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Daniel C. Rohrer, Kim J. Burchiel and David P. Gruber

✓ A diverse collection of unverified theories as to the etiology of extradural meningeal cysts have been previously proposed. One case of intraspinal extradural meningeal cyst of the thoracolumbar region is presented in which a ball-valve mechanism involving an idiopathic dural rent and a herniated segment of an underlying dorsal rootlet was suggested by the operative findings. Closure of the dural rent with marsupialization of the meningeal cyst obliterated this extradural lesion. The ball-valve mechanism of formation and other previously proposed theories are discussed.

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Kim J. Burchiel

✓ Sixty patients with trigeminal neuralgia or atypical facial pain were followed for an average of 1 year after percutaneous retrogasserian glycerol rhizolysis. The procedure was initially effective in relieving pain in 80% of the patients with typical trigeminal neuralgia and symptomatic trigeminal neuralgia secondary to multiple sclerosis. However, life-table analysis indicated that 50% of this group had persistence or recurrence of pain within 18 months after the operation. Percutaneous retrogasserian glycerol rhizolysis was ineffective in relieving atypical trigeminal neuralgia or atypical facial pain. Minor complications occurred in 23% of patients, and major morbidity was seen in 1.6%. Facial sensory loss which persisted for more than 1 month was found in 72% of patients, corneal hypesthesia occurred in 15%, and an additional 7% had corneal anesthesia. The data indicate that the success of percutaneous retrogasserian glycerol rhizolysis in relieving trigeminal neuralgia is directly related to the production of facial sensory loss.

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Kim J. Burchiel, Hadley Clarke, Michael Haglund and John D. Loeser

✓ Forty patients were followed for an average period of 8½ years after 44 consecutive suboccipital craniotomies for trigeminal neuralgia. Among these patients, 36 had microvascular decompression (MVD) of the nerve, four had repeat trigeminal rhizotomy after MVD was not successful in controlling their pain, and four had primary trigeminal rhizotomies. Of the 36 patients undergoing MVD, 17 (47%) experienced recurrent postoperative neuralgic pain: in 11 (31%) pain recurrence was major, and in six (17%) it was minor. Among the eight patients undergoing rhizotomy, four (50%) had major pain recurrences and one (13%) had a minor recurrence, for a 63% total recurrence rate. There was a strong statistical relationship between an operative finding of arterial cross-compression of the nerve and long-term complete pain relief. Patients with other compressive pathology (related to veins or bone structures) did not on the average fare as well. Despite this, there appeared to be no point in time in the postoperative interval when the patient could be considered “cured.” Major recurrences averaged 3.5% annually, and minor recurrences averaged 1.5% annually. The implications of these findings for the treatment of trigeminal neuralgia and the current understanding of the mechanism of MVD for this disorder are discussed.

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Terrence L. Pencek and Kim J. Burchiel

✓ Although it is well documented that retained foreign bodies are associated with delayed intracranial abscess, there are few reports of anaerobic organism growth. A case is presented in which a left parieto-occipital abscess surrounded a metallic fragment implanted when a mortar shell exploded in Vietnam 15 years before. The diagnostic evaluation and surgical management of this case are presented.

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Kim J. Burchiel and Lisa C. Russell

✓ The effect of topical glycerol application on normal and previously injured saphenous nerves was tested in 20 Sprague-Dawley rats. Anhydrous glycerol treatment of five normal nerves showed a rapid loss of C-fiber conduction within 5 minutes of application, while after 10 to 30 minutes, a complete conduction blockade in all fiber types was produced. The effect of anhydrous glycerol on both spontaneous firing from the neuroma and impulse propagation within the nerve was examined in 11 rats that had undergone saphenous neurotomy 7 days previously. In these animals, cessation of spontaneous action potential production from the neuroma was the earliest electrophysiological change noted, followed by loss first of C-fiber, then of A-fiber conduction. Graded concentrations of glycerol (25%, 50%, 75%, and 100%) were used in four rats with saphenous neuromas, which allowed selective blockade of spontaneous action potential generation and C-fiber conduction with minimal effect on A-fibers.

