Elevation of internal auditory canal pressure by vestibular schwannomas.

OBJECTIVE: The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test whether increased pressure in the internal auditory canal from tumor growth is responsible for this clinical finding, the intracanalicular pressure in patients harboring these tumors was measured. STUDY DESIGN: Prospective study. SETTING: Tertiary referral hospital. PATIENTS: Fifteen consecutive patients undergoing a retrosigmoid approach for resection of vestibular schwannomas were included in the study. INTERVENTION: The intracanalicular pressure in every patient was measured by introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then correlated with tumor size and respective preoperative hearing status. RESULTS: Placement of the pressure monitor into the internal auditory canal revealed a biphasic waveform in every patient. Whereas the mean intracanalicular pressure was 20 mm Hg, there was significant variability among patients (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.012) but not with the total tumor size (r 0.075). Furthermore, eight patients with class A preoperative hearing (American Academy of Otolaryngology-Head and Neck Surgery classification) had lower intracanalicular pressures than did five patients with class B hearing (16 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse correlation between the intracanalicular pressure and hearing function, the difference between the two groups was not statistically significant (p = 0.14). CONCLUSION: Pressure on the cochlear nerve as a result of tumor growth in the internal auditory canal may be responsible for hearing loss in patients with vestibular schwannomas. Modification of surgical techniques to address the elevated intracanalicular pressure may be beneficial in improving hearing preservation in these patients.

Long-term follow-up review of patients who underwent laminectomy for lumbar stenosis: a prospective study.

OBJECT: Decompressive laminectomy for stenosis is the most common operation performed in the lumbar spine in older patients. This prospective study was designed to evaluate long-term results in patients with symptomatic lumbar stenosis. METHODS: Between January 1984 and January 1995, 170 patients underwent surgery for lumbar stenosis (86 patients), lumbar stenosis and herniated disc (61 patients), or lateral recess stenosis (23 patients). The male/female ratio for each group was 43:43, 39:22, and 14:9, respectively. The average age for all groups was 61.4 years. For patients with lumbar stenosis, the success rate was 88.1 % at 6 weeks and 86.7% at 6 months. For patients with lumbar stenosis and herniated disc, the success rate was 80% at 6 weeks and 77.6% at 6 months, with no statistically significant difference between the two groups. For patients with lateral recess stenosis, the success rate was 58.7% at 6 weeks and 63.6% at 6 months; however, the sample was not large enough to be statistically significant. One year after surgery a questionnaire was sent to all patients; 163 (95.9%) responded. The success rate in patients with stenosis had declined to 69.6%, which was significant (p = 0.012); the rate for patients with stenosis and herniated disc was 77.2%; and that for lateral recess stenosis was 65.2%. Another follow-up questionnaire was sent to patients 1 to 11 years after surgery (average 5.1 years); 146 patients (85.9%) responded, 10 (5.9%) were deceased, and 14 (8.2%) were lost to follow-up review. At 1 to 11 years the success rate was 70.8% for patients with stenosis, 66.6% for those with stenosis and herniated disc, and 63.6% for those with lateral recess stenosis. Eleven patients who underwent reoperation were included in the group of patients whose surgeries proved unsuccessful, regardless of their ultimate outcome. There was no statistically significant difference in outcome between 1 year and 1 to 11 years with respect to stenosis, stenosis with herniated disc, and lateral recess stenosis. CONCLUSIONS: In conclusion, long-term improvement after laminectomy was maintained in two-thirds of these patients.

Lymphocyte-induced angiogenesis factor is produced by L3T4+ murine T lymphocytes, and its production declines with age.

Lymphocyte-induced angiogenesis factor (LIA) is a product of T lymphocytes which has been shown to stimulate new vessel formation. Because immune senescence most profoundly affects T lymphocyte functions, we suspected that LIA production would decline with age. An assay for angiogenesis stimulated by allogeneic reaction was performed by injecting spleen cells from young or old donor mice into the skin of irradiated allogeneic recipient mice. The spleen cells from young mice induced a significantly greater number of vessels than did cells from older mice. In additional experiments, spleen cells from young and old animals were treated with a monoclonal antibody GK 1.5) directed at the L3T4 antigen on murine T helper lymphocytes. Such treatment significantly reduced the new vessel formation induced by young lymphocytes but had no effect on that induced by lymphocytes from old animals. Studies employing indirect immunofluorescence demonstrated that the proportion of L3T4+ cells in the mononuclear fraction of splenocytes was nearly identical in both young and old mice. From these investigations we can conclude that (1) L3T4+ lymphocytes are responsible for LIA production, and (2) production, like that of other T lymphokines, declines with age.