Lumbar Drain After Endoscopic Surgery of the Skull Base: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Lumbar Drain After Endoscopic Surgery of the Skull Base (NCT03163134), a randomized na study. The primary outcome is Number of Participants With Cerebrospinal Fluid (CSF) Leak.

2. Clinical Question

The trial's stated purpose was to assess whether lumbar drain placement after EEA surgery was necessary in relation to postoperative CSF leak and to promote standardization of its use. The primary endpoint counts participants with a CSF leak; it is not a measure of leak severity, duration, or treatment burden. The registry also reports postoperative complications as a secondary outcome with a one-year timeframe.

The posted primary results are 18 participants with a CSF leak in the no-lumbar-drain group and 7 in the lumbar-drain group, with 85 participants recorded in each group. Those counts describe the observed trial results; they do not by themselves establish why the groups differed or how broadly the results apply. The record does not report the detailed population criteria needed to judge similarity to other skull base surgery populations.

3. Trial Design

The registry describes a randomized, parallel-group trial with triple masking. Participants were assigned to a no-lumbar-drain group or a lumbar-drain group. Although the masking designation is recorded as triple, the registry record does not identify which people or roles were masked, or describe how masking was maintained. The study phase is listed as NA.

The recorded enrollment is 170. Each arm lists 85 participants. The study sponsor is the University of Pittsburgh. The recorded study start date is 2011-02-03, primary completion date is 2015-04-27, and status is terminated. The registry record does not report a reason for termination, so the status alone should not be interpreted as evidence about the results or the conduct of the study.

The primary outcome is the number of participants with a CSF leak, measured at one month. The stated outcome description compares EEA patients who received lumbar drain placement with those who did not. The secondary outcome is the number of participants with postoperative complications, measured at one year.

The registry record does not report the original sample-size justification or the trial's design assumptions. It also does not give detailed information about eligibility, the allocation process, masking procedures, or the analysis population. These omissions limit assessment of how participants entered the trial and how closely the posted analyses follow the original plan. The planning illustrations associated with the posted results are recalculations from the observed effect, not documentation of the trial's original design.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Cerebrospinal Fluid (CSF) Leak, measured over 1month.

The primary endpoint counts participants who experienced a cerebrospinal fluid (CSF) leak after endoscopic endonasal approach surgery. Its timeframe is one month. The registry describes the measure as the number of participants with CSF leak and frames it as a comparison between participants who received a lumbar drain and participants who did not.

A participant count is a binary-outcome summary: each participant is classified according to whether the event was recorded. Comparing the counts in relation to the group sizes makes it possible to describe the event frequency in each arm and the difference between those frequencies. This endpoint is relevant to the trial's stated question because the study sought to assess lumbar drain placement in relation to postoperative CSF leak.

The endpoint does not capture every aspect of a leak. The record does not describe a measure of severity, timing within the one-month period, duration, recurrence, or consequences. Nor does it describe the operational criteria used to identify a CSF leak. Those details are not reported in the registry record, so the count should be interpreted as the recorded occurrence outcome rather than as a complete account of the clinical course.

The primary result is 18 participants with a CSF leak among 85 in the no-lumbar-drain group and 7 among 85 in the lumbar-drain group. The one-month timeframe matters: the result concerns the outcome as defined for that period and does not, by itself, describe longer-term CSF leak experience.

7. Results Posted in the Registry

• Lumbar Drain Group: 8.2% (7/85) versus 21.2% (18/85) on control; risk difference -12.9 percentage points (95% CI -23.4 to -2.5), risk ratio 0.39 (0.17–0.88); unadjusted two-proportion z-test p = 0.017.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Number of Participants With Postoperative Complications

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Lumbar Drain Group: 23.5% (20/85) versus 20.0% (17/85) on control; risk difference 3.5 percentage points (95% CI -8.9 to 15.9), risk ratio 1.18 (0.66–2.09); unadjusted two-proportion z-test p = 0.577.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Lumbar Drain Group and the control. The interval gives the range of effects that remain compatible with the data.

