Multidetector Computed Tomographic Angiography in Isolated Third Nerve Palsy

Clinical Prediction Score for Early Neuroimaging in Acquired Isolated Oculomotor Nerve Palsy

Purpose

An immediate neuroimaging investigation in patients with isolated oculomotor nerve palsy (ONP) remains controversial. We aimed to develop a clinical prediction score to determine whether or not acquired isolated ONP patients require prompt imaging.

Methods

A retrospective study was performed. Demographic data and clinical presentations were collected to determine predictive factors favored for early brain imaging using multivariate logistic regression analysis.

Results

Ninety-seven eyes of 96 patients diagnosed with isolated ONP were included. Forty-one eyes (42.3%) were caused by ischemia, while the other 56 eyes (57.7%) were caused by non-ischemic etiologies, namely aneurysm (n = 22), trauma (n = 18), inflammation (n = 5), tumor (n = 4), and others (n = 7). Eighty-two eyes (84.5%) had undergone neuroimaging study due to initially suspected non-ischemic causes. Only 36 (43.9%) revealed concordant diagnosis. The potential clinical predictors favored for neuroimaging using multivariate logistic regression analysis were age 10‒50 years (adjusted odds ratio [aOR] 9.01, 95% CI: 1.25‒64.8), age 51‒70 years (aOR 1.71, 95% CI: 0.46‒6.35), history of head trauma (aOR 7.14, 95% CI: 1.19‒42.9), absence of vascular risk factors (aOR 3.85, 95% CI: 1.23‒12.1), and poor pupillary response (aOR 6.96, 95% CI: 1.99‒24.3). The predictor scores with an area under the ROC curve of 0.852 were 4, 1, 4, 3, and 4, respectively. The optimum cut-point was 3 for a sensitivity of 96% and specificity of 44%.

Conclusion

Patients with acquired isolated ONP should be considered early neuroimaging studies when they are younger than 50 years old, have a history of head trauma, have no history of vascular risk factors, or have poor pupillary reaction.

Underdiagnosis of posterior communicating artery aneurysm in noninvasive brain vascular studies

BACKGROUND

Expert interpretation of modern noninvasive neuroimaging such as computed tomographic angiography (CTA) or MRA should detect nearly all aneurysms responsible for an isolated third nerve palsy. Whether a catheter angiogram should still be obtained in cases with negative CTA or MRA remains debated and mostly relies on whether the noninvasive study was correctly performed and interpreted. The aim of our study was to review the diagnostic strategies used to evaluate patients with isolated aneurysmal third nerve palsy at a large academic center.

METHODS

Retrospective review of all cases with posterior communicating artery (PCom A) aneurysmal third nerve palsies seen at our institution since 2001.

RESULTS

We identified 417 cases with third nerve palsy, aneurysm, or subarachnoid hemorrhage, among which 17 presented with an acute isolated painful third nerve palsy related to an ipsilateral PCom A aneurysm (mean age: 52 years; range: 33-83 years). Patients were classified into 3 groups based on the results of the noninvasive imaging obtained at initial presentation. Group I included 4 cases with subarachnoid hemorrhage on initial noncontrast head CT initially obtained in an emergency department for evaluation of their isolated third nerve palsy. Group II included 5 cases with isolated third nerve palsy and normal noncontrast head CT at presentation, immediately correctly diagnosed with a PCom A aneurysm at the referring institution. Group III included the 8 remaining cases who all had aneurysms that were missed on noninvasive studies at outside institutions. Review of these outside studies at our institution showed a PCom A aneurysm, confirming misinterpretation of these tests by the outside radiologists, rather than inadequate technique. Absence of specific training in neuroradiology and inaccurate clinical information provided to the interpreting radiologist were associated with test misinterpretation at the outside institutions. The average size of PCom A aneurysms causing an isolated third nerve palsy across all 3 groups was 7.3 mm and was similar in each group.

CONCLUSION

Our study suggests that aside from an accurate history, the training and experience of the interpreting radiologist is probably the most important factor in determining the reliability of a noninvasive scan in patients with isolated third nerve palsies.

Imaging of intracranial aneurysms causing isolated third cranial nerve palsy

Isolated third cranial nerve palsies may be caused by compressive intracranial aneurysms located at the junction of the internal carotid and posterior communicating arteries or, less commonly, at the apex of the basilar artery or its junction with the superior cerebellar or posterior cerebral arteries. Such aneurysms typically measure at least 4 mm in diameter. Technical improvements in noninvasive techniques, including CT and MRA, have yielded a detection rate of such aneurysms that approaches that of catheter cerebral angiography (CCA), which itself carries a small but serious risk. Multidetector technology, which allows a rapid scan time, has promoted CT to the first choice for investigating aneurysms in this setting except when dye or radiation exposure is unacceptable, as with pregnant women, children, and those with renal or severe cardiac disease. Major impediments to accurate detection are a lack of availability of trained technicians, who must perform manipulation of the raw imaging data ("post-processing"), and a paucity of certified neuroradiologists with the time, skill, and experience to devote to interpreting difficult cases. To avoid diagnostic mishaps, noninvasive studies should be reviewed by at least one neuroradiologist before aneurysm is rejected as the cause or before the patient undergoes CCA.