Trephination, or the creation of bur holes in the. Don t take the plunge: avoiding adverse events with cranial perforators.

Transcription

1 J Neurosurg 115: , 2011 Don t take the plunge: avoiding adverse events with cranial perforators Clinical article Timothy W. Vogel, M.D., Brian J. Dlouhy, M.D., and Matthew A. Howard III, M.D. Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa Object. The object of this study was to evaluate the causes of plunging events associated with automatic-releasing cranial perforators at the authors institution. Methods. The authors analyzed a consecutive series of 1652 cranial procedures involving one type of automaticreleasing cranial perforator over a 2-year period. Plunging occurrences were recorded for 2 drill speeds: 1000 rpm in the 1st year and 800 rpm during the 2nd year. Intraoperative observations, neuroimaging studies, and clinical data were evaluated for each plunging event. Results. The authors identified 9 plunging events for an overall incidence of 0.54%. In the 1st year, they identified 2 plunging events at a speed of 1000 rpm for an incidence of 0.19%. In an effort to reduce this occurrence, the speed of the drill was lowered to 800 rpm. There were 7 additional events, for a significantly increased incidence of 1.16% (p = 0.014, Fisher exact test) after the change was implemented. These cases spanned a number of procedures in adults and pediatric patients, including ventriculostomy placement, craniotomies for tumor resection, tumor biopsy, and endoscopic third ventriculostomy. Despite plunging, no immediate postoperative complications were noted on clinical examination. Conclusions. While technology continues to improve cranial perforator performance, the use of such a device is still associated with a risk of complications causing dural lacerations and injury to the underlying cortex. Decreasing the drill speed may not decrease the incidence of plunging. (DOI: / JNS101310) Key Words cranial perforator plunging craniotomy dural tear cortical injury cranial drill surgical technique Trephination, or the creation of bur holes in the skull, using various drills is a routine practice in neurosurgery. 11 Historically, twist drills such as the Hudson brace, invented by Robert J. Hudson in 1877, 1,6 were used for trephining the skull. With technological advances in automatic and pneumatic drills, automaticreleasing perforators have been developed and are now widely used at many neurosurgical centers. These perforator attachments were designed with a release mechanism 4,16 that automatically disengages the drill when the inner table of the calvaria is violated. This design reduces the incidence of plunging into the intracranial space. There are, however, complications associated with drilling a bur hole, 3 including skull fracture, enlarging pseudomeningocele, 3 infection, hemorrhage, 4,14 and death. 8 In addition, there is the potential to plunge the drill into the cranial cavity, lacerate the dura mater, and cause intracranial hemorrhage. 9,15 Plunging is defined as an uncontrolled rapid increase in depth of the cranial perforator or drill and is more common with manual drills than with automatic ones. 15 Plunging is a frequent but underreported complication of cranial drills and perforators. A previous study in Britain and Ireland documented 65.6% of surveyed neurosurgeons reporting at least 1 plunging event and 22.3% who experienced more than 1 event during their careers. 1 Plunging occurred during a variety of neurosurgical procedures requiring bur hole placement and was associated with intracranial hemorrhagic complications in 26% of the events. In addition, plunging was reported as carrying a 12% risk of death or permanent neurological morbidity. 1 As a result of the significant increase in the morbidity and mortality rates associated with cranial perforators, we identified the incidence of plunging during the use of 1 type of automatic-releasing perforator attachment (Fig. 1) at our institution. Here we describe 9 cases in which plunging occurred and describe our efforts to identify and correct the causes of these events. This work represents, to our knowledge, the first study in the US to address such complications arising from cranial perforators. 570 J Neurosurg / Volume 115 / September 2011

