Elizabeth M. Aradine, DO
The benefit of mechanical thrombectomy (MT) compared to IV thrombolysis (tPA) for the treatment of an acute posterior cerebral artery (PCA) occlusion is uncertain. Patients with a PCA occlusion can have a low NIH stroke scale (NIHSS), a population that is underrepresented in mechanical thrombectomy trials. The PCA territory provides vascularization to the thalamus, the hub of cerebral connections not only for motor and sensory pathways, but also for cognition. Impaired cognition is not represented on the NIHSS, which further underestimates the deficits of a PCA occlusion. The authors of “Thrombectomy and Thrombolysis of Isolated Posterior Cerebral Artery Occlusion” sought to understand the impact of revascularization with MT, tPA, or conservative treatment and assessed the outcomes of visual field deficit, cognitive impairment, and disability.
This retrospective observational study included all acute stroke patients with radiographic evidence of a P1, P2, or fetal PCA occlusion. Analysis was separated into three treatment groups: conservative therapy (no tPA), tPA, and MT. The following outcomes were assessed: visual field normalization on confrontation, 90-day modified Rankin Scale (mRS), and cognitive function. Cognitive function was evaluated by a neuropsychologist in the subacute hospital, and a favorable outcome was defined as less than or equal to 2 impaired cognitive domains.
106 patients were included in this analysis; 51 received conservative treatment, 34 received tPA, and 21 received MT. A total of 21 (19.8%) patients had a baseline NIHSS of 0-3, and 14 (27.4%) of the 21 patients were in the conservative treatment group. 85.3% who received tPA and 81% who had MT had a baseline visual field deficit, while this was seen in 72.5% in the conservative group. 32.1% had a P1 occlusion, and 67.9% had a P2 occlusion. 50% of patients in the MT group had normalization of visual fields at 90 days, compared to 34.5% in the tPA group and 18.4% in the conservative group. 50% in the MT group had 2 or less cognitive domains impaired, 22.7% in the tPA group, and 11.8% in the conservative group. 90-day mRS of 0-1 was similar in both the tPA and conservative treatment group (41.2% vs 40%), and 55% in the MT group.
This study shows a trend toward higher rates of normalization of visual fields in those treated with either tPA or MT compared to conservative treatment; however, the study is underpowered to adequately detect large differences in this outcome. Furthermore, confrontation visual field testing can underestimate a visual field defect, even if a large infarct is present. Normalization of visual fields does not always translate to functional normalization, for example, return to driving. Cognitive function was assessed in the subacute setting, which may be too early in the stroke recovery process to demonstrate a long-term deficit. Neuropsychology testing after 3-6 months may more accurately reflect post-stroke cognition.
Despite
these limitations, this study highlights the potential benefit of mechanical
thrombectomy for PCA occlusions, a population more likely to have a low NIHSS in
which the benefit of endovascular treatment is not well defined. Further
studies are needed to adequately determine which revascularization method is
most effective in PCA occlusions, keeping in mind that even a small defect can
impair the cerebral connections which are integral to the function of our
patients’ lives.
