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Pediatric Radiology

, Volume 48, Issue 8, pp 1130–1138 | Cite as

Two signs indicative of successful access in nuclear medicine cerebrospinal fluid diversionary shunt studies

  • Mohammed S. Bermo
  • Hedieh Khalatbari
  • Marguerite T. Parisi
Original Article

Abstract

Background

Successful shunt access is the first step in a properly performed nuclear medicine cerebrospinal fluid (CSF) shunt study.

Objective

To determine the significance of the radiotracer configuration at the injection site during initial nuclear medicine CSF shunt imaging and the lack of early systemic radiotracer activity as predictors of successful shunt access.

Materials and methods

With Institutional Review Board approval, three nuclear medicine physicians performed a retrospective review of all consecutive CSF shunt studies performed in children at our institution in 2015. Antecedent nuclear medicine CSF shunt studies in these patients were also assessed and included in the review. The appearance of the reservoir site immediately after radiotracer injection was classified as either figure-of-eight or round/ovoid configuration. The presence or absence of early systemic distribution of the tracer on the 5-min static images was noted and separately evaluated.

Results

A total of 98 nuclear medicine ventriculoperitoneal CSF shunt studies were evaluated. Figure-of-eight configuration was identified in 87% of studies and, when present, had 93% sensitivity, 78% specificity, 92% accuracy, 98% positive predictive value (PPV) and 54% negative predictive value (NPV) as a predictor of successful shunt access. Early systemic activity was absent in 89 of 98 studies. Lack of early systemic distribution of the radiotracer had 98% sensitivity, 78% specificity, 96% accuracy, 98% PPV and 78% NPV as a predictor of successful shunt access. Figure-of-eight configuration in conjunction with the absence of early systemic tracer activity had 99% PPV for successful shunt access.

Conclusion

Figure-of-eight configuration at the injection site or lack of early systemic radiotracer activity had moderate specificity for successful shunt access. Specificity and PPV significantly improved when both signs were combined in assessment.

Keywords

Cerebrospinal fluid Children Radionuclide scintigraphy Rickham reservoir Ventriculoperitoneal shunts 

Introduction

Malfunction is a frequent concern in patients who have undergone either ventriculoperitoneal (VP) or ventriculoatrial (VA) diversionary cerebrospinal fluid (CSF) shunts to treat hydrocephalus. Malfunction can be due to mechanical failure, occlusion, disruption or the development of a loculated collection or pseudocyst and can occur at either the proximal or distal limb of the shunt catheter or at the level of the valve. The clinical presentation of a shunt malfunction is often nonspecific. Despite using multimodality anatomical imaging, correctly diagnosing diversionary CSF shunt malfunction can be a vexing clinical problem. Nuclear medicine CSF shunt scintigraphy, while an infrequently performed procedure, is often crucial in determining the need for surgical intervention. Interpreting these studies requires a thorough understanding of the shunt’s mechanics and the complications that can occur, as well as a systematic approach to performing and interpreting the study [1, 2, 3, 4, 5, 6].

Several radiopharmaceuticals have been used to perform nuclear medicine CSF shunt studies; the earliest being iodine-131 serum albumin, mentioned now only for historical interest. The radiopharmaceuticals used to evaluate CSF diversionary shunts are bound to either indium-111 (111In) as 111In-Diethylenetriaminepenta acetic acid (111In-DTPA) or to technetium-99m (99mTc) as 99mTc-DTPA or 99mTc-pertechnetate. Because of the procedure’s short duration, decreased cost and improved radiation dosimetry, the technetium agents are preferred over 111In-DTPA. While not approved by the United States Food and Drug Administration (FDA) for CSF shunt scintigraphy, 99mTc-pertechnetate is the least expensive and most readily available radiotracer in most nuclear medicine departments and has been widely and safely used for CSF shunt scintigraphy in many institutions in the United States, Europe and Asia [7, 8, 9, 10].

The first step in performing nuclear medicine CSF shunt scintigraphy, after assessing prior imaging and confirming the type of shunt present, is to successfully access the shunt. Needle access of the CSF shunt reservoir can be challenging, especially in patients with multiple prior shunt surgeries [11, 12, 13, 14].