The registry posts one secondary outcome: participants with postoperative complications over one year. Its group pattern is not the same as the primary CSF leak pattern, and its estimate is less definitive because the interval spans zero and the reported p-value is 0.577. The primary endpoint concerns CSF leak within one month, whereas the secondary endpoint is broader in wording and has a longer timeframe. They address related aspects of postoperative outcomes but are not interchangeable measures.

The secondary result should be treated as an additional, exploratory piece of evidence rather than as a confirmation or refutation of the primary comparison. A secondary outcome may be useful for describing the wider outcome profile, but interpretation depends on its definition, follow-up, and analysis. The registry record does not report the components included in postoperative complications or provide further detail on how these events were ascertained.

Unadjusted secondary results carry less weight when multiple outcomes are examined because the chance of observing an apparently notable result can increase across a set of tests. As a general statistical principle, multiplicity procedures can account for that issue, but the registry record does not report a correction or a prespecified hierarchy for outcomes. This does not mean that the secondary result is invalid; it means that its p-value should not be treated as if it were the only planned statistical question.

The posted record identifies two outcome measures and one secondary outcome. It does not clarify whether all outcomes considered in the study are represented, whether this secondary outcome was prespecified in the analysis plan, or how the trial intended to handle multiple comparisons. The overall pattern is therefore best read as a primary CSF leak comparison accompanied by a less precise secondary complications comparison, with no reported multiplicity strategy.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Participants With Postoperative Complications

9. Statistical Interpretation

10. Statistical Methods Explained

What does a risk difference describe?

As a general statistical explanation, a risk difference compares the event probabilities in two groups by subtracting one group's probability from the other's. Its scale is absolute rather than relative: it describes the separation between the observed event risks. For this trial the posted comparison is lumbar drain versus no lumbar drain, so a negative risk difference corresponds to a lower observed event risk in the lumbar-drain group. The primary estimate is -0.129. The estimate is based on the posted participant counts and group sizes and is an unadjusted comparison.

An absolute contrast is useful because it keeps the comparison tied to the event frequency in the groups being studied. It should not be interpreted without the underlying counts, timeframe, and outcome definition. Here, the primary result concerns CSF leak within one month; the secondary result concerns postoperative complications over one year. A risk difference cannot resolve differences in outcome definitions or follow-up periods.

What does the chi-squared test address?

The sponsor's reported analysis method is chi-squared for both outcomes. As a general explanation, a chi-squared test evaluates whether the observed distribution of a categorical outcome across groups is compatible with a null model of no association, under the test's assumptions. For a binary outcome, it uses the event and non-event pattern in the groups. The reported primary p-value is 0.017 and the secondary p-value is 0.577.

A p-value is not an effect-size measure, and it does not state the chance that a result will replicate. It also does not describe how large a difference is or whether it matters in practice. Interpreting it requires the effect estimate, the interval, the endpoint definition, and the study design. The registry record does not report further detail about the sponsor's statistical procedures beyond the chi-squared method and p-values.

How should the confidence intervals be read?

As a general explanation, a confidence interval expresses uncertainty around an estimate under a specified statistical procedure. Its width indicates how precisely the data locate the estimate on the chosen scale: a narrower interval indicates greater precision, while a wider interval leaves more values compatible with the data. For the primary risk difference, the interval endpoints are -0.234 and -0.025. For the secondary risk difference, they are -0.089 and 0.159.

The confidence level for these intervals is not reported in the registry record. The intervals should therefore be described by their posted endpoints without assigning a confidence percentage. They are also unadjusted intervals; the record does not state that they account for testing multiple outcomes or other sources of uncertainty beyond the calculations used for the comparison.

What does randomization contribute?

As a general principle, random assignment aims to make comparison groups similar, on average, with respect to measured and unmeasured factors at the time of assignment. It provides a basis for comparing outcomes by assigned group. Randomization does not guarantee identical groups in a particular trial, nor does it address events after assignment such as missing outcome data, nonadherence, or departures from the assigned intervention.

