Introduction

Insertion of an external ventricular drain (EVD) is one of the most frequently practiced emergency neurosurgical procedures. Patients requiring EVD placement are usually in critical condition and are managed in an intensive care setting.17)

The universal standard technique of EVD placement is free-hand insertion, using surface landmarks to direct the ventricular catheter from a frontal burr hole toward the ipsilateral frontal horn of the lateral ventricle close to the foramen of Monro.7)9)15)

Most published studies have dealt with EVD complications such as infection and hemorrhage, but few have reported on the accuracy of standard techniques for EVD catheter positioning. In this study, the authors analyzed the institutional practice of EVD insertion in terms of the accurate localization of the EVD tip and performed a retrospective study to determine the accuracy of successful EVD placement.

Materials and Methods

All the EVD insertion procedures performed in our hospital during the study period from January 2007 to December 2009 were retrospectively analyzed. The patients's medical records were reviewed via an electronic medical information system.

All patients had at least one routine post-EVD computed tomographic (CT) head scan, which was reviewed using the hospital PACS system for the accuracy of the EVD tip position. The preoperative Evan's index (the maximal frontal horn ventricular width divided by the transverse inner diameter of the cranium at the same brain scan section) was also measured. EVD tip location was categorized into one of the following six groups:1) ipsilateral frontal horn of the lateral ventricle,2) contralateral frontal horn of the lateral ventricle,3) third ventricle,4) ipsilateral or contralateral body of the lateral ventricle,5) basal cistern, or6) brain parenchyma.

The estimated intracranial EVD length was measured on the scout images of the CT scan, measuring from the tip of the EVD to the inner table of the cranium at the burr hole. The standard practice in our institution is to perform all EVD insertion procedures in the operating room with the patient under local anesthesia after routine skin preparation and draping, with the patient's head in a neutral position. About a 3cm skin incision is made over the Kocher's point (2.5cm from midline and 1cm anterior to the coronal suture). A burr hole is made using a high-speed air drill (6mm in diameter), bipolar coagulation occurs, and then a dural opening is created and the stylet-loaded ventricular catheter is introduced, aimed at the medial epicanthus in the coronal plane and just anterior to the external auditory meatus in the sagittal plane. The desired target is the ipsilateral frontal horn of the lateral ventricle close to the foramen of Monro. The catheter is kept in a position that is not to be advanced beyond 6 cm from the brain surface. The used EVD catheter is 35cm in length and 2.8mm in outer diameter, has 3 markings at 5cm intervals, and 4 proximal fenestrations that extend over 2.4cm. Free flow of CSF is considered a sign of successful placement, which is usually followed by subcutaneous tunneling of the distal end of the ventricular catheter before closing the skin and fixing the catheter to avoid inadvertent postoperative pullout. The distal end of the catheter is then attached to a closed drainage bag system and/or intracranial pressure monitor unit.

Results

A total of 113 patients had emergency free hand EVD insertion procedures during the last 3 years. The mean age of the patients was 55.6±15.3 years (age range, 12~90 years), and there were 58 male and 55 female patients. The most common indication for EVD placement was supratentorial ICH and IVH (57.5%) (Table 1).

The EVD was inserted on the right side through Kocher's point in 67 procedures (59.3%), on the left in 34 (30.1%), and bilaterally in 12 (10.6%). The mean preoperative Evan's index was 0.37±0.065.

Forty-five of a total of 113 EVDs were placed by less experienced neurosurgical trainees, and the remaining 68 were placed by experienced practitioners. A postoperative CT scan was routinely performed in all 113 patients. Of those, 48 EVD tips (42.5%) were in the ipsilateral frontal horn of the lateral ventricle close to the foramen of Monro (considered to be the correct position); 22 (19.5%) were in the third ventricle, 16 (14.1%) in the body of the ipsilateral or contralateral lateral ventricle, 14 (12.4%) in the contralateral frontal horn of the lateral ventricle, 11 (9.7%) within the brain parenchyma, and 2 (1.8%) in the basal cistern (Fig. 1).

The mean estimated intracranial EVD length was 57± 8.4 mm. The mean length of the intracranial EVDs that were positioned in the ipsilateral frontal horn was 55±4.3mm, whereas those in the brain parenchyma and basal cistern were 64±14. mm and 72±3.5 mm, respectively. There was a statistically significant relationship between the EVD tip location (correct or wrong position) and the intracranial EVD length. This result comes out if the intracranial EVD length of 6 cm is set as a reference (p=0.001) (Table 4).

When the Evan's index of preoperative CT scans was less than 0.4, 37.2% of the EVD tips were not in the ipsilateral frontal horn of lateral ventricle compared to 20.4% with an Evan's index of more than 0.4 (p=0.180) (Table 2).

There was no statistically significant relationship between the surgeon's experience and the accuracy of the position of the EVD tip (p=0.411) (Table 3).

