Clinical outcome of subdural versus subgaleal drain after burr-hole drainage for chronic subdural hematoma.

BACKGROUND: Chronic subdural hematoma (CSDH) is commonly treated by burr-hole drainage with subgaleal or subdural drain insertion, mostly based on surgeon's preference. We analyzed the recurrence rate and clinical outcomes after burr-hole drainage for CSDH and subdural or subgaleal drain insertion in a single center, retrospective cohort study. METHODS: 700 cases of burr-hole drainage for CSDH between 2017 and 2022 were included. Subdural drain insertion was compared to subgaleal drain insertion. The primary outcome were the rates of recurrence and reoperation. The secondary outcomes consisted of morbidity, postoperative complications, and mortality. RESULTS: Baseline characteristics were comparable. The recurrence and reoperation rate after subdural drainage were respectively 15.3% (38/249) and 9.6% (24/249). The recurrence and reoperation rate after subgaleal drainage were respectively 13.4% (55/409) and 10.8% (44/409). There were no significant associations found in recurrence and reoperation rate between both drain insertions. No differences in morbidity, complication rate and mortality between drain insertion locations was found. CONCLUSION: We found relative equipoise between subdural or subgaleal drain insertion concerning recurrence, reoperation rate or clinical outcome. A large multicenter randomized controlled trial could be designed to further assess the outcomes of subdural and subgaleal drain placement after burr-hole drainage for CSDH.

Comparison between the use of subdural and subgaleal drainage in treatment of chronic subdural hematoma.

BACKGROUND AND OBJECTIVES: Chronic subdural hematoma (CSDH) is one of the most common pathologies in our daily practice. The standard treatment is the evacuation making a burr-hole and placement of a subdural drainage, which has shown to decrease its recurrence. However, this procedure can entail risks such as parenchymal damage, infection, or the onset of seizures, prompting the consideration of subgaleal drainage as an alternative. Our objective is to compare the use of subdural and subgaleal drainage in a cohort of patients undergoing intervention for CSDH, as well as to analyze the differences in complication rates and recurrence between the two groups. METHODOLOGY: A retrospective analytical observational study was conducted, analyzing 152 patients diagnosed with CSDH who underwent intervention at our center from January 2020 to April 2022. Patients in whom drainage was not placed were excluded. In all patients, a burr-hole was performed and the type of drainage was chosen by the neurosurgeon. RESULTS: Out of the 152 patients, subdural drainage was placed in 80 cases (52.63%), while subgaleal drainage was used in 72 cases (47.37%). There were no significant differences in the recurrence rate (30% in the subdural drainage group vs. 20.83% in the subgaleal drainage group; P = .134) or in the complication rate (7.5% in the subdural drainage group vs. 5.5% in the subgaleal drainage group; P = .749). CONCLUSIONS: Subgaleal drainage shows similar clinical outcomes with a recurrence and complication rate comparable to subdural drainage, suggesting it as a safe and effective alternative to subdural drainage in the treatment of CSDH.

"Mail-slot" Technique for Minimally Invasive Placement of Subdural Grid Electrodes: A Single-institution Experience.

BACKGROUND: In the management of multi-drug-resistant focal epilepsies, intracranial electrode implantation is used for precise localization of the ictal onset zone. In select patients, subdural grid electrode implantation is utilized. Subdural grid placement traditionally requires large craniotomies to visualize the cortex prior to mapping. However, smaller craniotomies may enable shorter operations and reduced risks. We aimed to compare surgical outcomes between patients undergoing traditional large craniotomies with those undergoing tailored "mini" craniotomies (the "mail-slot" technique) for subdural grid placement. METHODS: This retrospective cohort study included 23 patients who underwent subdural electrode implantation for epilepsy monitoring between 2014 and 2020. Patients were categorized into mini-craniotomies (n = 9) and traditional large craniotomies (n = 14) groups. Demographics, operative details, and outcomes were reviewed. Craniotomy size and number of electrodes were determined via post hoc radiographs. RESULTS: Of the 23 patients studied, the mini group had smaller craniotomy sizes (mean: 22.71 cm2 vs. 65.17 cm2, P < 0.001) and higher electrode-to-size ratios (mean: 4.25 vs. 1.71, P < 0.0001). The mini group had slightly fewer total electrodes (mean: 88.67 vs. 107.43, P = 0.047). No significant differences were found in operative duration, blood loss, invasive electroencephalography duration, complications, or Engel scores between the groups. One patient per group required further invasive epilepsy monitoring for localization; all patients underwent therapeutic surgery. CONCLUSIONS: Our findings suggest that mini-craniotomies for subdural grid placement in epilepsy monitoring offer significant advantages, including smaller craniotomy sizes and shorter operation durations, without compromising safety or efficacy. These results support the trend towards minimally invasive, patient-tailored surgical approaches in epilepsy treatment.

