Black Belt Sign on Diluted Contrast 3D Rotational Angiography as a Potential Neointimal Marker Associated with Intracranial Aneurysm Occlusion after Flow Diversion.

Abstract

Background and purpose: Neointimal formation at the aneurysm neck is essential after flow diverter (FD) treatment; however, reliable imaging markers are lacking. The white collar sign (WCS), an established endothelialization marker after coil embolization, is paradoxically associated with incomplete occlusion after flow diversion. We aimed to propose the black belt sign (BBS), an endoluminal bandlike filling defect on 3D rotational angiography (3DRA), as a neointimal marker, determine the optimal imaging technique, and assess its association with aneurysm occlusion.

Materials and methods: This single center, retrospective cohort study included consecutive patients who underwent FD placement from April 2015 to December 2024, completed 6- and 12-month followups, and underwent diluted 3DRA, pure 3DRA, and high-resolution conebeam CT at 6-months. Three blinded assessors graded the 6-month BBS (none, partial, full). The optimal technique was determined by interrater reliability. The BBS stage was compared across 6-month O'Kelly-Marotta (OKM) grades using the Cochran Armitage test. Among 6-month incompletely occluded aneurysms, 12-month complete occlusion rates were compared by BBS stage, and risk ratios were estimated using modified Poisson regression with cluster robust SEs at the patient level. The WCS on 6-month 2D DSA was recorded, and detection rates were examined across BBS stages and OKM grades.

Results: We analyzed 142 aneurysms in 123 patients. Diluted 3DRA showed superior interrater reliability (mean of all pair-wise weighted Cohen κ values [Light's κ] = 0.82). The predominant BBS stage transitioned from none to partial to full as the 6-month OKM grades improved (none/partial/full: OKM A, 62/38/0%; B, 25/75/0%; C, 3/59/38%; D, 1/7/91%, respectively; P for trend < .01). Among the 61 incompletely occluded aneurysms at 6-months, the 12-month complete occlusion rates were 10% for none-BBS, 22% for partial BBS, and 71% for full BBS. Compared with none-BBS, the risk ratio for 12-month occlusion was 2.16 (95% CI, 0.30-15.5) for partial BBS and 7.14 (95% CI, 1.07-47.8) for full BBS. The WCS was most frequent in aneurysms with partial BBS and OKM grade B (75%).

Conclusions: Diluted 3DRA was identified as the optimal technique. The BBS aligned with the concurrent aneurysm occlusion status and predicted subsequent complete occlusion, supporting its potential as a neointimal biomarker after FD treatment. The WCS may reflect immature neointimal formation after flow diversion.