Reservoirs are either integrated into the valve or, more commonly, placed as a separate structure between the proximal catheter and the valve. The latter results in easy access for CSF sampling, intracranial pressure measurements and radiotracer installation in nuclear medicine CSF shunt studies. At our institution, a Rickham reservoir, which was initially described by Rickham in 1964 [15], is usually placed when a patient undergoes CSF shunt placement [16, 17, 18]. Confirming the proper injection of the radiotracer into the shunt reservoir is essential to ensure that a diagnostic study will be obtained [9, 13, 19, 20].

The Rickham reservoir and adjacent valve have a characteristic figure-of-eight configuration on CSF shunt studies with the smaller loop adjacent to the proximal limb of the catheter representing the Rickham reservoir and the larger loop adjacent to the distal catheter representing the valve (Fig. 1). Imaging in the proper view, parallel to the long axis of the valve-reservoir complex, should show this figure-of-eight configuration at the time of the radiotracer instillation in cases of successful shunt access [4, 5].
Fig. 1

An example of a typical configuration of a cerebrospinal fluid shunt. a Surface-rendered 3-D CT of the calvarium of a 5-month-old boy with a history of multisuture craniosynostosis shows the typical configuration of the Rickham reservoir and valve components of a cerebrospinal fluid shunt. b Static planar image at the injection site shows typical figure-of-eight configuration (inset) conforming to the shunt reservoir and valve

The two most commonly encountered CSF diversionary shunts are the ventriculoperitoneal (VP) shunt in which the distal tip of the diversionary catheter lies within the peritoneal cavity and the ventriculoatrial (VA) shunt in which the distal tip of the diversionary catheter lies within the right atrium.

On nuclear medicine CSF shunt scintigraphy, the normally functioning (patent) VP shunt will demonstrate prompt egress of the radiotracer from the reservoir through the distal limb of the shunt catheter with free intraperitoneal spillage (Fig. 2).
Fig. 2

Nuclear medicine cerebrospinal fluid shunt scintigraphy in a patent, normally functioning ventriculoperitoneal shunt in a 16-month-old boy. a Serial post-injection images show the typical figure-of-eight configuration of the reservoir-valve complex at the injection site and linear egress of the radiotracer along the distal limb to the abdominal level. b Anterior planar image of the abdomen and pelvis obtained 10 min post injection shows free dispersion of the radiotracer throughout the peritoneum, an expected appearance in a normally functioning shunt. c Time activity curve demonstrates timely clearance of the reservoir (half time is 126 s)

A lack of radiotracer egress is usually seen in cases with either shunt malfunction [21] or inadvertent injection of the radiotracer in the subcutaneous tissue of the scalp outside the reservoir (extravasation). Differentiation between these two conditions can be challenging [22].

Early systemic radiotracer activity visualized in the blood pool, thyroid gland or stomach is expected in the normally functioning VA shunt (Fig. 3) but not in properly accessed VP shunts. Demonstration of early systemic radiotracer activity after instillation of the radiotracer in a VP shunt raises suspicion for partial or incomplete infiltration of the radiotracer dose in the subcutaneous tissue of the scalp with rapid absorption into the systemic circulation [23, 24, 25].
Fig. 3

Nuclear medicine cerebrospinal fluid shunt scintigraphy of a patent ventriculoatrial shunt in a 12-year-old girl. a Serial post-injection images show linear egress of the radiotracer along the distal limb down to the heart. Note early radiotracer activity in the thyroid gland (arrowhead). b Anterior image of the neck, chest and abdomen acquired at 5 min post injection shows early systemic activity in the thyroid gland (arrowhead), mediastinal blood pool (short arrow) and stomach (long arrow). c Time activity curve demonstrates timely clearance of the reservoir (half time is 54 s)

This study aims to determine the significance of the configuration of the radiotracer at the injection site during initial nuclear medicine CSF shunt imaging as well as the absence of early systemic distribution of the radiotracer as predictors of successful shunt access.

Materials and methods

After Institutional Review Board approval was obtained, three nuclear medicine physicians performed a retrospective review of all consecutive nuclear medicine CSF shunt studies for VP shunts obtained at our institution during 2015. Antecedent nuclear medicine CSF shunt studies in these same patients were also assessed and included in the review. This retrospective analysis evaluated a total of 98 nuclear medicine CSF shunt studies performed in 37 patients.

