PubMed · 2880085
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1987-01-31. Testing cerebrospinal fluid.. https://pubmed.ncbi.nlm.nih.gov/2880085/
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BACKGROUND: Detection of malignant cells on cytologic examination of the cerebrospinal fluid (CSF) is the diagnostic gold standard for leptomeningeal carcinomatosis. The absence of cells is a primary endpoint for most therapeutic trials. Unfortunately, false-negative results are common. Practical strategies are necessary to remedy this problem. METHODS: Four physician-dependent variables (CSF sample volume, site of CSF sampling, processing time, and frequency of CSF sampling) were identified, and their contributions to the false-negative rate of CSF cytology were evaluated prospectively in 39 patients with leptomeningeal carcinomatosis. Retrospective data were analyzed to estimate the importance of these variables in daily practice. RESULTS: False-negative CSF cytology results correlated with small CSF volume (P < 0.001), delayed processing (P < 0.001), not obtaining CSF from a site of symptomatic or radiographically demonstrated disease (P = 0.02), and sampling fewer than two times (P < 0.001). In 1 year, 97% of CSF specimens at the study institution were of inadequate volume; >25% were processed too slowly. CONCLUSIONS: False-negative CSF cytology results are common, but can be minimized by: 1) withdrawing at least 10.5 mL of CSF for cytologic analysis; 2) processing the CSF specimen immediately; 3) obtaining CSF from a site of known leptomeningeal disease; and 4) repeating this procedure once if the initial cytology is negative.
The prognosis of tuberculous meningitis (TBM) depends on early therapy based on rapid diagnosis. To study the clinical value of PCR in diagnosis of TBM, we investigated CSF specimens from 49 patients. After cell lysis and DNA preparation following a standard protocol, we performed a half-nested PCR with primers able to detect mycobacterial DNA. PCR results were evaluated according to clinical features, histopathological data, and bacteriological results. PCR detected four of five cases of confirmed TBM, corresponding to a sensitivity of 80%. Positive PCRs were also obtained in 25% CSF samples of non-TBM patients. Most of these false positive results were due to amplification of Mycobacteria fortuitum (M. fortuitum) as determined by direct sequencing analysis. To enhance specificity of our half nested protocol, the oligonucleotide primers that were specific for several mycobacterial subspecies were substituted by a primerpair, which allows selective amplification of DNA from Mycobacteria tuberculosis (M. tuberculosis). By using the altered PCR protocol, the screening of CSF samples revealed a much higher specificity (97%) and constant sensitivity (80%) in diagnosis of TBM. These findings indicate, that M. fortuitum, as an ubiquitous mycobacterial subtype of low pathogenicity, can potentially contaminate clinical specimens and account for false positive PCR results. Therefore, the clinical value of PCR in diagnosis of TBM strongly depends on appropriate oligonucleotide primers, that allow to differentiate between mycobacterial subtypes.
Dural tears located at the base of the skull are difficult to repair due to the difficulties in the appropriate access and the fragility of the dura in such areas. In our experience the biggest problem when attempting to perform a dural repair in a deep narrow field is not to place the stitches, but rather to set the knots. A newly designed, easy-to-learn technique has been developed for dural closure in these situations. We present here a new technique for dural suturing of special interest when the space available is limited. In our hands it is possible to obtain a watertight dural closure in most microsurgical operations performed through a small hole and/or into a narrow, deep surgical field. These techniques can also be applied during a secondary procedure following development of a postoperative CSF leak. While simple and easy to learn, these techniques require practice in the laboratory setting before clinical application.