Gap between the clip and coil mass as a predictor of aneurysm recurrence and occlusion: illustrative case.

backgroundMetal artifacts from clips and coils can interfere with follow-up imaging of treated aneurysms using CT or MRI. The authors report a case in which the gap between the clip and coil mass helped predict aneurysm recurrence and occlusion after clipping and coil embolization. OBSERVATIONS: A 50-year-old woman underwent craniotomy and clipping for a left internal carotid artery (ICA)-posterior communicating artery (PCoA) aneurysm at another hospital 22 years earlier. She presented to the authors' hospital with a headache and was diagnosed with subarachnoid hemorrhage. Cerebral angiography revealed recurrence of the left ICA-PCoA aneurysm, and coil embolization was performed. Because of the metal artifacts from the clip and coils, it was difficult to evaluate aneurysm recurrence using CT angiography and MR angiography. Serial skull radiographs revealed an increasing gap between the clip and coil mass, along with flattening of the coil mass, suggesting recurrence. Follow-up cerebral angiography confirmed the recurrence, and a flow diverter was placed. At 6 months after placement, skull radiographs revealed a reduction in the gap, indicating occlusion. Cerebral angiography confirmed complete aneurysm occlusion. LESSONS: In cases with significant metal artifacts from clips and coils, the gap between the clip and coil mass observed on skull radiographs may help predict aneurysm recurrence and occlusion. https://thejns.org/doi/10.3171/CASE25286.