2 Avoiding adverse events with cranial perforators to reduce plunging incidents by reducing the rotational speed from 1000 rpm to 800 rpm to comply with manufacturer specifications. Intraoperative observations and radiographic and clinical outcome data were recorded for each plunging event. Skull thickness was measured on postoperative head CT scans with a bone window. Preoperative CT or MR imaging was compared with postoperative studies. Either T2-weighted or FLAIR MR sequencing was used when available. The Fisher exact test with a 2-tailed p value was used to test for a statistical significance < Fig. 1. A: Photograph of the automatic-releasing cranial perforator model used in this study. B: Photograph of the cranial perforator with the inner bore resting on model skull revealing a 3-mm-thick gap between the inner and outer cutting surfaces. C: Photograph of inner and outer drill contacting the skull. D: Photograph of cranial perforator resting on an uneven bone surface of keyhole adjacent to frontozygomatic suture. Methods After identifying plunging events during surgical procedures, we surveyed the scientific literature for citations in MEDLINE/PubMed using the search phrases plunging, burr hole and complications, neurosurgery and drill and complications, and craniotomy and drill. We identified various reference articles and used these references to identify additional primary literature citations pertaining to cranial perforators. Between April 2008 and April 2010, 1652 cranial surgeries utilizing a single type of automatic-releasing disposable perforator attachment (ACRA-CUT with Hudson end # DGR-O 14/11MMR, ACRA-CUT, Inc.) on an electric cranial drill (Midas Rex, Medtronic, Inc.) were performed in adult and pediatric neurosurgical cases at our institution. We identified plunging incidents that were documented by the surgeon and nursing staff in the operative reports. In an effort to capture each plunging event, we formalized a reporting process between surgeons and nursing staff for patient safety documentation. During this reporting period, an attempt was made J Neurosurg / Volume 115 / September 2011 Results Patient Clinical Data After reviewing 1652 cranial cases performed over a 2-year period at our institution, we identified 9 cases in which plunging occurred, for an overall incidence of 0.54%. There were 2 cases in the 1st year, when 1000 rpm was used for the drill speed. During this period, 1050 cranial surgeries were performed using the same automaticreleasing disposable perforator attachment, yielding a plunging incidence of 0.19%. We consulted the optimal drill settings described by the manufacturer in an effort to reduce this incidence. The speed of the drill was lowered to 800 rpm the next year, and the same automaticreleasing disposable perforator attachment was used in 602 cranial cases (Fig. 2). Seven additional occurrences were identified, for a significantly increased plunging incidence of 1.16% (p = 0.014, Fisher exact test). Six cases involved adult patients 20 years of age or older, 2 cases involved elderly patients 60 years or older, and 1 case involved a 15-year-old pediatric patient. The average age of patients affected by a plunging incident was 45.8 years. Patients presented with a variety of pathologies necessitating a cranial procedure. Five patients (56%) presented with hydrocephalus caused by different factors including 1 case each of traumatic brain injury, subarachnoid hemorrhage, intraparenchymal hemorrhage, tumor obstructing the foramen of Monro, and shunt failure (Table 1). Three patients (33%) presented with a tumor that was not complicated by hydrocephalus, and the final patient (11%) had a complex skull fracture. Patients were evaluated for postoperative complications potentially arising from the plunge event. There were no clinical deficits directly attributable to the location of the plunge. Fig. 2. Bar graph showing the incidence of plunging events as compared with perforator speed. 571

3 TABLE 1: Summary of clinical data on 9 plunging events during cranial procedures* Pt Age (yrs) Pathology Procedure T. W. Vogel, B. J. Dlouhy, and M. A. Howard III Speed (rpm) Bur Hole Location Skull Thickness (mm) Dural Tear Reason for Failure 50 frontal oligoastrocytoma craniotomy 1000 keyhole 5.6 yes failure to stop 29 hydrocephalus w/ colloid cyst obstructing foramen bilat ventriculostomies 1000 frontal bone 12.0 yes failure to stop of Monro 30 frontal comminuted & depressed skull fracture w/ craniotomy 800 frontal sinus 8.7 no stop & restart spinal fluid leak 76 TBI & hydrocephalus ventriculostomy 800 frontal bone 7.5 yes failure to stop 59 cavernous sinus meningioma biopsy 800 sphenoid wing 4.2 yes failure to stop 60 hydrocephalus from