The registry identifies the allocation as randomized, but does not report the sequence-generation or allocation-concealment procedures. It also does not state which analysis population was used, such as whether participants were analyzed according to original assignment. Those details are not reported in the registry record, so the randomization label alone cannot answer those questions.

What is and is not reported about analysis?

The registry reports a chi-squared analysis and a p-value for each endpoint. It does not report an adjusted model, covariates, a missing-data method, or a confidence level for the intervals. It also does not report an analysis plan or identify whether subgroup or interim analyses were conducted. These matters should not be inferred from the posted p-values or the trial status.

The risk differences and intervals are simple unadjusted recalculations from the posted arm counts. The sponsor's reported p-values are retained as the sponsor's analyses. The primary recalculated comparison is consistent with the sponsor's reported p-value, and the secondary recalculated comparison is likewise consistent with its reported p-value. The trial's sponsor analysis remains the relevant reported analysis; a recalculation does not supply details absent from the registry record.

In short, the methods support a descriptive reading of the two group comparisons, but the available record does not establish every analytic choice needed for a complete audit. Effect estimates, intervals, and p-values each answer different questions and should be read together, with the limitations in outcome and analysis reporting kept in view.

11. Confidence Intervals and Precision

The primary risk difference is -0.129, with interval endpoints -0.234 and -0.025. This interval is entirely on the negative side of zero. In the stated comparison direction, that is consistent with a lower observed CSF leak risk in the lumbar-drain group, while the interval conveys uncertainty about the size of the difference.

The secondary risk difference is 0.035, with interval endpoints -0.089 and 0.159. This interval extends across zero, so the posted results are compatible with differences in either direction. It is not evidence that the groups are equivalent; a claim of equivalence would require a specified equivalence margin and an analysis designed for that question, neither of which is reported in the registry record.

Interval width matters as well as whether zero falls within the interval. The secondary interval includes a range of potentially meaningful directions and magnitudes, so the point estimate alone should not be treated as a settled description of the group contrast. For the primary endpoint, the interval gives a bounded range on the risk-difference scale, but it still does not resolve questions about the endpoint definition, missing outcomes, or how representative these participants are of other settings.

The confidence level associated with the intervals is not reported in the registry record. Accordingly, the endpoints can be quoted and interpreted as posted, but a confidence percentage should not be attached to them. The intervals are unadjusted, and the record does not report whether multiplicity was considered.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total participants and not total events. They are illustrations calculated from the observed effect, rather than the original trial's documented design calculation. The original sample-size assumptions and justification are not reported in the registry record.

The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for each illustration is the stated fraction of the observed effect. The primary endpoint scenarios include planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. For example, planning for 100% of the observed effect gives 117 participants per arm for 80% power and 156 participants per arm for 90% power.

The 80% power column means the planned group size intended to give an 80% chance of detecting the stated effect under the listed assumptions, if that effect and the assumptions hold. The 90% power column expresses the corresponding planning target for a 90% chance. These are design targets, not guarantees about any future study. They are not observed power.

The curve represents the same general planning relationship: the assumed effect size and the required group size move in opposite directions. Planning for a smaller fraction of the observed effect requires more participants per arm to reach the same power target. The figures are sensitive to the effect used and to the stated assumptions; they should not be read as a reconstruction of the terminated trial's original enrollment plan.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.212; treatment proportion p₁ = 0.082; average p̄ = 0.147.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5009 = 0.9817.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4924 = 0.4144.
4. n = (0.9817 + 0.4144)² / (-0.1294)² = 116.4, rounded up to 117 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.211764705882353                          # control proportion
p1 <- 0.0823529411764706                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(3163134)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 117 (80% power), 156 (90% power)
 75% of observed effect: n per arm = 227 (80% power), 303 (90% power)
 50% of observed effect: n per arm = 551 (80% power), 737 (90% power)
power.prop.test: 116.4 
Simulated power at n = 117 per arm: 0.813 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Analyses Reported by the Sponsor

The registry reports the sponsor's primary analysis as a chi-squared test with p = 0.017. It does not report a sponsor estimate or confidence interval in the analysis entry. The posted arm counts permit a simple unadjusted recalculation of the risk difference, which is -0.129, with interval endpoints -0.234 and -0.025. The recalculated comparison gives p = 0.017, matching the sponsor's reported p-value.

