Cerebral microaneurysms found incidentally during aneurysm surgery

Incidence, classification, and treatment of angiographically occult intracranial aneurysms found during microsurgical aneurysm clipping of known aneurysms

OBJECTIVE

During the microsurgical clipping of known aneurysms, angiographically occult (AO) aneurysms are sometimes found and treated simultaneously to prevent their growth and protect the patient from future rupture or reoperation. The authors analyzed the incidence, treatment, and outcomes associated with AO aneurysms to determine whether limited surgical exploration around the known aneurysm was safe and justified given the known limitations of diagnostic angiography.

METHODS

An AO aneurysm was defined as a saccular aneurysm detected using the operative microscope during dissection of a known aneurysm, and not detected on preoperative catheter angiography. A prospective database was retrospectively reviewed to identify patients with AO aneurysms treated microsurgically over a 20-year period.

RESULTS

One hundred fifteen AO aneurysms (4.0%) were identified during 2867 distinct craniotomies for aneurysm clipping. The most common locations for AO aneurysms were the middle cerebral artery (60 aneurysms, 54.1%) and the anterior cerebral artery (20 aneurysms, 18.0%). Fifty-six AO aneurysms (50.5%) were located on the same artery as the known saccular aneurysm. Most AO aneurysms (95.5%) were clipped and there was no attributed morbidity. The most common causes of failed angiographic detection were superimposition of a large aneurysm (type 1, 30.6%), a small aneurysm (type 2, 18.9%), or an adjacent normal artery (type 3, 36.9%). Multivariate analysis identified multiple known aneurysms (odds ratio [OR] 3.45, 95% confidence interval [CI] 2.16-5.49, p < 0.0001) and young age (OR 0.981, 95% CI 0.965-0.997, p = 0.0226) as independent predictors of AO aneurysms.

CONCLUSIONS

Meticulous inspection of common aneurysm sites within the surgical field will identify AO aneurysms during microsurgical dissection of another known aneurysm. Simultaneous identification and treatment of these additional undiagnosed aneurysms can spare patients later rupture or reoperation, particularly in those with multiple known aneurysms and a history of subarachnoid hemorrhage. Limited microsurgical exploration around a known aneurysm can be performed safely without additional morbidity.

Incidental Microaneurysms During Microvascular Surgery: Incidence, Treatment, and Significance

BACKGROUND

Although new imaging tools have been developed for the detection of smaller aneurysms, angiographically negative microaneurysms are still encountered during cerebral microsurgery. Currently, only limited information regarding incidence and efficacy of treatment of these microaneurysms is available.

METHODS

We investigated the incidence and treatment of incidental microaneurysms (IMAs) in the last 5 years. IMAs are unidentifiable and invisible on preoperative angiography, but are detected during microvascular surgery. The inclusion criteria were aneurysm cases treated with microsurgery via transsylvian approaches, and those undergoing preoperative digital subtraction angiography.

RESULTS

This study enrolled 484 surgical cases (248 cases of subarachnoid hemorrhage and 236 cases of unruptured aneurysms) in 460 patients, and 33 tiny aneurysms were found in 31 operative cases (6.4% incidence per operation). The most typical type was located on another branching site of the middle cerebral artery found during neck clipping of the middle cerebral artery bifurcation aneurysm. A patient with multiple aneurysms presented a statistically significant risk (375/78 vs. 15/16; P < 0.001) of IMA identification. IMAs were treated by clipping and wrapping in 18 and 15 cases, respectively, without complications.

CONCLUSIONS

This study revealed a 6.4% incidence of IMAs; however, this could be underestimated because of the limited range of inspection. Early detection of an IMA through careful inspection during microvascular surgery could be beneficial, especially in patients with multiple aneurysms.

Application of low injection rate and low contrast agent dose in three-dimensional rotational digital subtraction angiography of the intracranial aneurysm

OBJECTIVE

The objective of this article is to explore the feasibility of low injection rate and low contrast agent dose in three-dimensional rotational digital subtraction angiography (3D DSA) of the intracranial aneurysm.

MATERIALS AND METHODS

Fifty-one patients with suspected intracranial aneurysms were included. The catheter tip was kept within the internal carotid artery at the epistropheus level. Patients were divided into three groups randomly according to injection rate: group A (1.5 ml/s, n = 18), group B (2.0 ml/s, n = 18), and group C (3.0 ml/s, n = 15). The noise, signal-to-noise ratio (SNR), and carrier-to-noise ratio (CNR) of C2, C6, M1, and A1 segments were calculated. The continuous subtraction images and reconstructed images were evaluated by two technicians.

RESULTS

No significant differences were found in noise between groups A and B, and groups A and C. Significant differences were found in the SNR and CNR of M1 and A1 segments between groups A and B, and groups B and C, but for C2 and C6 segments, they were not significant. Significant differences were found in the SNR and CNR of all segments between groups A and C. Significant differences were found in the contrast agent dose between all three groups. No significant differences were found in scores evaluated by two physicians between the three groups.

CONCLUSION

The personalized injection protocol of low injection rate and low contrast agent dose in 3D DSA of the intracranial aneurysm is feasible. The application of this protocol can reduce the dose of iodine and obtain satisfactory images.

64-section multidetector CT angiography for evaluation of intracranial aneurysms: comparison with 3D rotational angiography

BACKGROUND

To assess the diagnostic performance of 64-section computed tomography angiography (CTA) for detection of cerebral aneurysms by comparison with the new gold standard three-dimensional (3D) digital subtraction angiography (DSA).

