Single-stage posterior vertebrectomy and replacement combined with posterior instrumentation for spinal metastasis.

The authors present a series of 25 patients who underwent single-stage complete spondylectomy, vertebral body reconstruction, and posterior segmental spinal stabilization for malignant metastatic disease involving multiple columns of the thoracolumbar spine. Patients were selected for this approach primarily because they were poor candidates for a transcavitary or lateral extracavitary approach or because the tumor involved both anterior and posterior columns of the spine. The operative approach used combines radical local resection of tumor via a bilateral transpedicular route, methylmethacrylate vertebral body reconstruction, and Luque rectangle stabilization in a single operation. Following surgery, the majority of patients experienced improvement in their neurological status, reduction in pain, or both. Most patients were functionally improved, or at least no worse, and spinal alignment was maintained in all. There was one local recurrence in a long-term survivor. Complications included cerebrospinal fluid fistulas, migrating graft material, and wound healing problems. The authors conclude that this surgical approach is safe and feasible for the radical resection of vertebral metastasis when combined with reconstruction and stabilization. This technique represents a useful alternative to other commonly used surgical approaches for the treatment of spinal metastases, and it should aid surgeons in selecting the optimum approach for individual patients.

Primitive neuroectodermal tumor of the median nerve. Case report with cytogenetic analysis.

The authors describe a malignant peripheral primitive neuroectodermal tumor (PNET) that originated in the median nerve in an elderly adult. After the diagnosis was made by biopsy, the patient underwent radical local resection with interpositional vein grafting of the brachial artery. The tumor had the typical appearance of a primitive neural tumor with small, round cells forming rosettes. It stained positively for both the Ewing's sarcoma/peripheral PNET antigen (HBA-71) and neuron-specific enolase, confirming its neural origin. Ultrastructural examination revealed dense core granules and suggested neural differentiation of the neoplasm. Cytogenetic analysis suggested a chromosome (11;22) translocation typical of peripheral PNET. Early reports consisted of tumors arising solely in peripheral nerves, but recent series have focused mainly on tumors arising in the soft tissues other than nerves. There are no other cases of true PNET of peripheral nerve in the modern literature that have been fully characterized by immunohistochemical, ultrastructural, and cytogenetic criteria. Although peripheral PNETs occur more commonly in children, this unusual neoplasm should be considered in the differential diagnosis of peripheral nerve neoplasms in adults. Early diagnosis is desirable because of its aggressive nature and poor outcome.

Management of benign and aggressive intracranial meningiomas.

Usually considered benign tumors, meningiomas can display aggressive behavior characterized by multiple recurrences and invasion of the brain, dura, and adjacent bone. The aggressive or malignant phenotype is difficult to characterize due to the broad spectrum of behaviors exhibited by meningiomas. Recent classification schemes based on features of anaplasia rather than histopathology have been used successfully to identify meningiomas that exhibit features of the aggressive phenotype. Some such tumors can be identified preoperatively by radiographic characteristics. Surgery is the cornerstone of treatment for all types of meningiomas. Conventional radiation therapy is beneficial for patients with recurrent (or incompletely resected) benign meningiomas and is recommended for those with aggressive and malignant meningiomas. Stereotactic radiation and interstitial brachytherapy are useful in some refractory or recurrent meningiomas. Traditional chemotherapeutic agents are not very effective against meningiomas, but hormonal manipulation is under study for patients with inoperable tumors or those who are medically unsuitable for surgery.

Processing of splanchnic and somatic input in thoracic spinal cord of the rat.

To better understand the spinal transmission of visceral afferent information, we conducted neurophysiological studies of single spinal neurons that receive input from the greater splanchnic nerve (GSN). Extracellular single-neuron recordings were made in the thoracic spinal cord of chloralose-anesthetized, paralyzed, and artificially ventilated rats, some of which had undergone acute spinal transection at C1. Neurons were divided into four classes according to their responses to GSN stimulation: one-burst excitatory, two-burst excitatory, biphasic, and inhibited. We then studied the characteristics of the convergent somatic input to each class of neurons using either natural somatic stimuli or electrical stimulation of the iliohypogastric nerve (IHN). Most splanchnic input was mediated by unmyelinated fibers, whereas somatic input was mediated by both unmyelinated and small myelinated fibers. Most of the neurons exhibited somatic receptive fields, and the majority responded to both innocuous and noxious somatic stimuli. However, a small number could be excited only by GSN stimulation. Although a careful analysis of response characteristics indicated that there was a tendency for neurons to exhibit similar responses to electrical stimulation of the GSN and the IHN, we observed many combinations of somatic and visceral responses. We suggest that visceral afferent activity, in addition to being processed via convergent somatovisceral pathways, may be processed by neurons that convey only visceral information or by neurons in which visceral and somatic information is differentially coded.

