Reliability of the radiopharmaceutical shunt flow study for the detection of a CSF shunt malfunction in the presence of stable ventricular size

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  • 1 Division of Neurosurgery, Children’s Hospital Los Angeles; and
  • | 2 Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California
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OBJECTIVE

The authors sought to determine the reliability of a radiopharmaceutical (RP) shunt flow study for the detection of a CSF-diverting shunt malfunction in the presence of stable ventricular size.

METHODS

After the authors obtained IRB approval, all CSF RP shunt flow studies done between January 1, 2014, and January 1, 2019, in pediatric patients at Children’s Hospital Los Angeles were identified. Included in the study were only those patients in whom an MRI or CT scan was done during the hospital admission for shunt malfunction and showed no increase in ventricular size compared with the most recent prior MRI or CT scan when the patient was asymptomatic. Data recorded for analysis were patient age and sex, etiology of the hydrocephalus, shunt distal site, nonprogrammable versus programmable valve, operative findings if the shunt was revised, and follow-up findings for a minimum of 90 days after admission. The RP shunt flow study consisted of tapping the reservoir and injecting technetium-99m DTPA according to a set protocol.

RESULTS

The authors identified 146 RP flow studies performed in 119 patients meeting the above criteria. Four of the 146 RP studies (3%) were nondiagnostic secondary to technical failure and were excluded from statistical analysis. Of the 112 normal flow studies, operative intervention was not undertaken in 102 (91%). The 10 (9%) remaining normal studies were performed in patients who underwent operative intervention, in which 8 patients had a proximal obstruction, 1 had a distal obstruction, and 1 patient had no obstruction. Of the 30 patients with abnormal flow studies, symptoms of shunt malfunction subsided in 9 (30%) patients and these patients did not undergo operative intervention. Of the 21 (70%) operated patients, obstruction was proximal in 9 patients and distal in 5, and for 7 patients the shunt tubing was either fractured or disconnected. Regression analysis indicated a significant association between the flow study interpretation and the odds for shunt revision (OR 27, 95% CI 10–75, p < 0.0001). No other clinical variables were significant. The sensitivity of a shunt flow study alone for detection of shunt malfunction in cases with stable ventricular size was the same as a shunt flow study plus an MRI or CT (70% vs 70%), but performing a shunt flow in addition to MRI or CT did increase the specificity from 92% to 100% and the accuracy from 87% to 94%.

CONCLUSIONS

RP shunt flow studies were of definite value in deciding whether to operatively intervene in patients with symptoms of shunt malfunction in whom no change in ventricular size was detected on current MRI or CT scans compared to scans obtained when the patients were asymptomatic.

ABBREVIATIONS

NLR = negative likelihood ratio; NPV = negative predictive value; PLR = positive likelihood ratio; PPV = positive predictive value; RP = radiopharmaceutical.

OBJECTIVE

The authors sought to determine the reliability of a radiopharmaceutical (RP) shunt flow study for the detection of a CSF-diverting shunt malfunction in the presence of stable ventricular size.

METHODS

After the authors obtained IRB approval, all CSF RP shunt flow studies done between January 1, 2014, and January 1, 2019, in pediatric patients at Children’s Hospital Los Angeles were identified. Included in the study were only those patients in whom an MRI or CT scan was done during the hospital admission for shunt malfunction and showed no increase in ventricular size compared with the most recent prior MRI or CT scan when the patient was asymptomatic. Data recorded for analysis were patient age and sex, etiology of the hydrocephalus, shunt distal site, nonprogrammable versus programmable valve, operative findings if the shunt was revised, and follow-up findings for a minimum of 90 days after admission. The RP shunt flow study consisted of tapping the reservoir and injecting technetium-99m DTPA according to a set protocol.