Nuclear medicine CSF shunt study technique

A nuclear medicine CSF shuntogram was requested based on clinical suspicion of shunt malfunction, including signs and symptoms such as headache, vomiting, change in ventricular size on CT or MRI, or apparent shunt disruption on plain film shunt survey. In all cases, prior imaging (CT head or shunt series) was reviewed before the procedure. The risks, benefits and potential complications were explained to the patient and accompanying parent. Their verbal consent was obtained. The shunt reservoir was palpated and accessed using an aseptic technique, typically by the pediatric radiologist or nuclear medicine physician or, in selected cases, by a member of the neurosurgical team using a 25-gauge needle. Opening CSF pressure was obtained when possible, using a Compass device (2-Compass® for Lumbar Puncture; Centurion Medical Products, Williamston, MI). A CSF fluid sample was obtained when requested by the referring clinician. A radiologist or nuclear medicine physician gently instilled 0.1 mCi of Technetium 99mTc-pertechnetate into the reservoir. In our practice, the distal limb of the catheter is not occluded at the time of injection. Only rarely is the shunt reservoir pumped during the procedure, typically when gravitational maneuvers such as upright positioning fail to show egress of tracer into the distal limb or when proximal limb obstruction is suspected. In all studies, sequential dynamic imaging parallel to the long axis of the valve-reservoir complex was obtained at 10-s intervals for a total of 5 min, followed immediately by anterior and lateral static images of the head and neck. Static anterior images of the chest, abdomen and pelvis were then obtained 10 min after radiotracer injection. Additional delayed static images of the abdomen and pelvis were obtained at varying intervals, typically at 20 min, to confirm free intraperitoneal spill of radiotracer if not present on the 10-min images. Gravity-assisted procedures such as placing the patient upright or having them ambulate, followed by delayed static imaging, were performed as needed.

Qualitative visual assessment

A total of 98 nuclear medicine CSF shunt studies were reviewed by three nuclear medicine physicians; one, a nuclear medicine fellow (M.S.B.), the other two, pediatric radiologists with nuclear medicine certification (H.K. with 10 years and M.T.P. with 27 years of experience). The gold standard for shunt obstruction or contrast extravasation included clinical correlation, follow-up imaging, operative reports or a combination depending on the individual patient.
  • The appearance of the reservoir site in the initial post-injection imaging was classified into either one of two configurations: figure-of-eight or round/ovoid.

  • The presence or absence of early systemic distribution of the radiotracer in the thyroid, heart or stomach on the 5-min static images was noted.

Two signs of successful shunt access were hypothesized based on prior clinical observations and historical data: figure-of-eight configuration and lack of early systemic activity. Statistical analysis included calculation of the sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for figure-of-eight configuration, lack of early systemic activity, figure-of-eight configuration AND lack of early systemic activity, and figure-of-eight configuration AND/OR lack of early systemic activity.

Results

A total of 98 nuclear medicine CSF shunt studies were evaluated in 37 patients: 19 patients underwent one study, 6 patients underwent 2 studies, and 12 patients underwent 3 or more studies. Fifty-seven studies were performed in males and 41 in females. Mean age was 112 months (range: 10-264 months). Clinical indications for 50 studies were either headache, vomiting or a combination of both. Other presenting complaints included visual changes, worsening neurological symptoms, or change in ventricular size on CT or MR.

Configuration at the injection site (Table 1)

The figure-of-eight configuration was present in 85 studies: 83 had successful shunt access (Fig. 4), 1 had partial extravasation and 1 had extravasation with tracking along a fibrous tract.
Table 1

Frequency of the two configurations of radiotracer at the injection site on initial imaging and their correlation with successful shunt access

Configuration

Successful shunt access

Extravasation

Total

Figure-of-eight

83

2

85

Round/ovoid

6

7

13

Total

89

9

98

Fig. 4

Obstructed ventriculoperitoneal (VP) shunt with proper injection into the VP shunt reservoir in a 3-year-old boy. a Magnified planar image at the injection site shows characteristic figure-of-eight configuration of the shunt reservoir and valve. b Time activity curve confirms the lack of clearance of the radiotracer at the injection site. c Delayed image of the head, neck, chest and upper abdomen acquired 30 min after allowing the patient to walk shows lack of early identified systemic activity and a lack of peritoneal spill of the radiotracer. Note that the configuration of radiotracer activity at the shunt-reservoir complex appears different than (a) due to a different imaging view. Obstruction of the distal limb of the cerebrospinal fluid shunt was confirmed at surgery