Splanchnic and somatic afferent convergence on cervical spinal neurons of the rat.

The rostral cervical spinal cord is increasingly being considered the source of important propriospinal regulation. To better understand the substrate for this function, we investigated the effects of stimulation of the greater splanchnic nerve (GSN) and both thoracic and cervical somatic afferents on the activity of cervical spinal neurons. Extracellular single-neuron recordings were made in the C2-C5 spinal segments of chloralose-anesthetized, paralyzed, and artificially ventilated rats. Neurons were classified according to their responses to GSN stimulation. Neurons were inhibited by this stimulation as frequently as they were excited. We then studied the characteristics of cervical and thoracic convergent somatic input to each class of neurons. Although all cervical neurons that responded to GSN stimulation responded to electrical stimulation of the iliohypogastric nerve (IHN), only the few neurons that exhibited whole body receptive fields (RF) responded to natural thoracic somatic stimuli. Responses to electrical stimulation of the GSN and IHN were similar for most neurons; most exhibited nociceptive cutaneous RFs in cervical dermatomes. These data indicate that input from cervical somatic afferents and from both thoracic visceral and thoracic somatic afferents converge on individual splanchnic-receptive cervical neurons. Although these neurons exhibited the predicted cervical somatic RFs, responses from thoracic levels did not exhibit discrete RFs, requiring instead more synchronous or more spatially convergent input.

Medial medullary contribution to tonic descending inhibition of visceral input.

In the present study, we sought to define the extent and source of tonic descending modulation of spinal neurons receiving visceral input from the afferent renal nerve (ARN). Spinal gray neurons responding to stimulation of the ARN in 64 chloralose-anesthetized rats were located primarily in laminae IV and V (70%), with fewer neurons located in laminae I and VII. ARN stimulation excited 76 and inhibited 8 neurons. Analysis of response latencies demonstrated that responses were due to activation of A delta- and/or C-fiber afferents. Reversible spinalization with cervical cold block (2-5 degrees C) affected activity in most neurons excited by ARN stimulation without affecting inhibited neurons. Cervical cold block increased the spontaneous activity of (disinhibited) the majority of neurons (54 of 76 neurons) and disfacilitated the spontaneous activity of 14 neurons. The evoked response to ARN stimulation was disinhibited by cold block in 51% and disfacilitated in 17% of the neurons, and there was a good correlation between neurons with disinhibited spontaneous activity and those with disinhibited evoked activity. Microinjections of muscimol (0.5-1 nmol) into the rostral medial medulla affected spontaneous and ARN-evoked activities similarly to cold block in 14 of 15 neurons, although the responses to muscimol were usually smaller in magnitude. We conclude that ARN input is modulated supraspinally and that the nucleus raphe magnus and adjacent neuropil contain neurons that contribute to tonic supraspinal inhibition of renal input in the rat.

Splanchnic input to thoracic spinal neurons and its supraspinal modulation in the rat.