RESULTS

The authors identified 146 RP flow studies performed in 119 patients meeting the above criteria. Four of the 146 RP studies (3%) were nondiagnostic secondary to technical failure and were excluded from statistical analysis. Of the 112 normal flow studies, operative intervention was not undertaken in 102 (91%). The 10 (9%) remaining normal studies were performed in patients who underwent operative intervention, in which 8 patients had a proximal obstruction, 1 had a distal obstruction, and 1 patient had no obstruction. Of the 30 patients with abnormal flow studies, symptoms of shunt malfunction subsided in 9 (30%) patients and these patients did not undergo operative intervention. Of the 21 (70%) operated patients, obstruction was proximal in 9 patients and distal in 5, and for 7 patients the shunt tubing was either fractured or disconnected. Regression analysis indicated a significant association between the flow study interpretation and the odds for shunt revision (OR 27, 95% CI 10–75, p < 0.0001). No other clinical variables were significant. The sensitivity of a shunt flow study alone for detection of shunt malfunction in cases with stable ventricular size was the same as a shunt flow study plus an MRI or CT (70% vs 70%), but performing a shunt flow in addition to MRI or CT did increase the specificity from 92% to 100% and the accuracy from 87% to 94%.

CONCLUSIONS

RP shunt flow studies were of definite value in deciding whether to operatively intervene in patients with symptoms of shunt malfunction in whom no change in ventricular size was detected on current MRI or CT scans compared to scans obtained when the patients were asymptomatic.

ABBREVIATIONS

NLR = negative likelihood ratio; NPV = negative predictive value; PLR = positive likelihood ratio; PPV = positive predictive value; RP = radiopharmaceutical.

In Brief

The authors analyzed the reliability of a radiopharmaceutical (RP) shunt flow study for the detection of a cerebrospinal fluid shunt malfunction in the presence of stable ventricular size. The findings demonstrated that the RP shunt flow study is of definite clinical value in deciding whether to operatively intervene in patients with symptoms of shunt malfunction in whom no change in ventricular size has occurred.

The protocol for evaluating possible CSF-diverting shunt malfunction has variations. At our institution, after the initial evaluation is completed, the next step is to obtain a limited MRI. In most cases, a previous MRI or CT study is available for comparison. If the CSF spaces have enlarged and the patient is symptomatic, operative intervention is undertaken. If the ventricles are not larger but also are not deflated, the shunt is tapped.1–10 If little or no CSF is obtained with appropriate aspiration, surgery is scheduled. If the ventricles are very small, a shunt tap is unlikely to be of value in determining obstruction as there would be little CSF to aspirate. Obtaining a shunt series is discouraged under most circumstances because it usually includes 4–6 radiographs, resulting in significant radiation exposure, especially if repeated multiple times, and is of limited value as the site of malfunction can be readily determined at the time of operation.11–14

In a patient whose vital signs are stable and whose ventricles and level of neurological function are unaltered, the initial approach is observation even if the patient has symptoms of headache, nausea/vomiting, and irritability. If the symptoms do not resolve, the next step is to do a radiopharmaceutical (RP) shunt flow study.

The purpose of this study was to evaluate the additional predictive value of a CSF shunt flow study in addition to MRI or CT scans in a cohort of pediatric patients with symptoms suggestive of shunt obstruction but stable ventricular size.

Methods

Patient Selection

After the study was approved by the Children’s Hospital Los Angeles Institutional Review Board, all RP CSF shunt flow studies done between January 1, 2014, and January 1, 2019, were identified. Patients were included only if data were available for an MRI or CT scan performed to detect possible shunt malfunction during the admission process and showed no visible increase in ventricular size when compared with the most recent prior MRI or CT scan obtained when the patient was asymptomatic (Figs. 1 and 2). The patient’s age, sex, etiology of hydrocephalus, shunt type (ventricular peritoneal, ventricular pleural, or ventricular atrial), operative findings if shunt revision was undertaken, and follow-up data for at least 90 days were all documented using a standardized spreadsheet for data collection.

FIG. 1.
FIG. 1.

Earlier T2-weighted axial MRI for ventricular size obtained when the patient shown in Fig. 2 was asymptomatic.

FIG. 2.
FIG. 2.

T2-weighted axial MRI for ventricular size obtained at the time of admission of the patient shown in Fig. 1 for symptoms consistent with increased intracranial pressure.

Shunt Characteristics

The ventricular catheter reservoir is a 1-piece unit (Phoenix) attached to a PS Medical Delta valve (or rarely a programmable Strata valve), with the distal catheter being an antibiotic-impregnated barium stripe open-ended catheter without distal slits (Codman Bactiseal).