MATERIAL AND METHODS

A total of 128 patients who underwent both 64-section CTA and 3D DSA for suspected intracranial aneurysms were included. The location, size, and shape of the aneurysm were assessed and compared with 3D DSA results. The sensitivity, specificity, positive and negative predictive values of 64-section CTA were calculated by using 3D DSA as reference standard.

RESULTS

According to the reference standard, a total of 145 aneurysms were detected at 3D DSA in 118 patients. Of these 145 aneurysms, 64-section CTA detected 139 aneurysms in 118 patients. The sensitivity of CTA for detection of aneurysm was 95.8% on a per-aneurysm basis. All missed aneurysms were non-causative very small aneurysms in patients harboring multiple aneurysms. On a per-patient basis, the sensitivity, specificity, positive and negative predictive values were 100%.

CONCLUSION

Compared with the new gold standard 3D DSA, 64-section CTA offers high sensitivity and specificity for detection of intracranial aneurysms. It could be readily used as a screening imaging method for detection of intracranial aneurysms.

Ruptured “Occult” Aneurysm Disclosed by Three-Dimensional Angiographic Reconstructions

Rotational angiographic sequences and their three-dimensional reconstructions have led to major improvements in angiographic diagnostics, especially in the study of brain aneurysms. Reconstructions accurately depict the morphology of the aneurysm, namely any wall irregularities and the possible origin of arterial branches from the aneurysmal sac, and display the aneurysm on multiple spatial planes, measuring its different diameters and ratios (particularly the dome to neck ratio). Lastly, three-dimensional angiographic reconstructions will sometimes disclose ruptured or intact aneurysms not depicted by digital subtraction angiography. A 43-year-old woman was admitted to the emergency room of Maggiore Hospital, Bologna Local Health Trust, presenting severe headache, confusion and nuchal rigidity. Emergency CT scan disclosed cisternal subarachnoid haemorrhage. Subsequent 3D sequences revealed an aneurysm of the left carotid artery siphon. This occult aneurysm found in our patient had been masked by the overlying infundibular origin of the posterior communicating artery. This prevented detection of the lesion not only in standard oblique anteroposterior, craniocaudal and lateral sequences but also in the rotational sequence. Identification of the aneurysm in our patient was the result of the diagnostic strategy adopted. When cisternal subarachnoid haemorrhage is detected, our protocol routinely includes a rotational angiographic sequence centred on the anterior circulation and on the posterior circulation when the standard examination fails to depict the course of all the vessels or when the features of subarachnoid haemorrhage strongly suggest aneurysm rupture in that anatomical location. Three-dimensional angiographic reconstructions are extremely useful not only to characterize brain aneurysms, but also to disclose ruptured occult aneurysms and additional zero grade lesions.

3D rotational angiography: the new gold standard in the detection of additional intracranial aneurysms

BACKGROUND AND PURPOSE

During surgery of symptomatic aneurysms, additional small angiographic occult aneurysms are commonly found. With 3D rotational angiography (3DRA) small aneurysms are more easily depicted than with digital subtraction angiography (DSA). In this study we compare 3DRA with DSA in the depiction of small additional aneurysms.

MATERIALS AND METHODS

Three hundred fifty 3D datasets of 1 vascular tree of 350 patients with at least 1 intracranial aneurysm on the dataset were re-evaluated for the presence of additional aneurysms by 2 observers in consensus. Two other observers, blinded to the 3D images, re-evaluated DSA images of the same 350 vascular trees for these additional aneurysms. Results were compared.

RESULTS

In 350 3D datasets, 350 target aneurysms and 94 additional aneurysms were detected. The mean size of 94 additional aneurysms was 3.54 mm (median, 3; range, 0.5-17 mm). The proportion of aneurysms <or=3 mm was significantly higher in additional aneurysms (61 of 94, 65%) than in the target aneurysms (61 of 350, 17%) (chi(2), P < .0001). Of 94 additional aneurysms, 27 (29%) were missed on DSA by both observers. The mean size of the missed aneurysms was 1.94 mm (median, 2; range, 0.5-4 mm). The proportion of aneurysms <or=3 mm in missed additional aneurysms (26 of 27, 96%) was significantly higher than that in all additional aneurysms (61 of 94, 65%) (chi(2), P = .0035). The location of missed additional aneurysms was not different from the location of all additional aneurysms.

CONCLUSION

3DRA depicts considerably more small (<or=3 mm) additional aneurysms than DSA. In selected patients, accurate detection of these aneurysms may have consequences for the choice of treatment technique and for the frequency and duration of imaging follow-up.

Biomathematical modeling and analysis of blood flow in an intracranial aneurysm

The basic hypothesis of this study is that the intracranial aneurysm may enlarge and rupture due to dynamic instabilities of the blood flow and pressure inside the aneurysm. The specific question we attempted to answer is: which parameter(s) of aneurysmal geometry can serve as a reliable predictor(s) for aneurysmal rupture? We consider an idealized cylindrical aneurysm of the human common carotid artery and develop a mathematical model of blood flow through a normal artery and aneurysm connected in series. The mathematical model is nonlinear. It comprises nonlinear rheological properties of the normal artery and aneurysmal materials, and the inertial and resistance properties of the blood flow. The model equations were solved numerically and analyzed by methods of nonlinear dynamics. The critical aneurysmal diameter (CAD) is defined as a boundary point between the stable and unstable states of the model equations. The results confirm that a limit point of flow stability can occur only for a certain difference between aneurysmal and artery radii which are pre-disposed from a difference in their material properties. It was shown that CAD is dependent on both aneurysmal length and age of patient. Finally, the results suggest that the ratio between aneurysmal and normal artery diameters is a more reliable predictor of the aneurysmal rupture than the diameter alone. We conclude that an aneurysm diameter twice that of the normal artery could be dangerous.