INTRAMEDULLARY PRESSURE IN SYRINGOMYELIA - CLINICAL AND PATHOPHYSIOLOGICAL CORRELATES OF SYRINX DISTENSION

OBJECTIVE: The pathophysiological effects of syrinx distension are inc ompletely understood. Although it is generally assumed that the accumu lation of fluid within syrinx cavities can contribute to neurological dysfunction, there are no reports describing intramedullary pressure i n syringomyelia. The purpose of the current study was to measure syrin x pressures in patients with progressive clinical deterioration and to correlate these data with neurological deficits and intraoperative ph ysiological findings. METHODS: Intramedullary fluid pressure was measu red manometrically in 32 patients undergoing syrinx shunting procedure s. The data were correlated with syrinx morphology, intraoperative som atosensory evoked potentials, laser Doppler measurements of local spin al cord blood flow (six patients), and neurological findings before an d after syrinx decompression. RESULTS: Syrinx pressures recorded under atmospheric conditions ranged from 0.5 to 22.0 cm H2O (mean = 7.7 cm) . There was a significant elevation of the cardiac pulse (mean = 0.7 c m H2O) and the respiratory pulse (mean = 1.1 cm H2O) that was consiste nt with raised cerebrospinal fluid pressure. Syrinx pressures decrease d to subatmospheric levels after surgical drainage. In 18 of 24 patien ts with predrainage somatosensory evoked potential abnormalities, syri nx decompression produced a consistent reduction of N-20 latencies (me an change = 0.49 ms +/- 0.094 SE right, P = 0.002; 0.61 ms +/- 0.089 S E left, P = 0.001) and a similar but less consistent increase in N-20 amplitudes (mean change = 0.17 mV +/- 0.103 SE right, P = 0.115; 0.31 mV +/- 0.097 SE left, P = 0.027). Measurements of local spinal cord bl ood flow revealed very low baseline values (mean = 12.2 arbitrary unit s +/- 13.9 standard deviation), which increased to intermediate levels (mean = 144.7 arbitrary units +/- 42.6 standard deviation) after syri nx decompression. Patients with syrinx pressures greater than 7.7 cm H 2O tended to have more rapidly progressive symptoms, exhibited greater improvements after shunting, and had a higher incidence of postoperat ive dysesthetic pain. CONCLUSION: The current study is the first to me asure intramedullary pressure in a human disease. Evidence is presente d that distended syringes are associated with varying levels of raised intramedullary pressure that can accentuate or induce neurological dy sfunction by the compression of long tracts, neurons, and the microcir culation. Symptoms referrable to raised intramedullary pressure are po tentially reversible by syrinx decompression.