Long Tu

Letter to the Editor Regarding “Preoperative Digital Subtraction Angiography in Incidental Unruptured Intracranial Aneurysms”

We would like to commend the authors Herzberg et al. for their study assessing the role of preoperative digital subtraction angiography (DSA) in unruptured intracranial aneurysms (UIAs) [1]; however we have some questions and comments about the study. The authors conclude that four-vessel angiography can be indicated in patients with multiple aneurysms because 4 out of 5 UIA missed on magnetic resonance imaging (MRI) in this study were in patients with multiple aneurysms; however, as the authors state, between 20% and 27% of all patients may have multiple UIAs. That would still be a significant proportion of patients with UIAs. All the UIAs missed on MRA were very small ( 3mm). We would like the authors to comment if these could be seen on the MRA in retrospect. The authors mention positive bias towards MRA in the limitations; however, the same bias applies to DSA, as the person performing DSA was aware of the MRA findings: the assumption here is that DSA is perfect. The implication of these additional findings on DSA is not clear. This is partly because the natural history of these small UIAs is not well understood [2]. Out of five aneurysms missed on MRA in this study four were not treated but received surveillance imaging. The guidelines do not specify the frequency and duration of imaging followup [3]. There is also significant heterogeneity in practice re-

Blunt Cerebrovascular Artery Injury and Stroke in Severely Injured Patients: An International Multicenter Analysis

Dear Editor, We would like to commend the authors Weber et al. [1] for their study assessing BCVI and stroke in such a large series of patients. However, we have a few questions and concerns about the study. Computed tomographic angiography (CTA) was applied for primary blunt cerebrovascular injury (BCVI) screening, but the authors do not specify whether all 76,480 individuals received a CTA study. If not, what criteria were used to screen patients with CTA? The conclusions drawn about the utility of screening criteria in predicting BCVI would be valid if all patients were screened. Retrospective analysis of risk factors may not be an accurate method if all patients were not consistently screened. The literature is very heterogeneous about the sensitivity and specificity of CTA, and different studies advocate conventional angiography in CTA-negative and CTApositive patients, respectively [2, 3]. We would request the authors to comment on the use of conventional angiography in their dataset. The reported incidence of BCVI in the literature is reflective of not only the screening criteria used, but also the sensitivity of the imaging used to screen patients. It would also be helpful to know from the authors the use of medical prophylaxis in both screened and unscreened patients. 30/58 strokes in this study happened despite prophylaxis, and 10/58 happened before start of therapy. The utility of screening criteria and CTAs has to be seen in the context of use of subsequent treatment and thereby prevention of stroke. Greater awareness of BCVI, the grading of injury and imaging pitfalls would help improve noninvasive imaging diagnosis [4]. Optimized, selective CTA in high-risk populations may be the most cost-effective strategy for BCVI detection [5].

Neuroimaging of Meckel’s cave in normal and disease conditions

Meckel’s cave is a dural recess in the posteromedial portion of the middle cranial fossa that acts as a conduit for the trigeminal nerve between the prepontine cistern and the cavernous sinus, and houses the Gasserian ganglion and proximal rootlets of the trigeminal nerve. It serves as a major pathway in perineural spread of pathologies such as head and neck neoplasms, automatically upstaging tumours, and is a key structure to assess in cases of trigeminal neuralgia. The purpose of this pictorial review is threefold: (1) to review the normal anatomy of Meckel’s cave; (2) to describe imaging findings that identify disease involving Meckel’s cave; (3) to present case examples of trigeminal and non-trigeminal processes affecting Meckel’s cave.Teaching points• Meckel’s cave contains the trigeminal nerve between prepontine cistern and cavernous sinus.• Assessment is essential for perineural spread of disease and trigeminal neuralgia.• Key imaging: neural enhancement, enlargement, perineural fat/CSF effacement, skull base foraminal changes.

Letter to the Editor Regarding “Growth of Untreated Unruptured Small-sized Aneurysms (<7 mm): Incidence and Related Factors”

We would like to commend the authors Choi et al. for their study assessing the growth of untreated unruptured small (<7mm) aneurysms [1]. The natural history of small unruptured intracranial aneurysms (UIA) is not well understood, and small UIAs have low growth and rupture rates reported in literature [2]. The high selection bias in the literature is also seen in the current study, with 994 UIAs being treated in the study period while 173 were followed up. Small (<7mm) UIAs may not be a homogeneous group. In a previous meta-analysis, we found the growth and rupture rates to be extremely low in <3mm and 3–5mm aneurysms relative to 5–7mm aneurysms [2]. This is also reflected in clinical practice as the authors confess that 4–7mm aneurysms may have been preferentially treated (only 13 out of 173 aneurysms in the study were >5mm). It is important therefore that the authors discuss the breakdown of the study group (173 UIAs) as to how many were <3mm and 3–5mm. Interestingly, only 1 out

Letter by Wu et al Regarding Article, “Safety of Computed Tomographic Angiography in the Evaluation of Patients With Acute Stroke: A Single-Center Experience”

We thank the authors Ehrlich et al for their study, which is a valuable effort to look at the safety of computed tomographic angiography (CTA) in acute stroke patients in terms of renal function.1 Multiple previous papers have also found the use of contrast to be safe in triage of acute stroke patients, some even concluding that contrast could be injected even before waiting for serum creatinine levels.2 However, we would like to raise a few concerns about this study. Of the 289 patients included in the …