The neurophysiological mechanism of glycerol neurolysis appears to be a nonspecific conduction blockade of large and small fibers, which is established within minutes of its application. Spontaneous firing within damaged axons, which may play a role in a variety of cranial and peripheral nerve sensorimotor syndromes, is also exquisitely sensitive to glycerol application.

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Kim J. Burchiel and Lisa C. Russell

✓ Thirty-five Sprague-Dawley rats with saphenous neuromas underwent acute microfilament recording in the proximal nerve. The effect of the potassium channel-blocking agents, tetraethylammonium bromide (TEA) and 4-aminopyridine, on spontaneous activity in A fibers terminating in the neuroma was observed. The effects of gallamine were also tested. Of the two channel-blocking agents, TEA reliably increased spontaneous firing in active fibers and initiated spontaneous activity in some fibers with no spontaneous baseline discharge. 4-Aminopyridine had no effect on baseline activity of either spontaneously active or quiescent fibers; however, it inhibited spontaneous activity induced by prior TEA treatment. Gallamine application produced effects similar to TEA in that spontaneous activity was dramatically increased. These results imply that a tonic potassium conductance is present in regenerating fibers in the neuroma and that this conductance moderates the tendency toward hyperexcitability and spontaneous firing. Spontanous activity in nociceptive afferent fibers may represent the mechanism of chronic pain and paresthesias that often accompany peripheral nerve injury. These results suggest that agents which either increase potassium conductance or selectively inhibit the sodium current in regenerating axons might be effective in the treatment of these chronic pain syndromes.

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Kim J. Burchiel and Lisa C. Russell

✓ In 18 Sprague-Dawley rats, the left sciatic nerve was divided at the mid-femur level. Seven to 9 days later, microfilament recordings were made from the ipsilateral L-5 ventral root. Spontaneous activity in the ventral root, ranging from 0.1 to 6.1 Hz, was recorded in 12 of the 18 animals. Conduction velocity determinations showed this activity to be in A-beta and A-delta fibers. Recordings in 10 normal L-5 ventral roots from five control rats showed no spontaneous activity. In the rats with sciatic nerve division, the ongoing discharge appeared to originate in the cut end of the nerve since mechanical stimulation of the neuroma produced synchronous ventral root activity. Furthermore, cooling of the neuroma inhibited the spontaneous discharge, whereas with rewarming it returned. Spontaneous ventral root activity was also increased by systemic application of epinephrine. This activity was qualitatively similar to spontaneous activity that has been recorded in dorsal root microfilaments after peripheral nerve injury. The observation of an ongoing discharge in potentially nociceptive ventral root axons subsequent to nerve injury may be relevant to the mechanism of chronic pain of peripheral origin.

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Brien Vlcek, Kim J. Burchiel and Thomas Gordon

✓ Subacute paraplegia progressing over 3 months due to spinal cord compression was the presenting symptom of tuberculous meningitis in this patient with a normal chest x-ray film and no radiological or autopsy evidence of Pott's vertebral tuberculosis. The obstructive myelopathy was the result of proliferative granulomatous meningitis. A review of the literature indicates that this is a very unusual presentation of tuberculous meningitis.

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Kim J. Burchiel, Cheng-Mei Shaw and William A. Kelly

✓ The authors describe a case of a mixed prolactin- and somatotropin-secreting pituitary adenoma and ganglioneuroma of the pituitary fossa in a patient with galactorrhea, hyperprolactinemia, and headaches. Histological and electron microscopic findings were typical for each element of the tumor, but the finding of a ganglioneuroma within the pituitary fossa is unusual; even more unusual was its proximity to an apparently unrelated tumor in the same location. The clinical, radiological, endocrinological, and pathological findings are discussed.