Topographic anatomy of paraclinoid carotid artery aneurysms: usefulness of MR angiographic source images

Efficacy of 3D evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® for determination of their intradural localization

BACKGROUND

Determination of the intradural unruptured paraclinoid aneurysm localization is difficult, but critical for selection of the optimal treatment strategy.

OBJECTIVE

To assess efficacy of the three-dimensional (3D) evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® (LGP; Elekta AB; Stockholm, Sweden) for determination of their intradural localization.

METHODS

Overall, 125 incidentally diagnosed unruptured paraclinoid aneurysms in 118 patients (mean age, 55 years) underwent 3D evaluation of their localization within LGP using post-contrast thin-slice constructive interference in steady state (CISS) images, which in 41 cases were additionally co-registered and fused with the axial computed tomography angiography (CTA) source images.

RESULTS

According to the evaluation within LGP, paraclinoid aneurysms were considered intradural, transitional, and extradural in 75, 25, and 25 cases respectively. Overall, 51 of 75 aneurysms deemed to be intradural, underwent microsurgical management, and intraoperative visual inspection confirmed their intradural localization in 45 cases, whereas it was transitional in 3, and extradural in 3. If during preoperative 3D evaluation within LGP only post-contrast CISS images were used, prediction of the pure intradural localization of aneurysm was correct in 88 % of cases (95 % CI: 79-97 %), and of the pure or partial (i.e., transitional) intradural localization in 94 % of cases (95 % CI: 88-100 %), whereas it was 100 % if co-registration and fusion of the contrast-enhanced CISS and CTA source images was done.

CONCLUSION

Intradural localization of the unruptured paraclinoid aneurysms may be effectively predicted based on their 3D evaluation within LGP using post-contrast thin-slice CISS and CTA source images, which may help with clinical decision-making.

The Intersection Between the Oculomotor Nerve and the Internal Carotid Artery to Distinguish Extracavernous and Intracavernous Paraclinoid Aneurysms Using Anatomic Dissections-A New 3T Magnetic Resonance Imaging Protocol Confirmed by Three-Dimensionally Printed Biomodels

OBJECTIVE

To evaluate the relationship between the oculomotor nerve (CNIII) and the internal carotid artery (ICA) as a new anatomic-radiologic landmark for distinguishing the exact location of a paraclinoid intracranial aneurysm (IA).

METHODS

Microanatomic dissections were performed in 20 cavernous sinuses to evaluate the ICA paraclinoid region. Based on anatomic observations, a new magnetic resonance (MRI) protocol to classify paraclinoid aneurysms was proposed. MRI of 42 IAs from 34 patients was independently analyzed and classified as intracavernous, extracavernous, or transitional by 2 neuroradiologists. To validate the proposed MRI protocol, each IA was classified by a three-dimensionally (3D) printed biomodel and agreement with the radiologic classifications was evaluated. Of 42 IAs, 23 undergoing microsurgeries were also classified by direct visualization.

RESULTS

We observed that the true cavernous sinus roof is defined by the carotid-oculomotor membrane, which has an intimate relationship with the intersection between the superior limit of the CNIII and the ICA. Based on this intersection, all 42 IAs were radiologically classified and agreement with the 3D printed biomodels was observed in 95% IAs. Concordance tests showed a statistically significant (P < 0.05) agreement between the classifications. All 23 IAs treated had the radiologic and 3D biomodel classification confirmed.

CONCLUSIONS

The intersection between the ICA and the CNIII, which crosses it transversely in its entire diameter, is a reliable anatomic-radiologic landmark to correctly classify paraclinoid aneurysms. Through a new MRI protocol, it is possible to radiologically identify this intersection and to easily distinguish the intracavernous and extracavernous ICA paraclinoid aneurysms.

Intracranial Aneurysm Detection with 3T Magnetic Resonance Angiography

Introduction: The new 3 Tesla (T) magnetic resonance (MR) scanners yield improved signalto-noise ratio and spatial resolution with superior background suppression compared to lower field strength systems. This is advantageous for MR angiograms. The purpose of our study was to compare unenhanced three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA) at 3T with catheter digital subtraction angiography (DSA) in detecting unruptured intracranial aneurysms. Materials and Methods: Out of 1375 consecutive patients who underwent unenhanced 3D TOF MRA at 3T, 15 patients with unruptured intracranial aneurysms were retrospectively identified. Nine of these 15 patients had DSA as the reference standard for comparison. Aneurysm size, location and morphology were independently assessed on both MRA and DSA by 2 radiologists. Results: Seventeen aneurysms ranging in size from 1 mm to 24 mm were identified in 15 patients on MRA. DSA confirmed the aneurysms in 9 patients with good anatomical correlation compared with the MRA findings. Conclusions: 3D TOF MRA at 3T has good correlation with DSA and aneurysms as small as 1 mm in size can be detected. This can be a promising, non-invasive method for aneurysm surveillance. Key words: Angiography, Cerebrovascular disorders, Diagnostic imaging

