How does research activity align with research need in chronic subdural haematoma: a gap analysis of systematic reviews with end-user selected knowledge gaps

The ‘Improving Care in Elderly Neurosurgery Initiative’ is a multidisciplinary working group which, with the input and support of professional bodies such as the Society of British Neurological Surgeons (SBNS) and the Neuroanaesthesia and Critical Care Society, is developing a clinical practice guideline for CSDH. The process is supported by further allied organisations including The Neurological Alliance and British Association of Neuroscience Nursing with methodological support from the THiS institute. The group was formed due to a shared consensus that many aspects of CSDH care were unstandardised. Funding was independently secured through application to the National Institute of Academic Anaesthesia with the SBNS identified as the lead sponsor and forward custodian of the final guideline [27]. Building on an initial meeting, working groups were convened to address five areas of CSDH care, i.e. diagnosis, non-operative management, surgical care, peri-operative care and rehabilitation, with work streams around Implementation and Global Health planned at a later stage. For each theme, a dedicated multidisciplinary working group was formed (Fig. 1), and through facilitated discussion, a provisional list of research questions developed. These were initially reviewed using a workshop for patients and members of the public, before final iterations were approved by the steering committee. These research questions thus provide a comprehensive overview of the requirements for the CSDH evidence base.

An umbrella review adhering to guidelines outlined by Fusar-Poli and Radua [10] was undertaken to critique the current evidence base. The review was prospectively registered in PROSPERO (CRD42022328562). No changes were made to the original protocol prior to extraction, and anonymised study data are available via the corresponding authors.

In our review, country was defined as the country of first listed affiliation of the first author. Review typology was defined according to Munn et al. [19], and review domains defined a priori according to the ICENI themes, and separately, a previously defined thematic analysis of CSDH education resources (Gillespie et al, unpublished data, 2022). Manuscripts were considered ‘similar’ if they reported the same research theme as an article published previously (i.e. recurrence rates following middle meningeal artery [MMA] embolization). If the article assessed the same research theme, was not published as part of a ‘review update’ by the same group of authors and was included the same outcomes, it was considered ‘duplicate’.

Forty-four questions were generated from the ICENI working groups and ratified by the steering committee (Table 1). These were felt to represent 12 distinct themes: anticoagulation (6 questions), communication (6 questions), decision making (2 questions), anaesthesia and surgical scheduling (7 questions), transfer and pathway (7 questions), perioperative care (3 questions), palliative care (3 questions), postop and recovery (5 questions), natural history (2 questions), surgical technique (3 questions) and MMA embolization (3 questions).

Seventy-three articles (Supplementary Table 3) reporting on 1914 studies and 206,379 patients were included (Supplementary Figure 2). A list of full-text articles screened, but excluded from the review, is included in Supplementary Table 4.

Study characteristics are outlined in Table 2. Almost all papers (98.6%, n=72/73) were published between 2010 and 2022. Most articles were from China (32.9%, n=24), followed by USA (20.5%, n=15), UK (8.2%, n=6), Netherlands (8.2%, n=6) and Canada (8.2%, n=6). The most common publishing journals were World Neurosurgery (21.9%, n=16), Acta Neurochirurgica (9.6%, n=7) and Frontiers in Neurology (6.8%, n=5). The median number of studies included per review was 13 (IQR 7–21), and the median number of participants was 1119 (IQR 441–3149). 76.7% (n=56) explicitly referenced following PRISMA guidelines. The most common review typology was effectiveness (71.2%, n=52). The overall mean adherence to PRISMA guidelines was 58.5% (SD 16.9).

The gap analysis of the 12 ICENI themes, mapped to AMSTAR-2 score, is shown in Fig. 3. In total, there was one high confidence review on anticoagulation, three on natural history, two on surgical technique and one on MMA embolisation. There was one moderate confidence review on perioperative care, two on natural history, two on surgical technique and two on MMA embolisation. All other reviews scored either low or critically low in confidence level when addressing ICENI themes. The reviews with high AMSTAR ratings are shown below in Online Supplementary Table 7.

This umbrella review and gap analysis identified that available systematic reviews on CSDH have critically low confidence in quality assessment. The CSDH evidence base focusses almost exclusively on procedural interventions, and binary outcomes (such as recurrence and mortality). Only 7 reviews targeted, with sufficient quality, questions posed for the proposed ICENI CSDH guidelines—indicating many areas relevant to CSDH management that are not addressed by current systematic reviews.

However, even within this narrow focus of procedural interventions, there exists a duplication of effort, and very often reviews were poorly placed to inform care; for example, almost two-thirds of reviews were categorised as having critically low confidence in their results according to AMSTAR-2. It is important to note that each component of AMSTAR-2 is not considered by all to have equal weighting or significance, for example factors such as protocol registration and the funding of included studies, which were the most poorly reported domains [12, 25]. Further, a risk of bias assessment was not formally completed. However, corroborating this finding, PRISMA compliance was also low.

Systematic reviews are important and influential—they inform future research, and are often required by research funders for trial applications [5, 11, 26]. Consequently, albeit a surrogate, the focus and activity within an umbrella review is an indication of the broader research environment. That CSDH is therefore focused on procedural interventions and their consequences is unsurprising. At present, despite a variety of other stakeholders that may be involved [29], the common focal point for anyone diagnosed with a CSDH is a consultation with Neurosurgery to determine whether treatment is required. The majority of CSDH research is undertaken by neurosurgical teams, and this therefore reflects their principal requirements [9]. Thus, whilst the evidence base around surgical management has improved and is ready to inform care, broader challenges remain. This reinforces the importance of the ICENI initiative, and specifically the role of multi stakeholder engagement to identify unsolved yet important challenges in the clinical pathway [4, 8, 9, 27].

This study therefore has simple but important implications for improving care in CSDH. Firstly, the information gathered by this manuscript and literature gaps identified can be used to guide future reviews [9]. In particular, peri-operative anaesthesia [16] and quality of life appear areas of unmet need. Second, we have produced a decision flow-chart (Fig. 4) that can be used to guide the process of selection of systematic reviews and meta-analyses, to avoid review saturation as a consequence of duplication of work produced in the CSDH field in the last 5 years. Further, it reinforces the importance of aiming for quality when conducting reviews, to ensure their conduct can inform care, for example through uptake in clinical practice guidelines. Broader strategies including PROSPERO registration, and PRISMA Reporting Guidelines have been important interventions, and adherence is key to ensuring optimal reviews are performed. Finally, it reinforces the need to capture a multi-stakeholder perspective when seeking to solve a clinical problem. Research shows that professionals gravitate towards procedural research, in contrast to priorities set by organisations such as the James Lind Alliance [7, 15].