subarachnoid hemorrhage ventriculostomy 800 frontal bone 14.2 yes failure to stop 49 intraparenchymal hemorrhage & hydrocephalus ventriculostomy 800 frontal bone 12.7 yes failure to stop 15 shunt failure & hydrocephalus ETV 800 frontal bone 7.0 yes failure to stop 41 petrous-tentorial meningioma craniotomy 800 keyhole 6.1 yes failure to stop * ETV = endoscopic third ventriculostomy; Pt = patient; TBI = traumatic brain injury. Procedure-Related Results Seven events (78%) occurred when senior trainees were operating (postgraduate year 4 or later), and 2 events (22%) involved faculty members. Two surgeons plunged more than once. The type of procedure utilizing the cranial perforator was recorded. Four incidents (44%) occurred during ventriculostomy placement, 3 (33%) during craniotomy, 1 (11%) during tumor biopsy, and 1 (11%) during bur hole placement for an endoscopic third ventriculostomy. Eight cases (89%) involved failure of the cranial perforator to stop as it passed through the inner table, and 1 case (11%) involved the starting, stopping, and then restarting of the cranial perforator, which led to a plunge. In 2 cases (22%) a plunging incident occurred during the second bur hole placement of the cranial procedure, whereas in the remaining cases the incident happened during the first bur hole placement. Bur hole locations during the plunge were also recorded. Five incidents (56%) took place in the frontal bone, 2 (22%) in the frontal bone just superior and posterior to the frontozygomatic suture (during drilling of the keyhole), 1 (11%) in the lateral sphenoid bone, and 1 (11%) adjacent to a fractured frontal sinus. The underlying dura was lacerated in 8 cases (89%; Table 1). There were no reports of intraoperative hemorrhage following bur hole placement with a cranial perforator. Radiographic Imaging Results There were 3 cases (33%) in which the underlying cortex showed increased T2 signal changes, indicating a possible cortical injury (Fig. 3 left). In 1 such case, followup MR imaging was available 3 months after the incident and revealed resolution of the cortical signal changes (Fig. 3 right). On postoperative imaging in all 9 cases, no intraparenchymal hemorrhages were noted to underlie the location of the plunge. The thickness of the skull was calculated at the site of bur hole placement. The mean skull thickness of involved bone for these 9 cases was 8.7 mm (range mm). The mean thickness of the frontal bone in which bur holes were placed (5 cases) was 10.7 mm (Table 1). Discussion Instrument Design The technology used in contemporary cranial perforators was developed over 60 years ago when the perforator was combined with a power drill to offer a reliable and efficient means of trephining the skull. 2,16 The design incorporates a release mechanism for safety that relies on pressure being maintained on the center point of the perforator as long as the drill is passing through intact skull (Fig. 4). 16 Once the inner table is removed by the action of the drill, pressure on the center bore decreases, which activates a releasing mechanism that disengages the driving force and stops the cutting bore. 4 From these pioneering designs, continuous improvements have been made to ensure a reduced rate of complications. Some examples include incorporating a clearing mechanism to remove bone fragments from the bur hole and modifying the perforator bit to leave a thin shelf of bone to protect underlying dura. The cranial perforator featured in this study possesses a cammed-lug release mechanism that activates only Fig. 3. Left: Axial T2-weighted MR image obtained 48 hours postoperatively, showing hyperintensity in the cortex directly underlying the bur hole where the plunging incident occurred. Right: Axial T2- weighted MR image obtained 3 months after surgery, showing resolved hyperintensity in underlying cortex. 572 J Neurosurg / Volume 115 / September 2011