Depth versus surface: A critical review of subdural and depth electrodes in intracranial electroencephalographic studies.

Intracranial electroencephalographic (IEEG) recording, using subdural electrodes (SDEs) and stereoelectroencephalography (SEEG), plays a pivotal role in localizing the epileptogenic zone (EZ). SDEs, employed for superficial cortical seizure foci localization, provide information on two-dimensional seizure onset and propagation. In contrast, SEEG, with its three-dimensional sampling, allows exploration of deep brain structures, sulcal folds, and bihemispheric networks. SEEG offers the advantages of fewer complications, better tolerability, and coverage of sulci. Although both modalities allow electrical stimulation, SDE mapping can tessellate cortical gyri, providing the opportunity for a tailored resection. With SEEG, both superficial gyri and deep sulci can be stimulated, and there is a lower risk of afterdischarges and stimulation-induced seizures. Most systematic reviews and meta-analyses have addressed the comparative effectiveness of SDEs and SEEG in localizing the EZ and achieving seizure freedom, although discrepancies persist in the literature. The combination of SDEs and SEEG could potentially overcome the limitations inherent to each technique individually, better delineating seizure foci. This review describes the strengths and limitations of SDE and SEEG recordings, highlighting their unique indications in seizure localization, as evidenced by recent publications. Addressing controversies in the perceived usefulness of the two techniques offers insights that can aid in selecting the most suitable IEEG in clinical practice.

The changing landscape of electrical stimulation language mapping with subdural electrodes and stereoelectroencephalography for pediatric epilepsy: A literature review and commentary.

Electrical stimulation mapping (ESM) is used to locate the brain areas supporting language directly within the human cortex to minimize the risk of functional decline following epilepsy surgery. ESM is completed by utilizing subdural grid or depth electrodes (stereo-electroencephalography [sEEG]) in combination with behavioral evaluation of language. Despite technological advances, there is no standardized method of assessing language during pediatric ESM. To identify current clinical practices for pediatric ESM of language, we surveyed neuropsychologists in the Pediatric Epilepsy Research Consortium. Results indicated that sEEG is used for functional mapping at >80% of participating epilepsy surgery centers (n = 13/16) in the United States. However, >65% of sites did not report a standardized protocol to map language. Survey results indicated a clear need for practice recommendations regarding ESM of language. We then utilized PubMed/Medline and PsychInfo to identify 42 articles that reported on ESM of language, of which 18 met inclusion criteria, which included use of ESM/signal recording to localize language regions in children (<21 years) and a detailed account of the procedure and language measures used, and region-specific language localization outcomes. Articles were grouped based on the language domain assessed, language measures used, and the brain regions involved. Our review revealed the need for evidence-based clinical guidelines for pediatric language paradigms during ESM and a standardized language mapping protocol as well as standardized reporting of brain regions in research. Relevant limitations and future directions are discussed with a focus on considerations for pediatric language mapping.

Comparative effectiveness of stereotactic, subdural, or hybrid intracranial EEG monitoring in epilepsy surgery.