Shunt Flow Study Techniques and Interpretation

The skin over the ventricular catheter reservoir was prepped with 2% chlorhexidine gluconate and 70% isopropyl alcohol. The dome of the reservoir was punctured with a 25-gauge butterfly needle and 1.1 mCi of technetium-99m DTPA in 3 mL normal saline was injected by a neurosurgical resident after the distal catheter was occluded just beyond the valve by compression against the skull. With the patient in a recumbent position, sequential anterior and posterior images of the head, neck, chest, and abdomen were made approximately every 15 minutes for 1 hour using a Siemens Intivo SPECT/CT or Symbia E SPECT dual-head gamma camera system. The written study request typically stated that the purpose was to rule out shunt malfunction. The studies were interpreted by a pediatric radiologist who was board certified in nuclear medicine.

A shunt flow study was determined to be normal if there was rapid reflux of tracer into the ventricles followed by rapid flow through the distal catheter into the peritoneum, pleural space, or vascular system (Figs. 35). Interpretations of abnormal shunt flow studies included the following: no reflux of the RP agent into the ventricles was reported to be a proximal obstruction, assuming a proper injection technique (Fig. 6); no or very slow distal runoff was reported to be distal obstruction (Fig. 7); and extravasation into the adjacent tissues raised the possibility of hardware fracture, tubing disconnection, or improper injection technique.

FIG. 3.
FIG. 3.

A normal RP shunt flow study showing reflux of the tracer into the ventricles with rapid distal flow. Arrow is at the site of injection into the reservoir.

FIG. 4.
FIG. 4.

A normal RP shunt flow study showing rapid flow of tracer distally.

FIG. 5.
FIG. 5.

A normal RP shunt flow study showing distribution of the tracer into the peritoneal cavity.

FIG. 6.
FIG. 6.

An abnormal RP shunt flow study showing proximal obstruction. No reflux of tracer is present in the ventricles. Arrow is at the site of injection into the reservoir.

FIG. 7.
FIG. 7.

An abnormal RP shunt flow study showing distal obstruction, with good reflux of tracer into the ventricles without evidence of tracer distally. Arrow is at the site of injection into the reservoir.

Analysis of Results

Results of shunt flow studies were interpreted as follows: an abnormal flow study with intraoperative verification of obstruction was labeled as a true positive; a normal flow study with confirmed intraoperative findings of obstruction was a false negative; a normal flow study with no operative revision within the 90-day study period or with intraoperative confirmation of shunt patency was a true negative; and an abnormal shunt flow study that was not revised within the study period of 90 days or one in which operative intervention found no evidence of obstruction was a false-positive study.

Statistical Analysis

Shunt flow study results and clinical categorical variables were analyzed with chi-square tests. Two-by-two binary classification statistical analyses were used to determine the specificity, sensitivity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), negative likelihood ratio (NLR), and accuracy for the RP shunt flow study independently and for the combination of modalities (CT or MRI scan plus RP shunt flow study). The odds ratio for surgical revision with 95% confidence interval was also calculated. A p value of less than 0.05 was considered significant. Statistical analyses were conducted using IBM SPSS Statistics version 25.0 (IBM Corp.).

Results

We analyzed 146 RP shunt flow studies and associated CT or MRI scans showing no increase in ventricular size in 119 patients treated during the 5-year study period (Table 1). Of this group, 14 patients underwent 2 shunt flow studies, 3 patients had 3 studies, 1 patient had 4 studies, and 1 patient underwent 5 studies. The number of shunt flow studies per patient was not significantly associated with the outcome of the examination (p = 0.50). Patient characteristics are summarized in Table 2. The mean patient age at the date of the shunt flow study was 12.6 years, and 53% of patients were female. The underlying etiologies of hydrocephalus are described in Table 3.

TABLE 1.

