neuralgia and cancer-related pain. At the time of discharge, good to excellent pain relief was present in 24/25 patients and fair relief in 1. At 1 month, 19/25 (76%) patients had good to excellent results and at 3 months following surgery, 17/25 (68%) continued to have good to excellent pain relief. One year following surgery, 18 patients could be evaluated, 12/18 (67%) still considered their relief as good to excellent, 2 fair and 4 poor. Transient postoperative ataxia was present in 15/25 patients (60%), but was largely resolved at 1 months. In 3/18 (17%) patients, a degree of ataxia was still present at 1 year although in none was it disabling. Two patients had transient diplopia, and 3 had increased corneal anesthesia with 1 later developing a keratitis. No surgical or postsurgical mortality was noted. This procedure has proven to be a satisfactory treatment for many patients with debilitating facial pain syndromes with acceptable morbidity.

Differential effects of trigeminal tractotomy on Adelta- and C-fiber-mediated nociceptive responses

In this study we have tested in the rat, whether trigeminal tractotomy, which deprives the spinal trigeminal nucleus caudalis (Sp5C) of its trigeminal inputs, affected differentially nociceptive responses mediated by C- vs. Adelta-nociceptors from oral and perioral regions. Tractotomy had no effect on the threshold of the jaw opening reflex, induced by incisive pulp stimulation (Adelta-fiber-mediated), but blocked the formalin response (mainly C-fiber-mediated). These results suggest that nociceptive responses mediated by trigeminal C-fibers completely depend on the integrity of the Sp5C, while intraoral sensations triggered Adelta-fibers (especially of dental origin) are primarily processed in the rostral part of the spinal trigeminal nucleus.

Stereotactic trigeminal nucleotomy for dysesthetic facial pain

Trigeminal nucleotomy is a relatively simple, straightforward stereotactic procedure, acting at the deafferentation site, i.e., at the nucleus caudalis. Patients were operated on in a seated position, by a posterior suboccipital approach. Out of a series of 196 patients, 143 underwent trigeminal nucleotomy for deafferentation. Clinical diagnoses were 52 cases of postherpetic pain dysesthesia, 35 of anesthesia dolorosa, 46 of dysesthetic state with superimposed tic-like sequelae of trigeminal surgery performed elsewhere and 9 of posttraumatic neuropathy. Abolition of allodynia or marked reduction in, or disappearance of deep background pain was achieved in 72.0% of the cases overall. Results are analyzed for each clinical category. There were no side effects of any kind. Follow-up ranged from 4 to 17 years. This seems to be the procedure of choice for deafferentation facial pain.

The Duke experience with the nucleus caudalis DREZ operation

The nucleus caudalis DREZ operation has been performed in three phases at Duke. Between 1982 and 1988 radiofrequency (RF) lesions were made in the trigeminal nucleus extending from the C2 root to the obex using a straight electrode. Complications include ipsilateral arm ataxia due to spinocerebellar tract injury and ipsilateral lower limb weakness from the pyramidal tract. The former occurred at least transiently in 90% of cases. The electrode employed from 1988 to 1989 had proximal insulation protecting the spinocerebellar tract. Since 1989 a ninety degree bend has been added to the electrode to allow better placement. Two electrodes are used to accommodate the shape of the caudalis nucleus. A total of 101 procedures have been performed. The newest electrodes were used in 46 procedures. Ataxia is recognized in 39%. Overall pain relief was excellent in 34% and good in 40%. In post herpetic neuralgia 71% enjoyed excellent or good relief. Indications include post herpetic neuralgia, deafferentation pain (anaesthesia dolorosa, post-tic dysesthesia, stroke, MS, gasserian tumour, Gamma Knife radiation injury), facial trauma/surgery, atypical facial pain, and migraine/cluster headache. A study to compare this operation to deep brain stimulation prospectively for the above indications has been initiated.

Ultrasonic lesion of the trigeminal nucleus caudalis for deafferentation facial pain

The deafferentation facial pain syndrome, caused by physical, herpetic or tumourous lesions of the trigeminal sensory root, was successfully managed with ultrasonic trigeminal nucleotomy. The article presents this new surgical technique and its results in 14 patients suffering from severe facial pain and dysaesthesias.

A new design of radiofrequency lesion electrodes for use in the caudalis nucleus DREZ operation. Technical note

Two new right-angled electrodes have been designed for use at the dorsal root entry zone (DREZ) of the caudalis nucleus to provide relief of chronic facial pain. The electrode design was based on an anatomical study of the human caudalis nucleus at the cervicomedullary junction. Previously, caudalis nucleus DREZ operations were often followed by ipsilateral ataxia, usually in the arm. The new electrodes have significantly reduced this complication. A group of 21 patients with varied types of chronic facial pain have been treated, with pain relief in 70%.

Facial pain relieved by dorsal root entry zone lesions in the trigeminal nucleus caudalis: report of two cases

Microvascular decompression by suboccipital craniectomy often cures medically untreatable trigeminal neuralgia. However, pain involving the same distribution persists in a few patients despite surgical treatment. In two cases, one with postherpetic pain and the other with tic douloureux, the author used the radiofrequency lesion technique in the dorsal root entry zone of the trigeminal nucleus caudalis to treat the surgically-failed cases of trigeminal neuralgia. The pain ceased postoperatively and has not recurred during three to four years of follow-up. Trigeminal nucleus caudalis surgery provides a satisfactory solution to this relatively rare pain syndrome.

Facial pain due to vascular lesions of the brain stem relieved by dorsal root entry zone lesions in the nucleus caudalis. Report of two cases

One patient with a pontine infarct due to a fusiform basilar artery aneurysm and one with an arteriovenous malformation within the tectum of the mesencephalon developed intractable facial pain. This pain was relieved in both patients by radiofrequency lesions in the dorsal root entry zone of the trigeminal nucleus caudalis.