OBJECTIVE: Surgical intervention can be curative or palliative for drug-resistant focal epilepsy. However, if the seizure onset zone (SOZ) cannot be adequately localized via noninvasive tests, intracranial EEG (iEEG) recordings are often carried out to develop surgical plans in appropriate candidates. Stereotactic EEG (SEEG), subdural EEG (SDE), and SDE with depth electrodes (hybrid) are major tools used for investigation, but there is no class 1 or 2 evidence comparing the effectiveness of these modalities. METHODS: The authors identified an institutional cohort of patients who underwent iEEG monitoring between 2001 and 2022. Demographic data, preoperative clinical features, iEEG intervention, and follow-up data were identified. Primary study endpoints included the following: 1) likelihood of SOZ localization; 2) likelihood of surgical treatment after iEEG; 3) seizure outcomes; and 4) complications. RESULTS: A total of 329 patients were identified (176 in the SEEG, 60 in the SDE, and 93 in the hybrid cohort) who were followed for a median of 5.4 (IQR 6.8) years. Baseline characteristics, including demographics, mean age at epilepsy diagnosis, mean age at iEEG investigation, number of preoperative antiseizure medications, and preoperative seizure frequency, were not statistically different across the 3 cohorts. Patients in the SEEG cohort were more likely to have their SOZ localized than were the patients in the SDE group (OR 2.3) and were less likely to undergo subsequent resection (OR 0.3) or to have complications (OR 0.4), although there was no statistical difference with respect to likelihood of undergoing any subsequent neurosurgical treatment, or with respect to favorable seizure outcomes. Patients in the hybrid cohort were more likely to have SOZ localized than were patients in the SDE group (OR 3.1), but were more likely to undergo resection (OR 4.9) or any neurosurgical treatment (OR 2.5) compared to patients in the SEEG group. Patients in the hybrid cohort had better seizure outcomes compared to the SDE (OR 2.3) but not to the SEEG group. CONCLUSIONS: Patients in the SEEG group were more likely to have their SOZ localized and patients in the SDE group were more likely to undergo resection, but they did not differ with respect to seizure outcomes.

Granuloma formation as a late complication of burr-hole surgery for chronic subdural hematoma.

BACKGROUND: Surgical treatment remains the mainstream therapeutic regimen for chronic subdural hematoma (CSDH), and burr-hole craniostomy with subdural drainage is the preferable approach. Herein, we reported a case of intracranial granuloma formation as a late complication of burr-hole surgery for CSDH. CASE PRESENTATION: A 31-year-old man presented with a 1-month history of headache. Head computed tomography (CT) showed a subdural hematoma in the left frontal-temporal-parietal region with significant midline shifting. A burr-hole evacuation of the hematoma with closed-system drainage was performed. CT obtained immediately after the surgery demonstrated that the hematoma was mostly evacuated. Nine months later, he presented to us again due to intermittent headache in the left temporoparietal region. Brain magnetic resonance imaging revealed a space-occupying mass at the site of the original hematoma. A bone-flap craniotomy was performed for resecting the mass. Histopathological examination revealed a granuloma. The microbial cultivation of the resected specimen was negative. The postoperative course was uneventful, and the headache was relieved. CONCLUSION: Granuloma formation is an extremely rare late complication of burr-hole surgery for CSDH. Physicians involved in the perioperative management of CSDH should be aware of this condition, and bone-flap craniotomy may be warranted.

The presence of a foramen of Luschka in the American alligator (Alligator mississippiensis) and the continuity of the intraventricular and subdural spaces.

In humans and most mammals, there is a notch-like portal, the foramen of Luschka (or lateral foramen), which connects the lumen of the fourth ventricle with the subdural space. Gross dissection, light and scanning electron microscopy, and µCT analysis revealed the presence of a foramen of Luschka in the American alligator (Alligator mississippiensis). In this species, the foramen of Luschka is a notch in the dorsolateral wall of the pons immediately caudal to the peduncular base of the cerebellum, near the rostral end of the telovelar membrane over the fourth ventricle. At the foramen of Luschka there was a transition from a superficial pia mater lining to a deep ependymal lining. There was continuity between the lumen of the fourth ventricle and the subdural space, via the foramen of Luschka. This anatomical continuity was further demonstrated by injecting Evans blue into the lateral ventricle which led to extravasation through the foramen of Luschka and pooling of the dye on the lateral surface of the brain. Simultaneous subdural and intraventricular recordings of cerebrospinal fluid (CSF) pressures revealed a stable agreement between the two pressures at rest. Perturbation of the system allowed for static and dynamic differences to develop, which could indicate varying flow patterns of CSF through the foramen of Luschka.

Radiographical presentations of inadvertent subdural placement of an epidural catheter for successful labor analgesia: A case report.