4 Avoiding adverse events with cranial perforators Fig. 4. A: Axial head CT with bone window revealing comminuted fracture of the frontal bone. B: Axial CT with brain window demonstrating underlying cortex. C: Axial CT with bone window obtained 24 hours postoperatively, showing bur holes adjacent to the previous fracture site. D: Axial CT with brain window obtained 24 hours postoperatively, revealing underlying cortex. when the outer drill bore is in firm contact with the skull and the inner drill fully penetrates the skull or when the inner drill moves forward 1 mm. The release mechanism can fail to function in a number of situations. Rocking or rotating the drill s hand piece can prevent the perforator mechanism from disengaging, leading to continued rotation of the drill bit as the device enters the cranial cavity. Rocking the perforator may also increase the size of the hole in the skull and increase the risk of dural tears. 4 The release mechanism can also fail to function properly if the surgeon creates a bur hole using a trajectory that is not orthogonal to the skull surface or if a bur hole is placed in a region of the skull where the bone is irregularly shaped. The manufacturer recommends operating the automatic-releasing perforator in this report by using psi of pressure and drilling speeds between 600 and 800 rpm (communications with manufacturer, 2009 and 2010). We initially used the drill at a higher rpm because we noted that the perforator would stop prematurely in thickened bone and would be difficult to restart. The cranial perforator will stop if bone chips accumulate or if soft bone is encountered. The accumulation of bone chips appears to prevent the perforator from reengaging in the bur hole and may override the release mechanism. After identifying 2 incidents of plunging at 1000 rpm during the 1st year, we reduced the drill speed to 800 rpm. Following this reduction in speed, the number of plunges increased significantly (p = 0.014, Fisher exact test). Based on this experience, we hypothesize that use of higher rpm may facilitate bone dust removal and prevent perforator malfunction. The significantly lower incidence of plunging at the higher rpm (Fig. 2) is consistent with this hypothesis. J Neurosurg / Volume 115 / September 2011 Patient Clinical Data A majority of the patients (56%) in the plunge event cases presented with hydrocephalus. Elevated intracranial pressure may increase the risk of dural tear by forcing the dura mater closer to the skull, leading to an increased risk of dural laceration during bur hole placement. In the current series, every patient with hydrocephalus sustained a dural laceration when a perforator plunging incident occurred. In this series there were no clinical deficits directly attributable to the perforator plunging incidents; however, it is difficult to assess complications specifically attributable to plunging events in certain clinical settings. As an example, ventriculostomies and endoscopes pass through the cortex underlying the bur hole, making it difficult to assess, based on radiographic evidence, whether cortical tissue has been injured by a plunging perforator or the device passed through that same brain area subsequently. In the 9 plunge events, no reports of cortical damage or hemorrhage were noted by surgeons in the operative report. These findings differ from those previously documented in which plunging was associated with a 12% increase in morbidity or death. 1 This difference may be attributable to a varied surgical technique, technological improvements, or differences in the patient populations studied. Procedure-Related Results A majority of the plunge events (78%) occurred when senior trainees were operating (postgraduate year 4 or later), and 2 cases (22%) involved faculty members. This finding is consistent with a previous report in which senior trainees were twice as likely to have a plunge event as their more experienced colleagues. 1 In addition, we identified 2 surgeons who experienced more than 1 plunge event over the 2-year period. This finding confirms in a contemporary patient series that perforator plunges still occur and that, given the method used to identify plunging incidents (operative report), the actual rate may be underreported. In an earlier series 22.3% of surgeons reported having more than 1 plunge event. 1 Five cases (56%) involved a single bur hole for ventriculostomy placement, endoscopic procedure, or tumor biopsy; the remaining cases involved fashioning several bur holes for craniotomy. In 2 of these craniotomies, a plunge event occurred during placement of the second bur hole. Plunging in such situations may be the result of bone fragments accumulating in the cranial perforator, preventing proper functioning of the release mechanism (Fig. 5). To address this issue, copious irrigation along with increased drill speeds may prevent bone from surrounding the automatic-releasing cranial perforator. Location of the bur hole in the skull also appeared to influence the occurrence of plunging (Table 2). The frontal bone was the most common location (56%) for a plunge event to occur, which is expected given that it is a frequent site of cranial entry for neurosurgical procedures. Plunging also occurred in 2 cases (22%) in which the bone of the uneven surface of a keyhole was drilled. Finally, 1 case of plunging occurred when a bur hole was placed adjacent to or involving fractured skull. Cranial 573