The urinary responses of 62 T8-T11 spinal neurons were recorded extracellularly following electrical stimulation of the greater splanchnic nerve (GSN) in chloralose-anesthetized rats. Recorded neurons were found in both the dorsal and ventral horns. Fifty-seven neurons increased their firing rate in response to GSN stimulation; 8 of these exhibited biphasic responses consisting of excitations followed by inhibitions. Excitatory responses to GSN stimulation consisted of either one or two bursts with latencies consistent with activation by either A delta or C fibers. GSN stimulation inhibited 5 neurons. The effects of reversible spinalization on spontaneous activity and on both synchronous and non-synchronous (afterdischarge) GSN-evoked responses were investigated using a cooling probe on the spinal cord between C1 and C2. Of 19 neurons tested in this way, 9 exhibited opposite directional changes in their spontaneous activities and their GSN-evoked responses upon spinalization. Differential effects of cold-block on first and second bursts, or on A delta- and C-fiber mediated responses, were not usually observed. However, differential effects of cold-block on synchronous and non-synchronous portions of the overall GSN-evoked response were often observed in that their magnitudes often changed independently of one another. Supraspinal pathways contributed to GSN-evoked responses of several neurons because their responses were diminished during cooling while spontaneous activity was increased or unchanged. These decreases in the magnitude of the GSN-evoked response were not always accounted for by decreases in the synchronous portions of the responses. However, most neurons did exhibit decreases in the number of non-synchronous responses, or afterdischarges, during spinal cooling, exhibiting in some cases biphasic responses. This study provides evidence for strong supraspinal regulation of splanchnic afferent input to the spinal cord of the rat. Further, this regulation exhibits some specificity toward different portions of splanchnic-evoked responses in spinal neurons.

Spinal projections of renal afferent nerves in the rat.

This study was designed to describe renal afferent information with respect to its intraspinal projections, convergence with cutaneous inputs, ascending projections, and modulation by descending fiber tracts. Extracellular recordings were made from neurons in the spinal gray while electrically stimulating the renal nerves in chloralose-anesthetized, artificially ventilated rats. Almost all neurons (n = 119) were spontaneously active. Some responses consisted of high-frequency bursts while others consisted of fewer than 6 action potentials. Response onset latencies to renal nerve stimulation were consistent with activation by thinly myelinated or unmyelinated afferents. Several neurons in deeper laminae were inhibited by stimulation of renal afferents. Most neurons were located in laminae IV and V. Some were located in laminae I, VII and VIII. All neurons were located at spinal levels T10 to L1. Most neurons responded to both noxious and non-noxious mechanical cutaneous stimuli from relatively large receptive fields on the ipsilateral flank. Response latencies to cutaneous electrical stimulation were shorter than those to renal nerve stimulation. Neurons in intact and spinally transected rats responded with similar onset latencies and durations to renal nerve stimulation. However, neurons in spinally transected rats exhibited prolonged responses to cutaneous stimulation. Axons of 25% of the neurons projected through the cervical spinal cord in the ventrolateral funiculus. They had conduction velocities of 12-32 m/s. These data provide the first electrophysiological description of spinal projections of renal afferent fibers in the rat.

Noradrenergic projections to brainstem nuclei: evidence for differential projections from noradrenergic subgroups.

Retrograde transport of the fluorescent tracer True Blue was used in combination with immunohistochemical staining of dopamine-beta-hydroxylase (a marker protein for noradrenergic neurons) to determine the origin of noradrenergic projections to three cranial nerve nuclei: 1) the motor nucleus of the trigeminal nerve, 2) the motor nucleus of the facial nerve, and 3) the spinal trigeminal nucleus pars interpolaris. Noradrenergic cells in the rat brainstem were divided into subgroups and their numbers were determined in serial sections stained with an antiserum to rat dopamine-beta-hydroxylase. Following tracer injections into the three brainstem nuclei, retrogradely labeled noradrenergic neurons were counted and the percentage of True Blue-labeled noradrenergic cells in each subgroup was calculated. Injections of tracer into the three cranial nerve nuclei resulted in distinctly different labeling patterns of noradrenergic cells. Of the total number of norepinephrine neurons projecting to the motor nucleus of the trigeminal nerve, 68% were observed within the A7 cell group; 75% of those innervating the motor nucleus of the facial nerve were found in the A5 cell group, and 65% of those projecting to the spinal trigeminal nucleus pars interpolaris were present in the locus ceruleus and subceruleus. These findings indicate that norepinephrine cells in the rat brainstem do not constitute a homogeneous population of cells but that several discrete systems can be identified that differ not only in topography but also in the terminal distribution of their axons. This combined retrograde transport-immunohistochemical study reveals a much higher degree of topographic order in the projections of norepinephrine neurons than has previously been recognized. The observation of differential projections of noradrenergic subgroups argues against the notion of a global influence of these cells over functionally diverse areas of the brainstem.