For postoperative complications, the sponsor's reported chi-squared p-value is 0.577. The unadjusted recalculation gives a risk difference of 0.035, with interval endpoints -0.089 and 0.159, and p = 0.577. The posted recalculations therefore agree with the reported p-values for both outcomes.

Agreement does not establish that every aspect of the original analysis has been reproduced. The registry record does not report a full statistical analysis plan, adjustments, missing-data procedures, or the confidence level for the intervals. The recalculations are straightforward comparisons of the posted summaries, while the sponsor's reported analyses remain the registry's own analyses.

15. Multiplicity, Missing Data and Analysis Populations

The registry reports a primary outcome and a secondary outcome, with a chi-squared p-value for each. It does not report whether the analysis plan specified a hierarchy among outcomes or any adjustment for testing multiple hypotheses. When several outcomes are tested, unadjusted p-values do not account for the increased chance of a chance finding across the collection of tests. This general issue is relevant to interpretation, but the record does not support reconstructing a multiplicity strategy.

The record identifies two outcome measures and one posted secondary outcome. It does not state whether additional outcomes were planned but not posted, or explain the selection of outcomes reported. There is no basis in the registry record for concluding that outcomes were omitted, nor for concluding that the posted set is exhaustive.

Information about missing data is also limited. The arm summaries give group sizes and event counts, but do not describe missing outcome assessments, exclusions, withdrawals, or how any unavailable observations were handled. The analysis population is not reported in enough detail to determine whether all randomized participants were included in each analysis or how assignment was reflected in the analysis.

These omissions matter because outcome completeness and analysis population can affect the interpretation of a group comparison. Random allocation is a feature of the design, but it cannot by itself resolve bias that may arise if outcomes are missing or participants are excluded after assignment. The registry record also does not report whether sensitivity analyses were used to examine the impact of missingness.

The trial's statistical analysis plan, including any interim analyses or stopping rules, is not reported in the registry record. The terminated status does not establish why the trial stopped or whether any particular analysis decision followed. These uncertainties should remain explicit rather than being filled in by assumptions.

16. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The serious-adverse-event fields report 0 affected participants among 85 at risk in the no-lumbar-drain group and 0 among 85 at risk in the lumbar-drain group. The fields for other adverse events likewise report 0 affected participants in each group, with 85 at risk in each. Deaths are reported as 0 in both groups.

These figures describe the adverse-event categories and counts recorded in the registry. They should not be read as proof that no events of any kind occurred, or that the interventions have no safety risks. The record does not list serious adverse-event terms, and its adverse-event summary does not explain collection procedures, reporting thresholds, or the period over which these events were assessed.

The adverse-event fields are separate from the secondary postoperative-complications outcome. The latter records 17 participants in the no-lumbar-drain group and 20 in the lumbar-drain group, over a one-year timeframe. A zero count in the adverse-event summary therefore should not be substituted for the complication outcome or taken to mean that no postoperative complications were recorded.

17. What the Result Does, and Does Not, Mean

The posted primary data show fewer recorded CSF leaks in the lumbar-drain group than in the no-lumbar-drain group during the one-month outcome period. The unadjusted risk difference is -0.129, and its interval endpoints, -0.234 and -0.025, are both below zero. The sponsor-reported chi-squared p-value is 0.017. Together, these statistics describe the direction and uncertainty of the observed comparison; they do not, by themselves, establish why the groups differed.

The secondary complications result is less conclusive. Its risk-difference interval spans zero, and the reported p-value is 0.577. This does not prove the groups have identical complication outcomes. It indicates that the posted comparison is compatible with a range of group differences, including differences in either direction.

The results do not establish the clinical importance of the observed contrast, because the registry record does not report a threshold for a meaningful difference or details about leak severity and consequences. The findings also do not provide a complete account of longer-term CSF leak outcomes, since the primary endpoint timeframe is one month. The broader one-year complication measure is not described in enough detail to identify its components.