5 T. W. Vogel, B. J. Dlouhy, and M. A. Howard III TABLE 2: Complicating factors that may have facilitated plunge events Factor No. of Plunge Events uneven bone at keyhole 2 failure on 2nd bur hole 2 bur hole over suture 1 comminuted skull fracture 1 Fig. 5. Upper: Intraoperative photograph of cranial perforator after plunge event. Bone remnants are present in the release mechanism. Lower: Intraoperative photograph revealing thin shelf of bone at the end of the cranial perforator. Bone fragments accumulated in the cranial perforator. perforators rely on an intact, evenly contoured skull for proper functioning of the release mechanism. 16 Utilizing cranial perforators for bur holes at the keyhole or in cases involving a fractured underlying skull may increase the risk of a failed release mechanism and subsequent perforator plunge. In addition, 1 case involved placing a bur hole over a cranial suture. The cranial sutures are regions of the skull where uneven bone is encountered. Selecting an acorn drill bit to perform the bur hole placement with direct inspection of the bur hole in such complicating circumstances may prevent plunging. Alternative solutions to cranial perforator use have also been described in the literature. 7,10,13,17 Radiographic Imaging Results There were 3 cases (33%) in which MR imaging performed hours postoperatively showed increased T2 signal changes within the brain tissue under the bur hole, indicating possible involvement of the cortex (Fig. 3 left). Increased T2 signal changes are consistent with prior reports on the radiographic features associated with plunging. 15 On T2-weighted MR imaging, the result of plunging may appear as a mushroom sign with a delayed high signal intensity of edema in the cortex underlying the bur hole. 9,15 Our series of plunge events was not associated with hemorrhagic complications, and no intraparenchymal hemorrhages were noted in the location of the plunge. These findings differ from those in a previous study reporting intracerebral hematoma in 71% of plunging cases and cortical lacerations in 16% of plunge incidents. 1 The difference between our results and those previous findings may arise from our surgical manipulation of the cranial perforator; that is, we ensure that our hands are braced on the calvaria to limit the depth of a plunge. In addition, there is difficulty in differentiating between radiographic findings attributable to the cranial perforator and those linked to the surgical procedure. The disposable attachment used for our operative cases has an outer drill diameter of 14 mm and an inner diameter of 11 mm and is designed for use in skull tissue that is at least 3 mm thick. All patients in this report satisfied the skull thickness criteria as verified by postoperative skull thickness measurements on CT (Table 1). The mean thickness of the involved frontal bones was 10.7 mm (5 cases) and is greater than the average range of frontal bone thicknesses reported in the literature as to 8 mm. 7 Frontal bone thickness exceeding 10 mm, especially in women older than 60 years of age, may be suggestive of hyperostosis frontalis interna, 12 which is a condition that remodels the inner table of the skull, leading to increased thickness, especially in elderly patients. 5,14 Increased skull thickness increases the amount of bone dust that must be removed during trephining. The accumulation of bone fragments (Fig. 5) along with the aforementioned design limitations in the drill may increase the incidence of failure of the release mechanism, and thus lead to plunging. Prior to selecting a cranial perforator, a patient s skull thickness should be carefully considered to avoid increasing the risk of a plunge event. Future Directions Current efforts are focused on reducing plunging incidents. We are using more vigorous irrigation to remove bone dust and prevent clogging of the release mechanism with bone. In addition, we have reported 1 case in which the drill stopped and restarted (Table 1), suggesting a potential early failure of the release mechanism as a result of bone dust accumulation or adjacent unevenness in the bone surface. The speed of the drill may also limit bone dust removal and increase the risk of disengaging the release mechanism. We are increasing our drill speed to previous levels to prevent any additional plunging events. 574 J Neurosurg / Volume 115 / September 2011