RATIONALE: Lumbar epidural analgesia is the gold standard for labor pain control. However, misplacement of epidural catheters into the subdural space may inadvertently happen. Unrecognized subdural administration of local anesthetics could result in serious consequences, including high spinal and brainstem blocks. This case report describes a case where subdural epidural catheter placement was recognized early but labor pain was adequately managed by dosage titration of subdural analgesia. PATIENT CONCERNS: This case report describes a 29-year-old primiparous pregnant woman who was admitted to our obstetric unit for labor induction at the gestational age of 38 weeks. An epidural catheter was inserted via the L2-3 intervertebral space using the standard loss of resistance to air technique. DIAGNOSES: The parturient experienced weakness in the lower extremities and numbness in the upper extremities within 15 minutes after administration of 5 mL of 2% v/v lidocaine as a loading dose and systolic blood pressure also dropped by 25%. INTERVENTIONS: The dose regimen (a mixture of 0.1% ropivacaine and 4 µg/mL fentanyl) for patient-controlled analgesia was given with bolus doses of 0.1 mL per demand and lockout intervals of 20 minutes. The analgesic effects were adequately maintained below the T8 dermatome for more than 12 hours without hypotensive episodes or obvious signs of neurological deficits. Computed tomographic myelography was performed by instillation of a nonionic iodinated contrast medium via the epidural catheter on postpartum day 2 for imaging confirmation of catheter placement in the extradural space. LESSONS: Early recognition that epidural catheters for neuraxial analgesia have been inserted into the subdural space is important for the prevention of high spinal blocks. Subdural analgesia could still be achieved by careful clinical assessment and titration of low analgesic doses. This report also presents important and clear serial computed tomographic images of catheter placement in the thoracic-lumbar subdural spaces and the extent of volume spread in the subdural space following administration of contrast medium.

Postoperative Spinal Subdural Extra-arachnoid Hygroma Because of Trauma: Resolution with Lumbar Puncture: A Case Report.

CASE: A 73-year-old woman, after spinal surgery, presented with symptomatic spinal subdural extra-arachnoid hygroma (SSEH) because of a fall on the third postoperative day. The hygroma was diagnosed by magnetic resonance imaging (MRI). Lumbar puncture was performed under local anesthesia, after which the leg pain disappeared immediately. MRI obtained immediately after puncture and 1 week later confirmed disappearance of the hygroma. CONCLUSION: Although dural transection is mentioned in most of the reports on treatment of symptomatic postoperative SSEH, we were able to treat this entity by epidural puncture. In the absence of paraplegia or cystorectal disturbance, puncture can be an effective and minimally invasive treatment option.

Comparison of subperiosteal or subgaleal drainage and subdural drainage in patients with chronic subdural hematoma: A systematic review and meta-analysis.

BACKGROUND: Chronic subdural hematoma (CSDH) is a relatively common disease, especially in the elderly, for which there is no clear standard of treatment available. The authors systematically evaluated the efficacy of various surgical procedures for the treatment of chronic subdural hematoma. METHODS: Electronic databases of PubMed, EmBase, Web of Science, Medicine, and the Cochrane Library were searched systematically. Based on the PRISMA template, we finally selected and analyzed 13 eligible papers to evaluate the effect of different drainage methods on CSDH. The primary outcomes were recurrence and clinical outcomes. Secondary outcomes were mortality and postoperative complications and other parameters. RESULTS: The meta-analysis included 3 randomized controlled trials and 10 retrospective studies (non-randomized controlled trials) involving 3619 patients. The pooled results showed no statistically significant difference between non-subdural drainage (NSD) and subdural drainage (SD) in mortality and complication rates (P > 0.05). Additionally, overall pooled results showed that the use of NSD (10.9%) has a lower recurrence rate than the use of SD (11.7%), but the results were not statistically significant (relative risk ratio [RR] = 0.98; 95% confidence interval [CI] = 0.70-1.45; I2 = 47%; P = .92). However, the difference between NSD and SD in postoperative bleeding rate reached statistical significance (RR = 2.39; 95% CI = 1.31-4.36; I2 = 0 %; P = .004). Subgroup analysis showed that SD was associated with similar recurrent CSDH (RR = 0.75; 95% CI = 0.52-1.09; I2 = 0%; P = .14), good recovery (RR = 0.98; 95% CI = 0.93-1.04; I2 = 0%; P = .50), and mortality (RR = 0.98; 95% CI = 0.37-2.57; I2 = 0%; P = .96), compared to NSD. CONCLUSIONS: These results suggest that NSD and SD are equally effective in the treatment of patients with CSDH, with no difference in final clinical characteristics and radiologic outcomes. However, in patients with limited subdural space after evacuation of a hematoma, NSD may be the preferred strategy to avoid iatrogenic brain injury.