Generalizability is difficult to assess because detailed eligibility criteria and a fuller description of the population are not reported in the registry record. The available results cannot settle how outcomes would compare in other surgical settings or populations. The record also lacks information about missing outcome data and analysis populations, which limits assessment of possible sources of bias.

Accordingly, the posted results support a description of the randomized groups and their recorded outcomes, not a treatment recommendation. They neither establish that lumbar drains should be used nor establish that they should not be used. Interpretation should remain specific to the trial's recorded outcomes and acknowledge the gaps in reporting.

18. Why This Trial Matters Statistically

This trial illustrates why an outcome count, an effect estimate, an interval, and a p-value answer different statistical questions. The event counts describe what was recorded in each group; the risk difference describes the unadjusted absolute contrast; the interval communicates uncertainty around that contrast; and the p-value summarizes compatibility with a no-difference model under the test assumptions. No single item replaces the others.

It also illustrates the importance of keeping endpoints distinct. CSF leak within one month and postoperative complications over one year are different outcomes with different timeframes. The primary result cannot be generalized automatically to every postoperative complication, and the secondary result cannot be used as a proxy for CSF leak.

Randomization is an important design feature for group comparisons, but interpretation still depends on transparent reporting of eligibility, allocation procedures, masking, outcome ascertainment, missing data, analysis populations, and the analysis plan. Several of those details are not reported in the registry record. Statistical summaries cannot repair those gaps.

Finally, planning calculations based on the observed effect show how strongly required sample size depends on the effect a future study aims to detect. Smaller assumed effects require larger groups under the stated planning assumptions. These illustrations can help readers understand planning tradeoffs, but they are not evidence about the trial's original design or its observed power.

19. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record gives limited detail about who was eligible, how participants were recruited, and the characteristics of the study population. Without that information, it is difficult to judge how closely the participants resemble those in other EEA surgery settings. The record also does not describe the criteria used to diagnose a CSF leak or the components of postoperative complications.

Although allocation is recorded as randomized and masking as triple, the procedures behind those labels are not described. The record does not identify the masked roles, explain allocation concealment, or specify the analysis population. It also does not describe adherence to the assigned group or any crossover between groups.

Missing-data methods and outcome completeness are not reported. The summaries give counts and group sizes, but do not explain whether any participants lacked outcome assessments or were excluded from analyses. The confidence level for the posted intervals is also not reported. These gaps limit evaluation of the precision and possible bias of the analyses.

The registry record does not provide a complete analysis plan, including any multiplicity approach, interim analyses, or original sample-size justification. It identifies one secondary outcome, but does not establish whether the posted outcomes represent the full set considered. The terminated status is recorded without a reason, so it cannot explain the study's outcome reporting or completion.

Finally, the primary endpoint is limited to CSF leak within one month, and the secondary outcome is a broad complications measure over one year. The record does not report severity or longer-term CSF leak measures. These outcome and reporting limits should constrain conclusions drawn from the observed group differences.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Lumbar Drain After Endoscopic Surgery of the Skull Base — NCT03163134.
• Registry record last updated 2017-08-16; status last verified 2017-05.
• Results first posted 2017-08-16.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

23. Record Summary

The registry describes a randomized, parallel-group trial with triple masking comparing postoperative lumbar drain placement with no lumbar drain after endoscopic endonasal approach surgery. The primary outcome is participants with CSF leak within one month. The secondary outcome is participants with postoperative complications over one year.

For CSF leak, the registry reports 18 participants in the no-lumbar-drain group and 7 in the lumbar-drain group, with 85 participants recorded in each group. The unadjusted risk difference is -0.129, with interval endpoints -0.234 and -0.025; the sponsor-reported chi-squared p-value is 0.017. The secondary complications comparison is less precise, with a risk difference of 0.035, interval endpoints -0.089 and 0.159, and p = 0.577.

The record lists enrollment as 170, sponsor as the University of Pittsburgh, and status as terminated. It does not report the reason for termination, detailed population criteria, missing-data procedures, the analysis population, or the original sample-size justification.