The round/ovoid configuration was seen in 13 studies: 7 had extravasation (Fig. 5) and 6 were false-positive. Causes of false positives included: injection into the valve (four cases), proximal shunt obstruction (one case) and a single case in which the figure-of-eight appearance was noted only after pumping the shunt.
Fig. 5

Inadvertent injection of the radiotracer in the subcutaneous tissue of the scalp of a 19-year-old man. a Serial post-injection images show round configuration at the injection site and lack of distal radiotracer egress. b Anterior image of the chest and abdomen acquired at 5 min post injection shows early systemic activity in the thyroid gland (arrowhead), mediastinal blood pool (short arrow) and stomach (long arrow). c Time activity curve confirms the lack of egress of the radiotracer. The constellation of findings of the lack of figure-of-eight configuration and early systemic radiotracer activity is indicative of extravasation. The study was repeated the following day: d Serial post-injection images show figure-of-eight configuration at the injection site and progressive distal radiotracer egress. e Anterior view of the abdomen acquired 10 min after injection shows the distal limb of the catheter and free peritoneal spill of the radiotracer. f Time activity curve demonstrates timely clearance of the reservoir (half time is 67 s)

The presence of the figure-of-eight configuration had 93% sensitivity, 78% specificity, 92% accuracy, 98% PPV and 54% NPV as a predictor of successful shunt access. The low NPV was due to confounding variables such as injection into the valve, non-egress of the radiotracer that improved after manual pumping, or obstruction of the shunt at the proximal limb, at the valve or at both levels.

Early systemic activity (Table 2)

Early systemic activity was absent in 89 studies: 87 had successful shunt access and 2 had extravasation along a fibrous tract or within a loculated scalp pseudomeningocele (Fig. 6).
Table 2

Frequency of visualization of early systemic radiotracer activity and its correlation with successful shunt access

Early systemic activity

Successful shunt access

Extravasation

Total

Early systemic activity

2

7

9

No early systemic activity

87

2

89

Total

89

9

98

Fig. 6

Inadvertent injection of the radiotracer into a scalp pseudomeningocele of a 2-year-old girl with shunted hydrocephalus following several resections of desmoplastic infantile ganglioglioma. a Magnified image at the injection site shows a bizarre-shaped configuration conforming to the shape of the scalp pseudomeningocele. b Coronal T2-W MRI demonstrates the scalp pseudomeningocele and adjacent artifact generated by the cerebrospinal fluid shunt valve. c Time activity curve shows slow clearance of the radiotracer at the injection site

Early systemic activity was present in nine studies: seven had extravasation and two had successful shunt access.

The absence of early systemic distribution of the radiotracer had 98% sensitivity, 78% specificity, 96% accuracy, 98% PPV and 78% NPV as a predictor for successful shunt access. False-negative cases demonstrating early systemic radiotracer activity in the presence of successful shunt access were due to reflux of radiotracer into the ventricles with resultant absorption into the systemic circulation. False positives (with absence of systemic radiotracer activity) were due to fibrosis around the site of extravasation impeding systemic absorption of the radiotracer as confirmed by palpation or surgical notes.

The presence of the figure-of-eight configuration when assessed in conjunction with the absence of early systemic tracer activity had 99% PPV for successful shunt access. At least one of the two signs was present in all cases of successful shunt access (Table 3).
Table 3

Sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of the two evaluated parameters as predictors of successful shunt access

Predictor of successful shunt access

Sensitivity

Specificity

Accuracy

PPV

NPV

(A) Figure-of-eight

93%

78%

92%

98%

54%

(B) Lack of early systemic activity

98%

78%

96%

98%

78%

(A) AND (B)

91%

89%

91%

99%

50%

(A) AND/OR (B)

100%

67%

97%

97%

100%

Successful shunt access was identified in 89 studies

In 81 cases, the figure-of-eight configuration was present and there was no early systemic activity (the typical pattern).

In six cases, a round/ovoid configuration was present, but no early systemic activity was seen due to either injection in the valve (n=4), proximal obstruction (n=1) or a single case in which the more typical figure-of-eight appearance (n=1) was noted only after pumping the shunt.

