Natural Dural Defect of the Posterior Fossa Dura as a Risk Factor for Postoperative Cerebrospinal Fluid Leakage

BACKGROUND

During microvascular decompression surgery (MVD), small (2-3 mm diameter) natural dural defects have been noticed occasionally but never reported. These tiny dural defects cannot be detected by preoperative imaging studies or even in anatomical cadaver dissection, but may lead to complications including cerebrospinal fluid (CSF) leakage. Our objective was to analyze the features of these natural defects in the posterior fossa dura.

METHODS

Surgical reports and videos of 593 consecutive patients who underwent MVD surgery for trigeminal neuralgia (TN) or hemifacial spasm (HFS) were analyzed retrospectively. Video recording confirmed that these small holes were not related to the craniotomy procedure itself and were natural defects.

RESULTS

Such natural defects of the posterior fossa dura were found in 6 of the 593 patients. All of the defects were about 2 mm in diameter and occurred on the left side in female patients with HFS. All were managed by patching with a fascial or muscle graft. Multivariate analysis showed that the defect was significantly associated with the left side and had a female predilection. Neither disease (HFS or TN) nor age was correlated with the presence of dural defects.

CONCLUSIONS

After posterior fossa craniotomies, CSF leakage or pseudomeningocele may occur at the dural suture site because of the hydrostatic pressure. Because such natural dural defects may be a cause of CSF complications after posterior fossa surgery, their possible occurrence should be considered. This is the first report to document the occurrence of such natural defects of the posterior fossa dura.

Single-Site Non-Fermi-Liquid Behaviors in a Diluted 4f^{2} System Y_{1-x}Pr_{x}Ir_{2}Zn_{20}

Electrical resistivity ρ(T) and specific heat C(T) measurements have been made on the diluted 4f^{2} system Y(Pr)Ir_{2}Zn_{20}. Both data of ρ and magnetic specific heat C_{m} per Pr ion are well scaled as a function of T/T_{0}, where T_{0} is a characteristic temperature of non-Fermi-liquid (NFL) behaviors. Furthermore, the temperature dependences of ρ and C_{m}/T agree with the NFL behaviors predicted by the two-channel Kondo model for the strong coupling limit. Therefore, we infer that the observed NFL behaviors result from the single-site quadrupole Kondo effect due to the hybridization of the 4f^{2} states with multichannel conduction electrons.

Okadaic acid stimulates the expression of vascular endothelial growth factor gene

Vascular endothelial growth factor (VEGF) is a specific mitogen for vascular endothelial cells and has been implicated in tumor angiogenesis. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, is a non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoter in two-stage carcinogenesis experiments in mouse skin. To elucidate the role of VEGF in the angiogenesis of these experimental tumors, the effect of okadaic acid on VEGF gene expression was examined. In NIH 3T3, Rat1, HeLa, and A431 cells, VEGF mRNA was upregulated by 5- to 10-fold after incubation with okadaic acid. Furthermore, the amount of VEGF protein in the culture medium was significantly increased after stimulation with okadaic acid. Interestingly, okadaic acid-induced upregulation of VEGF mRNA was not suppressed by protein kinase C (PKC) inhibitor or by tumor necrosis factor alpha blocking antibody, although TPA-induced VEGF upregulation was strongly suppressed by PKC inhibitor. Our results indicate that okadaic acid is a new and potent inducer of VEGF, suggesting the involvement of VEGF as an angiogenic factor during multistep carcinogenesis in vivo.

A cAMP response element and an Ets motif are involved in the transcriptional regulation of flt-1 tyrosine kinase (vascular endothelial growth factor receptor 1) gene

The flt-1 gene encodes a transmembrane tyrosine kinase, Flt-1, a receptor for vascular endothelial growth factor. The expression of flt-1 gene is restricted to endothelial cells in vivo. To understand the molecular mechanism underlying endothelial-specific expression of this gene, we studied the functional significance of transcriptional motifs in the 200-base pair region of the human flt-1 gene promoter, which has been identified to confer cell type specificity. By point mutation analysis using chloramphenicol acetyltransferase plasmids in 293E1 cells, which express significant levels of flt-1 mRNA, we found that an Ets motif, E4, at -54 to -51 and a cAMP response element (CRE) at -83 to -76 are involved in the transcriptional regulation of this gene. Disruption of either this CRE or E4 within the promoter sequence of 90 base pairs resulted in a decrease in chloramphenicol acetyltransferase activity of 90%, indicating that co-existence of both of CRE and Ets motif E4 is necessary for transcription of the flt-1 gene. Co-transfection of an expression vector containing c-ets-1, c-ets-2, or c-erg cDNA with this 90-base pair sequence yielded a 5-8-fold elevation of chloramphenicol acetyltransferase activity, further supporting the idea that Ets family protein(s) participates in the regulation of the flt-1 gene. Gel shift assays using nuclear extracts of 293E1 and endothelial cells demonstrated the existence of protein factor(s) that specifically binds to CRE and Ets motif E4, respectively. Taken together, our results strongly suggest cooperation of a CRE and an Ets motif for the function of the flt-1 gene promoter.

Characterization of the promoter region for flt-1 tyrosine kinase gene, a receptor for vascular endothelial growth factor

The flt-1 gene encodes a Vascular Endothelial Growth Factor receptor, (Flt-1), whose expression is restricted to vascular endothelial cells. To characterize the cell type specificity of flt-1 gene expression, we isolated the upstream genomic DNA of the human flt-1 gene and identified a single transcription initiation site 29 bp downstream of a TATA box. DNA sequencing revealed that one TATA box, four GC boxes, nine ETS motifs and one CRE motif were present in the upstream 489 bp region of exon 1. Functional analyses using CAT plasmids in 293E1 cells, which express significant levels of the flt-1 gene, showed that the -229 to +8 region is essential for the cell type-specific expression of this gene. Deletion mutant analysis also pointed to the possible existence of negative and positive regulatory elements in the region -911 to -435, and +8 to +276, respectively. These results suggest that multiple regulatory factors are involved in the transcriptional regulation of the flt-1 gene expression in a cell type-specific, or a more ubiquitous manner.

[Results of microvascular decompression in 16 cases of glossopharyngeal neuralgia]

Seven males and nine females with glossopharyngeal neuralgia were treated by microvascular decompression (MVD) over a 4-year period. Their ages ranged from 40 to 72 years (average, 54.7 years). The duration of pain ranged from 2 months to 13 years, and all except one patient had brief attacks of lancinating pain in the throat and/or ear. One patient reported dull, paroxysmal throat pain. At surgery, vascular compression of the 9th and 10th nerves at the root entry-exit zone was observed in all cases. The offending vessels were the posterior inferior cerebellar artery (PICA) in 11 cases, the PICA and the anterior inferior cerebellar artery (AICA) in two, the PICA and vertebral artery (VA), and AICA and VA in one case each. The patient with atypical pain had compression by a large vein. In 15 cases of arterial compression, the pain completely disappeared after MVD, and there was no recurrence during the follow-up period, which ranged from 1 month to 4 years. One patient with venous compression had significant pain relief, although mild throat pain persists. In one case, postoperative complications included transient 6th, 7th, and 10th nerve palsies and sensory disturbance, which were assumed to be due to disturbance of the circulation in the perforating branches from the compressing artery. The experience with these 16 patients indicates that vascular compression is the etiology of glossopharyngeal neuralgia and that MVD provides excellent results.