How I do it: simplified craniotomy for acute subdural hematoma in the elderly.

CONTEXT: Acute subdural hematoma (ASH) is responsible for significant morbidity and mortality in the elderly. As military neurosurgeons, we perform a simplified technique using a linear skin incision and a small craniotomy bone flap in order to ease perioperative tolerance. METHODS: The patient lies supine, a pad under the shoulder ipsilateral to the ASH, the head completely rotated on the other side and placed on a circular pad, without head clamp. The linear frontotemporal skin incision should be twice the size of the bone flap's diameter, allowing to access the whole subdural space. Care is taken to obtain complete decompression of the temporal fossa in order to alleviate uncal herniation. A subdural drain can be placed, and the subdural space is filled with warm saline solution in order to create a closed drainage system. CONCLUSION: The patient is allowed to sit at postoperative day 1 and to walk at postoperative day 2. Simplified craniotomy for ASH allows to reduce operative time and provides faster functional recovery.

Inflammatory human leucocyte antigen genotypes are not a risk factor in chronic subdural hematoma development.

BACKGROUND: Chronic subdural hematoma (CSDH) pathophysiology has undergone a paradigm shift from being regarded as solely traumatic to be driven mainly by inflammation. Human leucocyte antigen (HLA) is a gene complex involved in antigen processing and presentation to T lymphocytes, thereby mediating the adaptive immune responses. As specific HLA profiles are associated with inflammatory diseases, patients with a specific HLA profile may have a lower threshold for subdural inflammation, and therefore are predisposed for CSDH development. We hypothesized that (1) CSDH patients have a specific HLA profile compared to a Danish background population, and (2) patients with recurrent CSDH have a specific HLA profile compared to CSDH patients without recurrent CSDH. METHODS: Three specific HLA class II haplotypes known to drive inflammatory-mediated diseases were determined in 68 patients with CSDH. The distribution of these three haplotypes in our CSDH population was compared to a Danish population of blood donors using Monte Carlo Pearson's chi-square test. Furthermore, the distribution of the haplotypes was compared between CSDH patients with and without recurrent CSDH. RESULTS: We found no significant association between either of the haplotypes and the risk of CSDH, and neither of the haplotypes were associated with increased risk of CSDH recurrence. CONCLUSION: This study did not show an association between selected HLA class II haplotypes and the risk of CSDH or recurrence of CSDH compared with a healthy background population.

Early spontaneous cessation of subdural drainage after burr hole evacuation of chronic subdural hematoma and risk of recurrence.

OBJECTIVE: Subdural drainage reduces recurrence after evacuation of chronic subdural hematoma (CSDH). In the present study, the authors investigated the dynamics of drain production and potentially contributing factors for recurrence. METHOD: Patients treated with a single burr hole evacuation of CSDH between April 2019 and July 2020 were included. Patients were also participants in a randomized controlled trial. All patients included, had a passive subdural drain for exactly 24 hours. Drain production, Glasgow Coma Scale score, and degree of mobilization was recorded every hour for 24 hours. A CSDH successfully drained for 24 hours is referred to as a "case". Patients were followed for 90 days. Primary outcome was symptomatic recurrent CSDH requiring surgery. RESULTS: A total of 118 cases from 99 patients were included in the study. Of the 118 cases, 34 (29%) had spontaneous drain cessation within the first 0-8 hours after surgery (Group A), 32 (27%) within 9-16 hours (Group B), and 52 (44%) within 17-24 hours (Group C). Hours of production (P < 0.000) and total drain volume (P = 0.001) were significantly different between groups. The recurrence rate was 26.5% in group A, 15.6% in group B, and 9.6% in group C (P = 0.037). Multivariable logistic regression analysis show that cases in group C (OR: 0.13, P = 0.005) are significantly less likely to recur compared to group A. Only in 8 of the 118 cases (6.8%), the drain started draining again after an interval of three consecutive hours. CONCLUSIONS: Early spontaneous cessation of subdural drain production seems to be associated with increased risk of recurrent hematoma. Patients with early cessation of drainage did not benefit from further drain time. Observations of the present study indicate personalized drainage discontinuation strategy as a potentially alternative to a specific discontinuation time for all CSDH patients.