Summary of all shunt flow study results and operative findings

Value
Total no. of studies146
Negative shunt flow studies112/146 (77%)
 No op102/112 (91%)
 Op-confirmed patent shunt1/112 (<1%)
 Op-confirmed malfunctioning shunt9/112 (8%)
  Proximal obstruction8/9 (89%)
  Distal obstruction1/9 (11%)
  Shunt fracture0/9 (0%)
Positive shunt flow studies30/146 (20%)
 No op9/30 (30%)
 Op-confirmed patent shunt0/30 (0%)
 Op-confirmed malfunctioning shunt21/30 (70%)
  Proximal obstruction9/21 (43%)
  Distal obstruction5/21 (24%)
  Shunt fracture/disconnection7/21 (33%)
Failed shunt flow study4/146 (3%)
 Extravasation into adjacent tissues4/4 (100%)
TABLE 2.

Patient characteristics

CharacteristicMaleFemaleTotal
No. of patients56 (47%)63 (53%)119 (100%)
Mean age (range)12 yrs (6 mos–22 yrs)13 yrs (8 mos–23 yrs)12.6 yrs (6 mos–23 yrs)
Shunt type, no. of patients
 VP5454108
 VPl257
 VA044

VA = ventriculoatrial; VP = ventriculoperitoneal; VPl = ventriculopleural.

TABLE 3.

Etiologies of hydrocephalus

DiagnosisNo. of Patients (%)
Congenital18 (15)
Cyst5 (4.2)
Dandy-Walker syndrome2 (2)
Encephalocele5 (4.2)
Intraventricular hemorrhage26 (22)
Meningitis5 (4.2)
Chiari I/syringomyelia13 (11)
Open neural tube defect31 (26)
Tumor11 (8.9)
Other3 (2.5)
Total119 (100)

Of the 146 RP shunt flow studies, 112 (77%) were characterized as normal, which was indicative of rapid ventricular reflux of radiotracer, rapid flow through the distal catheter, and activity within the peritoneum, pleural space, or vascular system. In 102 of these 112 cases (91%), the examination results were considered true negatives and no surgical exploration was required because the patients’ symptoms abated. In 1 case for which the examination was deemed a true negative, shunt patency was confirmed intraoperatively, but the valve was changed in order to lower the drainage pressure because of the patient’s persistent symptomatology consisting of lethargy and emesis. Nine of these 112 shunt flow examinations (8%) were determined to be false-negative studies after surgical intervention confirmed a malfunctioning shunt. All 9 of the patients in these cases underwent surgical shunt exploration because of persistent headache and emesis, and an obstruction of the proximal catheter was found in all but 1 patient. The other operative finding was a patent distal catheter situated in an area of abdominal scarring.

Thirty of 146 shunt flow studies (20%) were characterized as abnormal (positive) due to the absence of ventricular reflux, no or slow distal flow, or the absence of activity in the peritoneum or pleural space. Shunt malfunction was confirmed intraoperatively (true positive) in 21 of these 30 studies (70%). Operative diagnoses included 9 cases with an obstructed proximal catheter (43%), 5 with an occluded distal catheter (24%), and 7 with distal catheter disconnections or fractures (33%). Nine of the 30 positive shunt flow studies (30%) were classified as false positive because the patients’ symptoms of possible shunt malfunction subsided and therefore surgical exploration was not undertaken. There were no situations in which surgical intervention revealed a patent shunt within the cohort of patients with abnormal shunt flow examinations.

Of all 146 RP shunt flow studies, 4 (3%) were nondiagnostic due to technical failure during injection of the radiotracer. In all 4 of these cases, the study report noted extravasation of isotope into the adjacent tissues.

Sensitivity, specificity, PPV, NPV, PLR, NLR, and accuracy for the diagnostic modalities are shown in Table 4. Specificity of 100% was achieved with the use of a CT or MRI examination in addition to a shunt flow study. Regression analysis revealed a significant association between the RP shunt flow study diagnosis and the odds for shunt revision (OR 27; 95% CI 10–75; p < 0.0001). Clinical variables tested with chi-square analyses were not significantly associated with the results of the shunt flow study: sex, p = 0.95; age, p = 0.8; etiology of hydrocephalus, p = 0.31; distal drainage location, p = 0.24; fixed versus programmable valve (Delta vs Strata), p = 0.84; and prior history of operatively confirmed shunt malfunction without ventricular enlargement, n = 5 and p = 0.99.

TABLE 4.