6 Avoiding adverse events with cranial perforators Our surgeons are more selective about their use of a cranial perforator, and they use acorn drill bits with direct visual inspection of the calvaria and underlying dura when appropriate. The use of alternative drill bits applies to surgeries in which uneven bone surfaces, thickened skulls, or fractured fragments are present. As with any instrument utilized during a neurosurgical case, care and judgment should govern when to use a cranial perforator. Adjustments to current cranial drill design limitations and more novel release mechanisms may be warranted to prevent the aforementioned complications. Conclusions The cranial perforators available for use in neurosurgical procedures are largely reliable. Nevertheless, a plunging event can be multifactorial and depends on a surgeon s technique (by avoiding unnecessary rocking of the perforator), perforator engineering, and performance of the release mechanism. Efforts should be made in both surgical technique and instrument design to reduce the risk to patients. Lowering the speed of the drill may lead to an increased incidence of plunging events, and additional studies into the etiology of this finding are warranted. Disclosure 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 to the study and manuscript preparation include the following. Conception and design: Vogel. Acquisition of data: Vogel, Dlouhy. Analysis and interpretation of data: Vogel, Dlouhy. Drafting the article: all authors. Critically revising the article: all authors. Reviewed final version of the manuscript and approved it for submission: all authors. Statistical analysis: Vogel. Administrative/technical/material support: Dlouhy, Howard. References 1. Caird JD, Choudhari KA: Plunging during burr hole craniostomy: a persistent problem amongst neurosurgeons in Britain and Ireland. Br J Neurosurg 17: , Carmody JT: A new combined perforator and drill. J Neurosurg 4:292, Dimopoulos VG, Kapsalakis IZ, Fountas KN: Skull morphology and its neurosurgical implications in the Hippocratic era. Neurosurg Focus 23(1):E10, Heifetz MD: A variable-depth motorized skull perforator. Technical note. J Neurosurg 61: , Hershkovitz I, Greenwald C, Rothschild BM, Latimer B, Dutour O, Jellema LM, et al: Hyperostosis frontalis interna: an anthropological perspective. Am J Phys Anthropol 109: , Hudson RS: On the use of the trephine in depressed fractures of the skull. Br Med J 2:75 76, Hwang SC, Im SB, Kim BT, Shin WH: Safe entry point for twist-drill craniostomy of a chronic subdural hematoma. Clinical article. J Neurosurg 110: , Ito M, Sonokawa T, Mishina H, Sato K: Penetrating injury of the brain by the burr of a high-speed air drill during craniotomy: case report. J Clin Neurosci 8: , Lanzieri CF, Larkins M, Mancall A, Lorig R, Duchesneau PM, Rosenbloom SA, et al: Cranial postoperative site: MR imaging appearance. AJNR Am J Neuroradiol 9:27 34, Maartens NF, Lustgarten L, Josan V, Aziz TZ: How safe is twistdrill craniostomy? Br J Neurosurg 16: , Missios S: Hippocrates, Galen, and the uses of trepanation in the ancient classical world. Neurosurg Focus 23(1):E11, Nikolić S, Djonić D, Živković V, Babić D, Juković F, Djurić M: Rate of occurrence, gross appearance, and age relation of hyperostosis frontalis interna in females: a prospective autopsy study. Am J Forensic Med Pathol 31: , Reiss G, Andersch G, Handrick W, Kellner C, Koy J, Pinzer T, et al: Percutaneous burrhole trephination of the skull: a study of 519 cases. Neurosurg Rev 17: , She R, Szakacs J: Hyperostosis frontalis interna: case report and review of literature. Ann Clin Lab Sci 34: , Sinclair AG, Scoffings DJ: Imaging of the post-operative cranium. Radiographics 30: , Smith GW: An automatic drill for craniotomy. J Neurosurg 7: , Williams GR, Baskaya MK, Menendez J, Polin R, Willis B, Nanda A: Burr-hole versus twist-drill drainage for the evacuation of chronic subdural haematoma: a comparison of clinical results. J Clin Neurosci 8: , 2001 Manuscript submitted August 1, Accepted March 1, Please include this information when citing this paper: published online April 1, 2011; DOI: / JNS Address correspondence to: Timothy W. Vogel, M.D., Department of Neurosurgery, UIHC 200 Hawkins Drive, Iowa City, Iowa, tim-vogel@uiowa.edu. J Neurosurg / Volume 115 / September