Detection of Intracranial Aneurysms with Two-dimensional and Three-dimensional Multislice Helical Computed Tomographic Angiography

To the Editor: The article by Kangasniemi et al. (4) provides useful insight on the first generation of multislice computed tomographic angiography (CTA) technology in the detection of intracranial aneurysms. Their informative and timely study reinforces the fact that the technique of CTA has evolved progressively since its inception in tandem with developments in high-resolution scanning machines and corresponding imaging software. Since the late 1990s, we have also been advocates of CTA as the sole diagnostic tool for detecting ruptured aneurysms (2, 3). We also use a protocol of subjecting all patients presenting with subarachnoid hemorrhage to CTA first. Digital subtraction angiography (DSA) is performed only if the results of CTA are negative or inconclusive or if the aneurysmal location and/or morphology is unusual. The senior author (KAC) has successfully operated on more than 120 patients with ruptured aneurysms in the past 5 years on the basis of CTA alone (unpublished data). During the process, however, we have observed certain inherent deficiencies in our approach in surgically treating aneurysms on the basis of CTA alone, recent technical advances in CTA technology notwithstanding. First, the actual pattern of blood flow is much better demonstrated by standard DSA as compared with CTA. This, we believe, is an important requisite for surgery for aneurysms located in the region of the AComA. Failure to realize the dominance of any side and to appreciate the precise state of cross-flow across the AComA with CTA has forced us to preserve the AComA each time surgery is undertaken in this region. This is not always mandatory and can be difficult (at times, almost impossible), hence risky. The relatively simpler option of trapping the AComA for difficult aneurysms ceases to exist unless adequate filling of respective distal anterior cerebral arteries (A2) from their ipsilateral proximal portions (A1) is ensured. In our experience, CTA, even with the newer generation of scanning machines, does not always provide sufficient information in this respect. Conversely, DSA with cross-compression studies can be invaluable. In addition, if there are any anatomic variations in this region, as there often are, CTA can, in fact, be misleading (1). It is possible to miss a vascular malformation on CTA. Only the flow aneurysms may be detected and erroneously blamed for the hemorrhage, thereby missing the actual culprit. Even with the best-quality CTA, the perforators around the aneurysm may not be picked up as well as on standard DSA and the images certainly are not comparable to those on three-dimensional DSA. Learning from our mistakes by operating on the basis of CTA alone, we are gradually moving back toward DSA, which has also undergone significant advances during the past few years. Perhaps the question is not one of “either/or.” Rather, both techniques have their own sets of advantages and disadvantages and, in fact, can complement each other in generating valuable diagnostic information, especially in cases of difficult aneurysms, irrespective of whether a surgical or endovascular means of treatment is adopted. Although we agree completely with the authors’ conclusions about CTA being noninvasive, fast, and credible in diagnosing ruptured aneurysms, the article stops short of elaborating on the intrinsic pitfalls of the technique, which equally deserve to be highlighted. On the basis of experience at our institute, we can recommend CTA as an excellent adjuvant but not complete substitute for the “gold standard” DSA, except in circumstances in which the patient’s rapidly deteriorating clinical condition is attributable to an expanding aneurysmal hematoma. Kishor A. Choudhari Nidhi Jain Belfast, United Kingdom