No abstract

Most reports regarding synovial cysts of the spinal canal have been presentations identifying an unusual pathological entity that is to be included in the differential diagnosis of cauda equina compression syndromes. Most of the 26 cases reported represent isolated examples of this pathological process. We present five cases of lumbar synovial cysts encountered in our practice in the past 8 years. Patients with lumbar synovial cysts do not demonstrate any predictable clinical picture. They may present with a unilateral sciatica or neurogenic claudication. Lumbar extension is usually restricted, whereas flexion is full. Mechanical signs of nerve root entrapment or lumbosacral plexus irritation are unimpressive. Neurological deficits are usually mild, if present. Radiological findings include degenerative spondylosis, spondylolisthesis, and a rounded posterolateral extradural mass of low attenuation value adjacent to a facet shown on computed tomographic scan. The etiology of lumbar synovial cysts is not known. Histological findings of myxoid degeneration, microcystic change, calcification, and hemosiderin deposits suggest that chronic microtrauma with occasional focal hemorrhage may play a major role in the etiology of the cysts. With resection of the cyst, the postoperative course is usually uneventful. Recurrences have not yet been encountered in our patients.

A correlated anatomical and physiological investigation of the effects of unilateral cervicothoracic dorsal rhizotomies upon lateral cuneate nucleus of the cat (LCN) is reported. Pairs of adult cats with identical survival times were selected to correlate structural and functional changes . Two phases are described in the development of alterations of neuronal firing patterns . In the first phase, a relative silence within LCN was associated with depletion of round synaptic vesicles in the presynaptic profiles (LR boutons) of primary dorsal root afferents . The second phase was characterized by a development of spontaneous electrical hyperactivity which corresponded anatomically to the presence of denuded postsynaptic specializations, transient increase of adjacent extracellular space and an apparent decrease in the number of dendritic spines . There was a persistence of an unaltered population of small presynaptic boutons with flattened vesicles (SF boutons) . The LCN neuronal membrane is viewed as having an intrinsic tendency for repetitive firing which is enhanced by the functional effects of denuded postsynaptic specialization . A marked similarity was found between some of the spontaneous firing patterns of normal animals (doublets) and the high frequency bursting firing pattern in deafferented preparation. Three models for repetitive spike production are considered in our analysis : oscillator-produced spikes ; EP SP-produced spikes ; and spike-evoked spikes . The spike-evoked spikes model is considered to be the 1 The authors thank