Discussion

Intraoperatively, neurosurgeons typically and repeatedly measure the success or failure of free hand EVD placement by the free flow of CSF from the distal end of the EVD catheter. Most ventricular catheters have multiple holes along the proximal 2 to 2.5cm, so successful placement of a few of these holes within the CSF space produces at least a brief period of CSF flow intraoperatively, even though the tip might be within the brain parenchyma. This explains our observation that approximately 50% of EVD tips were in CSF spaces other than the desired frontal horn of the lateral ventricle and that almost 10% of the tips were within the brain parenchyma. Our results are not far from the results of previous reports on the same subject.4)11)12)

Huyette et al.11) studied the accuracy of freehand ventriculostomy in 97 patients. In Huyette et al.'s study, 56.1% of EVD catheter tips were in the ipsilateral lateral ventricle, 7.1% in the contralateral lateral ventricle, 8.2% in the third ventricle, 6.1% within the interhemispheric fissure, and 22.4% within extraventricular spaces. Khanna et al.12) retrospectively compared the accuracy of practice for EVDs with parenchymal intracranial pressure (ICP) monitors. The rate of misplaced EVDs was 20% (21 out of 104) and included the EVD catheter tips that were placed in the third ventricle, thalamus, brainstem, and other areas. Bogdahn et al.4) reported an 11% rate of misplaced EVDs that had to be replaced.

In a study on the surgical management of EVD placement using a virtual reality simulator, 57 (73%) of 78 catheter tips successfully reached the ventricle, and the remaining 21 out of 78 attempts (27%) were unsuccessful. Among the successful attempts, 22 (38.5%) reached the anterior horn of the ipsilateral lateral ventricle, whereas 48 of 113 (42.5%) EVD tips were in the frontal horn in this current study. In addition, the study using the virtual reality simulator found that there was no statistically significant correlation between the number of neurosurgical training years of the surgeon and the performance3), which was also found in the present study.

Many techniques have been used in the past to improve the success rate and accuracy of ventricular catheter placement. Percutaneous CT controlled ventriculostomy has improved the accuracy of EVD placement and reduced the number of required EVD catheter passes as well as allowed the use of a twist drill hole as opposed to burr hole.13)18) HS Min and JH Song10) reported on the accuracy of placement of a parieto-occipital ventricular catheter using CT parameters during a ventriculoperitoneal shunt (VPS) procedure. In Min and Song's study, of 20 patients undergoing VPS insertion using this technique, none had poor location of the proximal ventricular catheter. In the counterpart (non-CT guided group), 9 out of 20 patients had poor location (p=0.001).

The Ghajar Guide (Neurodynamics Inc., New York, NY, USA) is a device that sits on the calvarial surface and guides the ventriculostomy perpendicular to the plane tangent to the calvarium at the burr hole. It is useful only when the patient's brain anatomy has not been distorted by a mass lesion. In a prospective trial assessing EVD placement accuracy using the Ghajar Guide, the average distance from the ventriculostomy catheter tip to the foramen of Monro was 3.7±5.7mm using the guide and 9.7±6.3mm without the guide16). Comparing the results of the free hand group in this study to those of the study of Huyette et al. in terms of the success rate of placing the EVD catheter tip in the ipsilateral lateral ventricle (96.0% versus 56.1%) raises the question of whether placement accuracy is related to the competitive nature of a prospective and retrospective study or to the emphasis on keeping a 5.5cm of intracranial EVD length.11)

In a study of image-guided robotic placement of 16 ventricular catheters, successful placement with a single pass was reported with no intraparenchymal catheter tip placement. The mean distance of the catheter tip from the target was 1.5±2.8mm. Furthermore, 9 of 16 patients (56%) had a ventricular diameter of 5mm of less.14) A potential advantage of image-guided methods is one-pass catheter placement, which may decrease procedural time, especially when the patient's anatomy is grossly distorted and the superficial anatomical landmarks are rendered useless. On the contrary, the disadvantages of image-guided techniques are that they are considerably more expensive, require equipment that may be awkward to use or bulky, and have a limited capability for real-time upgrading of the images.11)

Other proposed methods to improve the accuracy of ventricular catheter placement include the use of a localizer device or endoscope,2) and stylet guidance using ultrasonography.8) In addition, training simulation has been used in neurosurgery education and can be applied to ventriculostomy training to improve the performance of the procedure.3)6)

This study has several limitations common to retrospective studies. We did not investigate in any case whether there was a revision due to the wrong placement of an EVD, the outcome and its relation to the malposition of the EVD tips. We also did not count and analyze the number of passes of the EVD catheter needed for successful CSF drainage; this number, can be related to outcome.

Conclusion

The results of the present analysis show that there was a statistically significant relationship between the EVD tip location and intracranial EVD length. On the other hand, there was no statistical significance between the tip location and Evan's index, as well as between the tip location and surgeon's experience.

Many neurosurgeons may feel that the current practice of EVD placement is adequate. However, we consider that emergency free-hand insertion of an EVD may be an inaccurate procedure. The results of this study show that there is much room for improvement.

Further multi-institutional prospective study is required to assess the accuracy and complications of free hand placement of an EVD, as well as the feasibility of routine use of intra operative neuro-navigation using other guidance tools, such as an ultrasonography.

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