Statistical analysis of shunt flow study and combined modalities for diagnosis of shunt dysfunction in patients with stable ventricular size (excluding 4 failed studies)

RP Shunt Flow StudyCT or MRI & RP Shunt Flow Study
Sensitivity70% (50–85)70% (50–85)
Specificity92% (85–96)100% (97–100)
PLR8.7 (4.5–17)NA
NLR0.33 (0.19–0.57)0.30 (0.17–0.52)
PPV70% (55–82)100%
NPV92% (87–95)93% (88–96)
Accuracy87% (81–92)94% (88–97)

NA = not applicable.

Values are presented as the percentage or ratio (95% CI).

Discussion

In treating a large group of pediatric patients with shunted hydrocephalus, it is uncommon for a day to pass without seeing one or more patients in the emergency department for possible shunt malfunction. Imaging, now mostly accomplished with an MRI limited for ventricular size, and tapping the shunt will sort out the majority of patients whose symptoms are not related to shunt malfunction.7,15 This still leaves a residual pool of patients with headache, nausea and vomiting, and irritability, often with small ventricles, whose symptoms are not readily assigned to an etiology other than shunt malfunction.7–10,13,16–23 Fever is not a sign of shunt malfunction unless it is associated with a shunt infection. Under these circumstances an RP shunt flow study is ordered to add additional information as well as a temporizing measure to provide more time for observation.20,21,24 This practice raises the question as to how much value a shunt flow study adds to the decision-making process. We found that an RP flow study alone compared to an RP flow study plus MRI or CT did not change the sensitivity (70% vs 70%), but did increase the specificity from 92% to 100% and the accuracy from 87% to 94%.

Only 10 of the 112 RP flow studies (9%) with positive findings were surgically addressed, with findings of 1 distal and 8 proximal obstructions. One symptomatic patient had no proximal or distal obstruction, but responded to a change in the valve to one with a lower opening pressure. The incidence of distal obstruction was low and may reflect that the tubing used had an open end without any slits in either the wall of the tubing or at its end.

During the injection of the RP into the reservoir, if the tubing distal to the valve is not adequately compressed, much of the isotope could be delivered distally, thus reducing ventricular visualization, which may lead to the false impression of a proximal obstruction.19,22 This phenomenon was not observed to have occurred in any of the flow studies in this series. There were, however, 8 patients who had a significant amount of isotope reflux into the ventricles for the study to be read as normal and whose ventricular catheter was obstructed at the time of operation and required replacement. This scenario may reflect partial obstruction of the ventricular catheter, but with enough force, adequate tracer for visualization was injected into the ventricles.21,22 This suggests that enough ventricular catheter obstruction was present to cause symptoms, but not enough to result in ventricular dilatation.

Thirty of the 146 shunt flow studies (20%) were positive, indicating flow obstruction. In 9 of the patients in this group, symptoms resolved and so no operation was performed. All 21 operated patients were found to have an obstruction: 9 proximal (43%), 5 distal (24%), and 7 fractured/disconnected (33%).

Four of the 146 flow studies (3%) were technical failures as the tracer was seen only in the tissues adjacent to the shunt reservoir, with not enough tracer entering the shunt to enable a diagnostic study.

As mentioned in the Introduction, we do not routinely obtain a series of radiographs of the shunt system because it exposes the patient to radiation and has a low diagnostic yield.6,13 Shuaib et al. reported the mean radiation dose of 223 CT scans was 1.87 ± 0.45 mSv and that of 223 shunt series was 1.57 ± 0.60 mSv, which indicates the radiation dose of a shunt series was only slightly less than for a CT scan.25 As pediatric patients with shunts often get multiple studies, in some cases even on a routine basis for follow-up, the total amount of radiation can be significant. The reported dose for a shunt flow study using technetium-99m DTPA is 0.07–0.10 mSv and thus only a fraction of the dose from a shunt series.26 The only diagnostic feature that can be ascertained from a shunt series is that of a tubing disconnection/fracture, as was the case with 7 of the 119 patients (6%) in this study. Occasionally, an incidental shunt disconnection/fracture can be observed on radiographs taken for another purpose in an otherwise asymptomatic patient. As reported by McComb,27 in asymptomatic patients without increased ventricle size, the finding of shunt fracture just distal to the valve with migration of all of the tubing into the abdominal cavity most definitely indicates that the shunt is not working and is not needed, and thus there is no need for operative intervention. For the radiographic finding in an otherwise asymptomatic patient of a relatively short gap between the 2 catheter segments, CSF can drain within the tubular connective tissue scar for a period of time, but eventually the passageway will diminish, resulting in symptomatic shunt malfunction. An RP shunt flow study may be helpful in this case. The shunt may be revised if adequate tracer flow across the separation is found but not if no flow is observed.27