In two cases, the figure-of-eight appearance was present in conjunction with early systemic radiotracer activity due to intraventricular reflux.

Extravasation was present in nine studies

In six cases, round/ovoid configuration at the injection site was present in conjunction with early systemic activity, a classic pattern indicating radiotracer extravasation at the time of injection.

In one case, the figure-of-eight configuration was associated with early systemic radiotracer activity due to partial extravasation at the injection site.

In another case, the figure-of-eight configuration was present without associated systemic radiotracer activity due to tracer tracking along a fibrous tract.

There was a single case with an atypical configuration of radiotracer at the injection site without the presence of early systemic activity due to injection within a loculated scalp pseudomeningocele (Fig. 6).

Discussion

Knowledge of the type of CSF shunt present and correlation with anatomical imaging in conjunction with measurement of opening CSF pressures are crucial for properly interpreting CSF shunt scintigraphy.

Observing the characteristic figure-of-eight configuration of the Rickham reservoir and adjacent valve on nuclear medicine CSF shunt studies confirms that the radiotracer has been correctly instilled into the Rickham reservoir (with subsequent flow into the valve) during injection.

Complete extravasation of radiotracer into the soft tissues of the scalp has a round or ovoid configuration. This has been previously described is several early reports [10, 25, 26, 27, 28]; however, the accuracy of this finding as a predictor of extravasation has not been further studied. It has been suggested that a round/ovoid configuration at the injection site in conjunction with lack of radiotracer egress after digital pumping will be more specific for diagnosing extravasation [25]. Our data showed that round/ovoid configuration had only moderate PPV (54%) for extravasation and could also be seen in cases with successful injection of the radiotracer in the shunt system, for example in cases of shunt obstruction with lack of CSF egress or in cases where the radiotracer is instilled into the valve rather than the Rickham reservoir.

While early systemic radiotracer activity is normal in patients with a properly functioning VA shunt [29], it is an unexpected finding in functioning as well as in obstructed VP shunts due to either relatively slow transit to the peritoneal cavity in obstructed shunts or slow absorption from the peritoneal surface in patent shunts. Early systemic radiotracer activity should raise suspicion for rapid absorption in the subcutaneous tissues of the scalp due to extravasation [10, 23, 27, 28].

In our series, early systemic activity was occasionally seen in cases with successful shunt access but significant unprovoked intraventricular reflux of the injected radiotracer resulting in rapid absorption of the radiotracer into the systemic circulation. Intraventricular reflux of the radiotracer is an occasional finding during CSF shunt scintigraphy that indicates patency of the proximal limb. Some centers recommend digital compression on the distal limb during radiotracer injection to force radiotracer into the ventricles to confirm patency of the proximal limb. Other centers accept the presence of normal CSF opening pressure and flow into the distal shunt tubing as sufficient indicators of proximal limb patency. Unfortunately, digital compression is not always sufficient to occlude the distal limb and further, and as seen in our study, further intraventricular reflux of the radiotracer may result in early systemic activity mimicking extravasation [29].

Visualization of early systemic radiotracer activity may be lacking in cases of extravasation if there is significant fibrosis at the injection site due to multiple prior shunt surgeries; this extensive fibrosis is expected to limit systemic absorption of the radiotracer.

While isolated figure-of-eight configuration or lack of early systemic radiotracer activity had moderate specificity for predicting successful access of the shunt reservoir, combining the two signs significantly improved the specificity (91%). Conversely, when both signs were absent (i.e. round/ovoid configuration at the injection site and the presence of early systemic activity), failed shunt access and extravasation were present.

The study is limited by relatively small number of CSF shunt studies with failed shunt access.

Conclusion

The figure-of-eight configuration at the injection site or lack of early systemic radiotracer activity had moderate specificity for successful shunt access. The specificity and PPV significantly improved when these two signs were combined in assessment. At least one of those signs was present in all cases of successful shunt access. Proper identification of the signs of failed shunt access is important to avoid a misdiagnosis of shunt malfunction.

Notes

Compliance with ethical standards

Conflicts of interest

None

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of RadiologyUniversity of WashingtonSeattleUSA
  2. 2.Department of RadiologySeattle Children’s HospitalSeattleUSA
  3. 3.Department of Pediatrics, Seattle Children’s HospitalUniversity of Washington School of MedicineSeattleUSA

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