Reducing morbidity associated with subdural drain placement after burr-hole drainage of unilateral chronic subdural hematomas: a retrospective series comparing conventional and modified Nelaton catheter techniques.

PURPOSE: Placement of a subdural drain after burr-hole drainage of chronic subdural hematoma (cSDH) significantly reduces risk of its recurrence and lowers mortality at 6 months. Nonetheless, measures to reduce morbidity related to drain placement are rarely addressed in the literature. Toward reducing drain-related morbidity, we compare outcomes achieved by conventional insertion and our proposed modification. METHODS: In this retrospective series from two institutions, 362 patients underwent burr-hole drainage of unilateral cSDH with subsequent subdural drain insertion by conventional technique or modified Nelaton catheter (NC) technique. Primary endpoints were iatrogenic brain contusion or new neurological deficit. Secondary endpoints were drain misplacement, indication for computed tomography (CT) scan, re-operation for hematoma recurrence, and favorable Glasgow Outcome Scale (GOS) score (≥ 4) at final follow-up. RESULTS: The 362 patients (63.8% male) in our final analysis included drains inserted in 56 patients by NC and 306 patients by conventional technique. Brain contusions or new neurological deficits occurred significantly less often in the NC (1.8%) than conventional group (10.5%) (P = .041). Compared with the conventional group, the NC group had no drain misplacement (3.6% versus 0%; P = .23) and significantly fewer non-routine CT imaging related to symptoms (36.5% versus 5.4%; P < .001). Re-operation rates and favorable GOS scores were comparable between groups. CONCLUSION: We propose the NC technique as an easy-to-use measure for accurate drain positioning within the subdural space that may yield meaningful benefits for patients undergoing treatment for cSDH and vulnerable to complication risks.

Nine decades of electrocorticography: A comparison between epidural and subdural recordings.

In recent years, electrocorticography (ECoG) has arisen as a neural signal recording tool in the development of clinically viable neural interfaces. ECoG electrodes are generally placed below the dura mater (subdural) but can also be placed on top of the dura (epidural). In deciding which of these modalities best suits long-term implants, complications and signal quality are important considerations. Conceptually, epidural placement may present a lower risk of complications as the dura is left intact but also a lower signal quality due to the dura acting as a signal attenuator. The extent to which complications and signal quality are affected by the dura, however, has been a matter of debate. To improve our understanding of the effects of the dura on complications and signal quality, we conducted a literature review. We inventorized the effect of the dura on signal quality, decodability and longevity of acute and chronic ECoG recordings in humans and non-human primates. Also, we compared the incidence and nature of serious complications in studies that employed epidural and subdural ECoG. Overall, we found that, even though epidural recordings exhibit attenuated signal amplitude over subdural recordings, particularly for high-density grids, the decodability of epidural recorded signals does not seem to be markedly affected. Additionally, we found that the nature of serious complications was comparable between epidural and subdural recordings. These results indicate that both epidural and subdural ECoG may be suited for long-term neural signal recordings, at least for current generations of clinical and high-density ECoG grids.

Subdural open drains as an effective and low-cost modality for the treatment of chronic subdural hematomas.

PURPOSE: We present a series that describes the presenting features and clinical outcomes in patients with CSDH treated with a standardised technique and an open-drain placement. METHODS: We reviewed the medical records of 155 consecutive patients at a single centre who underwent CSDH evacuation by placing burr holes, accompanied by intraoperative irrigation and a subdural Penrose drain between 2014 and 2018. RESULTS: The mean age was 65.9 years, 81.9% were males. The most common clinical characteristics were an altered mental state (21.9%) and headache (12.9%). It was necessary to perform a second surgical intervention due to the evidence in the postoperative tomography of a residual hematoma in 10.3% of the cases; there were 2 cases of recurrence in 6 months (1.3%). Pneumonia (6.5%) and seizures (5.8%) were the most frequent medical complications. Intracranial infections accounted for 1.9%, and the mortality rate was 6.4% of cases. CONCLUSIONS: We provided our experience with a low-cost and less-commonly used technique in the management of CSDH. This technique showed similar recurrence, mortality and intracranial infection rates to those reported in the literature for closed drainage systems. Additional studies will be required to assess this technique.