Familial Intracranial Aneurysms: Screening with MRA

ABSTRACT & COMMENTARY
Source: Ronkainen A, et al. Familial intracranial aneurysms. Lancet 1997;349:380-384.

Magnetic resonance angiography (mra) provides an almost risk-free tool to visualize intracranial arteries and has made screening for intracranial aneurysms (IA) in asymptomatic individuals feasible. The authors used MRA as a preliminary screening test to determine the prevalence of incidental IAs in first-degree relatives aged 30 years or more of patients with IAs. Participants were also screened for polycystic kidney disease (PCKD) by ultrasonography.

In a series of 1150 patients with IA treated at one hospital in Finland between 1977 and 1990, there were 91 families with at least two IA cases. Eighty-five families comprising 191 IA patients had no other known heritable disease. In six families, there were 16 IA patients of whom 10 had PCKD. Six hundred ninety-eight living asymptomatic, first-degree relatives of the 207 IA patients were found who were 30 years of age or older. Four hundred thirty-eight (233 women; mean age, [SD] 49 [14] years and 205 men; mean age, 47 [13] years) from 85 families completed screening with MRA.

Thirty-six individuals had 60 IAs confirmed by cerebral arteriography. Seven patients with positive MRAs had negative arteriograms. Two elderly patients with positive MRAs who were not considered surgical candidates did not have cerebral arteriography. The prevalence of incidental IA among first-degree relatives over 30 years of age was 8.7 ± 1.3% (mean ± SEM; 95% CI 6.2-11.7). Before screening, 66 out of 85 families (78%) were known to have only two affected members. After screening, nearly half of the families (41/85) had three or more affected members. The most common relationship between two affected individuals was as siblings (42%). No cases of PCKD were found in members of families with no known heritable disease, and no previously undetected cases of polycystic kidneys were found in members of the PCKD families.

These results indicate that the risk of having an IA is four times higher for close relatives than for the general population and that PCKD families are only a small fraction of the families with IAs. The risk of having IAs was similar in PCKD and familial IA families.

COMMENTARY

The editors have previously reviewed the topic of familial subarachnoid hemorrhage (SAH) (Neuro Alert 1996;14:45-46). Among others, a community-based study in Rochester, MN, (Schievink WI, et al. J Neurosurg 1995;83:426-29) indicated that first-degree relatives were at a significantly elevated risk of SAH compared to the general population and that the largest risk was among siblings. Based on these data, we recommended that first-degree relatives of SAH patients undergo MRI and MRA screening to detect unruptured aneurysms. In this regard, the present study provides important information on the use of MRA as a screening test. First of all, in this study, MRA had a high false-positive rate: seven out of 43 patients with suspected IAs on MRA had negative cerebral arteriograms. Second, although the false-negative rate cannot be determined because only patients with positive MRAs were referred for arteriograms, it is noteworthy that 12 additional IAs were detected by arteriography in individuals in whom one or more aneurysms had already been detected by MRA. The sensitivity of MRA on a per aneurysm basis, therefore, was 82% (53 aneurysms on both MRA and arteriography, 12 false-negative MRAs; 53/[53 + 12]). This contrasts with the reported 95% sensitivity of MRA in detecting IAs 3 mm in size or greater (Atlas SW. Radiology 1994;193:1-16). The false-negatives in this series may be due to the inherent lower sensitivity of MRA compared to arteriography or to another factor the authors mention—"a reduced need for diligence in finding all possible aneurysms after the first."

This study confirms that MRA is a good screening test for IAs but needs to be followed by conventional four vessel arteriography to verify suspected aneurysms and identify additional small aneurysms missed by MRA. —jjc