Dynamics of intraventricular hemorrhage in patients with spontaneous intracerebral hemorrhage: risk factors, clinical impact, and effect of hemostatic therapy with recombinant activated factor VII

OBJECTIVE

To evaluate predictors of intraventricular hemorrhage (IVH) and IVH growth, impact of IVH growth on outcome, and impact of recombinant activated factor VII (rFVIIa) in patients with intracerebral hemorrhage (ICH).

METHODS

We analyzed 374 patients out of 399 who were randomized to rFVIIa (40, 80, or 160 mug/kg) or placebo for ICH (diagnosed within 3 h of symptoms). Risk factors for IVH growth (>2 ml increase in IVH volume at 24 h), and death or severe disability (modified Rankin scale score 4-6) at 3 months were identified (logistic regression).

RESULTS

IVH was present in 38% (n = 141) of patients at baseline and 45% (n = 169) by 24 hours. IVH growth, by 24 hours, occurred in 17 and 10% of placebo- and rFVIIa-treated patients, respectively (P = 0.037). Risk factors for IVH growth included baseline mean arterial pressure greater than 120 mmHg, larger baseline ICH volume, IVH present at baseline, shorter time from symptom onset to baseline computed tomographic scan, and treatment (rFVIIa versus placebo) (all, P < or = 0.037). Predictors of death or severe disability included older age, lower baseline Glasgow Coma Score, larger baseline ICH volume, IVH growth greater than 2 ml, IVH present at baseline or 24 hours, and treatment (rFVIIa versus placebo) (all, P < or = 0.0405).

CONCLUSION

Presence of IVH at any time and early IVH growth worsen clinical outcome and increase mortality. Elevated mean arterial pressure at baseline may be a modifiable risk factor for IVH growth. Beneficial effects of rFVIIa on ICH outcome may be mediated, at least in part, by reducing IVH growth.

Optic Strut as a Radiographic Landmark in Evaluating Neck Location of a Paraclinoid Aneurysm

OBJECTIVE:

The optic strut (OS) is a candidate landmark in computed tomographic (CT) angiographic scans for the discrimination of intradural and extradural/intracavernous aneurysms involving the paraclinoid segment of the internal carotid artery. The goal of this study is to examine and confirm the qualifications of the OS as a landmark in CT angiographic scans for the preoperative evaluation of aneurysms in this region.

METHODS:

Seventeen consecutive patients with 18 unruptured paraclinoid aneurysms who underwent preoperative CT angiography scans and direct surgery between 1998 and 2005 were evaluated retrospectively. We focused on the relationships of the necks of aneurysms to the OS in CT angiographic scans and that of the necks to proximal dural rings during intraoperative examinations.

RESULTS:

Direct surgery revealed that 14 aneurysms, the necks of which were distal to the OS on CT angiographic scans, arose distal to the proximal dural rings. All aneurysms were clipped, except one exhibiting calcification of the neck. Three aneurysms, for which the neck was proximal to the OS on CT angiographic scans, revealed only a portion or nothing of their domes instead of their necks through the proximal dural rings after dissection of the distal dural rings. Dome coating with fibrin glue and a piece of muscle tissue or mere exploration was performed. Another aneurysm, of which the neck straddled the OS on CT angiographic scans, was found to arise across the proximal dural ring. Clipping of the neck was performed after dissection of the proximal dural ring. Of the source images of CT angiographic scans, the axial images were the most useful in evaluating the relationship of the neck of an aneurysm to the OS.

CONCLUSION:

On CT angiographic scans, the OS is a precise identification of the proximal dural ring that forms the superior border of the cavernous sinus. The aneurysms whose necks arise obviously distal to the OS on CT angiographic scans are able to be clipped without dissection of the proximal dural ring.