Included in the decision-making process is whether a patient’s ventricles had dilated at the time of a previous malfunction if such had occurred. In our study, analysis of this factor was of no significance, but the number was very small.

Finally, it is also possible that both normal and abnormal shunt flow groups included patients who were shunt independent and whose symptoms were secondary to another cause.

Study Limitations

Our study’s generalizability is limited due to its retrospective design, sample size, and heterogeneous cohort. Because our subjects consisted of only symptomatic patients with stable ventricular size, selection bias may have influenced the results. Ultimately, the decision for obtaining a shunt flow examination was left to the discretion of one of 4 different staff neurosurgeons. Varying criteria on whether to order a shunt flow study may have affected the sensitivity and specificity of the study. Each RP flow study was reviewed by a single radiologist, so intra- and inter-observer variation was not analyzed.

Conclusions

For the detection of a CSF-diverting shunt malfunction in the presence of stable ventricular size, the sensitivity of a shunt flow study was the same as that for a shunt flow study plus MRI or CT (70% vs 70%), but the specificity did increase from 92% to 100% and the accuracy from 87% to 94%.

Naturally, experienced clinical judgment is critical in the evaluation of pediatric patients with suspected shunt malfunction with stable ventricular size. The results of this review of our RP shunt flow data support its use in helping clinicians to decide whether to surgically intervene in these cases. Until a more accurate diagnostic modality is found, a shunt flow study is the best diagnostic test to add value to the decision-making process after MRI or CT imaging and tapping the shunt.

Acknowledgments

This study and our research assistant, Jeffrey Quezada, are financially supported by the Rudi Schulte Research Institute of Santa Barbara, California (project no. RDD000051).

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: McComb. Acquisition of data: Quezada. Analysis and interpretation of data: both authors. Drafting the article: both authors. Critically revising the article: both authors. Reviewed submitted version of manuscript: both authors. Approved the final version of the manuscript on behalf of both authors: McComb. Statistical analysis: both authors. Administrative/technical/material support: both authors. Study supervision: McComb.

Supplemental Information

Previous Presentations

Portions of this work were presented at the 43rd Annual Meeting of the American Society of Pediatric Neurosurgeons, January 26–31, 2020, Nassau, The Bahamas.

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Illustration from Guida et al. (pp 346–352). Copyright Lelio Guida. Published with permission.

Contributor Notes

Correspondence J. Gordon McComb: Children’s Hospital Los Angeles, CA. gmccomb@chla.usc.edu.

INCLUDE WHEN CITING Published online July 17, 2020; DOI: 10.3171/2020.4.PEDS2020.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

  • View in gallery

    Earlier T2-weighted axial MRI for ventricular size obtained when the patient shown in Fig. 2 was asymptomatic.

  • View in gallery

    T2-weighted axial MRI for ventricular size obtained at the time of admission of the patient shown in Fig. 1 for symptoms consistent with increased intracranial pressure.

  • View in gallery

    A normal RP shunt flow study showing reflux of the tracer into the ventricles with rapid distal flow. Arrow is at the site of injection into the reservoir.

  • View in gallery

    A normal RP shunt flow study showing rapid flow of tracer distally.

  • View in gallery

    A normal RP shunt flow study showing distribution of the tracer into the peritoneal cavity.

  • View in gallery

    An abnormal RP shunt flow study showing proximal obstruction. No reflux of tracer is present in the ventricles. Arrow is at the site of injection into the reservoir.

  • View in gallery

    An abnormal RP shunt flow study showing distal obstruction, with good reflux of tracer into the ventricles without evidence of tracer distally. Arrow is at the site of injection into the reservoir.

  • 1

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