Radiographic imaging of the distal dural ring for determining the intradural or extradural location of aneurysms

The effectiveness of several anatomical and radiological landmarks proposed to determine whether an aneurysm is located intradurally or extradurally is still debated. In anatomical and radiological studies, we examined the relationships of the distal dural ring (DDR) to the internal carotid artery (ICA) and surrounding bony structures to aid in the localization of aneurysms near the DDR. Anatomical relationships were examined by performing dissections on 10 specimens (5 formalin-fixed cadaveric heads). After the position of the DDR, optic nerve, and tuberculum sellae were marked with surgical steel wire, radiographs were taken in multiple projections. The only bony landmark consistently visible on radiographs was the planum sphenoidale. The superior border of the DDR is located at or below the level of the tuberculum sellae, which laterally becomes the superomedial aspect of the optic strut; thus, the optic strut marks the dorsal limit of the DDR. On 50 dry skulls, we measured the vertical distance between the planum sphenoidale and medial aspect of the optic strut (5.0 +/- 0.4 mm), the interoptic strut distance (14.4 +/- 1.4 mm), and the linear distance between the most posterior aspect of the planum sphenoidale (limbus sphenoidale) and the tuberculum sellae (6.0 +/- 0.5 mm). Using these measurements and the planum sphenoidale, tuberculum sellae, and optic strut as reference landmarks, we determined the location of the aneurysm relative to the DDR on angiographic images. In this way, we were able to identify whether lesions were intra- or extradural.

MRI location of the distal dural ring plane: anatomoradiological study and application to paraclinoid carotid artery aneurysms

The distal dural ring plane (DDRP) separates the intradural from the extradural paraclinoid internal carotid artery. The purpose of this study was to evaluate its position with MR imaging. The protocol used a T2-weighted sequence in two orthogonal planes: diaphragmatic (DIA-P) and carotid (CAR-P). The DDRP passes through four anatomoradiological reference points (RefP). We developed on a cadaveric model a correlation method supported by correlation lines and angles (CA) projecting the RefP toward the DDRP. RefP were correlated to the DDRP in 65-84% of cases in the DIA-P and 60-76% of cases in the CAR-P. CA were identified and correlated to the DDRP, respectively, in 87% and 60% of cases in the DIA-P, and 60% and 51% of cases in the CAR-P (failure often related to a lack of visibility of just one RefP). A higher tissular contrast in living subjects allowed the identification of CA in 90% and 80% of cases, respectively, in the DIA-P and the CAR-P. We propose that CA, when identified, should be considered as an approximation of the inferior radiological limit of the DDRP curve. In difficult angiographical cases, this MRI protocol could help to locate paraclinoid aneurysms on both sides of the cavernous sinus roof.

Contrast-enhanced MR angiography of the intracranial circulation

NCE MRA can provide the authors with useful diagnostic information in patients suffering from intracranial vascular disease, often leading to improved or altered treatment decisions. Most centers have used 3D TOF for evaluation of stroke-the most common cerebral vascular disease. Because of slow and disturbed flow, conventional 3D TOF MRA tends to overestimate stenotic lesions and occluded arteries and this can confound neurovascular assessment in stroke patients. Post contrast 3D TOF techniques provide a more robust and more specific method for imaging the intracranial circulation that overcomes the drawbacks of conventional 3D TOF. In the setting of acute ischemic stroke, the authors have found that the combination of conventional and CE 3D TOF MRA improves their overall diagnostic ability. Dynamic and time-resolved CE MRA techniques have evolved rapidly. Time-resolved CE MRA, in particular, is emerging as a useful technique for imaging dynamic vascular pathologies such as AVMs. Unfortunately, time-resolved MRA of the intracranial circulation provides images with low spatial resolution and is currently limited to subsecond frame rate 2D acquisitions, and less than 2 seconds frame rates for 3D acquisitions. Nevertheless, like in other vascular regions, CE MRA represents a milestone for non-invasive intracranial vascular imaging. The continuing development of CE MRA techniques and of new contrast agents will lessen the need for intra-arterial angiography in the future.

Helical high-resolution volume-rendered 3-dimensional computer tomography angiography in the detection of intracranial aneurysms

BACKGROUND AND PURPOSE

This study was carried out to determine whether high-resolution 3-dimensional prospective-volume-rendered computed tomographic (CT) angiography can replace conventional intra-arterial digital subtractional angiography in the diagnostic evaluation of patients with an acute subarachnoid hemorrhage (SAH) due to ruptured intracranial aneurysm.

METHODS

Both techniques were performed in 30 consecutive patients within 2 to 12 hours after their admission to the hospital.

RESULTS

In this group of 30 patients, CT angiography with 3-dimensional volume-rendered reconstruction detected 31 aneurysms in 25 patients. Two aneurysms were missed on CT angiography. Conventional angiography detected 33 aneurysms in 27 patients. The authors considered angiograms in 3 patients presenting with SAH as normal. In all cases where an aneurysm was detected on CT angiography, the finding was confirmed by conventional angiography.

CONCLUSIONS

CT angiography with 3-dimensional post-processing is a sensitive, noninvasive method that provides a 3-dimensional view of intracranial vessels and the aneurysm. It is also very useful in planning either surgical or endovascular treatment.